DRC-2012-001189 - 0901a068802b2d20

DENISO
MINES
lis Qnison Mines (USA) Corp
1050 17th Street, Suite 950
Denver CO 80265
USA
Tel [phone]
Fax [phone]
www denisonmines com
February 27 2012
/
VIA PDF AND FEDERAL EXPRESS
Mr Rusty Lundberg
Executive Secretary
Utah Division of Radiation Control
Utah Department of Environmental Quality
195 North 1950 West
Salt Lake City UT 84116 3097
Re Response to January 19, 2012 DRC/URS Comments on Nitrate Corrective Action Plan -
Docket No UGW09 03
Dear Mr Lundberg
Please find enclosed Denison Mines (USA) Corp s ( Denison s ) revisions dated February 27 2012 to
the Nitrate Corrective Action Plan for the White Mesa Mill Site (the Plan )
This revision has been prepared in response to comments from the Utah Division of Radiation Control
and URS Corporation dated January 19 2012 The revision has been provided in both clean and track
changes (redline ) format for ease of review
The responses to comments are summanzed below Each response below has been identified by the
number of the corresponding comment in the January 19 2012 letter
1 Different symbols were used for the more recently installed wells to distinguish them from older
wells in which water levels and constituent concentrations have had time to stabilize Time is
required for water levels and constituent concentrations to stabilize due to the low hydraulic
conductivity conditions encountered over most of the site The figures have been revised using
unique symbols for chloroform extraction wells and where appropriate for proposed nitrate
extraction wells A unique symbol has also been used for the most recently installed MW senes
wells MW 36 and MW 37 The same symbol is now used for MW 33 34 and 35 as for the other
perched monitoring wells
2 All references to permeability' have been replaced with hydraulic conductivity* as requested
3 A statement has been added on page 1 that all nitrate concentrations in the Plan document are
expressed in mg/L as nitrogen as requested
4 A new large scale Figure 1 1 has been added that shows the indicated features Existing Figure 1
IS now Figure 1 2
5 The histoncal pond is the irregularly shaped red figure in the area of TWN 2 and has been
labeled on Figure 8 as requested
Y \Nitrate Investigation and CIR\Corrective Action Plan (CAP)\01 1912 DRC commts and resp on draft CAP\02
27 12 ltr to R Lundberg Nitrate CAP comment responses (2) JAT prefinal docx

HYDRO GEO CHEM, INC.
Environmental Science & Technology

CORRECTIVE ACTION PLAN FOR NITRATE
WHITE MESA URANIUM MILL
NEAR BLANDING, UTAH

February 27, 2012

Prepared for:

DENISON MINES (USA) CORP.
Independence Plaza, Suite 950
1050 Seventeenth Street
Denver, Colorado 80265

Prepared by:

HYDRO GEO CHEM, INC.
51 W. Wetmore Road, Suite 101
Tucson, Arizona 85705
[phone]

Project Number 7180000.00-7.0

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CORRECTIVE ACTION PLAN FOR NITRATE
WHITE MESA URANIUM MILL
NEAR BLANDING, UTAH

Prepared for:

DENISON MINES (USA) CORP.
Independence Plaza, Suite 950
1050 Seventeenth Street
Denver, Colorado 80265

Prepared, Reviewed, and Approved by:

_____________________________________
Stewart J. Smith, UT P.G. No. 5336166-2250
Associate Hydrogeologist

February 27, 2012 Deleted: November 30
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Corrective Action Plan for Nitrate
White Mesa Uranium Mill Near Blanding, Utah
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i
TABLE OF CONTENTS
1. INTRODUCTION, OVERVIEW, AND SCOPE............................................................... 1
2. HISTORY OF NITRATE CONTAMINATION INVESTIGATION................................ 3
2.1 Summary of Contamination Investigation Report Activities..................................3
2.2 Conclusions from the Contamination Investigation ...............................................6
3. FRAMEWORK AND OBJECTIVES OF THE CAP......................................................... 9
3.1 Applicable Regulations and Requirements.............................................................9
3.2 Objectives of the CAP ..........................................................................................10
3.2.1 Summary of Phase I Objectives and Scope.............................................. 10
3.2.2 Summary of Phase II Objectives and Scope............................................. 11
3.2.3 Summary of Phase III Objectives and Scope............................................ 12
3.3 Preliminary Milestones for the CAP.....................................................................13
4. BACKGROUND.............................................................................................................. 15
4.1 Geologic Setting....................................................................................................15
4.2 Hydrogeologic Setting..........................................................................................16
4.3 Perched Zone Hydrogeology................................................................................16
4.3.1 Lithologic and Hydraulic Properties......................................................... 17
4.3.1.1 Dakota........................................................................................18
4.3.1.2 Burro Canyon............................................................................. 18
4.3.2 Perched Groundwater Flow...................................................................... 19
4.3.3 Saturated Thickness.................................................................................. 20
4.4 Summary...............................................................................................................21
4.5 Nitrate Occurrence................................................................................................22
4.5.1 Source Areas............................................................................................. 22
4.5.2 Nitrate Concentration Trends....................................................................24
5. CHARACTERIZATION OF STUDY AREA.................................................................. 25
5.1 Extent of Study Area.............................................................................................25
5.2 Hydrogeology .......................................................................................................26
6. CORRECTIVE ACTION CONCENTRATION LIMITS................................................ 27
7. CORRECTIVE ACTION PLAN - CONSTRUCTION AND OPERATION.................. 29
7.1 Phase I Description and Rationale........................................................................30
7.1.1 Approximation of the Lateral Extent of Contamination and
Concrete Cover ......................................................................................... 30
7.1.1.1 Soil Sampling Program Objective and Design.......................... 30
7.1.1.2 Field Activities/Sampling Methods ........................................... 31
7.1.1.3 Sample Handling and Custody................................................... 32
7.1.1.4 Analytical Methods.................................................................... 33
7.1.1.5 Quality Control.......................................................................... 33
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TABLE OF CONTENTS (Continued)

7.1.2 Construction of the Phase I Action........................................................... 33
7.1.3 Maintenance of the Phase I Action........................................................... 34
7.1.4 Estimation and Removal of Contaminated Soil During
Mill Reclamation ......................................................................................35
7.2 Phase II Description and Rationale.......................................................................36
7.2.1 Well Abandonment................................................................................... 40
7.2.2 Groundwater Pumping System................................................................. 41
7.2.3 Water Level Monitoring ........................................................................... 41
7.2.4 Water Quality Monitoring......................................................................... 41
7.2.5 Reporting................................................................................................... 43
7.3 Phase III................................................................................................................43
7.3.1 Water Level and Water Quality Monitoring............................................. 44
8. ASSESSMENT OF CORRECTIVE ACTION AND PROTECTION OF
PUBLIC HEALTH AND THE ENVIRONMENT AND
CONTINGENCY PLAN.................................................................................................. 45
8.1 Stability of Plume Boundary (Phase II)................................................................46
8.2 Concentration Trends within the Plume (Phase II)...............................................46
8.3 Nitrate Mass Removal Rates Resulting from Pumping (Phase II) .......................47
8.4 Stability of the Proportion of the Nitrate Plume under
Hydraulic Capture (Phase II)................................................................................47
8.5 Phase III................................................................................................................48
8.6 Permanent Effect of Corrective Action.................................................................48
8.7 In-Place Contaminant Control..............................................................................48
9. IMPACTS OF OFFSITE ACTIVITIES........................................................................... 49
10. PROPOSED PLUME CORRECTIVE ACTION ACTIVITIES...................................... 51
10.1 Phase I...................................................................................................................51
10.2 Phase II..................................................................................................................51
10.2.1 Groundwater Pumping.............................................................................. 51
10.2.2 Water Level Monitoring ........................................................................... 51
10.2.3 Water Quality Monitoring......................................................................... 51
10.2.4 Estimation of Capture Zones ....................................................................52
10.2.5 Estimation of Pumped Nitrate Mass......................................................... 52
10.2.6 Reporting................................................................................................... 52
10.2.7 Additional Measures................................................................................. 52
10.3 Phase III................................................................................................................52
11. REFERENCES ................................................................................................................. 55
12. LIMITATIONS STATEMENT........................................................................................ 57

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Corrective Action Plan for Nitrate
White Mesa Uranium Mill Near Blanding, Utah
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TABLE OF CONTENTS (Continued)

TABLES

1 Nitrate Corrective Action Schedule
2 Hydraulic Conductivity Estimates for Wells in the Nitrate Plume Area
3 Nitrate Concentrations (mg/L) at Wells within the Nitrate Plume
4 Comparison of Chloroform Pumping Well Transmissivities to Proposed Nitrate Pumping
Well Transmissivities

FIGURES

1-1 White Mesa Mill Site Plan Showing Locations of Seeps and Springs
1-2 Site Plan Showing Perched Well Locations and 3rd Quarter, 2011 Nitrate Plume Extent,
White Mesa Site
2 Photograph of the Contact Between the Burro Canyon Formation and the Brushy Basin
Member
3 Kriged Top of Brushy Basin Elevations, White Mesa Site
4 Kriged 3rd Quarter, 2011 Water Levels, White Mesa Site
5 3rd Quarter, 2011 Saturated Thickness, White Mesa Site
6 3rd Quarter, 2011 Depths to Water, White Mesa Site
7 Kriged 3rd Quarter, 2011 Nitrate (mg/L) (Nitrate + Nitrite as N), White Mesa Site
8 Potential Nitrate Source Areas and Geoprobe Locations Showing the Thickness of the
Mancos Shale
9-1 Nitrate Concentrations in MW-30 and MW-31
9-2 Comparison of Nitrate Plume Boundaries, 3rd Quarter, 2010 and 3rd Quarter, 2011
10 3rd Quarter, 2011 Nitrate and Chloroform Plumes, White Mesa Site
11-1 Ammonium Sulfate Contamination
11-2A Ammonium Sulfate Tank Area (Current Layout)
11-2B Ammonium Sulfate Concrete Cover (Proposed Location)
11-3 Fire System Schematic
11-4 General Area of Proposed Concrete Cover
11-5 Well Pumping Transfer Lines
12 Estimated Extent of Capture of Chloroform Pumping Well MW-26, 3rd Quarter, 2011
13 Anticipated Minimum Downgradient Extent of Capture Resulting from Pumping
TW4-22, TW4-24, TW4-25, and TWN-2

APPENDICES

A Hydrogeologic Cross Sections
B Lithologic Logs for MW-3A, MW-30, MW-31, MW-34, and MW-37
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1. INTRODUCTION, OVERVIEW, AND SCOPE
This document presents a Corrective Action Plan (CAP) to address nitrate + nitrite (as nitrate)
(heretofore referred to as “nitrate”) contamination in a shallow perched groundwater zone
beneath the White Mesa Uranium Mill (the “site” or the “Mill”), located on White Mesa near
Blanding, Utah, operated by Denison Mines (USA) Corp. (“Denison”). Figure 1-1 is a map
showing site features including seeps and springs at the margins of White Mesa. Figure 1-2 is a
map of the site showing the locations of perched zone monitoring wells and the area of the
perched groundwater zone affected by nitrate concentrations exceeding 10 milligrams per liter
(mg/L) that is the focus of this CAP. For the purposes of this document, all nitrate concentrations
in groundwater have been expressed as mg/L nitrogen. Elevated concentrations of chloride were
also detected in the monitoring wells having elevated concentrations of nitrate. In a letter dated
December 1, 2009, the Co-Executive Secretary of the Utah Water Quality Board (the “Executive
Secretary”) recommended that Denison also address and explain the elevated chloride
concentrations.
Nitrate within the area shown in Figure 1 was first detected in wells TW4-19, TW4-22, TW4-24,
and TW4-25 that were installed as part of the investigation of a chloroform plume discovered at
perched well MW-4 in 1999. Pumping of chloroform-laden perched water began in 2003 (HGC,
2007a) and continues to the present time via pumping of wells MW-4, MW-26, TW4-4, TW4-
19, and TW4-20.
Investigation of nitrate exceeding 10 mg/L in the perched water included installation of 19
temporary TWN-series wells shown in Figure 1 and numerous shallow borings as part of a
source investigation. Denison identified and prioritized potential sources of the nitrate in the
December 2009 Source Review Report for Nitrate and Chloride in Groundwater at the White
Mesa Mill, (INTERA, 2009a) and in the subsequent August 2011 Nitrate Investigation Revised
Phases 2 through 5 Work Plan. (INTERA, 2011).
Based on the investigations, Denison and the Executive Secretary have agreed that the corrective
actions will involve three Phases. Phase I will involve source control in the vicinity of the Mill’s
ammonium sulfate tanks, the one remaining potential source of contamination. Phase II will
involve near term active remediation of the nitrate contamination by pumping contaminated
water into the Mill’s tailings cells for disposal, combined with monitored natural attenuation.
Phase III, if necessary, will be at the discretion of Denison and would involve a long term
solution for the nitrate contamination, in the event that the continuation of Phase II is not
considered adequate or appropriate. Phases I and II are addressed in this CAP and will
commence shortly upon Executive Secretary approval of this CAP. Phase III is not covered in
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detail in this CAP and, if determined to be necessary, will be addressed in a separate CAP
revision.
The elements of this CAP document include the following items:
• A History of the Nitrate Contamination Investigation
• A discussion of the decision to proceed with Corrective Action
• A summary of the applicable requirements
• CAP objectives
• A description of the site hydrogeology
• The nature and extent of nitrate in the perched zone
• Proposed corrective remedial actions and concentration limits
• Proposed corrective action contingencies

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2. HISTORY OF NITRATE CONTAMINATION INVESTIGATION
A brief discussion of the Nitrate Contamination Investigation and the decision to proceed with
corrective action is provided in Sections 2.1 and 2.2.
2.1 Summary of Contamination Investigation Report Activities
On January 27, 2009 the Executive Secretary of the Utah Division of Radiation Control (“DRC”)
and Denison entered into the 2009 Stipulated Consent Agreement (“SCA”), which set forth the
requirement that Denison would submit a written Contaminant Investigation Report (CIR) for
Executive Secretary review and approval, to among other things, characterize the source(s),
physical extent, transfer mechanisms and characteristics of the Nitrate contamination of the
shallow aquifer at the site.
Denison submitted to the Executive Secretary a CIR which had been prepared by their consultant
INTERA, Inc. The CIR was dated December 30, 2009 (INTERA, 2009b) and entitled "Nitrate
Contamination Investigation Report White Mesa Uranium Mill Site Blanding, Utah" (2009 CIR).
On October 5, 2010 the Executive Secretary issued a Notice of Additional Required Action
(NARA) letter that notified Denison of the Executive Secretary’s determination that the 2009
CIR was incomplete.
On December 20, 2010 Denison and the Executive Secretary entered into a Tolling Agreement
(Tolling Agreement (Rev. 0)) to defer any monetary penalties that might accrue under the 2009
SCA, in order to provide a time period (Tolling Period) for:
1. Denison to prepare and submit a plan and schedule (Plan and Schedule) by which to
conduct additional investigations to resolve open issues identified in the October 5, 2010
NARA on or before February 15, 2011,
2. The Executive Secretary to provide his initial comments on the Plan and Schedule on or
before March 15, 2011, and for Denison and the Executive Secretary to finalize the Plan
and Schedule, and
3. Denison and the Executive Secretary to negotiate, finalize and execute a revised or
replacement SCA that incorporates the Plan and Schedule.

In addition, the Tolling Agreement (Rev. 0) required that the Tolling Period be extended from
January 4, 2010 (submittal of the 2009 CIR to the Executive Secretary) until Apri1 30, 2011.
Pursuant to the Tolling Agreement (Rev. 0), Denison submitted a Plan and Schedule on February
14, 2011 and a revised Plan and Schedule on February 18, 2011, and the Executive Secretary
provided his comments on the revised Plan and Schedule on March 21, 2011. In an April 20,
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2011 meeting, Denison and the Executive Secretary agreed that the Plan and Schedule to conduct
additional nitrate investigations would be composed of at least four (4) and possibly five (5)
phases of study, including:
1. Phase 1A through C - including geoprobe drilling, and soil sampling/analysis of soils to
investigate:
a. Possible natural nitrate salt reservoir in the vadose zone beyond the mill site area
(Phase 1A);
b. Potential nitrate sources in the mill site area (Phase 1 B); and
c. Other potential nitrate sources (Phase 1 C).
2. Phase 2 - including groundwater quality sampling and analysis of existing monitoring
wells for non-isotopic analytes.
3. Phase 3 - including deep bedrock core sampling/analysis of possible natural nitrate
reservoir and potential nitrate source locations, with similar objectives as Phases 1 A
through C.
4. Phase 4 - including stable isotopic sampling/analysis of groundwater in existing
monitoring wells. Details of this investigation were to be determined at a later date, and
approved by both parties.
5. Phase 5 - including stable isotopic sampling/analysis of soil/core samples, if needed.

On April 28, 2011, Denison and the Executive Secretary entered into a Revised Tolling
Agreement (Tolling Agreement (Rev. 1), to extend the Tolling Period through June 30, 2011 and
adopt the agreements made in the April 20, 2011 meeting. Under the Tolling Agreement (Rev.
1), Denison agreed to submit a Revised Phase 1 (A through C) Work Plan on or before May 6,
2011 and a Revised Phase 2 through 5 Work Plan and Schedule on or before June 3, 2011.
Pursuant to the Tolling Agreement (Rev. 1), Denison submitted a May 6, 2011 Revised Phase 1
Work Plan and Schedule for the Phase 1 A - C investigation prepared by INTERA, for Executive
Secretary review. On May 11, 2011, the DRC: 1) provided via email, comments on the May 6,
2011 INTERA document, and requested that Denison resolve all DRC comments before
initiation of field activities. All comments were resolved, and Denison conducted field and
laboratory work for the Phase l A-C study in May and June, 2011.
Pursuant to the Tolling Agreement (Rev. 1), Denison submitted a June 3, 2011 Revised Phase 2
through 5 Work Plan and Schedule (Phase 2 - 5 Work Plan), prepared by INTERA, for Executive
Secretary review. In a letter dated June 23, 2011 DRC provided comments on this Denison
document in the form of a URS memorandum, dated June 23, 2011 and advised Denison that in
order to revise the 2009 SCA to incorporate the deliverables and timelines set out in an
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approvable Phase 2 through 5 Work Plan, it would be necessary to provide a level of detail in
revisions of that Work Plan for Phases 2, 3, 4, and 5 comparable to the level of detail for Phase 1
contained in Attachment 1 of the Tolling Agreement (Rev. 1).
On June 30, 2011, Denison and the Executive Secretary entered into a Revised Tolling
Agreement [Tolling Agreement (Rev. 2)] to extend the Tolling Period to August 31, 2011, in
order to facilitate the revision of the Phase 2 through 5 Work Plan to provide the level of detail
required to construct a replacement SCA. Pursuant to the Tolling Agreement (Rev.2), Denison
submitted a separate July 1, 2011 detailed Work Plan and Quality Assurance Plan ("QAP") for
the Phase 2 investigation (Phase 2 Plan, Revision 0). Executive Secretary comments on this
document were provided in a July 7, 2011 DRC letter. Denison provided a revised July 12, 2011
Phase 2 QAP and Work Plan (Phase 2, Revision 1.0), which DRC conditionally approved in a
letter dated July 18, 2011.
On August 1 and 2, 2011 Denison submitted by email preliminary laboratory results for the
Phase l A-C study to the Executive Secretary.
On August 4, 2011, Denison provided a revision to the Phase 2 - 5 Work Plan (Phase 2-5 Work
Plan, Revision 1.0), prepared by INTERA, for Executive Secretary review. DRC comments on
the Phase 2-5 Work Plan, Revision 1.0 and on the August 1, 2011 preliminary laboratory results
for the Phase l A-C study, were provided to Denison on August 11, 2011 as part of a conference
call, and a DRC email, which included an August 11, 2011 URS memorandum. Under a cover
letter dated August 18, 2011, Denison submitted a revised Phase 2-5 Work Plan (Phase 2-5 Work
Plan, Revision 2.0) for Executive Secretary review, in response to the comments provided to
Denison on August 11, 2011.
As discussed in the following Sections, DRC and Denison have agreed to proceed with
corrective action.
In an August 25, 2011 DRC letter, the Executive Secretary advised that per review of the Phase
2-5 Work Plan, Revision 2.0, the Executive Secretary has determined that a finalized Plan and
Schedule, that meets the satisfaction of the Executive Secretary, and which would allow the
preparation of a replacement SCA, is not possible at this time; and that the development of a
replacement SCA for continued contaminant investigation activities is not supported.
At a meeting between Denison and DRC on August 29, 2011 to discuss the Executive
Secretary’s August 25, 2011 findings related to the Phase 2-5 Work Plan Rev. 2.0, the
preliminary laboratory results for the Phase I A-C study, and the approach forward, Denison and
DRC agreed that:
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1. After more than two years of investigation it has been determined that there are site
conditions that make it difficult to determine the source(s) of the contamination at the
White Mesa site;
2. As a result, resources will be better spent in developing a CAP in accordance with UAC
R317-6-6.15(D), rather than continuing with further investigations as to the source(s) of
the contamination.

During discussion throughout October 2011, Denison and the Executive Secretary acknowledged
that it has not been possible to date to determine the source(s), cause(s), attribution, magnitudes
of contribution, and proportion(s) of the local nitrate and chloride in groundwater, and thereby
cannot eliminate Mill activities as a potential cause, either in full or in part, of the contamination.
As a result, Denison and the Executive Secretary agreed that resources will be better spent in
developing a CAP in accordance with UAC R317-6-6.15(D), rather than continuing with further
investigations as to the source(s) and attribution of the groundwater contamination.
2.2 Conclusions from the Contamination Investigation
The contamination investigation program from 2009 to 2011 has provided a basis for
development of a CAP. Specifically the investigation has determined:
• the areal and spatial extent of the plume,
• that the plume does not appear to be increasing in size or concentration,
• that there are no known unaddressed current or ongoing sources of contamination.

As discussed above, a number of potential mill and non-mill sources were identified in the
December 2009 Source Review Report for Nitrate and Chloride in Groundwater at the Mill, and
in the subsequent August 2011 Nitrate Investigation Revised Phases 2 through 5 Work Plan.
Based on the investigation and source evaluations, there are no known current unidentified or
unaddressed sources. There appear to have been a number of known and potential historic
sources; however, it has not been possible to confirm or quantify the contribution of each.
Analytical results indicate that neither the average concentration of the plume nor the areal extent
of the plume have increased during the monitored period. The only potential current source
identified and potentially requiring control is the ammonium sulfate tanks. This potential source
is addressed in Phase I of the CAP, discussed in Sections 3.2.1 and 7.1 below.
The Executive Secretary determined that a CAP is required at the White Mesa facility, pursuant
to UAC R317-6-6.15(C)(I) and Denison agreed to develop, secure Executive Secretary approval,
and implement a CAP. The Executive Secretary has therefore determined, and Denison agreed to
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past two years, it would appear that there is no significant
unaddressed currently active source. That is,
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submit a CAP, pursuant to the requirements of the Utah Ground Water Quality Protection Rules
[UAC R317 -6-6.15(C - E)].
The purpose of Phase I of this CAP is to remedy the effects of the ammonium sulfate tank
potential source. The purpose of each of the proposed phases of this CAP is discussed further in
section 3.2.
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3. FRAMEWORK AND OBJECTIVES OF THE CAP
Applicable regulations and requirements governing the CAP, and preliminary milestones are
discussed in Sections 3.1 through 3.3.
3.1 Applicable Regulations and Requirements
Denison agreed to submit a CAP for Executive Secretary review and approval, on or before
November 30, 2011 that meets the CAP related requirements of UAC R317-6-6.15 (D.2, 3 and
E). This document constitutes the “Nitrate CAP”.
The remaining sections of this CAP are intended to demonstrate, per the requirements in UAC
R317 -6-6.15(D)(2) and (3), that:
• the proposed action(s) are protective of public health and the environment, including
consideration of future impacts of the nitrate plume on land and water resources not
owned and controlled by Denison.
• the corrective action meets the State Ground Water Quality Standards, pursuant to UAC
R317 -6-6.15(F). Alternatively, Denison may petition the Utah Water Quality Board for
approval of an Alternate Corrective Action Concentration Limit as part of the CAP,
Phase III, pursuant to UAC R317 -6-6.15(G).
• the action will produce a permanent effect.

Per UAC R317 -6-6.15(D)(2) and (3) the action proposed in the CAP is required to meet any
other additional measure required by the Executive Secretary under UAC R317 -6-6.15(E)(5).
Denison has agreed with the Executive Secretary that these additional measures shall include, but
are not limited to:
• Remediation guidance found in the April, 2004 EPA Handbook of Groundwater
Protection and Cleanup Policies for RCRA Corrective Action (EPA530-R-04-030) or
equivalent, to the extent applicable, as determined by the Executive Secretary;
• Determination of corrective action performance standards, objectives, and criteria for
groundwater remediation system design, construction, operations and/or maintenance, as
approved by the Executive Secretary in accordance with applicable regulations;
• Determination of long term operation, maintenance, system performance and
groundwater quality monitoring requirements to evaluate effectiveness of the approved
corrective action(s), at a frequency, and by methods approved by the Executive Secretary;
• Submittal of written quarterly Denison reports of pumping and monitoring well system
performance and groundwater quality monitoring information for Executive Secretary
review and approval. In the event that additional information is required of any report,
Denison shall respond to and provide a Plan and Schedule for Executive Secretary
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approval to resolve all issues /concerns within 30 calendar days of receipt of written
Executive Secretary notice;
• Timely Denison verbal and written notification of process or equipment failures, and
corrective actions taken, or a timely schedule by which corrective action will be taken to
return the facility to full compliance with CAP performance standards, objectives, and
criteria; and
• Periodic Denison review, summation, and report submittal, for Executive Secretary
approval, to demonstrate if the approved corrective action is protective of public health
and the environment. The interval of said report period shall not exceed five (5) years.

3.2 Objectives of the CAP
The objectives of the CAP are the following:
• Minimize or prevent further downgradient migration of the perched nitrate plume (Figure
1-2) by a combination of pumping and reliance on natural attenuation,
• Prevent nitrate concentrations exceeding the action level from migrating to any potential
point of exposure,
• Monitor to track changes in concentrations within the plume and to establish whether the
plume boundaries are expanding, contracting, or stable,
• Provide contingency plans to address potential continued expansion of the plume and the
need for additional monitoring and/or pumping points, and
• Ultimately reduce nitrate concentrations at all monitoring locations to the action level or
below.

To achieve these objectives, the CAP proposes a phased approach.
3.2.1 Summary of Phase I Objectives and Scope
Per Section 11A(1) of the SCA, Phase I is required to include a control for the soil contamination
observed at the ammonium sulfate tanks, a potential source of perched groundwater
contamination. Pursuant to UAC 317-6-6.15 (E)(4)(b) this control will include at a minimum:
Determination, to the satisfaction of the Executive Secretary, of the physical extent of the soil
contamination observed at the ammonium sulfate tanks near borings GP-25B (Nitrate + Nitrite
(as N) 1,530 mg/kg-dry at depth of 6 feet) and GP-26B (Ammonia (as N) 1,590 mg/kg-dry at a
depth of 16 feet) that were part of the nitrate investigation. Such effort shall include an estimate
of the volume (the "Contaminated Soil Volume") of the contaminated soils down to but not
including bedrock, and an estimate of the surface area (the "Contaminated Surface Area") at or
above the estimated location of the Contaminated Soil Volume; and either a Plan and Schedule,
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to be submitted on or before January 1, 2012, for Executive Secretary approval, to cover the
Contaminated Surface Area with at least six inches of concrete, to the extent not already covered
by concrete or existing buildings, to prevent infiltration of surface water into the contaminated
soils; and/or a Plan and Schedule, to be submitted on or before January 1, 2012, for Executive
Secretary approval, to remove the Contaminated Soil Volume and dispose of the contaminated
soils in the Mill's tailings impoundments. If Denison chooses to cover the Contaminated Surface
Area with concrete, Denison must remove the Contaminated Soil Volume at a later date prior to
site closeout and must submit a revised surety estimate on or before March 4, 2012 to include
future costs to remove the Contaminated Soil Volume.
As discussed in Section 7.1 of this CAP, Denison proposes to construct a sloped and drained
concrete pad of six inches in depth over an area covering the lateral extent of contamination to be
determined as discussed in Section 7.1. Denison also proposes a future removal of contaminated
soil at the time of Mill site reclamation and, for conservatism, proposes to revise the reclamation
surety estimate to include a volume of soil to be removed and placed in the tailings area of twice
the volume of contaminated soil identified in the contamination investigation. Further details are
discussed in Section 7.1, below.
3.2.2 Summary of Phase II Objectives and Scope
Per Section 11A(2) of the SCA, Phase II is to include near term active remediation of the nitrate
contamination by pumping contaminated water into the Mill's tailings cells for disposal. Said
phase shall also include: 1) the development, implementation, operation, and monitoring
requirements for a pumping well network designed to contain and hydraulically control the
nitrate groundwater plume to maintain concentrations at or below the Utah Groundwater Quality
Standard (10 mg/L), i.e., prevent physical expansion of said plume, and 2) monitoring of
chloride concentrations.
Phase II constitutes an interim remedial action that consists of a combination of “active” and
“passive” strategies. The active strategy consists of removing nitrate mass as rapidly as practical
by pumping areas within the plume that have high nitrate concentrations and relatively high
productivity. Continued monitoring within and outside the plume is considered part of the active
strategy. The passive strategy consists of relying on natural attenuation processes to reduce
nitrate concentrations. Reductions in concentrations would be achieved by physical processes
such as hydrodynamic dispersion, and dilution via mixing with recharge and waters outside the
plume.
Natural attenuation is expected to reduce nitrate concentrations within the entire plume.
However, within upgradient portions of the plume that have the highest concentrations, direct
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mass removal via pumping will be the primary means to reduce concentrations. In downgradient
portions of the plume where concentrations are lower, natural attenuation will be a more
important mechanism in reducing concentrations.
3.2.3 Summary of Phase III Objectives and Scope
Per the SCA, Phase III is to include a comprehensive long term solution for the nitrate
groundwater contamination at the Mill Site. This phase will be undertaken at a later date after
public participation and Executive Secretary approval. Phase III may include, but is not limited
to: continuation of Phases I and II activities alone or in combination with monitored natural
attenuation, evaluation of additional remediation and monitoring technologies/techniques,
determination of any additional hydrogeologic characterization, groundwater contaminant travel
times and directions, determination of ultimate points of exposure to the public and/or wildlife,
appropriate risk analysis, a cost/benefit analysis, and the possible development of and petition to
the Board for alternate corrective action concentration limits pursuant to UAC R317 -6-6 .15 (G).
This CAP does not specify the details of Phase III, at this time. A Phase III preliminary plan and
schedule for the evaluation of alternatives, for the completion of any further studies, analyses,
applications and petitions, and for the ultimate definition of Phase III, may be proposed by
Denison at a later date, after completion of such studies and evaluations, followed by submittal
of a proposed CAP revision to the Executive Secretary. Until such time, the activities of the
Phase I and Phase II remediation will continue as stipulated in the approved CAP.
The CAP is not intended to address contamination located outside the Mill's restricted area and
that is not contiguous with groundwater contamination inside the Mill's restricted area. The CAP
will therefore evaluate which of the existing monitoring wells will be maintained and which
wells (including certain upgradient and off-site wells) can be abandoned, subject to prior
Executive Secretary approval.
It should be noted that while Phase II of the CAP requires monitoring of chloride concentrations,
the CAP does not explicitly identify measures for controlling chloride levels per se, because
there is no health standard for chloride in groundwater. However, as discussed and agreed to
with DRC during meetings in October 2011, chloride appears to be co-located with nitrate in
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3.3 Preliminary Milestones for the CAP
Per the SCA, Denison has committed to the following milestones for corrective action. Dates for
the following milestones will be established based on the date of the Executive Secretary’s
approval of the CAP and issuance of a Consent Order approving the CAP.
• Within 30 calendar days of the Executive Secretary’s approval of the CAP, pursuant to
UAC R317-6-6.15(E), Denison shall commence implementation and execution of all
corrective actions required under a future Consent Order to be issued by the Executive
Secretary that addressed the approved CAP. A proposed schedule for implementation of
the CAP is included as Table 1 to this CAP.
• Within 60 calendar days of the Executive Secretary’s issuance of a future Consent Order
regarding the approved CAP, pursuant to UAC R317-6-6.15(E), Denison will submit a
revised Reclamation Plan and financial surety cost estimate (Revised Surety), for
Executive Secretary review and approval which addresses the groundwater corrective
action, with the surety sufficient to recover the anticipated cost and time frame for
achieving compliance, before the land is transferred to the federal government for long-
term custody. At a minimum, the Denison surety will provide for all costs for Phases I
and II of the approved CAP for a period of time until Executive Secretary approval of
Phase III of the CAP to restore groundwater to the established site specific groundwater
cleanup standards pursuant to UAC R317-6-6.15 before the site is transferred to the
federal government for long term custody.
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4. BACKGROUND
Sections 3.1 through 3.4 provide a brief description of site hydrogeology that is based primarily
on TITAN (1994), but includes the results of more recent site investigations. Section 3.5
discusses the occurrence of nitrate in the perched water at the site and focuses on the nitrate
plume shown in Figure 1-2.
4.1 Geologic Setting
The Mill is located within the Blanding Basin of the Colorado Plateau physiographic province.
Typical of large portions of the Colorado Plateau province, the rocks underlying the site are
relatively undeformed. The average elevation of the site is approximately 5,600 feet above mean
sea level (ft amsl).
The site is underlain by unconsolidated alluvium and indurated sedimentary rocks consisting
primarily of sandstone and shale. The indurated rocks are relatively flat lying with dips generally
less than 3º. The alluvial materials consist mostly of aeolian silts and fine-grained aeolian sands
with a thickness varying from a few feet to as much as 25 to 30 feet across the site. The alluvium
is underlain by the Dakota Sandstone and Burro Canyon Formation, which are sandstones having
a total thickness ranging from approximately 100 to 140 feet. In portions of the site, a few feet to
as much as about 30 feet of Mancos Shale lies between the alluvium and the Dakota Sandstone.
Beneath the Burro Canyon Formation lies the Morrison Formation, consisting, in descending
order, of the Brushy Basin Member, the Westwater Canyon Member, the Recapture Member,
and the Salt Wash Member. Figure 2 is a photograph of the contact between the Burro Canyon
Formation and the underlying Brushy Basin Member taken from a location along highway 95
immediately north of the Mill. This photograph illustrates the transition from the cliff-forming
sandstone of the Burro Canyon Formation to the slope-forming Brushy Basin Member.
The Brushy Basin and Recapture Members of the Morrison Formation, classified as shales, are
very fine-grained and have a very low hydraulic conductivity. The Brushy Basin Member is
primarily composed of bentonitic mudstones, siltstones, and claystones. The Westwater Canyon
and Salt Wash Members also have a low average vertical hydraulic conductivity due to the
presence of interbedded shales.
Beneath the Morrison Formation lie the Summerville Formation, an argillaceous sandstone with
interbedded shales, and the Entrada Sandstone. Beneath the Entrada lies the Navajo Sandstone.
The Navajo and Entrada Sandstones constitute the primary aquifer in the area of the site. The
Entrada and Navajo Sandstones are separated from the Burro Canyon Formation by
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approximately 1,000 to 1,100 feet of materials having a low average vertical hydraulic
conductivity. Groundwater within this system is under artesian pressure in the vicinity of the site,
is of generally good quality, and is used as a secondary source of water at the site.
4.2 Hydrogeologic Setting
The site is located within a region that has a dry to arid continental climate, with an average
annual precipitation of approximately 13.3 inches, and an average annual lake evaporation rate
of approximately 47.6 inches. Recharge to the principal aquifers occurs mainly along the
mountain fronts (for example, the Henry, Abajo, and La Sal Mountains), and along the flanks of
folds such as Comb Ridge Monocline.
Although the water quality and productivity of the Navajo/Entrada aquifer are generally good,
the depth of the aquifer (approximately 1,200 feet below land surface [ft bls]) makes access
difficult. The Navajo/Entrada aquifer is capable of yielding significant quantities of water to
wells (hundreds of gallons per minute [gpm]). Water in wells completed across these units at the
site rises approximately 800 feet above the base of the overlying Summerville Formation.
Perched groundwater in the Dakota Sandstone and Burro Canyon Formation originates mainly
from precipitation and local recharge sources such as unlined reservoirs (Kirby, 2008) and is
used on a limited basis to the north (upgradient) of the site because it is more easily accessible
than the Navajo/Entrada aquifer. Water quality of the Dakota Sandstone and Burro Canyon
Formation is generally poor due to high total dissolved solids (TDS). The saturated thickness of
the perched water zone is generally higher to the north of the site.
4.3 Perched Zone Hydrogeology
Perched groundwater beneath the site occurs primarily within the Burro Canyon Formation.
Perched groundwater at the site has a generally low quality due to high total TDS in the range of
approximately 1,100 to 7,900 milligrams per liter (mg/L), and is used primarily for stock
watering and irrigation in the areas upgradient (north) of the site where generally higher
saturated thicknesses increase well yields. Perched water is supported within the Burro Canyon
Formation by the underlying, fine-grained Brushy Basin Member. Figure 3 is a contour map
showing the approximate elevation of the contact of the Burro Canyon Formation with the
Brushy Basin Member, which essentially forms the base of the perched water zone at the site.
Contact elevations between the Burro Canyon Formation and Brushy Basin Member in Figure 3
are based on perched monitoring well drilling and geophysical logs and surveyed land surface
elevations. As indicated, the Burro Canyon Formation/Brushy Basin Member contact (although
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irregular because it represents an erosional surface) generally dips to the south/southwest beneath
the site.
Appendix A contains hydrogeologic cross-sections that intersect within the nitrate plume. These
cross-sections show the site lithology above the Brushy Basin Member, perched water within the
Dakota Sandstone/Burro Canyon Formation, and the occurrence of nitrate within the perched
water. As shown in Figure A.2, relatively thick conglomeratic intervals exist within the saturated
zone at MW-31, located at the downgradient edge of the nitrate plume. As discussed below,
these intervals appear to pinch out to the south (downgradient) and to the west (cross-gradient) of
MW-31.
Less conglomeratic material is present in the saturated zone at MW-30 and MW-3A than at MW-
31, as shown in the attached lithologic logs (Appendix B). Thin conglomeratic zones
(approximately 1-2 feet thick) occur at the base of the perched zone in MW-31 and MW-3A.
Detailed lithologic logs for MW-5, MW-11, MW-14 and MW-15 are not available to assess the
presence of conglomeratic material at those locations. However, saturated conglomeratic
materials were not encountered at MW-34 and MW-37 (located adjacent to MW-15), as shown
in the attached lithologic logs.
Based on the available information, significant conglomeratic horizons within the saturated
perched zone do not appear to exist at or downgradient of MW-30. Furthermore, hydraulic test
data from MW-30 and MW-31 indicate that the conglomeratic zones in MW-31 do not enhance
the permeability at MW-31. The hydraulic conductivity estimates (based on KGS solution
analysis of automatically logged slug test data) for MW-30 and MW-31 are similar. The
hydraulic conductivity estimates for MW-30 and MW-31, respectively, are 1 x 10-4 cm/s and 7 x
10-5 cm/s (HGC, 2005).
4.3.1 Lithologic and Hydraulic Properties
Although the Dakota Sandstone and Burro Canyon Formations are often described as a single
unit due to their similarity, previous investigators at the site have distinguished between them.
The Dakota Sandstone is a relatively hard to hard, generally fine-to-medium grained sandstone
cemented by kaolinite clays. The Dakota Sandstone locally contains discontinuous interbeds of
siltstone, shale, and conglomeratic materials. Porosity is primarily intergranular. The underlying
Burro Canyon Formation hosts most of the perched groundwater at the site. The Burro Canyon
Formation is similar to the Dakota Sandstone but is generally more poorly sorted, contains more
conglomeratic materials, and becomes argillaceous near its contact with the underlying Brushy
Basin Member. The hydraulic conductivities of the Dakota Sandstone and Burro Canyon
Formation at the site are generally low.
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No significant joints or fractures within the Dakota Sandstone or Burro Canyon Formation have
been documented in any wells or borings installed across the site (Knight-Piésold, 1998). Any
fractures observed in cores collected from site borings are typically cemented, showing no open
space.
4.3.1.1 Dakota
Porosities of the Dakota Sandstone range from 13.4% to 26%, averaging 20%, and water
saturations range from 3.7% to 27.2%, averaging 13.5%, based on samples collected during
installation of wells MW-16 (abandoned) and MW-17 (Figure 1-2). The average volumetric
water content is approximately 3%. The hydraulic conductivity of the Dakota Sandstone based
on packer tests in borings installed at the site ranges from approximately 2.7 x 10-6 centimeters
per second (cm/s) to 9.1 x 10-4 cm/s, with a geometric average of 3.9 x 10-5 cm/s.
4.3.1.2 Burro Canyon
The average porosity of the Burro Canyon Formation is similar to that of the Dakota Sandstone.
Porosity ranges from 2% to 29.1%, averaging 18.3%, and water saturations of unsaturated
materials range from 0.6% to 77.2%, averaging 23.4%, based on samples collected from the
Burro Canyon Formation at MW-16 (abandoned), located beneath new tailings Cell #4A. TITAN
(1994) reported that the hydraulic conductivity of the Burro Canyon Formation ranges from 1.9 x
10-7 to 1.6 x 10 -3 cm/s, with a geometric mean of 1.1 x 10-5 cm/s, based on the results of
12 pumping/recovery tests performed in monitoring wells and 30 packer tests performed in
borings prior to 1994. Subsequent hydraulic testing of perched zone wells has yielded a range of
2 x 10-7 to 0.01 cm/s (HGC, 2009a).
In general, the highest hydraulic conductivities and well yields are in the area of the site
immediately northeast and east (upgradient to cross gradient) of the tailings cells. A relatively
continuous, higher conductivity zone that is associated with the chloroform plume (HGC,
2007b) has been inferred to exist in this portion of the site. Analysis of drawdown data collected
from this zone during long-term pumping of MW-4, MW-26, and TW4-19 (Figure 1-2) yielded
estimates of hydraulic conductivity ranging from 4 x 10-5 to 1 x 10-3 cm/s (HGC, 2004). The
decrease in perched zone hydraulic conductivity south to southwest of this area indicates that this
higher conductivity zone “pinches out” (HGC, 2007b).
Hydraulic conductivities downgradient of the tailings cells are generally low. Hydraulic tests at
wells located at the downgradient edge of the cells, and south and southwest of the cells yielded
geometric average hydraulic conductivities of 2.3 x 10-5 and 4.3 x 10-5 cm/s depending on the
testing and analytical methods. The low hydraulic conductivities and shallow hydraulic gradients
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downgradient of the tailings cells result in average perched groundwater pore velocity estimates
that are among the lowest on site (approximately 1.7 ft/yr to 3.2 ft/yr based on calculations
presented in HGC, 2009a).
Hydraulic conductivities within the general area of the nitrate plume are based primarily on
analysis of slug tests at wells MW-27, MW-30, MW-31, TW4-20, TW4-21, TW4-22, TW4-24,
TW-25, TWN-1, TWN-2, TWN-3, and TWN-18 (HGC, 2005 and HGC, 2009a). The hydraulic
conductivity at MW-11 was based on a pumping test reported by UMETCO (1993) and the
hydraulic conductivity at TW4-19 was based on long-term pumping of that well for chloroform
removal (HGC, 2004). Hydraulic conductivity estimates range from approximately 2.7 x 10-5 to
1.4 x 10-3 cm/s, and have a geometric average of 1.2 x 10-4 cm/s, assuming unconfined
conditions (Table 2). The transmissivities of many wells within the nitrate plume are similar to
wells that are pumped for chloroform removal.
4.3.2 Perched Groundwater Flow
Perched groundwater flow at the site has historically been to the south/southwest (HGC, 2007b).
Figure 4 is a perched groundwater elevation contour map for the third quarter of 2011. These
contours are based on water levels measured in the perched groundwater monitoring wells shown
in the figure. Local depression of the perched water table occurs near wells MW-4, TW4-4,
TW4-19, TW4-20, and MW-26. These wells are pumped to reduce chloroform mass in the
perched zone east and northeast of the tailings cells as discussed in HGC (2007a).
Perched water mounds are associated with wildlife ponds on the east side of the site. The
mounds are likely the result of seepage from the unlined ponds. An apparent perched water
mound also exists in the vicinity of TWN-2 just north of the Mill site. The apparent perched
water mound near TWN-2 is likely a residual mound resulting from low permeability conditions
(Table 2) and the location of TWN-2 within the footprint of the historical pond (Figure 8).
Although the historical pond no longer exists and does not contain standing water, the remaining
topographic depression associated with the pond likely resulted in enhanced infiltration of
precipitation before recent re-grading of the land surface in that area. Slightly enhanced
infiltration of precipitation and low permeability conditions at TWN-2 likely allowed the mound
to persist. The decay of the mound is expected to be slow because of the low permeability.
A dry area to the southwest of Cell 4B is defined by the area where the kriged Brushy Basin
contact elevation rises above the kriged perched water level elevation. The lateral extent of the
dry area shown in Figure 4 is currently under investigation. The installation of wells along the
southern and western margins of Cell 4B in August, 2010 and April, 2011 indicate that the dry
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zone extends at least from the southwest central portion of Cell 4B to the southwest corner of
Cell 4B.
Beneath and downgradient of the tailings cells, on the west side of the site, perched water flow is
south-southwest to southwest. On the eastern side of the site perched water flow is more
southerly. Because of mounding near wildlife ponds, flow direction ranges locally from westerly
(west of the ponds) to easterly (east of the ponds). Perched zone hydraulic gradients currently
range from a maximum of approximately 0.07 ft/ft east of tailings Cell #2 (near well TW4-14) to
approximately 0.01 ft/ft downgradient of the tailings cells. Gradients may be steeper locally near
pumping wells (for example near TW4-20, where the gradient reaches approximately 0.09 ft/ft)
Perched water discharges in springs and seeps along Westwater Creek Canyon and Cottonwood
Canyon to the west-southwest of the site, and along Corral Canyon to the east of the site, (Figure
1-1) where the Burro Canyon Formation outcrops. The closest discharge points downgradient of
the tailings cells are Westwater Seep (approximately 2800 feet downgradient) and Ruin Spring
(approximately 9,400 feet downgradient [HGC, 2010]).
4.3.3 Saturated Thickness
The saturated thickness of the perched zone as of the third quarter of 2011 ranges from
approximately 92 feet in the northeastern portion of the site to less than 5 feet in the southwest
portion of the site (Figure 5). A saturated thickness of approximately 2 feet occurs in well
MW-34 along the south dike of new tailings Cell 4B, and the perched zone is apparently dry at
MW-33 located at the southwest corner of Cell 4B. Depths to water range from approximately 17
to 18 feet in the northeastern portion of the site (near the wildlife ponds) to approximately 114
feet at the southwest margin of tailings Cell #3 (Figure 6). The relatively large saturated
thicknesses in the northeastern portion of the site are likely related to seepage from the wildlife
ponds located northeast and east of the tailings cells.
Although sustainable yields of as much as 4 gpm have been achieved in wells intercepting the
larger saturated thicknesses and higher conductivity zones in the northeast portion of the site,
perched zone well yields are typically low (<0.5 gpm) due to the generally low hydraulic
conductivity of the perched zone. Sufficient productivity can generally be obtained only in areas
where the saturated thickness is greater, which is the primary reason that the perched zone has
been used on a limited basis as a water supply to the north (upgradient) of the site, but has not
been used downgradient of the site.
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4.4 Summary
Perched groundwater at the site is hosted primarily by the Burro Canyon Formation, which
consists of a relatively hard to hard, fine- to medium-grained sandstone containing siltstone,
shale and conglomeratic materials. The Burro Canyon Formation is separated from the
underlying regional Navajo/Entrada aquifer by approximately 1,000 to 1,100 feet of Morrison
Formation and Summerville Formation materials having a low average vertical hydraulic
conductivity. The Brushy Basin Member of the Morrison Formation is a bentonitic shale that lies
immediately beneath the Burro Canyon Formation and forms the base of the perched water zone
at the site. Figure 2 is a photograph of the contact between the Burro Canyon Formation and the
underlying Brushy Basin Member taken from a location along highway 95 immediately north of
the Mill. This photograph illustrates the transition from the cliff-forming sandstone of the Burro
Canyon Formation to the slope-forming Brushy Basin Member. Based on hydraulic tests at
perched zone monitoring wells, the hydraulic conductivity of the perched zone ranges from
approximately 2 x 10-7 to 0.01 cm/s.
Perched water flow is generally from northeast to southwest across the site. Beneath and
downgradient of the tailings cells, on the west side of the site, perched water flow is
south-southwest to southwest. On the eastern side of the site perched water flow is more
southerly. Because of mounding near wildlife ponds, flow direction ranges locally from westerly
(west of the ponds) to easterly (east of the ponds). Perched water generally has a low quality,
with total dissolved solids ranging from approximately 1,100 to 7,900 mg/L, and is used
primarily for stock watering and irrigation north (upgradient) of the site.
Depths to perched water range from approximately 17 to 18 feet near the wildlife ponds in the
northeastern portion of the site to approximately 114 feet at the southwestern margin of tailings
Cell #3. Saturated thicknesses range from approximately 92 feet near the wildlife ponds to less
than 5 feet in the southwest portion of the site, downgradient of the tailings cells. A saturated
thickness of approximately 2 feet occurs in well MW-34 along the south dike of new tailings
Cell 4B, and the perched zone is apparently dry at MW-33 located at the southwest corner of
Cell 4B. Although sustainable yields of as much as 4 gpm have been achieved in wells
penetrating higher transmissivity zones, well yields are typically low (<0.5 gpm) due to the
generally low hydraulic conductivity of the perched zone.
Hydraulic testing of perched zone wells has yielded a range of approximately 2 x 10-7 to 0.01
cm/s. In general, the highest hydraulic conductivities and well yields are in the area of the site
immediately northeast and east (upgradient to cross gradient) of the tailings cells. A relatively
continuous, higher hydraulic conductivity zone associated with the chloroform plume has been
inferred to exist in this portion of the site. Analysis of drawdown data collected from this zone
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during long-term pumping of MW-4, TW4-19, and MW-26 (TW4-15) yielded estimates of
hydraulic conductivity ranging from 4 x 10-5 to 1 x 10-3 cm/s.
Hydraulic conductivities downgradient of the tailings cells are generally low. Hydraulic tests at
wells located at the downgradient edge of the cells, and south and southwest of the cells yielded
geometric average hydraulic conductivities of 2.3 x 10-5 and 4.3 x 10-5 cm/s depending on the
testing and analytical method. The low hydraulic conductivities and shallow hydraulic gradients
downgradient of the tailings cells result in average perched groundwater pore velocity estimates
that are among the lowest on site.
Hydraulic conductivities within the general area of the nitrate plume are based primarily on
analysis of hydraulic tests as discussed in Section 4.3. Hydraulic conductivity estimates ranged
from approximately 2.7 x 10-5 to 1.4 x 10-3 cm/s, and have a geometric average of 1.2 x 10-4
cm/s, assuming unconfined conditions. The transmissivities of many wells within the nitrate
plume are similar to wells that are pumped for chloroform removal.
4.5 Nitrate Occurrence
Nitrate within the area shown in Figure 1-2 was first detected in wells TW4-19, TW4-22, TW4-
24, and TW4-25 that were installed as part of the investigation of a chloroform plume first
discovered at perched well MW-4 in 1999. Investigation of nitrate has included the installation
of 19 temporary (TWN-series) perched zone nitrate monitoring wells to delineate and monitor
the nitrate (Figure 1-2). The extent of nitrate contamination is described below and in further
detail in Section 5.1 and its associated figures.
Nitrate concentrations in the perched zone as of the third quarter of 2011 are shown in Figure 7.
Nitrate concentrations in the perched zone have ranged from non-detect to a maximum of 69
µg/L at well TWN-2 in the second and third quarters of 2010. Nitrate concentrations at
downgradient wells MW-30 and MW-31 have been relatively stable, ranging from 15 to 17 mg/L
at MW-30 and from 20 to 22 mg/L at MW-31 between the first quarter of 2010 through the third
quarter of 2011.
Constituents associated with the nitrate include chloride, and in the east-central portion of the
plume, chloroform. The association of nitrate with chloroform is discussed in HGC, 2007b.
4.5.1 Source Areas
As discussed above, a number of potential Mill and non-Mill sources were identified in the
December 2009 Source Review Report for Nitrate and Chloride in Groundwater at the White
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Mesa Mill (INTERA, 2009), and in the subsequent August 2011 Nitrate Investigation Revised
Phases 2 through 5 Work Plan (INTERA, 2011), as listed below:
1. Main leach field (also known as leach field east of scale house, 1985 to present)
2. Sewage vault/lift station (currently active)
3. Scale house leach field, (also known as leach field south of scale house, 1977-1979)
4. Former office leach field
5. Ammonia tanks
6. SAG leach field (leach field north of Mill building, 1998 to 2009)
7. Cell 1 leach field (leach field east of Cell #1, up to 1985)
8. Fly Ash Pond
9. Sodium chlorate tanks (as a potential chloride source)
10. Ammonium sulfate crystal tanks
11. Lawzy sump
12. Lawzy Lake
13. Former vault/lift station (to former office leach field, 1992 to 2009)
14. Truck shop leach field (1979-1985)
15. New Counter Current Decant/Solvent Extraction (“CCD/SX”) leach field (currently
active)
16. Historical Pond
17. Wildlife pond
18. CCD (included inadvertently and eliminated)
19. YC Precip Mini-Lab
20. V2O5 Mini-Lab & V2O5 Precip
21. SX Mini-Lab
22. Chem Lab
23. Met Lab
24. V2O5 oxidation tanks
25. Natural nitrate reservoir
26. – 32. Seven other ponds or pond-like sources
Figure 8 shows the locations of potential source areas 1 through 24.
Based on the investigation and source evaluations completed to date, there are no known current
unidentified or unaddressed ongoing sources. There appear to have been a number of known and
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potential historic sources; however, it has not been possible to confirm or quantify the
contribution of each. Soil contamination associated with the ammonium sulfate tanks as a
potential source to perched groundwater is addressed as Phase I of this CAP.
Although the actual source or sources have not been identified and quantified, based on analysis
of the concentrations within and the areal extent of the plume over the past two years, Denison
and DRC have concluded there is no known significant unaddressed currently active source. That
is, analytical results indicate that neither the average concentration within the plume nor the areal
extent of the plume has increased during the period it has been monitored. Therefore, although
the source or sources have not been definitively determined, sufficient information exists to
bound and characterize the plume and plan remedial actions for its control.
4.5.2 Nitrate Concentration Trends
Table 3 provides nitrate concentrations detected at wells within the nitrate plume from the first
quarter, 2010 through the third quarter of 2011. Over the last year (between the third quarter,
2010 and third quarter, 2011) three wells decreased in concentration, three increased, and three
remained the same. The well with the highest concentrations, TWN-2, decreased from 69 mg/L
to 33 mg/L. The average nitrate concentration within the plume decreased from 24.4 mg/L to
19.7 mg/L. At the downgradient edge of the plume, monitor wells MW-30 and MW-31 have
been sampled since June 2005. During the period from June 2005 to December 2011, samples
from MW-30 have had an average nitrate concentration of 16 mg/L with a standard deviation of
1.4 mg/L (Figure 9-1). During the same period, samples from MW-31 have had an average
nitrate concentration of 22 mg/L with a standard deviation of 2.7 mg/L (Figure 9-1). Thus, the
downgradient edge of the plume has been relatively stable over a six and one half year period.
The information presented above indicates that concentrations within the plume are relatively
stable but the highest concentrations appear to be declining. Figure 9-2 compares the extent of
the nitrate plumes in the third quarter of 2010 and the third quarter of 2011. As indicated, the
plume boundaries are relatively stable, likely the result of the generally low hydraulic
conductivity of the perched zone, and the ongoing pumping related to the chloroform plume.

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5. CHARACTERIZATION OF STUDY AREA
The study area encompasses a region in the northeastern portion of the site where the nitrate
plume (defined by concentrations > 10 mg/L) has been detected and bounded by a series of
nitrate and chloroform investigation wells (Figure 1-2). Wells within the plume are MW-30 and
MW-31, and temporary wells TW4-19, TW4-21, TW4-22, TW4-24, TW4-25, TWN-2 and
TWN-3 (Figure 7). Wells MW-5, MW-11, MW-25, MW-26, MW-27, MW-28, MW-29, MW-
32, TW4-16, TW4-18, TWN-1, TWN-4, TWN-7, and TWN-18 bound the plume. As of the
second quarter of 2011, MW-5, MW-11, MW-25, MW-29, and MW-32 were non-detect for
nitrate. Hydraulic characterization of the study area has been based on data collected from wells
within and near the plume as discussed in Section 4. The extent and hydrogeology of the study
area is discussed below.
5.1 Extent of Study Area
The nitrate plume that is the focus of this CAP is confined to the region of the perched zone
containing nitrate concentrations exceeding 10 mg/L located south of TWN-18 and north of
MW-11. The area having nitrate exceeding 10 mg/L, as of the third quarter of 2011, is shown in
Figures 1-2 and 7. This area extends from the northeast portion of the tailings cells to the area
upgradient (north-northeast) of the tailings cells. The highest nitrate concentrations have
historically been detected at TWN-2, within the northern (upgradient) portion of the plume.
TWN-2 is located within the area of the historical pond (Figure 8).
The historical pond was active as far back as the 1920s, as much as 60 years prior to the
establishment of the White Mesa Mill. Satellite photos taken over the years and dating back to
the 1950s indicate that the historical pond was one of the major agricultural/livestock ponds in
the area and typically contained water. Records or information have not been obtained to
evidence the actual uses of the pond over the years. The historical pond likely collected runoff
from nearby agricultural land, which may have been fertilizer-laden. The pond may have also
been used as a stock pond and have been influenced by the ranching or agricultural activities.
Regardless of the specific uses of the pond, water within the pond appears to have been elevated
in nitrate and chloride. Because the pond was unlined, significant seepage of nitrate and chloride
laden water is expected to have reached the perched zone.
Areas of detectable nitrate that are not continuous with the above defined area exist to the
northwest (near TWN-9 and TWN-17) and to the east-southeast associated with the chloroform
plume. Nitrate concentrations within these areas are typically less than 10 mg/L although
sporadic detections at or slightly above 10 mg/L have occurred at some locations. Areas to the
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northeast are not a target of this CAP, and nitrate associated with the chloroform plume is
addressed by the ongoing chloroform pumping.
The nitrate plume, as defined by the 10 mg/L concentration boundary, is bounded by wells MW-
5, MW-11, MW-25, MW-26, MW-27, MW-28, MW-29, MW-32, TW4-16, TW4-18, TWN-1,
TWN-4, TWN-7, and TWN-18. As of the second quarter of 2011, MW-5, MW-11, MW-25,
MW-29, and MW-32 were non-detect for nitrate. The plume is bounded to the south by MW-5
and MW-11, to the east by MW-27, MW-28, MW-29 and TWN-7, to the north by TWN-18, and
to the west by MW-25, MW-26, MW-32, TWN-1, TWN-4, TW4-18, TW4-16, and TW4-20.
Additional wells to the south (downgradient) of the plume include MW-3, MW-14, MW-15 and
MW-37.
5.2 Hydrogeology
A description of the hydrogeology of the site in the vicinity of the nitrate plume is provided in
Section 3, and hydrogeologic cross-sections are provided in Appendix A. Perched zone hydraulic
conductivities in the vicinity of the nitrate plume are in the middle to high end of the range
measured at the site. The geometric average of approximately 1.2 x 10-4 cm/s is slightly lower
than typical for the area of the chloroform plume located east and southeast of the nitrate plume
(Figure 10).
Perched groundwater flow in the area of the nitrate plume is generally southwesterly. Saturated
thicknesses in the vicinity of the plume are generally higher than in areas to the south and
southwest. In the vicinity of the nitrate plume (Figure 5) they range from a maximum of
approximately 87 ft at TW4-25 to approximately 30 ft at MW-30. In general, saturated
thicknesses increase toward the northeast, where the wildlife ponds are located, and are locally
affected in the vicinity of the plume by pumping at MW-26, TW4-19, and TW4-20.
Hydraulic conductivities within the general area of the nitrate plume are based primarily on
analysis of slug tests as discussed in Section 3. Hydraulic conductivity estimates range from
approximately 2.7 x 10-5 to 1.4 x 10-3 cm/s, and have a geometric average of 1.2 x 10-4 cm/s
(Table 2). The transmissivities of many wells within the nitrate plume are similar to wells that
are pumped for chloroform removal.
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6. CORRECTIVE ACTION CONCENTRATION LIMITS
The corrective action concentration limit for nitrate is 10 mg/L. This concentration is considered
to bound the outer extent of the plume and is the ultimate target for reducing nitrate
concentrations within the plume. As discussed in Section 9, once the nitrate concentrations in all
monitoring wells are 10mg/L or less, concurrence with DRC will be sought that the plume is
remediated and the corrective action complete.
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7. CORRECTIVE ACTION PLAN - CONSTRUCTION AND OPERATION
The corrective action for the nitrate plume is proposed to occur in three phases.
In Phase I, Denison proposes to construct a sloped, curbed and drained concrete pad of six inches
in depth over an area covering at least twice the areal extent of contamination identified during
the contamination investigation. Denison also proposes a future removal of contaminated soil at
the time of Mill site reclamation and, for conservatism, proposes to revise the reclamation surety
estimate to include a volume of soil to be removed and placed in the tailings cells of twice the
volume of contaminated soil identified in the contamination investigation.
Phase II will consist of pumping four wells within the nitrate plume (TW4-22, TW4-24, TW4-
25, and TWN-2). Phase II relies on both pumping and natural attenuation to remove nitrate mass,
reduce nitrate concentrations within the plume, and minimize or prevent plume migration.
Included in Phase II are continued monitoring within and outside the plume to verify plume
boundaries (as defined by a concentration of 10 mg/L), estimate changes in hydraulic capture,
and track changes in nitrate concentrations within the plume.
If implemented, Phase III will consist of a transport assessment, a hazard assessment, and an
exposure assessment along with a corrective action assessment including an evaluation of best
available remedial technologies. Selection of a technology for implementation will be based on
an evaluation whether the technology will remediate contamination to as low as is reasonably
achievable, if the 10 mg/L standard is not reasonably achievable. One possible outcome of these
evaluations could be an application for alternate corrective action concentration limits (ACACL).
After implementation of Phase II and Phase III and once residual concentrations have dropped to
10 mg/L or less at all monitored locations or an ACACL has been granted, concurrence with the
Executive Secretary will be sought that the corrective action is complete. Phase II has
contingencies to be implemented if needed based on monitoring as discussed in Section 8. The
termination of Phase II and implementation of Phase III will be with the concurrence of the
Executive Secretary and will be based on assessments conducted during Phase II.
An important goal of Phase III is to ensure that nitrate concentrations exceeding the action level
will not migrate to any point of exposure within the applicable regulatory time frame. This
migration of the nitrate plume is not expected to occur. However, the decision as to when to
terminate Phase II and implement Phase III will be based on Phase II monitoring data and
quantitative calculations that indicate that, based on Phase II results, this Phase III goal is
attainable.
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7.1 Phase I Description and Rationale
The potential contamination source to be addressed in Phase I consists of alluvial soil in the area
of the Mill’s outdoor ammonium sulfate storage tanks as depicted in Figure 11-1. As shown in
Figure 11-1, the ammonium sulfate tanks and associated soil contamination are located to the
east of the Mill process building. The tanks are currently situated over an uncurbed concrete slab,
which has suffered some deterioration over the years. The tank area is bounded to the west by the
Mill building, to the south by the V2O5 Mini Lab and Precipitation Area, and to the north by the
Mill’s Pulp Storage Tanks. That is, the ammonium sulfate tanks are located in a relatively
congested and (on three sides) built out area. The proximity of the Mill building and other tanks
precludes the ability to perform an extensive soil excavation/contaminated soil removal at the
current time. Therefore, consistent with the SCA, Denison proposes to perform the contaminated
soil corrective action phase in two steps; 1) construction of a concrete cover to remain in place
during the operating life of the Mill, and 2) a contaminated soil excavation to occur during the
Mill reclamation at final Mill closure.
7.1.1 Approximation of the Lateral Extent of Contamination and Concrete Cover
Per Section 11A(1) of the SCA, Phase I is required to include a control for the soil contamination
observed at the ammonium sulfate tanks. To meet this objective, Denison proposes to construct a
sloped and drained concrete pad of six inches in depth over an area covering the areal extent of
contamination identified during the contamination investigation to prevent infiltration of surface
water into the contaminated soil. Existing data consists of analytical data from two of the soil
borings collected during the June 2011 contamination investigation as shown in Figure 11-1. In
order to verify that the proposed concrete pad meets the objective of covering the lateral extent
of contamination, Denison will implement a soil sampling program prior to the completion of the
concrete pad. The soil sampling program is designed to provide data to delineate, approximately,
the lateral extent of contamination.
The soil sampling program will be conducted substantially in accordance with the DRC-
approved field and quality assurance procedures implemented during the Phase 1, (Part 1) Nitrate
Investigation as described in the Nitrate Investigation Phase 1 Work Plan, dated May 13, 2011.
A summary of the soil sampling program to be conducted during Phase I of the CAP, with any
necessary changes from the Nitrate Investigation Phase 1 Work Plan, dated May 13, 2011, is as
follows.
7.1.1.1 Soil Sampling Program Objective and Design
The objective of this soil sampling program is to delineate, approximately, the lateral extent of
contamination in order to determine the extent of the concrete pad necessary to cover the soil
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contamination identified during the Phase I investigation. To meet this objective, 18 Geoprobe
borings will be conducted down to bedrock refusal at each of the locations shown on Figure 11-
2B. Three (3) samples will be collected from each Geoprobe core location. Soil core samples
will be collected from the bottom one foot of each of the following intervals, based on the total
depth of penetration at each site: top 1/3, middle 1/3, and bottom 1/3.
Select soil core samples will be sent to the analytical laboratory for analysis of nitrate (as N), and
ammonia (as N) as described below. Since the purpose of this sampling program is to confirm
the lateral extent of soil contamination (in the form of nitrate and ammonia) resulting from the
ammonium sulfate tank source, no other analytes are required. Soil analysis will be conducted by
an environmental laboratory currently certified by the State of Utah, using EPA approved sample
and analysis methods.
Denison anticipates that the presence of ammonia contamination will diminish with distance
from the ammonium sulfate tanks. The initial row of samples will be collected 3 feet from the
northeast edge of the proposed concrete pad shown in Figure 11-2B. If the results of the analysis
of the initial sample row indicate that ammonia and nitrate levels do not exceed DRC’s proposed
screening levels of 20 times the background levels determined in the June 2011 investigation,
specifically 42.9 mg/kg for ammonia and 43.8 mg/kg for nitrate, no further samples will be
analyzed and the pad will be constructed as shown in Figure 11-2B. That is, if the initial samples
are below the screening levels, it will be concluded that the contamination will be adequately
covered by the proposed design, and the soil sampling program will be considered complete.
If the results of analysis of the initial sample row indicate that the contamination extends beyond
the area delineated by the initial row, that is, one or more samples in the initial row exceed the
screening levels, the remaining samples for one or more additional sampling rows will be
analyzed for nitrate (as N), and ammonia (as N). The concrete pad will be sized to extend to the
first row of samples whose analysis do not indicate nitrate or ammonia exceeding the screening
levels.
7.1.1.2 Field Activities/Sampling Methods
In order to minimize the potential for multiple mobilizations of the Geoprobe unit, three discreet
sets of samples will be collected in one sampling event during this investigation. Each discreet
set of samples will be collected in a lateral line or “row” along the northeast face of the proposed
concrete pad as shown in Figure 11-2B. Samples will be collected every approximately 12.5 feet
laterally along the edge of the concrete pad. The first row of discreet samples will be
approximately three feet from the edge of the proposed concrete pad. The two successive rows
will be stepped-out approximately ten feet from the previous row of samples. The samples
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collected in the two successive rows will be archived for potential later analysis of nitrate and
ammonia if necessary. All archived samples will be stored in accordance with the analytical
method requirements for temperature. Expedited turn around will be requested for the analysis of
the first row of soil samples, so that if any additional analyses are required, the additional
analyses can be completed within the specified analytical holding times. Based on this sampling
strategy, 54 soil samples (and 6 duplicates and 3 rinsates), will be collected.
7.1.1.3 Sample Handling and Custody
Each sample collected during this sampling program will be identified using a unique sample
identification number (lD). The description of the sample type and the sample name will be
recorded on the chain-of-custody (COC) forms, as well as in the field notes. Geoprobe boring
samples will be named according to the boring location and top and bottom of the depth interval
at which they were collected, following the convention P1AXX-tt-dd, where P1AXX is the first
boring in the first row of samples and tt is the top of the depth interval and dd is the bottom of
depth interval expressed in feet below ground surface. Additional rows of samples will be
identified as P1A2XX-tt-dd. Duplicate samples will carry the same identification as the parent
sample with the terminal letter “D” to identify them as a duplicate. Similarly, rinsate samples
will carry the sample identification of the sample collected prior to the rinsate followed by the
terminal letter “R”.
Samples will be collected into re-sealable plastic bags, which will be labeled with the sample
identification and homogenized by vigorously shaking and mixing the contents until the samples
are visibly uniform. A minimum sample volume of 100 grams will be collected from each
location. Sample containers will be provided by the laboratory, certified as clean, and will be
filled directly from the plastic bags. Archive sample aliquots will be maintained in the plastic
bags at the Mill for the duration of the analytical holding times to provide additional backup
sample for analysis if necessary. Archive sample aliquots will be stored in accordance with the
analytical method requirements for sample preservation.
Standard sample custody procedures as described in the DRC-approved Nitrate Investigation
Phase 1 Work Plan, dated May 13, 2011 will be used to maintain and document sample integrity
during collection, transportation, storage, and analysis.
Samples will be shipped to the analytical laboratory using an overnight carrier such as Federal
Express. Samples will be analyzed within the analytical method specified holding times.
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7.1.1.4 Analytical Methods
For comparability, the soil analytical methods will be the same as those used for the 2011 nitrate
contamination investigation.
All soil samples will be submitted to the analytical laboratory for SPLP using EPA Method 1312
using Extraction Fluid #3. Method 1312 will produce a leachate of all soil samples which will be
analyzed for nitrate and nitrogen as ammonia using EPA Method 353.2, and EPA method 350.1
respectively. Method 1312 will produce a sufficient volume of leachate to complete the nitrate
and ammonia analyses as well as any method-required QC analyses.
The soil samples are being leached and analyzed using water methodologies, which will yield
concentrations in liquid units (such as mg/L). The laboratory will report all soil samples in two
ways: 1) as a leachate in mg/L and 2) as a soil in mg/kg on a dry weight basis.
The reporting limits (“RLs”) for the methods are 0.1 milligrams per liter (“mg/L”) for nitrate and
0.5 mg/L for ammonia. These RLs are sufficiently sensitive to allow determination of soil
contamination. The RLs from the DRC-approved Nitrate Investigation Phase 1 Work Plan, dated
May 13, 2011 have been raised to 0.1 mg/L to eliminate false positive results from low-level
interferences present in the SPLP blanks.
7.1.1.5 Quality Control
Quality control (“QC”) samples will be collected in the field during the sampling effort and will
include one duplicate per ten analytical samples and one rinsate sample per twenty samples.
Rinsate samples will be collected using deionized (“DI”) water from the Mill’s DI system which
is routinely used for all other sampling programs at the Mill. Duplicates will be assessed through
the calculation of a relative percent difference (“RPD”) and rinsate samples will be assessed
based on any detections reported and their magnitude relative to the sample results. The QC
procedures set forth in the Nitrate Investigation Phase 1 Work Plan, dated May 13, 2011 will be
used for the assessment of the soil samples collected during this program.
Analytical laboratory QC, audits, instrument calibration, internal QC procedures, detailed COC
procedures, organizational responsibilities, and other specific details regarding sample collection
will be completed in accordance with the DRC-approved Nitrate Investigation Phase 1 Work
Plan, dated May 13, 2011.
7.1.2 Construction of the Phase I Action
Denison proposes to construct a sloped, curbed, and drained concrete pad of six inches in depth
over an area covering the lateral extent of contamination identified during the contamination
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investigation. Because the ammonium sulfate tanks are surrounded by existing concrete
structures to the south, west, and north, the new concrete pad will extend to the east of the Mill
building. The existing concrete pad will be resurfaced and sloped to drain to the existing
collection area/sump inside the Mill building, which returns solutions to the process. This
resurfaced area will be constructed with a curb of approximately 6 inches in height. In addition, a
new concrete slab will be extended to the eastern edge of the surrounding structures. This new
slab will also be sloped to drain to an existing collection area/sump in the Mill building. A rolled
curb will be constructed with an access ramp to allow supplier trucks sufficient access to refill
the tanks. The proposed cover design is depicted in Figure 11-2A and B.
The only subsurface piping in the vicinity of the ammonium sulfate tanks is a segment of the
underground portion of the Mill fire water system. Figure 11-3 shows the location of the
subsurface portion of the fire water line. Due to the need to maintain continual pressure on the
fire water system, the system already contains instrumentation (an alarm system) to indicate
when the pressure makeup pump starts up as a response to leaks, breaks, or loss of pressure. As
indicated by the pump alarm history, the firewater system has no history of leakage, and is not
expected to be a source of hydraulic head in the vicinity. The only other subsurface process
piping on the Mill site consists of two pairs of lines: one cooling water recirculation loop, and
one vanadium product liquor loop, for which the buried portion begins approximately more than
100 feet southeast the ammonium sulfate tanks (75 feet from the nearest corner of the concrete
pad proposed in Figure 11-4), and “around the corner” from the ammonium sulfate tanks – east
of the easternmost wall of the building’s “L”. These two piping loops are new, have had no
history of leakages, and are too far from the ammonium sulfate tanks to be a source of hydraulic
head in the vicinity of the tanks. All other process piping is above grade.
Consistent with Section 11A(1)(b)(i) of the SCA, Denison provided a detailed plan and schedule
for construction of the concrete cover to DRC in Section 7.1 and Figures 11-1 and 11-2A and B
of the November 30, 2011 version of this CAP.
7.1.3 Maintenance of the Phase I Action
Denison will provide a plan for annual inspection, required repairs, and annual documentation of
the condition of the pad in a revised version of the Discharge Minimization Technology
(“DMT”) Plan, to be submitted following approval of the CAP by the Executive Secretary. The
revised DMT Plan will address:
• frequency of inspection and photographic documentation of the condition of the pad
(annually),
• contents of inspection reports,
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• inspection criteria,
• conditions requiring repairs,
• timing of repairs, and
• contents of repair reports.
7.1.4 Estimation and Removal of Contaminated Soil During Mill Reclamation
Denison also proposes a future excavation of contaminated soil at the time of Mill site
reclamation, and disposal of the excavated soil in the tailings cells. To ensure a sufficient surety
amount for reclamation of the known contaminated soil volume to the depth of bedrock, Denison
proposes to revise the reclamation surety estimate to include a volume of soil of twice the
volume of contaminated soil volume identified in the contamination investigation.
The following process will be used to estimate the volume of contaminated soil to be removed
during reclamation. Once the total area to be covered by concrete has been determined based on
the borehole analyses, the area will be multiplied by the average depth to bedrock, as determined
from the logging of the boreholes.
Based on the geologic logging performed during the soil probe sampling in the Phase I
Investigation in June, 2011, borings number GP-25B and GP-26B in the vicinity of the
ammonium sulfate tanks indicated depth to bedrock of 19 feet and 16 feet, respectively. These
values will be included, along with depths determined during the additional Geoprobe sampling
to develop an average depth to bedrock. This average depth to bedrock will be multiplied by the
area of contamination. For conservatism, Denison will double the volume determined by the
above method for purposes of the reclamation surety estimate.
Consistent with Section 11A(1) of the SCA, Denison will provide a revised surety estimate to
DRC by March 4, 2012. The March 4, 2012 surety estimate will include an overly conservative
estimate for removal of the contaminated soil volume that is based on:
1. The preliminary proposed concrete cover area as depicted in Figure 11-2B
2. An approximate depth to bedrock of 20 feet (1 foot deeper than the maximum depth to
bedrock measured to date during the June 2011 investigation)
3. A conservative overestimation factor of 3 times the volume estimated from items 1 and 2
above

Following receipt of the additional depth-to-bedrock data and estimated lateral extent of
contamination data that will be developed from the soil sampling program described above,
Denison will review the March 4, 2012 volume and cost estimate. If additional data indicates an
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increase of the conservatively estimated soil volume in the March 4, 2012 surety estimate,
Denison will provide a revised volume and cost estimate within 60 calendar days following
issuance of the Consent Order contemplated in Section 11.E of the SCA.
7.2 Phase II Description and Rationale
Phase II consists of three active components and one passive component. The active components
are:
1. Removal of nitrate mass from the perched zone as rapidly as is practical by pumping
from wells located in areas having high nitrate concentrations, relatively high
productivities, or both.
2. Perched zone water level and nitrate monitoring to assess changes in nitrate
concentrations within the plume, verify the location of the plume boundary over time,
and estimate hydraulic capture zones. A general lowering of nitrate concentrations within
the plume is expected as a result of Phase II operation.
3. Abandonment of TWN-series wells not needed for implementation of item 2.

Pumped water will be disposed in the tailings cells. In addition, all samples analyzed for nitrate
will also be analyzed for chloride.
The passive component consists of relying on natural attenuation to reduce nitrate
concentrations. Physical mechanisms that will reduce nitrate concentrations include processes
such as hydrodynamic dispersion, and dilution via mixing with nitrate-free recharge and low
nitrate waters outside the plume. Neither biologically mediated decomposition of nitrate nor
abiotic chemical decomposition are expected to be significant mechanisms in reducing nitrate
concentrations because the majority of the perched water is likely aerobic and unsuitable for
rapid decomposition of either chloroform or nitrate. The persistence of chloroform and the
persistence of nitrate associated with the chloroform plume are consistent with predominantly
aerobic conditions. The presence of iron oxides within the perched zone in most of the site
borings is also consistent with aerobic conditions.
As discussed in HGC (2007) chloroform daughter products, such as dichloromethane (DCM),
have been detected but at low concentrations. The persistence of chloroform and the low
concentrations of daughter products imply relatively low rates of chloroform degradation. Owing
to its relatively high oxidation state, chloroform would be expected to degrade relatively rapidly,
yielding higher concentrations of daughter products such as DCM, under primarily anaerobic
conditions.

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That chloroform daughter products have been detected suggests that conditions are locally
favorable for anaerobic degradation. The presence of carbonaceous material in many of the site
borings and the presence of pyrite in most of the borings suggests that at least local anaerobic
conditions favorable to degradation of chloroform and nitrate exist. The formation hosting the
perched zone was likely anaerobic in the past, and conducive to the preservation of carbonaceous
material and the formation and preservation of pyrite, but, at least some areas of the site, is now
mainly aerobic with pyrite oxidizing to iron oxide. The oxidation of pyrite is likely enhanced
near perched wells which provide a conduit for oxygen to the perched zone.
As a result, wherever conditions may be favorable to anaerobic degradation, the actual
degradation rates of nitrate from either abiotic or biologically mediated degradation may be, in
fact, larger than anticipated, which will be favorable for removal of nitrate from the perched
zone. However, Denison is not relying on either abiotic or biologically mediated degradation as
important removal mechanisms.
Furthermore, nitrate is not expected to be retarded by adsorption onto aquifer materials because
of its high solubility and negative charge. The combination of pumping, hydrodynamic
dispersion, and dilution by recharge are expected to be effective considering that less than an
order of magnitude reduction in concentration is needed to reduce the highest detected nitrate
concentrations within the plume (approximately 69 mg/L) to the target of 10 mg/L. The
downgradient portion of the plume, defined by MW-30 and MW-31, will require reduction in
concentration by only a factor of two to meet the 10 mg/L goal.
In general, Phase II is expected to function in a manner similar to ongoing chloroform removal
from perched water at the site. Construction and operation will be similar to the chloroform
pumping system which consists of five wells (MW-4, MW-26, TW4-4, TW4-19, and TW4-20)
located within the chloroform plume that are pumped as continuously as practical and at rates
that are as large as practical. Water from those wells is disposed in the tailings cells.
The nitrate pumping system will consist of four wells: TW4-22, TW4-24, TW4-25, and TWN-2
(Figure 1-2). Water will be pumped from these wells as continuously as practical and at rates as
high as practical. These wells were selected for pumping because 1) they are located in middle to
upgradient areas of the plume having the highest nitrate concentrations and will minimize the
downgradient migration of these high concentrations, 2) they are expected to have productivities
similar to the chloroform pumping wells, 3) pumping these wells is not expected to enhance the
downgradient migration of chloroform, and 4) they are temporary chloroform (TW4-series) or
nitrate (TWN-series) investigation wells and converting them to pumping wells will not impact
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tailings cell point of compliance monitoring under the Mill’s Groundwater Discharge Permit
(“GWDP”).
Pumping these wells is expected to remove nitrate mass from the perched zone as rapidly as
practical, and flatten hydraulic gradients within the plume to reduce rates of downgradient
migration and allow natural attenuation to be more effective. Furthermore, the depression of the
water table resulting from pumping in the upgradient portion of the plume will reduce interaction
between the perched water and any residual shallow vadose zone sources that may exist. As a
result plume migration is expected to be minimal or cease once Phase II is implemented.
Currently the plume appears to be changing very slowly. Figure 9-2 compares the extents of the
nitrate plume in the third quarters of 2010 and 2011. Over this period, the plume appears to be
relatively stable, having expanded slightly in some areas and contracted slightly in others. The
apparent stability of the plume is likely the result of the generally low hydraulic conductivities of
the perched zone, and ongoing pumping within the adjacent chloroform plume. Implementation
of Phase II is expected to further reduce or halt downgradient migration and to reduce
concentrations within the plume. If ongoing monitoring indicates the plume continues to migrate,
then contingencies will be implemented.
As discussed above, the productivities of the proposed nitrate pumping wells are expected to be
similar to those of the chloroform pumping wells. The transmissivities at proposed nitrate
pumping wells TW4-22, TW4-24, and TW4-25 are estimated to be between those of chloroform
pumping wells MW-26 and TW4-19; and the transmissivity at TWN-2 is estimated to be about
one third that of chloroform pumping well TW4-20 (Table 4). Therefore, the long-term
productivities of TW4-22, TW4-24, and TW4-25 are expected to be between those of MW-26
and TW4-19; and the long-term productivity of TWN-2 is expected to be about one third that of
TW4-20. Although expected pumping rates at TWN-2 will be relatively low, the high
concentrations detected at that well will result in relatively high nitrate removal rates. Pumping
at TWN-2 is expected to reduce or eliminate the apparent residual perched water mound at that
location. As the mound is depleted, the productivity of TWN-2 is expected to diminish.
However, continued operation of TWN-2, even at low average extraction rates, is expected to be
beneficial.
The potential interaction of the chloroform plume with the nitrate pumping system is of concern.
Figure 10 shows the locations of the nitrate and chloroform plumes as of the third quarter of
2011. The chloroform plume is located generally east-southeast of the nitrate plume, but the
plumes mingle in the vicinity of TW4-19, TW4-20 and TW4-22 (northeast corner of tailings Cell
#2). Pumping the proposed nitrate wells will impact chloroform migration to some extent, and
any pumping that enhances downgradient migration of chloroform is undesirable. It is expected
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that pumping the proposed wells will at most draw chloroform cross-gradient to the west-
northwest. However, pumping of any wells to the southwest of the chloroform plume (such as
MW-30 and MW-31) would have the undesirable impact of enhancing the downgradient
migration of chloroform, and is not considered to be an option. Furthermore, converting MW-30
or MW-31 to nitrate pumping wells would degrade the usefulness of these wells for tailings cell
point of compliance monitoring under the GWDP.
Data collected during Phase II monitoring will be used to estimate the extent of the capture zone,
and to calculate nitrate mass removal rates by pumping. Denison will calculate the capture zones
after four quarters of water level measurements have been taken, and will include the
calculations, with figures, in the next quarterly nitrate monitoring report. Numerical and/or
analytical models will be used if needed to assist in evaluating the data and estimating natural
attenuation.
It is expected that the four pumping wells, in combination with the existing chloroform pumping
wells, will adequately capture the nitrate plume, such that concentrations of nitrate in excess of
the 10 mg/L standard are not expected to migrate beyond the current boundaries of the plume.
Based on experience from the chloroform pumping results to date, it is expected that the capture
zone from the four nitrate pumping wells will, by themselves extend upgradient to capture the
entire plume north of TW4-22 and TW4-24 as well as more than 400 feet downgradient of TW4-
22 and TW4-24. For example, the downgradient extent of the combined capture zone of
chloroform pumping wells MW-26, TW4-19, and TW4-20 (Figure 12) extends more than 400
feet downgradient of MW-26. The capture zone from the four nitrate pumping wells alone is
expected to likewise extend at least 400 feet southwest of TW4-22 and TW4-24, encompassing
by themselves approximately three quarters of the plume (Figure 13). However, the proportion of
the nitrate plume under hydraulic capture is expected to be larger than this estimate as the nitrate
capture zone merges and is enhanced by the chloroform capture zone. The result is that either
complete hydraulic capture will be achieved, or if not achieved, concentrations of nitrate in
excess of 10 mg/L are not expected to migrate beyond the current boundaries of the plume.
Hydraulic capture will be considered successful if the concentrations of nitrate in MW-30 and
MW-31 remain stable or decline and concentrations of nitrate in downgradient wells MW-5 and
MW-11 do not exceed the 10 mg/L standard.
The nitrate plume is defined as that portion of the perched aquifer that has a concentration of
nitrate in excess of 10 mg/L. In evaluating whether the pumping system has contained the plume,
the proper parameter to evaluate is therefore whether the 10 mg/L boundary has moved beyond
the currently defined plume boundary. MW-5 and MW-11 presently do not exceed the 10 mg/L
Groundwater Quality Standard; that is, they are outside the currently defined plume, and act as
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bounding wells for the plume. So long as they continue to be less than or equal to 10 mg/L they
will remain as bounding wells outside of the plume, and the plume will not have expanded.
It is possible that there may still be some movement of impacted water (i.e., there may not be
complete hydraulic capture), but so long as that movement of water does not cause the
concentration in any downgradient well to exceed 10 mg/L, the plume itself will not have
expanded and adequate hydraulic control will have been demonstrated. As a result, it is possible
that there may be some future impact on MW-5 and MW-11, even though the plume has not
expanded. However, any impacts on MW-5 and MW-11 will be monitored to ensure that the
concentrations in those wells, if they do increase over time, do not exceed 10 mg/L. If the
concentration of nitrate in either or both of those wells increases above 10 mg/L, then the plume
will have expanded and plume capture will not have been successful. Further actions, such as
modeling or the addition of more nitrate pumping wells, would need to be investigated at that
time. Because numerous monitoring wells currently exist downgradient of MW-5 and MW-11
(i.e., MW-35, MW-36, MW-37, MW-15 and MW-14 as a first line of defense, and beyond that
line, MW-17, MW-03, and MW-20), existing wells would continue to bound the plume, and
there would be no chance that the plume could expand beyond the downgradient edge of the
Mill’s existing tailings cells, without being detected and without ample time to institute further
mitigative actions.
7.2.1 Well Abandonment
Currently there are 19 TWN-series wells that were installed for the investigation of nitrate at the
site. Wells in the vicinity of the nitrate plume will be retained for monitoring. TWN-series wells
located north–northeast of TWN-18 are not needed for this purpose and are therefore selected for
abandonment. Wells proposed for abandonment are TWN-5, TWN-6, TWN-8, TWN-9, TWN-
10, TWN-11, TWN-12, TWN-13, TWN-15, TWN-16, and TWN-17. . Wells to be retained for
nitrate and chloride monitoring are TWN-1, TWN-2, TWN-3, TWN-4, TWN-7, and TWN-18.
The foregoing wells will be abandoned within one year from the date of approval of this CAP, in
accordance with applicable regulations (State of Utah Administrative Rules for Water Wells R655-4-
14). Although not needed for nitrate plume monitoring, wells TWN-14 and TWN-19 will be
retained for water level monitoring only, to provide ongoing water level data for the northeast
portion of the site.
A well abandonment report will be submitted to the Executive Secretary within 15 months after
the date of approval of this CAP.
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7.2.2 Groundwater Pumping System
The Phase II corrective action groundwater pumping system will consist of wells TW4-22, TW4-
24, TW4-25, and TWN-2 (Figure 1-2). Each well will be equipped with a Grundfos Series SQE
1x200-240 Volt, 6.2Amp submersible pump. To prevent damage to the pumps, each will operate
on a cycle that allows pumping only when sufficient water is present in the well. The capacity of
each pump will be greater than the sustainable pumping rate for each well. Therefore, the
average amount of water pumped from each well will be, in general, the maximum practical.
These wells were selected for pumping because they are located in areas of the perched zone
having both high nitrate concentrations and relatively high transmissivities that allow relatively
high rates of mass removal, and because they are not expected to have a negative impact on
chloroform migration from the adjacent chloroform plume.
Water pumped from each well will be routed by ½ inch high-density polyethylene Drisco
discharge lines, comparable to the transfer lines in the chloroform pumping system, to the
tailings cells for disposal. A schematic drawing of the transfer piping system is provided in
Figure 11-5. The discharge line near each wellhead will be equipped with an in-line Carlon ½”
flow meter/totalizer (or equivalent). The flow meter/totalizer will be housed in an insulated
wooden box with a heat source to prevent freezing. Readings from each totalizer will be used to
report quarterly pumped volumes and average pumping rates.
Operation of the nitrate wellfield will be similar to that for the chloroform wellfield. The
contingencies described in Section 8 will be implemented should nitrate mass removal rates drop
significantly due to losses in well productivity.
7.2.3 Water Level Monitoring
Water levels will be monitored weekly in each of the four nitrate pumping wells. Water levels in
the remaining wells listed in Table 3 will be monitored monthly for the first twelve months after
commencement of Phase II pumping, and thereafter quarterly. Depths to water will be measured
using an electric water level meter in the same way they are currently collected. Hydraulic
capture zones will be estimated from water level contour maps generated quarterly from the
water level data, with the first capture zones estimated after twelve months of data have been
obtained. The contingencies described in Section 8 will be implemented should the proportion of
the remaining nitrate plume that is under hydraulic capture shrink significantly.
7.2.4 Water Quality Monitoring
Pumping wells TW4-22, TW4-24, TW4-25, and TWN-2, and the other wells listed in Table 3,
will be monitored quarterly. Sampling and analytical procedures will be the same as currently
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employed for the nitrate monitoring as described in the quarterly monitoring reports submitted
by Denison to DRC. Each well will be sampled for the following constituents with respect to
monitoring the nitrate plume:
• Chloride
• Nitrogen, Nitrate + Nitrite as N
• pH
• Temperature

Dissolved oxygen was not included in the Plan due to unique conditions at White Mesa. The
required three pore volume purge when sampling monitor wells at the site and low hydraulic
conductivity in the perched aquifer causes slow recharge to the well bore after purging. This
slow recharge allows oxygen to diffuse into the groundwater as it enters the well bore rendering
any dissolved oxygen measurement unreliable.
Denison has also assessed the need for analyzing data from selected on site wells for other
groundwater quality parameters that could be relevant to this Plan, and has concluded that the
existing groundwater monitoring in existing GWDP compliance wells is adequate, and that no
further constituents, other than nitrate and chloride in the TWN wells, need be added to any wells
at the site, for the reasons discussed below.
The Mill is the subject of an ongoing groundwater compliance monitoring program, which
monitors the complete list of constituents regulated in Table 2 of the GWDP. If any contaminant
sources, whether or not associated with the nitrate plume, reach levels of concern in
groundwater, they will be detected in the GWDP compliance monitoring program. It is therefore
not necessary for the nitrate corrective action to attempt to monitor the same constituents which
are adequately monitored under the existing GWDP program.
Further, since the Plan provides a nitrate plume pumping program designed to bound and control
the known contamination, any other constituents present within the nitrate plume, related to
nitrate as precursors or byproducts or otherwise, will also be captured by the pumping system.
Quarterly reports will be prepared that contain the same elements of the current chloroform
corrective action monitoring reports submitted by Denison to DRC. Specific information
elements to be included in the reports are listed in Sections 10.2.3 and 10.2.6.
Existing nitrate and chloride monitoring will continue in each other monitoring wells at the site
at the frequency required under the GWDP or the chloroform investigation, as the case may be.
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Maintaining the current quarterly frequency at the closest downgradient well MW-11 and semi-
annual frequency at the next-closest downgradient well MW-5 is reasonable considering the
apparent stability of the plume at MW-30 and MW-31 and the hydraulic conductivity at MW-5
(3.5 x 10-6 cm/s) which is nearly three orders of magnitude lower than at MW-11 (1.4 x 10-3
cm/s)[HGC, 2007]. The sampling frequency for MW-5 and MW-11 was established under the
GWDP based on the velocity of flow in the perched aquifer at these locations. More frequent
monitoring was considered inappropriate due to the low flow rates and the potential to sample
the same water or similar water in consecutive sampling events at each well.
Should concentrations within the plume begin to generally increase (disregarding short-term
fluctuations), or the plume boundaries begin to expand, the contingencies discussed in Section 8
will be implemented.
7.2.5 Reporting
Reporting is proposed to occur quarterly, using a format and content similar to the quarterly
chloroform monitoring reports submitted by Denison to DRC. The quarterly reports will include
the following details:
1. calculation of quarterly nitrate mass removed by pumping,
2. comparison of the current areal extent of the nitrate plume from the latest quarter with the
latest quarter of the previous reporting period, and
3. discussion of any contingencies to be implemented.
7.3 Phase III
Phase III may be implemented at the discretion of Denison at any time if Denison determines
that continuation of Phase II is not necessary or appropriate. If Denison decides to implement
Phase III, Denison will submit a revised CAP to the Executive Secretary for approval, which
incorporates Phase III. Phase II will continue until Phase III is approved by the Executive
Secretary.
If implemented, Phase III will consist of a transport assessment, a hazard assessment, and an
exposure assessment along with a corrective action assessment including an evaluation of best
available remedial technologies. Selection of a technology for implementation will be based on
an evaluation whether the technology will remediate contamination to as low as is reasonably
achievable, if the 10 mg/L standard is not reasonably achievable. One possible outcome of these
evaluations could be an application for alternate corrective action concentration limits (ACACL).
As required by UAC R317-6-6.15(G), the proposed ACACL must be protective of human health,
and the environment, and must utilize best available technologies. If an ACACL is proposed, the
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revised CAP will include the information required, under UAC R317-6-6.15(G), and any
ACACL would require the approval of the Utah Water Quality Board.
The transport assessment will identify any data gaps that exist and develop work plans to collect
any data needed to support hydrologic and geochemical modeling. Such modeling will consist of
appropriate quantitative models to predict flow paths, travel times, and potential points of
exposure of nitrate contaminated groundwater. Any potential geochemical reactions or other
attenuation mechanisms will also be identified. The transport assessment will inform the hazard
assessment and the exposure assessment.
The hazard assessment will identify the risks and hazards to human health and the environment
associated with nitrate to determine whether an ACACL should be proposed, if the subsequent
exposure assessment concludes that an exposure is reasonably likely.
The purpose of the exposure assessment is to evaluate the potential harm to human health and the
environment from the hazards identified in the hazard assessment. The exposure assessment
takes into account site-specific circumstances that may reduce or enhance the potential for
exposure to nitrate. This assessment identifies and evaluates exposure pathways, and provides
forecasts of human and environmental population responses, based on the projected constituent
concentrations, and available information on the chemical toxicity effects of the constituents.
The assessment also addresses the underlying assumptions, variability, and uncertainty of the
projected health and environmental effects. Exposure pathways are identified and evaluated
using water classification and water use standards, along with existing and anticipated water
uses.
The corrective action assessment consists of a review of ground-water corrective action
alternatives in conjunction with the hazard assessment and the exposure assessment. Past,
current, and proposed practicable corrective actions will be identified and evaluated against the
costs and benefits associated with implementing each corrective action alternative. If ACACLs
are identified as the proposed alternative, the corrective action assessment will demonstrate that
the proposed ACACL is as low as is reasonably achievable, considering practicable corrective
actions, and is therefore conservative and cost- effective, and would be granted with good cause.
A principal way of demonstrating this is by estimating and comparing the benefits imparted by a
corrective action measure against the cost of implementing that measure.
7.3.1 Water Level and Water Quality Monitoring
Water level and water quality monitoring plans will be proposed in the revised Phase III CAP
prior to implementation of any proposed corrective action alternative.
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8. ASSESSMENT OF CORRECTIVE ACTION AND PROTECTION OF
PUBLIC HEALTH AND THE ENVIRONMENT AND
CONTINGENCY PLAN
The effectiveness of Phase II of the corrective action will be assessed based on the following
criteria:
1. stability of plume boundaries
2. concentration trends within the plume
3. nitrate mass removal rates resulting from pumping, and
4. stability of capture zones.

Plume boundaries and capture zones will be considered stable if concentrations of nitrate in
excess of the 10 mg/L standard do not migrate beyond the current boundaries of the plume.
Hydraulic capture will be considered successful if the concentrations of nitrate in MW-30 and
MW-31 remain stable or decline and concentrations of nitrate in downgradient wells MW-5 and
MW-11 do not exceed the 10 mg/L standard.
The Contingency Plan schedules for each of the foregoing criteria are set out in the Sections 8.1
through 8.4 as applicable.
The criteria for assessment of the effectiveness of Phase III of the corrective action will be
determined once the elements of Phase III have been developed. As discussed in Section 3.2.3,
Phase III will be undertaken at a later date after public participation and Executive Secretary
approval. Phase III may include, but is not limited to: continuation of Phases I and II activities
alone or in combination with monitored natural attenuation, evaluation of additional remediation
and monitoring technologies/techniques, determination of any additional hydrogeologic
characterization, groundwater contaminant travel times and directions, determination of ultimate
points of exposure to the public and/or wildlife, appropriate risk analysis, a cost/benefit analysis,
and the possible development of and petition to the Board for alternate corrective action
concentration limits pursuant to UAC R317 -6-6 .15 (G).
This CAP does not specify the details of Phase III, at this time. A Phase III preliminary plan and
schedule for the evaluation of alternatives, for the completion of any further studies, analyses,
applications and petitions, and for the ultimate definition of Phase III, may be proposed by
Denison at a later date, after completion of such studies and evaluations, followed by submittal
of a proposed CAP revision to the Executive Secretary.
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8.1 Stability of Plume Boundary (Phase II)
The stability of the plume boundary, based on Phase II CAP monitoring activities discussed in
Sections 7 and 10, will be used to determine the following:
• Whether any additional pumping wells are needed, and
• The need to reevaluate the Phase II strategy.

Under conditions where the plume boundaries remain stable or contract, no additional pumping
wells will be needed, and no reevaluation of Phase II will be needed. Under conditions where the
plume migrates, with the concurrence of the Executive Secretary, one or more additional
pumping wells will be added, if suitable wells are available, to slow the migration rates and/or to
bring more of the plume under hydraulic capture. The installation of additional downgradient
monitoring wells is not anticipated because two lines of wells currently exist downgradient of the
nitrate plume. Any such additional pumping wells will be added in accordance with a schedule to
be approved by the Executive Secretary. If the plume continues to migrate, or suitable additional
pumping well locations are not available, then Phase II will be reevaluated, which may include
commencement of Phase III. Analytical or numerical models will be used if needed in the
reevaluation to develop a response. The reevaluation process will be completed in accordance
with a schedule to be approved by the Executive Secretary.
8.2 Concentration Trends within the Plume (Phase II)
Concentration trends within the plume will be used to determine the need for reevaluation of
Phase II. Concentration trends will be based on analytical data collected from Table 3 wells
through Phase II CAP monitoring.
Under conditions where concentrations within the plume are generally stable or declining
(disregarding short-term fluctuations), no reevaluation will be required. Should concentrations
within the plume begin to generally increase (disregarding short term fluctuations), then
reevaluation of Phase II will be required. Analytical or numerical models will be used in the
reevaluation if needed to develop a response. The reevaluation process will be completed in
accordance with a schedule to be approved by the Executive Secretary. Anticipated responses to
this condition would likely include adding existing or new wells to the pumping network, if
suitable well locations are available, or other measures designed to achieve a more rapid rate of
mass reduction. If suitable well locations are not available, then Phase III will be considered.
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8.3 Nitrate Mass Removal Rates Resulting from Pumping (Phase II)
Under conditions where nitrate mass removal rates by pumping drop substantially as a result of
reduced concentrations within the plume, no action will be taken. Under conditions where nitrate
mass removal rates by pumping drop substantially as a result of lost well productivities, then an
evaluation of the lost productivity will be undertaken. If the lost productivity is determined to be
a well efficiency problem, the inefficient wells will be re-developed or replaced in accordance
with a schedule to be approved by the Executive Secretary. Should the lost productivity be
determined to be due to a general reduction in saturated thickness, analytical or numerical
models will be used to evaluate the potential effectiveness of adding existing or new wells to the
pumping network to improve overall productivity, if suitable well locations are available. If the
analysis indicates that overall productivity will not improve significantly by adding wells, or if
suitable well locations are not available, then no action will be taken.
A loss in productivity due to a general decrease in saturated thickness will likely be offset by the
benefits of the reduced saturated thickness. First, this condition would indicate that removal of a
substantial amount of nitrate laden water had already taken place. Second, the reduced saturated
thickness within the nitrate plume would reduce average hydraulic gradients and reduce the
potential for downgradient migration. These factors will be considered in any reevaluation that
may be performed.
8.4 Stability of the Proportion of the Nitrate Plume under Hydraulic
Capture (Phase II)
Under conditions where concentrations of nitrate in excess of the 10 mg/L standard migrate
beyond the current boundaries of the plume, as evidenced by concentrations of nitrate in MW-30
and MW-31 increasing and/or concentrations of nitrate in downgradient wells MW-5 and MW-
11 exceeding the 10 mg/L standard, an evaluation of the factors resulting in this condition will be
undertaken. If the condition is determined to result from lost productivity of the pumping wells
due to well efficiency problems, the inefficient wells will be re-developed or replaced in
accordance with a schedule to be approved by the Executive Secretary. Should the loss in capture
be determined to result from other conditions, then Phase II will be reevaluated, which may
include commencement of Phase III. Analytical or numerical models will be used in the
reevaluation if needed to develop a response. The reevaluation process will be completed in
accordance with a schedule to be approved by the Executive Secretary.
Anticipated responses to this condition would likely include adding existing or new wells to the
pumping network to bring a larger proportion of the plume within hydraulic capture, it suitable
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well locations are available. If suitable well locations are not available, then Phase III will be
considered.
8.5 Phase III
As discussed in Section 3.2.3, Phase III will be undertaken at a later date after public
participation and Executive Secretary approval. Phase III may include, but is not limited to:
continuation of Phases I and II activities alone or in combination with monitored natural
attenuation, evaluation of additional remediation and monitoring technologies/techniques,
determination of any additional hydrogeologic characterization, groundwater contaminant travel
times and directions, determination of ultimate points of exposure to the public and/or wildlife,
appropriate risk analysis, a cost/benefit analysis, and the possible development of and petition to
the Board for alternate corrective action concentration limits pursuant to UAC R317 -6-6 .15 (G).
This CAP does not specify the details of Phase III, at this time. A Phase III preliminary plan and
schedule for the evaluation of alternatives, for the completion of any further studies, analyses,
applications and petitions, and for the ultimate definition of Phase III, may be proposed by
Denison at a later date, after completion of such studies and evaluations, followed by submittal
of a proposed CAP revision to the Executive Secretary. Until such time, the activities of the
Phase I and Phase II remediation will continue as stipulated in the approved CAP.
8.6 Permanent Effect of Corrective Action
Phase II, Phase III, and the contingencies outlined above (Sections 8.1 through 8.5) are designed
to protect the public health and the environment by containing the nitrate plume within the site
property boundary and reducing nitrate concentrations within the plume to the concentration
limit of 10 mg/L. As concentrations will then continue to be reduced by natural attenuation,
demonstration that the corrective action will have a permanent effect will be based on
appropriate future evaluations.
8.7 In-Place Contaminant Control
As discussed in Section 7, the corrective action relies on active and passive strategies to meet
CAP objectives. The passive strategy includes in-place contaminant control by reducing nitrate
concentrations via natural attenuation. Formatted: Bullets and Numbering
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9. IMPACTS OF OFFSITE ACTIVITIES
As discussed in Section 7, nitrate will be treated in place by natural attenuation and removed
from the perched zone by pumping. Because all pumped water will be disposed onsite in the
tailings cells, there will be no offsite impacts resulting from CAP implementation.
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10. PROPOSED PLUME CORRECTIVE ACTION ACTIVITIES
Phase II and Phase III corrective action activities and contingencies are discussed in detail in
Sections 7 and 8. These activities are summarized in Sections 10.1 and 10.2 below.
10.1 Phase I
The Phase I source control action was discussed in Section 7.1, above.
10.2 Phase II
Phase II corrective action activities include pumping of wells TW4-22, TW4-24, TW4-25, and
TWN-2, monitoring and maintenance of the pumping system, water level monitoring, monitoring
for nitrate and chloride, estimation of hydraulic capture, implementation of contingencies as
needed, and reporting.
10.2.1 Groundwater Pumping
Wells TW4-22, TW4-24, TW4-25, and TWN-2 (Figure 1-2) will be pumped at the maximum
practical rates. Pumped water will be disposed in the tailings cells. The wellfield will be operated
and maintained in the same fashion as the chloroform removal wellfield. Monitoring will include
pumping rates and volumes for each well.
10.2.2 Water Level Monitoring
Water level monitoring will consist of weekly water level monitoring of pumping wells TW4-22,
TW4-24, TW4-25, and TWN-2, and, for the first twelve months after approval of this CAP,
monthly monitoring of non-pumped wells MW-27, MW-30, MW-31, TW4-21, TWN-1, TWN-3,
TWN-4, TWN-7, and TWN-18 (Figure 1-2). Thereafter, water level monitoring of those non-
pumping wells will continue quarterly. Water level contour maps of the data will be generated
quarterly.
10.2.3 Water Quality Monitoring
Water quality monitoring for pumped wells TW4-22, TW4-24, TW4-25, and TWN-2 and all
other wells listed on Table 3 will be quarterly. Samples will be analyzed for chloride, and for
nitrogen (nitrate and nitrite as N). Field parameters pH and temperature will be recorded.
(Section 6.2.4). Water quality monitoring for chloride, nitrate, and field parameters for all other
wells at the site will continue at the frequency required under the GWDP or chloroform
investigation, as the case may be.
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10.2.4 Estimation of Capture Zones
Hydraulic capture zones will be generated from the quarterly water level contour maps in the
same manner as they are currently generated for the chloroform pumping.
10.2.5 Estimation of Pumped Nitrate Mass
Quarterly estimates of nitrate mass removed by pumping will be made based on cumulative
pumped volumes at each pumped well and nitrate concentrations at each pumped well.
10.2.6 Reporting
Quarterly reports will be prepared that contain the same elements of the current chloroform
corrective action monitoring reports submitted by Denison to DRC and will include the
following:
1. Tabular compilations of groundwater level measured in non-pumped wells over time,
2. Water level data from pumped wells over time,
3. Running and cumulative groundwater volumes removed from each pumping well,
4. Calculations and/or spreadsheets documenting quarterly nitrate mass removed by
pumping,
5. comparison of the areal extent of the nitrate plume from the latest quarter with the latest
quarter of the previous reporting period, and
6. discussion of any contingencies implemented or to be implemented.

10.2.7 Additional Measures
Based on Phase II monitoring, and the criteria discussed in Section 8, contingencies that include
potential installation of additional wells, well rehabilitation or replacement, potential expansion
of the pumping well network, if suitable well locations are available, and reevaluation of the
Phase II strategy and consideration of commencement of Phase III activities will be implemented
as needed. Factors that could trigger the implementation of contingencies include 1) expansion of
the plume boundaries, 2) generally increasing nitrate concentrations within the plume, 3)
reductions in nitrate mass removal rates due to losses in pumping well productivities, and 4)
decreases in the effectiveness of hydraulic capture.
10.3 Phase III
As discussed in Section 3.2.3, Phase III will be undertaken at a later date after public
participation and Executive Secretary approval. Phase III may include, but is not limited to:
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continuation of Phases I and II activities alone or in combination with monitored natural
attenuation, evaluation of additional remediation and monitoring technologies/techniques,
determination of any additional hydrogeologic characterization, groundwater contaminant travel
times and directions, determination of ultimate points of exposure to the public and/or wildlife,
appropriate risk analysis, a cost/benefit analysis, and the possible development of and petition to
the Utah Water Quality Board for alternate corrective action concentration limits pursuant to
UAC R317 -6-6 .15 (G).
This CAP does not specify the details of Phase III, at this time. A Phase III preliminary plan and
schedule for the evaluation of alternatives, for the completion of any further studies, analyses,
applications and petitions, and for the ultimate definition of Phase III, may be proposed by
Denison at a later date, after completion of such studies and evaluations, followed by submittal
of a proposed CAP revision to the Executive Secretary. Until such time, the activities of the
Phase I and Phase II remediation will continue as stipulated in the approved CAP.
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11. REFERENCES
HGC. 2004. Final Report. Long Term Pumping at MW-4, TW4-19, and TW4-15, White Mesa
Uranium Mill Near Blanding, Utah. Submitted to International Uranium (USA)
Corporation, Denver, Colorado.
HGC. 2005. Perched Monitoring Well Installation and Testing at the White Mesa Uranium Mill,
April Through June, 2005. Submitted to International Uranium (USA) Corporation,
Denver, Colorado.
HGC 2007a. Preliminary Corrective Action Plan, White Mesa Uranium Mill Near Blanding,
Utah. August 20, 2007
HGC. 2007b. Preliminary Contamination Investigation Report. White Mesa Uranium Mill Site
Near Blanding, Utah. November 20, 2007.
HGC. 2009a. Site Hydrogeology and Estimation of Groundwater Pore Velocities in the Perched
Zone. White Mesa Uranium Mill Near Blanding, Utah. December 29, 2009
HGC. 2010. Hydrogeology of the Perched Groundwater Zone and Associated Seeps and Springs
Near the White Mesa Uranium Mill Site, Blanding, Utah.
INTERA 2009a. Source Review Report for Nitrate and Chloride in Groundwater at the Mill.
December, 2009.
INTERA 2009b. Nitrate Contamination Investigation Report White Mesa Uranium Mill Site
Blanding, Utah. December 30, 2009.
INTERA. 2011. Nitrate Investigation Revised Phases 2 through 5 Work Plan. August, 2011.
Kirby. 2008. Geologic and Hydrologic Characterization of the Dakota-Burro Canyon Aquifer
Near Blanding, San Juan County, Utah. Utah Geological Survey Special Study 123.
Knight-Piésold. 1998. Evaluation of Potential for Tailings Cell Discharge – Mill. Attachment 5,
Groundwater Information Report, White Mesa Uranium Mill, Blanding, Utah. Submitted
to DRC.
TITAN. 1994. Hydrogeological Evaluation of White Mesa Uranium Mill. Submitted to Energy
Fuels Nuclear.
UMETCO. 1993. Groundwater Study. White Mesa Facilities. Blanding, Utah. Prepared by
UMETCO Minerals Corporation and Peel Environmental Services.
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12. LIMITATIONS STATEMENT
The opinions and recommendations presented in this report are based upon the scope of services
and information obtained through the performance of the services, as agreed upon by HGC and
the party for whom this report was originally prepared. Results of any investigations, tests, or
findings presented in this report apply solely to conditions existing at the time HGC’s
investigative work was performed and are inherently based on and limited to the available data
and the extent of the investigation activities. No representation, warranty, or guarantee, express
or implied, is intended or given. HGC makes no representation as to the accuracy or
completeness of any information provided by other parties not under contract to HGC to the
extent that HGC relied upon that information. This report is expressly for the sole and exclusive
use of the party for whom this report was originally prepared and for the particular purpose that
it was intended. Reuse of this report, or any portion thereof, for other than its intended purpose,
or if modified, or if used by third parties, shall be at the sole risk of the user.
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TABLES

FIGURES

APPENDIX A

HYDROGEOLOGIC CROSS SECTIONS

APPENDIX B

LITHOLOGIC LOGS FOR
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1. INTRODUCTION, OVERVIEW, AND SCOPE............................................................... 1
2. HISTORY OF NITRATE CONTAMINATION INVESTIGATION................................ 3
2.1 Summary of Contamination Investigation Report Activities..................................3
2.2 Conclusions from the Contamination Investigation ...............................................6
3. FRAMEWORK AND OBJECTIVES OF THE CAP......................................................... 9
3.1 Applicable Regulations and Requirements.............................................................9
3.2 Objectives of the CAP ..........................................................................................10
3.2.1 Summary of Phase I Objectives and Scope .............................................. 10
3.2.2 Summary of Phase II Objectives and Scope............................................. 11
3.2.3 Summary of Phase III Objectives and Scope............................................ 12
3.3 Preliminary Milestones for the CAP.....................................................................13
4. BACKGROUND .............................................................................................................. 15
4.1 Geologic Setting....................................................................................................15
4.2 Hydrogeologic Setting..........................................................................................16
4.3 Perched Zone Hydrogeology ................................................................................16
4.3.1 Lithologic and Hydraulic Properties......................................................... 17
4.3.1.1 Dakota 18

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4.3.1.2 Burro Canyon 18

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4.3.2 Perched Groundwater Flow 19

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4.3.3 Saturated Thickness 20

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4.4 Summary 21

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4.5 Nitrate Occurrence 22

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4.5.1 Source Areas............................................................................................. 22
4.5.2 Nitrate Concentration Trends 24

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5. CHARACTERIZATION OF STUDY AREA 27

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5.1 Extent of Study Area 27

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5.2 Hydrogeology 28

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6. CORRECTIVE ACTION CONCENTRATION LIMITS 29

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7. CORRECTIVE ACTION PLAN – CONSTRUCTION AND OPERATION
31

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7.1 Phase I Description and Rationale 32

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7.2 Phase II Description and Rationale 38

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7.2.1 Well Abandonment 42

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7.2.2 Groundwater Pumping System 43

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7.2.3 Water Level Monitoring 43

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7.2.4 Water Quality Monitoring 44

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7.2.5 Reporting 45

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TABLE OF CONTENTS (Continued)

7.3 Phase III 45

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7.3.1 Water Level and Water Quality Monitoring 46

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November 30, 2011

HYDRO GEO CHEM, INC.
Environmental Science & Technology

CORRECTIVE ACTION PLAN FOR NITRATE
WHITE MESA URANIUM MILL
NEAR BLANDING, UTAH

February 27, 2012

Prepared for:

DENISON MINES (USA) CORP.
Independence Plaza, Suite 950
1050 Seventeenth Street
Denver, Colorado 80265

Prepared by:

HYDRO GEO CHEM, INC.
51 W. Wetmore Road, Suite 101
Tucson, Arizona 85705
[phone]

Project Number 7180000.00-7.0

Corrective Action Plan for Nitrate
White Mesa Uranium Mill Near Blanding, Utah
Revised Nitrate Corrective Action Plan_FINAL_02.27.12.doc
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i
TABLE OF CONTENTS
1. INTRODUCTION, OVERVIEW, AND SCOPE............................................................... 1
2. HISTORY OF NITRATE CONTAMINATION INVESTIGATION................................ 3
2.1 Summary of Contamination Investigation Report Activities..................................3
2.2 Conclusions from the Contamination Investigation ...............................................6
3. FRAMEWORK AND OBJECTIVES OF THE CAP......................................................... 9
3.1 Applicable Regulations and Requirements.............................................................9
3.2 Objectives of the CAP ..........................................................................................10
3.2.1 Summary of Phase I Objectives and Scope .............................................. 10
3.2.2 Summary of Phase II Objectives and Scope............................................. 11
3.2.3 Summary of Phase III Objectives and Scope............................................ 12
3.3 Preliminary Milestones for the CAP.....................................................................13
4. BACKGROUND.............................................................................................................. 15
4.1 Geologic Setting....................................................................................................15
4.2 Hydrogeologic Setting..........................................................................................16
4.3 Perched Zone Hydrogeology................................................................................16
4.3.1 Lithologic and Hydraulic Properties......................................................... 17
4.3.1.1 Dakota........................................................................................18
4.3.1.2 Burro Canyon............................................................................. 18
4.3.2 Perched Groundwater Flow...................................................................... 19
4.3.3 Saturated Thickness.................................................................................. 20
4.4 Summary...............................................................................................................21
4.5 Nitrate Occurrence................................................................................................22
4.5.1 Source Areas............................................................................................. 22
4.5.2 Nitrate Concentration Trends....................................................................24
5. CHARACTERIZATION OF STUDY AREA.................................................................. 25
5.1 Extent of Study Area.............................................................................................25
5.2 Hydrogeology .......................................................................................................26
6. CORRECTIVE ACTION CONCENTRATION LIMITS................................................ 27
7. CORRECTIVE ACTION PLAN - CONSTRUCTION AND OPERATION.................. 29
7.1 Phase I Description and Rationale........................................................................30
7.1.1 Approximation of the Lateral Extent of Contamination and
Concrete Cover ......................................................................................... 30
7.1.1.1 Soil Sampling Program Objective and Design .......................... 30
7.1.1.2 Field Activities/Sampling Methods ........................................... 31
7.1.1.3 Sample Handling and Custody................................................... 32
7.1.1.4 Analytical Methods.................................................................... 33
7.1.1.5 Quality Control .......................................................................... 33

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TABLE OF CONTENTS (Continued)

7.1.2 Construction of the Phase I Action........................................................... 33
7.1.3 Maintenance of the Phase I Action........................................................... 34
7.1.4 Estimation and Removal of Contaminated Soil During
Mill Reclamation ......................................................................................35
7.2 Phase II Description and Rationale.......................................................................36
7.2.1 Well Abandonment................................................................................... 40
7.2.2 Groundwater Pumping System................................................................. 41
7.2.3 Water Level Monitoring ........................................................................... 41
7.2.4 Water Quality Monitoring......................................................................... 41
7.2.5 Reporting................................................................................................... 43
7.3 Phase III................................................................................................................43
7.3.1 Water Level and Water Quality Monitoring............................................. 44
8. ASSESSMENT OF CORRECTIVE ACTION AND PROTECTION OF
PUBLIC HEALTH AND THE ENVIRONMENT AND
CONTINGENCY PLAN.................................................................................................. 45
8.1 Stability of Plume Boundary (Phase II)................................................................46
8.2 Concentration Trends within the Plume (Phase II)...............................................46
8.3 Nitrate Mass Removal Rates Resulting from Pumping (Phase II) .......................47
8.4 Stability of the Proportion of the Nitrate Plume under
Hydraulic Capture (Phase II)................................................................................47
8.5 Phase III................................................................................................................48
8.6 Permanent Effect of Corrective Action.................................................................48
8.7 In-Place Contaminant Control..............................................................................48
9. IMPACTS OF OFFSITE ACTIVITIES ........................................................................... 49
10. PROPOSED PLUME CORRECTIVE ACTION ACTIVITIES ...................................... 51
10.1 Phase I...................................................................................................................51
10.2 Phase II..................................................................................................................51
10.2.1 Groundwater Pumping.............................................................................. 51
10.2.2 Water Level Monitoring ........................................................................... 51
10.2.3 Water Quality Monitoring......................................................................... 51
10.2.4 Estimation of Capture Zones ....................................................................52
10.2.5 Estimation of Pumped Nitrate Mass......................................................... 52
10.2.6 Reporting................................................................................................... 52
10.2.7 Additional Measures................................................................................. 52
10.3 Phase III................................................................................................................52
11. REFERENCES ................................................................................................................. 55
12. LIMITATIONS STATEMENT........................................................................................ 57

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TABLE OF CONTENTS (Continued)

TABLES

1 Nitrate Corrective Action Schedule
2 Hydraulic Conductivity Estimates for Wells in the Nitrate Plume Area
3 Nitrate Concentrations (mg/L) at Wells within the Nitrate Plume
4 Comparison of Chloroform Pumping Well Transmissivities to Proposed Nitrate Pumping
Well Transmissivities

FIGURES

1-1 White Mesa Mill Site Plan Showing Locations of Seeps and Springs
1-2 Site Plan Showing Perched Well Locations and 3rd Quarter, 2011 Nitrate Plume Extent,
White Mesa Site
2 Photograph of the Contact Between the Burro Canyon Formation and the Brushy Basin
Member
3 Kriged Top of Brushy Basin Elevations, White Mesa Site
4 Kriged 3rd Quarter, 2011 Water Levels, White Mesa Site
5 3rd Quarter, 2011 Saturated Thickness, White Mesa Site
6 3rd Quarter, 2011 Depths to Water, White Mesa Site
7 Kriged 3rd Quarter, 2011 Nitrate (mg/L) (Nitrate + Nitrite as N), White Mesa Site
8 Potential Nitrate Source Areas and Geoprobe Locations Showing the Thickness of the
Mancos Shale
9-1 Nitrate Concentrations in MW-30 and MW-31
9-2 Comparison of Nitrate Plume Boundaries, 3rd Quarter, 2010 and 3rd Quarter, 2011
10 3rd Quarter, 2011 Nitrate and Chloroform Plumes, White Mesa Site
11-1 Ammonium Sulfate Contamination
11-2A Ammonium Sulfate Tank Area (Current Layout)
11-2B Ammonium Sulfate Concrete Cover (Proposed Location)
11-3 Fire System Schematic
11-4 General Area of Proposed Concrete Cover
11-5 Well Pumping Transfer Lines
12 Estimated Extent of Capture of Chloroform Pumping Well MW-26, 3rd Quarter, 2011
13 Anticipated Minimum Downgradient Extent of Capture Resulting from Pumping
TW4-22, TW4-24, TW4-25, and TWN-2

APPENDICES

A Hydrogeologic Cross Sections
B Lithologic Logs for MW-3A, MW-30, MW-31, MW-34, and MW-37

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1. INTRODUCTION, OVERVIEW, AND SCOPE
This document presents a Corrective Action Plan (CAP) to address nitrate + nitrite (as nitrate)
(heretofore referred to as “nitrate”) contamination in a shallow perched groundwater zone
beneath the White Mesa Uranium Mill (the “site” or the “Mill”), located on White Mesa near
Blanding, Utah, operated by Denison Mines (USA) Corp. (“Denison”). Figure 1-1 is a map
showing site features including seeps and springs at the margins of White Mesa. Figure 1-2 is a
map of the site showing the locations of perched zone monitoring wells and the area of the
perched groundwater zone affected by nitrate concentrations exceeding 10 milligrams per liter
(mg/L) that is the focus of this CAP. For the purposes of this document, all nitrate concentrations
in groundwater have been expressed as mg/L nitrogen. Elevated concentrations of chloride were
also detected in the monitoring wells having elevated concentrations of nitrate. In a letter dated
December 1, 2009, the Co-Executive Secretary of the Utah Water Quality Board (the “Executive
Secretary”) recommended that Denison also address and explain the elevated chloride
concentrations.
Nitrate within the area shown in Figure 1 was first detected in wells TW4-19, TW4-22, TW4-24,
and TW4-25 that were installed as part of the investigation of a chloroform plume discovered at
perched well MW-4 in 1999. Pumping of chloroform-laden perched water began in 2003 (HGC,
2007a) and continues to the present time via pumping of wells MW-4, MW-26, TW4-4, TW4-
19, and TW4-20.
Investigation of nitrate exceeding 10 mg/L in the perched water included installation of 19
temporary TWN-series wells shown in Figure 1 and numerous shallow borings as part of a
source investigation. Denison identified and prioritized potential sources of the nitrate in the
December 2009 Source Review Report for Nitrate and Chloride in Groundwater at the White
Mesa Mill, (INTERA, 2009a) and in the subsequent August 2011 Nitrate Investigation Revised
Phases 2 through 5 Work Plan. (INTERA, 2011).
Based on the investigations, Denison and the Executive Secretary have agreed that the corrective
actions will involve three Phases. Phase I will involve source control in the vicinity of the Mill’s
ammonium sulfate tanks, the one remaining potential source of contamination. Phase II will
involve near term active remediation of the nitrate contamination by pumping contaminated
water into the Mill’s tailings cells for disposal, combined with monitored natural attenuation.
Phase III, if necessary, will be at the discretion of Denison and would involve a long term
solution for the nitrate contamination, in the event that the continuation of Phase II is not
considered adequate or appropriate. Phases I and II are addressed in this CAP and will
commence shortly upon Executive Secretary approval of this CAP. Phase III is not covered in

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detail in this CAP and, if determined to be necessary, will be addressed in a separate CAP
revision.
The elements of this CAP document include the following items:
• A History of the Nitrate Contamination Investigation
• A discussion of the decision to proceed with Corrective Action
• A summary of the applicable requirements
• CAP objectives
• A description of the site hydrogeology
• The nature and extent of nitrate in the perched zone
• Proposed corrective remedial actions and concentration limits
• Proposed corrective action contingencies

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2. HISTORY OF NITRATE CONTAMINATION INVESTIGATION
A brief discussion of the Nitrate Contamination Investigation and the decision to proceed with
corrective action is provided in Sections 2.1 and 2.2.
2.1 Summary of Contamination Investigation Report Activities
On January 27, 2009 the Executive Secretary of the Utah Division of Radiation Control (“DRC”)
and Denison entered into the 2009 Stipulated Consent Agreement (“SCA”), which set forth the
requirement that Denison would submit a written Contaminant Investigation Report (CIR) for
Executive Secretary review and approval, to among other things, characterize the source(s),
physical extent, transfer mechanisms and characteristics of the Nitrate contamination of the
shallow aquifer at the site.
Denison submitted to the Executive Secretary a CIR which had been prepared by their consultant
INTERA, Inc. The CIR was dated December 30, 2009 (INTERA, 2009b) and entitled "Nitrate
Contamination Investigation Report White Mesa Uranium Mill Site Blanding, Utah" (2009 CIR).
On October 5, 2010 the Executive Secretary issued a Notice of Additional Required Action
(NARA) letter that notified Denison of the Executive Secretary’s determination that the 2009
CIR was incomplete.
On December 20, 2010 Denison and the Executive Secretary entered into a Tolling Agreement
(Tolling Agreement (Rev. 0)) to defer any monetary penalties that might accrue under the 2009
SCA, in order to provide a time period (Tolling Period) for:
1. Denison to prepare and submit a plan and schedule (Plan and Schedule) by which to
conduct additional investigations to resolve open issues identified in the October 5, 2010
NARA on or before February 15, 2011,
2. The Executive Secretary to provide his initial comments on the Plan and Schedule on or
before March 15, 2011, and for Denison and the Executive Secretary to finalize the Plan
and Schedule, and
3. Denison and the Executive Secretary to negotiate, finalize and execute a revised or
replacement SCA that incorporates the Plan and Schedule.

In addition, the Tolling Agreement (Rev. 0) required that the Tolling Period be extended from
January 4, 2010 (submittal of the 2009 CIR to the Executive Secretary) until Apri1 30, 2011.
Pursuant to the Tolling Agreement (Rev. 0), Denison submitted a Plan and Schedule on February
14, 2011 and a revised Plan and Schedule on February 18, 2011, and the Executive Secretary
provided his comments on the revised Plan and Schedule on March 21, 2011. In an April 20,

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2011 meeting, Denison and the Executive Secretary agreed that the Plan and Schedule to conduct
additional nitrate investigations would be composed of at least four (4) and possibly five (5)
phases of study, including:
1. Phase 1A through C - including geoprobe drilling, and soil sampling/analysis of soils to
investigate:
a. Possible natural nitrate salt reservoir in the vadose zone beyond the mill site
area (Phase 1A);
b. Potential nitrate sources in the mill site area (Phase 1 B); and
c. Other potential nitrate sources (Phase 1 C).
2. Phase 2 - including groundwater quality sampling and analysis of existing monitoring
wells for non-isotopic analytes.
3. Phase 3 - including deep bedrock core sampling/analysis of possible natural nitrate
reservoir and potential nitrate source locations, with similar objectives as Phases 1 A
through C.
4. Phase 4 - including stable isotopic sampling/analysis of groundwater in existing
monitoring wells. Details of this investigation were to be determined at a later date, and
approved by both parties.
5. Phase 5 - including stable isotopic sampling/analysis of soil/core samples, if needed.

On April 28, 2011, Denison and the Executive Secretary entered into a Revised Tolling
Agreement (Tolling Agreement (Rev. 1), to extend the Tolling Period through June 30, 2011 and
adopt the agreements made in the April 20, 2011 meeting. Under the Tolling Agreement (Rev.
1), Denison agreed to submit a Revised Phase 1 (A through C) Work Plan on or before May 6,
2011 and a Revised Phase 2 through 5 Work Plan and Schedule on or before June 3, 2011.
Pursuant to the Tolling Agreement (Rev. 1), Denison submitted a May 6, 2011 Revised Phase 1
Work Plan and Schedule for the Phase 1 A - C investigation prepared by INTERA, for Executive
Secretary review. On May 11, 2011, the DRC: 1) provided via email, comments on the May 6,
2011 INTERA document, and requested that Denison resolve all DRC comments before
initiation of field activities. All comments were resolved, and Denison conducted field and
laboratory work for the Phase l A-C study in May and June, 2011.
Pursuant to the Tolling Agreement (Rev. 1), Denison submitted a June 3, 2011 Revised Phase 2
through 5 Work Plan and Schedule (Phase 2 - 5 Work Plan), prepared by INTERA, for Executive
Secretary review. In a letter dated June 23, 2011 DRC provided comments on this Denison
document in the form of a URS memorandum, dated June 23, 2011 and advised Denison that in
order to revise the 2009 SCA to incorporate the deliverables and timelines set out in an

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approvable Phase 2 through 5 Work Plan, it would be necessary to provide a level of detail in
revisions of that Work Plan for Phases 2, 3, 4, and 5 comparable to the level of detail for Phase 1
contained in Attachment 1 of the Tolling Agreement (Rev. 1).
On June 30, 2011, Denison and the Executive Secretary entered into a Revised Tolling
Agreement [Tolling Agreement (Rev. 2)] to extend the Tolling Period to August 31, 2011, in
order to facilitate the revision of the Phase 2 through 5 Work Plan to provide the level of detail
required to construct a replacement SCA. Pursuant to the Tolling Agreement (Rev.2), Denison
submitted a separate July 1, 2011 detailed Work Plan and Quality Assurance Plan ("QAP") for
the Phase 2 investigation (Phase 2 Plan, Revision 0). Executive Secretary comments on this
document were provided in a July 7, 2011 DRC letter. Denison provided a revised July 12, 2011
Phase 2 QAP and Work Plan (Phase 2, Revision 1.0), which DRC conditionally approved in a
letter dated July 18, 2011.
On August 1 and 2, 2011 Denison submitted by email preliminary laboratory results for the
Phase l A-C study to the Executive Secretary.
On August 4, 2011, Denison provided a revision to the Phase 2 - 5 Work Plan (Phase 2-5 Work
Plan, Revision 1.0), prepared by INTERA, for Executive Secretary review. DRC comments on
the Phase 2-5 Work Plan, Revision 1.0 and on the August 1, 2011 preliminary laboratory results
for the Phase l A-C study, were provided to Denison on August 11, 2011 as part of a conference
call, and a DRC email, which included an August 11, 2011 URS memorandum. Under a cover
letter dated August 18, 2011, Denison submitted a revised Phase 2-5 Work Plan (Phase 2-5 Work
Plan, Revision 2.0) for Executive Secretary review, in response to the comments provided to
Denison on August 11, 2011.
As discussed in the following Sections, DRC and Denison have agreed to proceed with
corrective action.
In an August 25, 2011 DRC letter, the Executive Secretary advised that per review of the Phase
2-5 Work Plan, Revision 2.0, the Executive Secretary has determined that a finalized Plan and
Schedule, that meets the satisfaction of the Executive Secretary, and which would allow the
preparation of a replacement SCA, is not possible at this time; and that the development of a
replacement SCA for continued contaminant investigation activities is not supported.
At a meeting between Denison and DRC on August 29, 2011 to discuss the Executive
Secretary’s August 25, 2011 findings related to the Phase 2-5 Work Plan Rev. 2.0, the
preliminary laboratory results for the Phase I A-C study, and the approach forward, Denison and
DRC agreed that:

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1. After more than two years of investigation it has been determined that there are site
conditions that make it difficult to determine the source(s) of the contamination at the
White Mesa site;
2. As a result, resources will be better spent in developing a CAP in accordance with UAC
R317-6-6.15(D), rather than continuing with further investigations as to the source(s) of
the contamination.

During discussion throughout October 2011, Denison and the Executive Secretary acknowledged
that it has not been possible to date to determine the source(s), cause(s), attribution, magnitudes
of contribution, and proportion(s) of the local nitrate and chloride in groundwater, and thereby
cannot eliminate Mill activities as a potential cause, either in full or in part, of the contamination.
As a result, Denison and the Executive Secretary agreed that resources will be better spent in
developing a CAP in accordance with UAC R317-6-6.15(D), rather than continuing with further
investigations as to the source(s) and attribution of the groundwater contamination.
2.2 Conclusions from the Contamination Investigation
The contamination investigation program from 2009 to 2011 has provided a basis for
development of a CAP. Specifically the investigation has determined:
• the areal and spatial extent of the plume,
• that the plume does not appear to be increasing in size or concentration,
• that there are no known unaddressed current or ongoing sources of contamination.

As discussed above, a number of potential mill and non-mill sources were identified in the
December 2009 Source Review Report for Nitrate and Chloride in Groundwater at the Mill, and
in the subsequent August 2011 Nitrate Investigation Revised Phases 2 through 5 Work Plan.
Based on the investigation and source evaluations, there are no known current unidentified or
unaddressed sources. There appear to have been a number of known and potential historic
sources; however, it has not been possible to confirm or quantify the contribution of each.
Analytical results indicate that neither the average concentration of the plume nor the areal extent
of the plume have increased during the monitored period. The only potential current source
identified and potentially requiring control is the ammonium sulfate tanks. This potential source
is addressed in Phase I of the CAP, discussed in Sections 3.2.1 and 7.1 below.
The Executive Secretary determined that a CAP is required at the White Mesa facility, pursuant
to UAC R317-6-6.15(C)(I) and Denison agreed to develop, secure Executive Secretary approval,
and implement a CAP. The Executive Secretary has therefore determined, and Denison agreed to

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submit a CAP, pursuant to the requirements of the Utah Ground Water Quality Protection Rules
[UAC R317 -6-6.15(C - E)].
The purpose of Phase I of this CAP is to remedy the effects of the ammonium sulfate tank
potential source. The purpose of each of the proposed phases of this CAP is discussed further in
section 3.2.

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3. FRAMEWORK AND OBJECTIVES OF THE CAP
Applicable regulations and requirements governing the CAP, and preliminary milestones are
discussed in Sections 3.1 through 3.3.
3.1 Applicable Regulations and Requirements
Denison agreed to submit a CAP for Executive Secretary review and approval, on or before
November 30, 2011 that meets the CAP related requirements of UAC R317-6-6.15 (D.2, 3 and
E). This document constitutes the “Nitrate CAP”.
The remaining sections of this CAP are intended to demonstrate, per the requirements in UAC
R317 -6-6.15(D)(2) and (3), that:
• the proposed action(s) are protective of public health and the environment, including
consideration of future impacts of the nitrate plume on land and water resources not
owned and controlled by Denison.
• the corrective action meets the State Ground Water Quality Standards, pursuant to UAC
R317 -6-6.15(F). Alternatively, Denison may petition the Utah Water Quality Board for
approval of an Alternate Corrective Action Concentration Limit as part of the CAP,
Phase III, pursuant to UAC R317 -6-6.15(G).
• the action will produce a permanent effect.

Per UAC R317 -6-6.15(D)(2) and (3) the action proposed in the CAP is required to meet any
other additional measure required by the Executive Secretary under UAC R317 -6-6.15(E)(5).
Denison has agreed with the Executive Secretary that these additional measures shall include, but
are not limited to:
• Remediation guidance found in the April, 2004 EPA Handbook of Groundwater
Protection and Cleanup Policies for RCRA Corrective Action (EPA530-R-04-030) or
equivalent, to the extent applicable, as determined by the Executive Secretary;
• Determination of corrective action performance standards, objectives, and criteria for
groundwater remediation system design, construction, operations and/or maintenance, as
approved by the Executive Secretary in accordance with applicable regulations;
• Determination of long term operation, maintenance, system performance and
groundwater quality monitoring requirements to evaluate effectiveness of the approved
corrective action(s), at a frequency, and by methods approved by the Executive Secretary;
• Submittal of written quarterly Denison reports of pumping and monitoring well system
performance and groundwater quality monitoring information for Executive Secretary
review and approval. In the event that additional information is required of any report,
Denison shall respond to and provide a Plan and Schedule for Executive Secretary

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approval to resolve all issues /concerns within 30 calendar days of receipt of written
Executive Secretary notice;
• Timely Denison verbal and written notification of process or equipment failures, and
corrective actions taken, or a timely schedule by which corrective action will be taken to
return the facility to full compliance with CAP performance standards, objectives, and
criteria; and
• Periodic Denison review, summation, and report submittal, for Executive Secretary
approval, to demonstrate if the approved corrective action is protective of public health
and the environment. The interval of said report period shall not exceed five (5) years.

3.2 Objectives of the CAP
The objectives of the CAP are the following:
• Minimize or prevent further downgradient migration of the perched nitrate plume (Figure
1-2) by a combination of pumping and reliance on natural attenuation,
• Prevent nitrate concentrations exceeding the action level from migrating to any potential
point of exposure,
• Monitor to track changes in concentrations within the plume and to establish whether the
plume boundaries are expanding, contracting, or stable,
• Provide contingency plans to address potential continued expansion of the plume and the
need for additional monitoring and/or pumping points, and
• Ultimately reduce nitrate concentrations at all monitoring locations to the action level or
below.

To achieve these objectives, the CAP proposes a phased approach.
3.2.1 Summary of Phase I Objectives and Scope
Per Section 11A(1) of the SCA, Phase I is required to include a control for the soil contamination
observed at the ammonium sulfate tanks, a potential source of perched groundwater
contamination. Pursuant to UAC 317-6-6.15 (E)(4)(b) this control will include at a minimum:
Determination, to the satisfaction of the Executive Secretary, of the physical extent of the soil
contamination observed at the ammonium sulfate tanks near borings GP-25B (Nitrate + Nitrite
(as N) 1,530 mg/kg-dry at depth of 6 feet) and GP-26B (Ammonia (as N) 1,590 mg/kg-dry at a
depth of 16 feet) that were part of the nitrate investigation. Such effort shall include an estimate
of the volume (the "Contaminated Soil Volume") of the contaminated soils down to but not
including bedrock, and an estimate of the surface area (the "Contaminated Surface Area") at or
above the estimated location of the Contaminated Soil Volume; and either a Plan and Schedule,

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to be submitted on or before January 1, 2012, for Executive Secretary approval, to cover the
Contaminated Surface Area with at least six inches of concrete, to the extent not already covered
by concrete or existing buildings, to prevent infiltration of surface water into the contaminated
soils; and/or a Plan and Schedule, to be submitted on or before January 1, 2012, for Executive
Secretary approval, to remove the Contaminated Soil Volume and dispose of the contaminated
soils in the Mill's tailings impoundments. If Denison chooses to cover the Contaminated Surface
Area with concrete, Denison must remove the Contaminated Soil Volume at a later date prior to
site closeout and must submit a revised surety estimate on or before March 4, 2012 to include
future costs to remove the Contaminated Soil Volume.
As discussed in Section 7.1 of this CAP, Denison proposes to construct a sloped and drained
concrete pad of six inches in depth over an area covering the lateral extent of contamination to be
determined as discussed in Section 7.1. Denison also proposes a future removal of contaminated
soil at the time of Mill site reclamation and, for conservatism, proposes to revise the reclamation
surety estimate to include a volume of soil to be removed and placed in the tailings area of twice
the volume of contaminated soil identified in the contamination investigation. Further details are
discussed in Section 7.1, below.
3.2.2 Summary of Phase II Objectives and Scope
Per Section 11A(2) of the SCA, Phase II is to include near term active remediation of the nitrate
contamination by pumping contaminated water into the Mill's tailings cells for disposal. Said
phase shall also include: 1) the development, implementation, operation, and monitoring
requirements for a pumping well network designed to contain and hydraulically control the
nitrate groundwater plume to maintain concentrations at or below the Utah Groundwater Quality
Standard (10 mg/L), i.e., prevent physical expansion of said plume, and 2) monitoring of
chloride concentrations.
Phase II constitutes an interim remedial action that consists of a combination of “active” and
“passive” strategies. The active strategy consists of removing nitrate mass as rapidly as practical
by pumping areas within the plume that have high nitrate concentrations and relatively high
productivity. Continued monitoring within and outside the plume is considered part of the active
strategy. The passive strategy consists of relying on natural attenuation processes to reduce
nitrate concentrations. Reductions in concentrations would be achieved by physical processes
such as hydrodynamic dispersion, and dilution via mixing with recharge and waters outside the
plume.
Natural attenuation is expected to reduce nitrate concentrations within the entire plume.
However, within upgradient portions of the plume that have the highest concentrations, direct

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mass removal via pumping will be the primary means to reduce concentrations. In downgradient
portions of the plume where concentrations are lower, natural attenuation will be a more
important mechanism in reducing concentrations.
3.2.3 Summary of Phase III Objectives and Scope
Per the SCA, Phase III is to include a comprehensive long term solution for the nitrate
groundwater contamination at the Mill Site. This phase will be undertaken at a later date after
public participation and Executive Secretary approval. Phase III may include, but is not limited
to: continuation of Phases I and II activities alone or in combination with monitored natural
attenuation, evaluation of additional remediation and monitoring technologies/techniques,
determination of any additional hydrogeologic characterization, groundwater contaminant travel
times and directions, determination of ultimate points of exposure to the public and/or wildlife,
appropriate risk analysis, a cost/benefit analysis, and the possible development of and petition to
the Board for alternate corrective action concentration limits pursuant to UAC R317 -6-6 .15 (G).
This CAP does not specify the details of Phase III, at this time. A Phase III preliminary plan and
schedule for the evaluation of alternatives, for the completion of any further studies, analyses,
applications and petitions, and for the ultimate definition of Phase III, may be proposed by
Denison at a later date, after completion of such studies and evaluations, followed by submittal
of a proposed CAP revision to the Executive Secretary. Until such time, the activities of the
Phase I and Phase II remediation will continue as stipulated in the approved CAP.
The CAP is not intended to address contamination located outside the Mill's restricted area and
that is not contiguous with groundwater contamination inside the Mill's restricted area. The CAP
will therefore evaluate which of the existing monitoring wells will be maintained and which
wells (including certain upgradient and off-site wells) can be abandoned, subject to prior
Executive Secretary approval.
It should be noted that while Phase II of the CAP requires monitoring of chloride concentrations,
the CAP does not explicitly identify measures for controlling chloride levels per se, because
there is no health standard for chloride in groundwater. However, as discussed and agreed to
with DRC during meetings in October 2011, chloride appears to be co-located with nitrate in
groundwater at the Mill and hydrogeological measures to contain nitrate will also contain
chloride.

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3.3 Preliminary Milestones for the CAP
Per the SCA, Denison has committed to the following milestones for corrective action. Dates for
the following milestones will be established based on the date of the Executive Secretary’s
approval of the CAP and issuance of a Consent Order approving the CAP.
• Within 30 calendar days of the Executive Secretary’s approval of the CAP, pursuant to
UAC R317-6-6.15(E), Denison shall commence implementation and execution of all
corrective actions required under a future Consent Order to be issued by the Executive
Secretary that addressed the approved CAP. A proposed schedule for implementation of
the CAP is included as Table 1 to this CAP.
• Within 60 calendar days of the Executive Secretary’s issuance of a future Consent Order
regarding the approved CAP, pursuant to UAC R317-6-6.15(E), Denison will submit a
revised Reclamation Plan and financial surety cost estimate (Revised Surety), for
Executive Secretary review and approval which addresses the groundwater corrective
action, with the surety sufficient to recover the anticipated cost and time frame for
achieving compliance, before the land is transferred to the federal government for long-
term custody. At a minimum, the Denison surety will provide for all costs for Phases I
and II of the approved CAP for a period of time until Executive Secretary approval of
Phase III of the CAP to restore groundwater to the established site specific groundwater
cleanup standards pursuant to UAC R317-6-6.15 before the site is transferred to the
federal government for long term custody.

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4. BACKGROUND
Sections 3.1 through 3.4 provide a brief description of site hydrogeology that is based primarily
on TITAN (1994), but includes the results of more recent site investigations. Section 3.5
discusses the occurrence of nitrate in the perched water at the site and focuses on the nitrate
plume shown in Figure 1-2.
4.1 Geologic Setting
The Mill is located within the Blanding Basin of the Colorado Plateau physiographic province.
Typical of large portions of the Colorado Plateau province, the rocks underlying the site are
relatively undeformed. The average elevation of the site is approximately 5,600 feet above mean
sea level (ft amsl).
The site is underlain by unconsolidated alluvium and indurated sedimentary rocks consisting
primarily of sandstone and shale. The indurated rocks are relatively flat lying with dips generally
less than 3º. The alluvial materials consist mostly of aeolian silts and fine-grained aeolian sands
with a thickness varying from a few feet to as much as 25 to 30 feet across the site. The alluvium
is underlain by the Dakota Sandstone and Burro Canyon Formation, which are sandstones having
a total thickness ranging from approximately 100 to 140 feet. In portions of the site, a few feet to
as much as about 30 feet of Mancos Shale lies between the alluvium and the Dakota Sandstone.
Beneath the Burro Canyon Formation lies the Morrison Formation, consisting, in descending
order, of the Brushy Basin Member, the Westwater Canyon Member, the Recapture Member,
and the Salt Wash Member. Figure 2 is a photograph of the contact between the Burro Canyon
Formation and the underlying Brushy Basin Member taken from a location along highway 95
immediately north of the Mill. This photograph illustrates the transition from the cliff-forming
sandstone of the Burro Canyon Formation to the slope-forming Brushy Basin Member.
The Brushy Basin and Recapture Members of the Morrison Formation, classified as shales, are
very fine-grained and have a very low hydraulic conductivity. The Brushy Basin Member is
primarily composed of bentonitic mudstones, siltstones, and claystones. The Westwater Canyon
and Salt Wash Members also have a low average vertical hydraulic conductivity due to the
presence of interbedded shales.
Beneath the Morrison Formation lie the Summerville Formation, an argillaceous sandstone with
interbedded shales, and the Entrada Sandstone. Beneath the Entrada lies the Navajo Sandstone.
The Navajo and Entrada Sandstones constitute the primary aquifer in the area of the site. The
Entrada and Navajo Sandstones are separated from the Burro Canyon Formation by

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approximately 1,000 to 1,100 feet of materials having a low average vertical hydraulic
conductivity. Groundwater within this system is under artesian pressure in the vicinity of the site,
is of generally good quality, and is used as a secondary source of water at the site.
4.2 Hydrogeologic Setting
The site is located within a region that has a dry to arid continental climate, with an average
annual precipitation of approximately 13.3 inches, and an average annual lake evaporation rate
of approximately 47.6 inches. Recharge to the principal aquifers occurs mainly along the
mountain fronts (for example, the Henry, Abajo, and La Sal Mountains), and along the flanks of
folds such as Comb Ridge Monocline.
Although the water quality and productivity of the Navajo/Entrada aquifer are generally good,
the depth of the aquifer (approximately 1,200 feet below land surface [ft bls]) makes access
difficult. The Navajo/Entrada aquifer is capable of yielding significant quantities of water to
wells (hundreds of gallons per minute [gpm]). Water in wells completed across these units at the
site rises approximately 800 feet above the base of the overlying Summerville Formation.
Perched groundwater in the Dakota Sandstone and Burro Canyon Formation originates mainly
from precipitation and local recharge sources such as unlined reservoirs (Kirby, 2008) and is
used on a limited basis to the north (upgradient) of the site because it is more easily accessible
than the Navajo/Entrada aquifer. Water quality of the Dakota Sandstone and Burro Canyon
Formation is generally poor due to high total dissolved solids (TDS). The saturated thickness of
the perched water zone is generally higher to the north of the site.
4.3 Perched Zone Hydrogeology
Perched groundwater beneath the site occurs primarily within the Burro Canyon Formation.
Perched groundwater at the site has a generally low quality due to high total TDS in the range of
approximately 1,100 to 7,900 milligrams per liter (mg/L), and is used primarily for stock
watering and irrigation in the areas upgradient (north) of the site where generally higher
saturated thicknesses increase well yields. Perched water is supported within the Burro Canyon
Formation by the underlying, fine-grained Brushy Basin Member. Figure 3 is a contour map
showing the approximate elevation of the contact of the Burro Canyon Formation with the
Brushy Basin Member, which essentially forms the base of the perched water zone at the site.
Contact elevations between the Burro Canyon Formation and Brushy Basin Member in Figure 3
are based on perched monitoring well drilling and geophysical logs and surveyed land surface
elevations. As indicated, the Burro Canyon Formation/Brushy Basin Member contact (although

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irregular because it represents an erosional surface) generally dips to the south/southwest beneath
the site.
Appendix A contains hydrogeologic cross-sections that intersect within the nitrate plume. These
cross-sections show the site lithology above the Brushy Basin Member, perched water within the
Dakota Sandstone/Burro Canyon Formation, and the occurrence of nitrate within the perched
water. As shown in Figure A.2, relatively thick conglomeratic intervals exist within the saturated
zone at MW-31, located at the downgradient edge of the nitrate plume. As discussed below,
these intervals appear to pinch out to the south (downgradient) and to the west (cross-gradient) of
MW-31.
Less conglomeratic material is present in the saturated zone at MW-30 and MW-3A than at MW-
31, as shown in the attached lithologic logs (Appendix B). Thin conglomeratic zones
(approximately 1-2 feet thick) occur at the base of the perched zone in MW-31 and MW-3A.
Detailed lithologic logs for MW-5, MW-11, MW-14 and MW-15 are not available to assess the
presence of conglomeratic material at those locations. However, saturated conglomeratic
materials were not encountered at MW-34 and MW-37 (located adjacent to MW-15), as shown
in the attached lithologic logs.
Based on the available information, significant conglomeratic horizons within the saturated
perched zone do not appear to exist at or downgradient of MW-30. Furthermore, hydraulic test
data from MW-30 and MW-31 indicate that the conglomeratic zones in MW-31 do not enhance
the permeability at MW-31. The hydraulic conductivity estimates (based on KGS solution
analysis of automatically logged slug test data) for MW-30 and MW-31 are similar. The
hydraulic conductivity estimates for MW-30 and MW-31, respectively, are 1 x 10-4 cm/s and 7 x
10-5 cm/s (HGC, 2005).
4.3.1 Lithologic and Hydraulic Properties
Although the Dakota Sandstone and Burro Canyon Formations are often described as a single
unit due to their similarity, previous investigators at the site have distinguished between them.
The Dakota Sandstone is a relatively hard to hard, generally fine-to-medium grained sandstone
cemented by kaolinite clays. The Dakota Sandstone locally contains discontinuous interbeds of
siltstone, shale, and conglomeratic materials. Porosity is primarily intergranular. The underlying
Burro Canyon Formation hosts most of the perched groundwater at the site. The Burro Canyon
Formation is similar to the Dakota Sandstone but is generally more poorly sorted, contains more
conglomeratic materials, and becomes argillaceous near its contact with the underlying Brushy
Basin Member. The hydraulic conductivities of the Dakota Sandstone and Burro Canyon
Formation at the site are generally low.

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No significant joints or fractures within the Dakota Sandstone or Burro Canyon Formation have
been documented in any wells or borings installed across the site (Knight-Piésold, 1998). Any
fractures observed in cores collected from site borings are typically cemented, showing no open
space.
4.3.1.1 Dakota
Porosities of the Dakota Sandstone range from 13.4% to 26%, averaging 20%, and water
saturations range from 3.7% to 27.2%, averaging 13.5%, based on samples collected during
installation of wells MW-16 (abandoned) and MW-17 (Figure 1-2). The average volumetric
water content is approximately 3%. The hydraulic conductivity of the Dakota Sandstone based
on packer tests in borings installed at the site ranges from approximately 2.7 x 10-6 centimeters
per second (cm/s) to 9.1 x 10-4 cm/s, with a geometric average of 3.9 x 10-5 cm/s.
4.3.1.2 Burro Canyon
The average porosity of the Burro Canyon Formation is similar to that of the Dakota Sandstone.
Porosity ranges from 2% to 29.1%, averaging 18.3%, and water saturations of unsaturated
materials range from 0.6% to 77.2%, averaging 23.4%, based on samples collected from the
Burro Canyon Formation at MW-16 (abandoned), located beneath new tailings Cell #4A. TITAN
(1994) reported that the hydraulic conductivity of the Burro Canyon Formation ranges from 1.9 x
10-7 to 1.6 x 10 -3 cm/s, with a geometric mean of 1.1 x 10-5 cm/s, based on the results of
12 pumping/recovery tests performed in monitoring wells and 30 packer tests performed in
borings prior to 1994. Subsequent hydraulic testing of perched zone wells has yielded a range of
2 x 10-7 to 0.01 cm/s (HGC, 2009a).
In general, the highest hydraulic conductivities and well yields are in the area of the site
immediately northeast and east (upgradient to cross gradient) of the tailings cells. A relatively
continuous, higher conductivity zone that is associated with the chloroform plume (HGC, 2007b)
has been inferred to exist in this portion of the site. Analysis of drawdown data collected from
this zone during long-term pumping of MW-4, MW-26, and TW4-19 (Figure 1-2) yielded
estimates of hydraulic conductivity ranging from 4 x 10-5 to 1 x 10-3 cm/s (HGC, 2004). The
decrease in perched zone hydraulic conductivity south to southwest of this area indicates that this
higher conductivity zone “pinches out” (HGC, 2007b).
Hydraulic conductivities downgradient of the tailings cells are generally low. Hydraulic tests at
wells located at the downgradient edge of the cells, and south and southwest of the cells yielded
geometric average hydraulic conductivities of 2.3 x 10-5 and 4.3 x 10-5 cm/s depending on the
testing and analytical methods. The low hydraulic conductivities and shallow hydraulic gradients

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downgradient of the tailings cells result in average perched groundwater pore velocity estimates
that are among the lowest on site (approximately 1.7 ft/yr to 3.2 ft/yr based on calculations
presented in HGC, 2009a).
Hydraulic conductivities within the general area of the nitrate plume are based primarily on
analysis of slug tests at wells MW-27, MW-30, MW-31, TW4-20, TW4-21, TW4-22, TW4-24,
TW-25, TWN-1, TWN-2, TWN-3, and TWN-18 (HGC, 2005 and HGC, 2009a). The hydraulic
conductivity at MW-11 was based on a pumping test reported by UMETCO (1993) and the
hydraulic conductivity at TW4-19 was based on long-term pumping of that well for chloroform
removal (HGC, 2004). Hydraulic conductivity estimates range from approximately 2.7 x 10-5 to
1.4 x 10-3 cm/s, and have a geometric average of 1.2 x 10-4 cm/s, assuming unconfined
conditions (Table 2). The transmissivities of many wells within the nitrate plume are similar to
wells that are pumped for chloroform removal.
4.3.2 Perched Groundwater Flow
Perched groundwater flow at the site has historically been to the south/southwest (HGC, 2007b).
Figure 4 is a perched groundwater elevation contour map for the third quarter of 2011. These
contours are based on water levels measured in the perched groundwater monitoring wells shown
in the figure. Local depression of the perched water table occurs near wells MW-4, TW4-4,
TW4-19, TW4-20, and MW-26. These wells are pumped to reduce chloroform mass in the
perched zone east and northeast of the tailings cells as discussed in HGC (2007a).
Perched water mounds are associated with wildlife ponds on the east side of the site. The
mounds are likely the result of seepage from the unlined ponds. An apparent perched water
mound also exists in the vicinity of TWN-2 just north of the Mill site. The apparent perched
water mound near TWN-2 is likely a residual mound resulting from low permeability conditions
(Table 2) and the location of TWN-2 within the footprint of the historical pond (Figure 8).
Although the historical pond no longer exists and does not contain standing water, the remaining
topographic depression associated with the pond likely resulted in enhanced infiltration of
precipitation before recent re-grading of the land surface in that area. Slightly enhanced
infiltration of precipitation and low permeability conditions at TWN-2 likely allowed the mound
to persist. The decay of the mound is expected to be slow because of the low permeability.
A dry area to the southwest of Cell 4B is defined by the area where the kriged Brushy Basin
contact elevation rises above the kriged perched water level elevation. The lateral extent of the
dry area shown in Figure 4 is currently under investigation. The installation of wells along the
southern and western margins of Cell 4B in August, 2010 and April, 2011 indicate that the dry

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zone extends at least from the southwest central portion of Cell 4B to the southwest corner of
Cell 4B.
Beneath and downgradient of the tailings cells, on the west side of the site, perched water flow is
south-southwest to southwest. On the eastern side of the site perched water flow is more
southerly. Because of mounding near wildlife ponds, flow direction ranges locally from westerly
(west of the ponds) to easterly (east of the ponds). Perched zone hydraulic gradients currently
range from a maximum of approximately 0.07 ft/ft east of tailings Cell #2 (near well TW4-14) to
approximately 0.01 ft/ft downgradient of the tailings cells. Gradients may be steeper locally near
pumping wells (for example near TW4-20, where the gradient reaches approximately 0.09 ft/ft)
Perched water discharges in springs and seeps along Westwater Creek Canyon and Cottonwood
Canyon to the west-southwest of the site, and along Corral Canyon to the east of the site, (Figure
1-1) where the Burro Canyon Formation outcrops. The closest discharge points downgradient of
the tailings cells are Westwater Seep (approximately 2800 feet downgradient) and Ruin Spring
(approximately 9,400 feet downgradient [HGC, 2010]).
4.3.3 Saturated Thickness
The saturated thickness of the perched zone as of the third quarter of 2011 ranges from
approximately 92 feet in the northeastern portion of the site to less than 5 feet in the southwest
portion of the site (Figure 5). A saturated thickness of approximately 2 feet occurs in well
MW-34 along the south dike of new tailings Cell 4B, and the perched zone is apparently dry at
MW-33 located at the southwest corner of Cell 4B. Depths to water range from approximately 17
to 18 feet in the northeastern portion of the site (near the wildlife ponds) to approximately 114
feet at the southwest margin of tailings Cell #3 (Figure 6). The relatively large saturated
thicknesses in the northeastern portion of the site are likely related to seepage from the wildlife
ponds located northeast and east of the tailings cells.
Although sustainable yields of as much as 4 gpm have been achieved in wells intercepting the
larger saturated thicknesses and higher conductivity zones in the northeast portion of the site,
perched zone well yields are typically low (<0.5 gpm) due to the generally low hydraulic
conductivity of the perched zone. Sufficient productivity can generally be obtained only in areas
where the saturated thickness is greater, which is the primary reason that the perched zone has
been used on a limited basis as a water supply to the north (upgradient) of the site, but has not
been used downgradient of the site.

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4.4 Summary
Perched groundwater at the site is hosted primarily by the Burro Canyon Formation, which
consists of a relatively hard to hard, fine- to medium-grained sandstone containing siltstone,
shale and conglomeratic materials. The Burro Canyon Formation is separated from the
underlying regional Navajo/Entrada aquifer by approximately 1,000 to 1,100 feet of Morrison
Formation and Summerville Formation materials having a low average vertical hydraulic
conductivity. The Brushy Basin Member of the Morrison Formation is a bentonitic shale that lies
immediately beneath the Burro Canyon Formation and forms the base of the perched water zone
at the site. Figure 2 is a photograph of the contact between the Burro Canyon Formation and the
underlying Brushy Basin Member taken from a location along highway 95 immediately north of
the Mill. This photograph illustrates the transition from the cliff-forming sandstone of the Burro
Canyon Formation to the slope-forming Brushy Basin Member. Based on hydraulic tests at
perched zone monitoring wells, the hydraulic conductivity of the perched zone ranges from
approximately 2 x 10-7 to 0.01 cm/s.
Perched water flow is generally from northeast to southwest across the site. Beneath and
downgradient of the tailings cells, on the west side of the site, perched water flow is
south-southwest to southwest. On the eastern side of the site perched water flow is more
southerly. Because of mounding near wildlife ponds, flow direction ranges locally from westerly
(west of the ponds) to easterly (east of the ponds). Perched water generally has a low quality,
with total dissolved solids ranging from approximately 1,100 to 7,900 mg/L, and is used
primarily for stock watering and irrigation north (upgradient) of the site.
Depths to perched water range from approximately 17 to 18 feet near the wildlife ponds in the
northeastern portion of the site to approximately 114 feet at the southwestern margin of tailings
Cell #3. Saturated thicknesses range from approximately 92 feet near the wildlife ponds to less
than 5 feet in the southwest portion of the site, downgradient of the tailings cells. A saturated
thickness of approximately 2 feet occurs in well MW-34 along the south dike of new tailings
Cell 4B, and the perched zone is apparently dry at MW-33 located at the southwest corner of
Cell 4B. Although sustainable yields of as much as 4 gpm have been achieved in wells
penetrating higher transmissivity zones, well yields are typically low (<0.5 gpm) due to the
generally low hydraulic conductivity of the perched zone.
Hydraulic testing of perched zone wells has yielded a range of approximately 2 x 10-7 to 0.01
cm/s. In general, the highest hydraulic conductivities and well yields are in the area of the site
immediately northeast and east (upgradient to cross gradient) of the tailings cells. A relatively
continuous, higher hydraulic conductivity zone associated with the chloroform plume has been
inferred to exist in this portion of the site. Analysis of drawdown data collected from this zone

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during long-term pumping of MW-4, TW4-19, and MW-26 (TW4-15) yielded estimates of
hydraulic conductivity ranging from 4 x 10-5 to 1 x 10-3 cm/s.
Hydraulic conductivities downgradient of the tailings cells are generally low. Hydraulic tests at
wells located at the downgradient edge of the cells, and south and southwest of the cells yielded
geometric average hydraulic conductivities of 2.3 x 10-5 and 4.3 x 10-5 cm/s depending on the
testing and analytical method. The low hydraulic conductivities and shallow hydraulic gradients
downgradient of the tailings cells result in average perched groundwater pore velocity estimates
that are among the lowest on site.
Hydraulic conductivities within the general area of the nitrate plume are based primarily on
analysis of hydraulic tests as discussed in Section 4.3. Hydraulic conductivity estimates ranged
from approximately 2.7 x 10-5 to 1.4 x 10-3 cm/s, and have a geometric average of 1.2 x 10-4
cm/s, assuming unconfined conditions. The transmissivities of many wells within the nitrate
plume are similar to wells that are pumped for chloroform removal.
4.5 Nitrate Occurrence
Nitrate within the area shown in Figure 1-2 was first detected in wells TW4-19, TW4-22, TW4-
24, and TW4-25 that were installed as part of the investigation of a chloroform plume first
discovered at perched well MW-4 in 1999. Investigation of nitrate has included the installation
of 19 temporary (TWN-series) perched zone nitrate monitoring wells to delineate and monitor
the nitrate (Figure 1-2). The extent of nitrate contamination is described below and in further
detail in Section 5.1 and its associated figures.
Nitrate concentrations in the perched zone as of the third quarter of 2011 are shown in Figure 7.
Nitrate concentrations in the perched zone have ranged from non-detect to a maximum of 69
µg/L at well TWN-2 in the second and third quarters of 2010. Nitrate concentrations at
downgradient wells MW-30 and MW-31 have been relatively stable, ranging from 15 to 17 mg/L
at MW-30 and from 20 to 22 mg/L at MW-31 between the first quarter of 2010 through the third
quarter of 2011.
Constituents associated with the nitrate include chloride, and in the east-central portion of the
plume, chloroform. The association of nitrate with chloroform is discussed in HGC, 2007b.
4.5.1 Source Areas
As discussed above, a number of potential Mill and non-Mill sources were identified in the
December 2009 Source Review Report for Nitrate and Chloride in Groundwater at the White

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Mesa Mill (INTERA, 2009), and in the subsequent August 2011 Nitrate Investigation Revised
Phases 2 through 5 Work Plan (INTERA, 2011), as listed below:
1. Main leach field (also known as leach field east of scale house, 1985 to present)
2. Sewage vault/lift station (currently active)
3. Scale house leach field, (also known as leach field south of scale house, 1977-1979)
4. Former office leach field
5. Ammonia tanks
6. SAG leach field (leach field north of Mill building, 1998 to 2009)
7. Cell 1 leach field (leach field east of Cell #1, up to 1985)
8. Fly Ash Pond
9. Sodium chlorate tanks (as a potential chloride source)
10. Ammonium sulfate crystal tanks
11. Lawzy sump
12. Lawzy Lake
13. Former vault/lift station (to former office leach field, 1992 to 2009)
14. Truck shop leach field (1979-1985)
15. New Counter Current Decant/Solvent Extraction (“CCD/SX”) leach field (currently
active)
16. Historical Pond
17. Wildlife pond
18. CCD (included inadvertently and eliminated)
19. YC Precip Mini-Lab
20. V2O5 Mini-Lab & V2O5 Precip
21. SX Mini-Lab
22. Chem Lab
23. Met Lab
24. V2O5 oxidation tanks
25. Natural nitrate reservoir
26. – 32. Seven other ponds or pond-like sources
Figure 8 shows the locations of potential source areas 1 through 24.
Based on the investigation and source evaluations completed to date, there are no known current
unidentified or unaddressed ongoing sources. There appear to have been a number of known and

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potential historic sources; however, it has not been possible to confirm or quantify the
contribution of each. Soil contamination associated with the ammonium sulfate tanks as a
potential source to perched groundwater is addressed as Phase I of this CAP.
Although the actual source or sources have not been identified and quantified, based on analysis
of the concentrations within and the areal extent of the plume over the past two years, Denison
and DRC have concluded there is no known significant unaddressed currently active source. That
is, analytical results indicate that neither the average concentration within the plume nor the areal
extent of the plume has increased during the period it has been monitored. Therefore, although
the source or sources have not been definitively determined, sufficient information exists to
bound and characterize the plume and plan remedial actions for its control.
4.5.2 Nitrate Concentration Trends
Table 3 provides nitrate concentrations detected at wells within the nitrate plume from the first
quarter, 2010 through the third quarter of 2011. Over the last year (between the third quarter,
2010 and third quarter, 2011) three wells decreased in concentration, three increased, and three
remained the same. The well with the highest concentrations, TWN-2, decreased from 69 mg/L
to 33 mg/L. The average nitrate concentration within the plume decreased from 24.4 mg/L to
19.7 mg/L. At the downgradient edge of the plume, monitor wells MW-30 and MW-31 have
been sampled since June 2005. During the period from June 2005 to December 2011, samples
from MW-30 have had an average nitrate concentration of 16 mg/L with a standard deviation of
1.4 mg/L (Figure 9-1). During the same period, samples from MW-31 have had an average
nitrate concentration of 22 mg/L with a standard deviation of 2.7 mg/L (Figure 9-1). Thus, the
downgradient edge of the plume has been relatively stable over a six and one half year period.
The information presented above indicates that concentrations within the plume are relatively
stable but the highest concentrations appear to be declining. Figure 9-2 compares the extent of
the nitrate plumes in the third quarter of 2010 and the third quarter of 2011. As indicated, the
plume boundaries are relatively stable, likely the result of the generally low hydraulic
conductivity of the perched zone, and the ongoing pumping related to the chloroform plume.

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5. CHARACTERIZATION OF STUDY AREA
The study area encompasses a region in the northeastern portion of the site where the nitrate
plume (defined by concentrations > 10 mg/L) has been detected and bounded by a series of
nitrate and chloroform investigation wells (Figure 1-2). Wells within the plume are MW-30 and
MW-31, and temporary wells TW4-19, TW4-21, TW4-22, TW4-24, TW4-25, TWN-2 and
TWN-3 (Figure 7). Wells MW-5, MW-11, MW-25, MW-26, MW-27, MW-28, MW-29, MW-
32, TW4-16, TW4-18, TWN-1, TWN-4, TWN-7, and TWN-18 bound the plume. As of the
second quarter of 2011, MW-5, MW-11, MW-25, MW-29, and MW-32 were non-detect for
nitrate. Hydraulic characterization of the study area has been based on data collected from wells
within and near the plume as discussed in Section 4. The extent and hydrogeology of the study
area is discussed below.
5.1 Extent of Study Area
The nitrate plume that is the focus of this CAP is confined to the region of the perched zone
containing nitrate concentrations exceeding 10 mg/L located south of TWN-18 and north of
MW-11. The area having nitrate exceeding 10 mg/L, as of the third quarter of 2011, is shown in
Figures 1-2 and 7. This area extends from the northeast portion of the tailings cells to the area
upgradient (north-northeast) of the tailings cells. The highest nitrate concentrations have
historically been detected at TWN-2, within the northern (upgradient) portion of the plume.
TWN-2 is located within the area of the historical pond (Figure 8).
The historical pond was active as far back as the 1920s, as much as 60 years prior to the
establishment of the White Mesa Mill. Satellite photos taken over the years and dating back to
the 1950s indicate that the historical pond was one of the major agricultural/livestock ponds in
the area and typically contained water. Records or information have not been obtained to
evidence the actual uses of the pond over the years. The historical pond likely collected runoff
from nearby agricultural land, which may have been fertilizer-laden. The pond may have also
been used as a stock pond and have been influenced by the ranching or agricultural activities.
Regardless of the specific uses of the pond, water within the pond appears to have been elevated
in nitrate and chloride. Because the pond was unlined, significant seepage of nitrate and chloride
laden water is expected to have reached the perched zone.
Areas of detectable nitrate that are not continuous with the above defined area exist to the
northwest (near TWN-9 and TWN-17) and to the east-southeast associated with the chloroform
plume. Nitrate concentrations within these areas are typically less than 10 mg/L although
sporadic detections at or slightly above 10 mg/L have occurred at some locations. Areas to the

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northeast are not a target of this CAP, and nitrate associated with the chloroform plume is
addressed by the ongoing chloroform pumping.
The nitrate plume, as defined by the 10 mg/L concentration boundary, is bounded by wells MW-
5, MW-11, MW-25, MW-26, MW-27, MW-28, MW-29, MW-32, TW4-16, TW4-18, TWN-1,
TWN-4, TWN-7, and TWN-18. As of the second quarter of 2011, MW-5, MW-11, MW-25,
MW-29, and MW-32 were non-detect for nitrate. The plume is bounded to the south by MW-5
and MW-11, to the east by MW-27, MW-28, MW-29 and TWN-7, to the north by TWN-18, and
to the west by MW-25, MW-26, MW-32, TWN-1, TWN-4, TW4-18, TW4-16, and TW4-20.
Additional wells to the south (downgradient) of the plume include MW-3, MW-14, MW-15 and
MW-37.
5.2 Hydrogeology
A description of the hydrogeology of the site in the vicinity of the nitrate plume is provided in
Section 3, and hydrogeologic cross-sections are provided in Appendix A. Perched zone hydraulic
conductivities in the vicinity of the nitrate plume are in the middle to high end of the range
measured at the site. The geometric average of approximately 1.2 x 10-4 cm/s is slightly lower
than typical for the area of the chloroform plume located east and southeast of the nitrate plume
(Figure 10).
Perched groundwater flow in the area of the nitrate plume is generally southwesterly. Saturated
thicknesses in the vicinity of the plume are generally higher than in areas to the south and
southwest. In the vicinity of the nitrate plume (Figure 5) they range from a maximum of
approximately 87 ft at TW4-25 to approximately 30 ft at MW-30. In general, saturated
thicknesses increase toward the northeast, where the wildlife ponds are located, and are locally
affected in the vicinity of the plume by pumping at MW-26, TW4-19, and TW4-20.
Hydraulic conductivities within the general area of the nitrate plume are based primarily on
analysis of slug tests as discussed in Section 3. Hydraulic conductivity estimates range from
approximately 2.7 x 10-5 to 1.4 x 10-3 cm/s, and have a geometric average of 1.2 x 10-4 cm/s
(Table 2). The transmissivities of many wells within the nitrate plume are similar to wells that
are pumped for chloroform removal.

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6. CORRECTIVE ACTION CONCENTRATION LIMITS
The corrective action concentration limit for nitrate is 10 mg/L. This concentration is considered
to bound the outer extent of the plume and is the ultimate target for reducing nitrate
concentrations within the plume. As discussed in Section 9, once the nitrate concentrations in all
monitoring wells are 10mg/L or less, concurrence with DRC will be sought that the plume is
remediated and the corrective action complete.

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7. CORRECTIVE ACTION PLAN - CONSTRUCTION AND OPERATION
The corrective action for the nitrate plume is proposed to occur in three phases.
In Phase I, Denison proposes to construct a sloped, curbed and drained concrete pad of six inches
in depth over an area covering at least twice the areal extent of contamination identified during
the contamination investigation. Denison also proposes a future removal of contaminated soil at
the time of Mill site reclamation and, for conservatism, proposes to revise the reclamation surety
estimate to include a volume of soil to be removed and placed in the tailings cells of twice the
volume of contaminated soil identified in the contamination investigation.
Phase II will consist of pumping four wells within the nitrate plume (TW4-22, TW4-24, TW4-
25, and TWN-2). Phase II relies on both pumping and natural attenuation to remove nitrate mass,
reduce nitrate concentrations within the plume, and minimize or prevent plume migration.
Included in Phase II are continued monitoring within and outside the plume to verify plume
boundaries (as defined by a concentration of 10 mg/L), estimate changes in hydraulic capture,
and track changes in nitrate concentrations within the plume.
If implemented, Phase III will consist of a transport assessment, a hazard assessment, and an
exposure assessment along with a corrective action assessment including an evaluation of best
available remedial technologies. Selection of a technology for implementation will be based on
an evaluation whether the technology will remediate contamination to as low as is reasonably
achievable, if the 10 mg/L standard is not reasonably achievable. One possible outcome of these
evaluations could be an application for alternate corrective action concentration limits (ACACL).
After implementation of Phase II and Phase III and once residual concentrations have dropped to
10 mg/L or less at all monitored locations or an ACACL has been granted, concurrence with the
Executive Secretary will be sought that the corrective action is complete. Phase II has
contingencies to be implemented if needed based on monitoring as discussed in Section 8. The
termination of Phase II and implementation of Phase III will be with the concurrence of the
Executive Secretary and will be based on assessments conducted during Phase II.
An important goal of Phase III is to ensure that nitrate concentrations exceeding the action level
will not migrate to any point of exposure within the applicable regulatory time frame. This
migration of the nitrate plume is not expected to occur. However, the decision as to when to
terminate Phase II and implement Phase III will be based on Phase II monitoring data and
quantitative calculations that indicate that, based on Phase II results, this Phase III goal is
attainable.

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7.1 Phase I Description and Rationale
The potential contamination source to be addressed in Phase I consists of alluvial soil in the area
of the Mill’s outdoor ammonium sulfate storage tanks as depicted in Figure 11-1. As shown in
Figure 11-1, the ammonium sulfate tanks and associated soil contamination are located to the
east of the Mill process building. The tanks are currently situated over an uncurbed concrete slab,
which has suffered some deterioration over the years. The tank area is bounded to the west by the
Mill building, to the south by the V2O5 Mini Lab and Precipitation Area, and to the north by the
Mill’s Pulp Storage Tanks. That is, the ammonium sulfate tanks are located in a relatively
congested and (on three sides) built out area. The proximity of the Mill building and other tanks
precludes the ability to perform an extensive soil excavation/contaminated soil removal at the
current time. Therefore, consistent with the SCA, Denison proposes to perform the contaminated
soil corrective action phase in two steps; 1) construction of a concrete cover to remain in place
during the operating life of the Mill, and 2) a contaminated soil excavation to occur during the
Mill reclamation at final Mill closure.
7.1.1 Approximation of the Lateral Extent of Contamination and Concrete Cover
Per Section 11A(1) of the SCA, Phase I is required to include a control for the soil contamination
observed at the ammonium sulfate tanks. To meet this objective, Denison proposes to construct a
sloped and drained concrete pad of six inches in depth over an area covering the areal extent of
contamination identified during the contamination investigation to prevent infiltration of surface
water into the contaminated soil. Existing data consists of analytical data from two of the soil
borings collected during the June 2011 contamination investigation as shown in Figure 11-1. In
order to verify that the proposed concrete pad meets the objective of covering the lateral extent
of contamination, Denison will implement a soil sampling program prior to the completion of the
concrete pad. The soil sampling program is designed to provide data to delineate, approximately,
the lateral extent of contamination.
The soil sampling program will be conducted substantially in accordance with the DRC-
approved field and quality assurance procedures implemented during the Phase 1, (Part 1) Nitrate
Investigation as described in the Nitrate Investigation Phase 1 Work Plan, dated May 13, 2011.
A summary of the soil sampling program to be conducted during Phase I of the CAP, with any
necessary changes from the Nitrate Investigation Phase 1 Work Plan, dated May 13, 2011, is as
follows.
7.1.1.1 Soil Sampling Program Objective and Design
The objective of this soil sampling program is to delineate, approximately, the lateral extent of
contamination in order to determine the extent of the concrete pad necessary to cover the soil

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contamination identified during the Phase I investigation. To meet this objective, 18 Geoprobe
borings will be conducted down to bedrock refusal at each of the locations shown on Figure 11-
2B. Three (3) samples will be collected from each Geoprobe core location. Soil core samples
will be collected from the bottom one foot of each of the following intervals, based on the total
depth of penetration at each site: top 1/3, middle 1/3, and bottom 1/3.
Select soil core samples will be sent to the analytical laboratory for analysis of nitrate (as N), and
ammonia (as N) as described below. Since the purpose of this sampling program is to confirm
the lateral extent of soil contamination (in the form of nitrate and ammonia) resulting from the
ammonium sulfate tank source, no other analytes are required. Soil analysis will be conducted by
an environmental laboratory currently certified by the State of Utah, using EPA approved sample
and analysis methods.
Denison anticipates that the presence of ammonia contamination will diminish with distance
from the ammonium sulfate tanks. The initial row of samples will be collected 3 feet from the
northeast edge of the proposed concrete pad shown in Figure 11-2B. If the results of the analysis
of the initial sample row indicate that ammonia and nitrate levels do not exceed DRC’s proposed
screening levels of 20 times the background levels determined in the June 2011 investigation,
specifically 42.9 mg/kg for ammonia and 43.8 mg/kg for nitrate, no further samples will be
analyzed and the pad will be constructed as shown in Figure 11-2B. That is, if the initial samples
are below the screening levels, it will be concluded that the contamination will be adequately
covered by the proposed design, and the soil sampling program will be considered complete.
If the results of analysis of the initial sample row indicate that the contamination extends beyond
the area delineated by the initial row, that is, one or more samples in the initial row exceed the
screening levels, the remaining samples for one or more additional sampling rows will be
analyzed for nitrate (as N), and ammonia (as N). The concrete pad will be sized to extend to the
first row of samples whose analysis do not indicate nitrate or ammonia exceeding the screening
levels.
7.1.1.2 Field Activities/Sampling Methods
In order to minimize the potential for multiple mobilizations of the Geoprobe unit, three discreet
sets of samples will be collected in one sampling event during this investigation. Each discreet
set of samples will be collected in a lateral line or “row” along the northeast face of the proposed
concrete pad as shown in Figure 11-2B. Samples will be collected every approximately 12.5 feet
laterally along the edge of the concrete pad. The first row of discreet samples will be
approximately three feet from the edge of the proposed concrete pad. The two successive rows
will be stepped-out approximately ten feet from the previous row of samples. The samples

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collected in the two successive rows will be archived for potential later analysis of nitrate and
ammonia if necessary. All archived samples will be stored in accordance with the analytical
method requirements for temperature. Expedited turn around will be requested for the analysis of
the first row of soil samples, so that if any additional analyses are required, the additional
analyses can be completed within the specified analytical holding times. Based on this sampling
strategy, 54 soil samples (and 6 duplicates and 3 rinsates), will be collected.
7.1.1.3 Sample Handling and Custody
Each sample collected during this sampling program will be identified using a unique sample
identification number (lD). The description of the sample type and the sample name will be
recorded on the chain-of-custody (COC) forms, as well as in the field notes. Geoprobe boring
samples will be named according to the boring location and top and bottom of the depth interval
at which they were collected, following the convention P1AXX-tt-dd, where P1AXX is the first
boring in the first row of samples and tt is the top of the depth interval and dd is the bottom of
depth interval expressed in feet below ground surface. Additional rows of samples will be
identified as P1A2XX-tt-dd. Duplicate samples will carry the same identification as the parent
sample with the terminal letter “D” to identify them as a duplicate. Similarly, rinsate samples
will carry the sample identification of the sample collected prior to the rinsate followed by the
terminal letter “R”.
Samples will be collected into re-sealable plastic bags, which will be labeled with the sample
identification and homogenized by vigorously shaking and mixing the contents until the samples
are visibly uniform. A minimum sample volume of 100 grams will be collected from each
location. Sample containers will be provided by the laboratory, certified as clean, and will be
filled directly from the plastic bags. Archive sample aliquots will be maintained in the plastic
bags at the Mill for the duration of the analytical holding times to provide additional backup
sample for analysis if necessary. Archive sample aliquots will be stored in accordance with the
analytical method requirements for sample preservation.
Standard sample custody procedures as described in the DRC-approved Nitrate Investigation
Phase 1 Work Plan, dated May 13, 2011 will be used to maintain and document sample integrity
during collection, transportation, storage, and analysis.
Samples will be shipped to the analytical laboratory using an overnight carrier such as Federal
Express. Samples will be analyzed within the analytical method specified holding times.

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7.1.1.4 Analytical Methods
For comparability, the soil analytical methods will be the same as those used for the 2011 nitrate
contamination investigation.
All soil samples will be submitted to the analytical laboratory for SPLP using EPA Method 1312
using Extraction Fluid #3. Method 1312 will produce a leachate of all soil samples which will be
analyzed for nitrate and nitrogen as ammonia using EPA Method 353.2, and EPA method 350.1
respectively. Method 1312 will produce a sufficient volume of leachate to complete the nitrate
and ammonia analyses as well as any method-required QC analyses.
The soil samples are being leached and analyzed using water methodologies, which will yield
concentrations in liquid units (such as mg/L). The laboratory will report all soil samples in two
ways: 1) as a leachate in mg/L and 2) as a soil in mg/kg on a dry weight basis.
The reporting limits (“RLs”) for the methods are 0.1 milligrams per liter (“mg/L”) for nitrate and
0.5 mg/L for ammonia. These RLs are sufficiently sensitive to allow determination of soil
contamination. The RLs from the DRC-approved Nitrate Investigation Phase 1 Work Plan, dated
May 13, 2011 have been raised to 0.1 mg/L to eliminate false positive results from low-level
interferences present in the SPLP blanks.
7.1.1.5 Quality Control
Quality control (“QC”) samples will be collected in the field during the sampling effort and will
include one duplicate per ten analytical samples and one rinsate sample per twenty samples.
Rinsate samples will be collected using deionized (“DI”) water from the Mill’s DI system which
is routinely used for all other sampling programs at the Mill. Duplicates will be assessed through
the calculation of a relative percent difference (“RPD”) and rinsate samples will be assessed
based on any detections reported and their magnitude relative to the sample results. The QC
procedures set forth in the Nitrate Investigation Phase 1 Work Plan, dated May 13, 2011 will be
used for the assessment of the soil samples collected during this program.
Analytical laboratory QC, audits, instrument calibration, internal QC procedures, detailed COC
procedures, organizational responsibilities, and other specific details regarding sample collection
will be completed in accordance with the DRC-approved Nitrate Investigation Phase 1 Work
Plan, dated May 13, 2011.
7.1.2 Construction of the Phase I Action
Denison proposes to construct a sloped, curbed, and drained concrete pad of six inches in depth
over an area covering the lateral extent of contamination identified during the contamination

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investigation. Because the ammonium sulfate tanks are surrounded by existing concrete
structures to the south, west, and north, the new concrete pad will extend to the east of the Mill
building. The existing concrete pad will be resurfaced and sloped to drain to the existing
collection area/sump inside the Mill building, which returns solutions to the process. This
resurfaced area will be constructed with a curb of approximately 6 inches in height. In addition, a
new concrete slab will be extended to the eastern edge of the surrounding structures. This new
slab will also be sloped to drain to an existing collection area/sump in the Mill building. A rolled
curb will be constructed with an access ramp to allow supplier trucks sufficient access to refill
the tanks. The proposed cover design is depicted in Figure 11-2A and B.
The only subsurface piping in the vicinity of the ammonium sulfate tanks is a segment of the
underground portion of the Mill fire water system. Figure 11-3 shows the location of the
subsurface portion of the fire water line. Due to the need to maintain continual pressure on the
fire water system, the system already contains instrumentation (an alarm system) to indicate
when the pressure makeup pump starts up as a response to leaks, breaks, or loss of pressure. As
indicated by the pump alarm history, the firewater system has no history of leakage, and is not
expected to be a source of hydraulic head in the vicinity. The only other subsurface process
piping on the Mill site consists of two pairs of lines: one cooling water recirculation loop, and
one vanadium product liquor loop, for which the buried portion begins approximately more than
100 feet southeast the ammonium sulfate tanks (75 feet from the nearest corner of the concrete
pad proposed in Figure 11-4), and “around the corner” from the ammonium sulfate tanks – east
of the easternmost wall of the building’s “L”. These two piping loops are new, have had no
history of leakages, and are too far from the ammonium sulfate tanks to be a source of hydraulic
head in the vicinity of the tanks. All other process piping is above grade.
Consistent with Section 11A(1)(b)(i) of the SCA, Denison provided a detailed plan and schedule
for construction of the concrete cover to DRC in Section 7.1 and Figures 11-1 and 11-2A and B
of the November 30, 2011 version of this CAP.
7.1.3 Maintenance of the Phase I Action
Denison will provide a plan for annual inspection, required repairs, and annual documentation of
the condition of the pad in a revised version of the Discharge Minimization Technology
(“DMT”) Plan, to be submitted following approval of the CAP by the Executive Secretary. The
revised DMT Plan will address:
• frequency of inspection and photographic documentation of the condition of the pad
(annually),
• contents of inspection reports,

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• inspection criteria,
• conditions requiring repairs,
• timing of repairs, and
• contents of repair reports.
7.1.4 Estimation and Removal of Contaminated Soil During Mill Reclamation
Denison also proposes a future excavation of contaminated soil at the time of Mill site
reclamation, and disposal of the excavated soil in the tailings cells. To ensure a sufficient surety
amount for reclamation of the known contaminated soil volume to the depth of bedrock, Denison
proposes to revise the reclamation surety estimate to include a volume of soil of twice the
volume of contaminated soil volume identified in the contamination investigation.
The following process will be used to estimate the volume of contaminated soil to be removed
during reclamation. Once the total area to be covered by concrete has been determined based on
the borehole analyses, the area will be multiplied by the average depth to bedrock, as determined
from the logging of the boreholes.
Based on the geologic logging performed during the soil probe sampling in the Phase I
Investigation in June, 2011, borings number GP-25B and GP-26B in the vicinity of the
ammonium sulfate tanks indicated depth to bedrock of 19 feet and 16 feet, respectively. These
values will be included, along with depths determined during the additional Geoprobe sampling
to develop an average depth to bedrock. This average depth to bedrock will be multiplied by the
area of contamination. For conservatism, Denison will double the volume determined by the
above method for purposes of the reclamation surety estimate.
Consistent with Section 11A(1) of the SCA, Denison will provide a revised surety estimate to
DRC by March 4, 2012. The March 4, 2012 surety estimate will include an overly conservative
estimate for removal of the contaminated soil volume that is based on:
1. The preliminary proposed concrete cover area as depicted in Figure 11-2B
2. An approximate depth to bedrock of 20 feet (1 foot deeper than the maximum depth to
bedrock measured to date during the June 2011 investigation)
3. A conservative overestimation factor of 3 times the volume estimated from items 1 and 2
above

Following receipt of the additional depth-to-bedrock data and estimated lateral extent of
contamination data that will be developed from the soil sampling program described above,
Denison will review the March 4, 2012 volume and cost estimate. If additional data indicates an

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increase of the conservatively estimated soil volume in the March 4, 2012 surety estimate,
Denison will provide a revised volume and cost estimate within 60 calendar days following
issuance of the Consent Order contemplated in Section 11.E of the SCA.
7.2 Phase II Description and Rationale
Phase II consists of three active components and one passive component. The active components
are:
1. Removal of nitrate mass from the perched zone as rapidly as is practical by pumping
from wells located in areas having high nitrate concentrations, relatively high
productivities, or both.
2. Perched zone water level and nitrate monitoring to assess changes in nitrate
concentrations within the plume, verify the location of the plume boundary over time,
and estimate hydraulic capture zones. A general lowering of nitrate concentrations within
the plume is expected as a result of Phase II operation.
3. Abandonment of TWN-series wells not needed for implementation of item 2.

Pumped water will be disposed in the tailings cells. In addition, all samples analyzed for nitrate
will also be analyzed for chloride.
The passive component consists of relying on natural attenuation to reduce nitrate
concentrations. Physical mechanisms that will reduce nitrate concentrations include processes
such as hydrodynamic dispersion, and dilution via mixing with nitrate-free recharge and low
nitrate waters outside the plume. Neither biologically mediated decomposition of nitrate nor
abiotic chemical decomposition are expected to be significant mechanisms in reducing nitrate
concentrations because the majority of the perched water is likely aerobic and unsuitable for
rapid decomposition of either chloroform or nitrate. The persistence of chloroform and the
persistence of nitrate associated with the chloroform plume are consistent with predominantly
aerobic conditions. The presence of iron oxides within the perched zone in most of the site
borings is also consistent with aerobic conditions.
As discussed in HGC (2007) chloroform daughter products, such as dichloromethane (DCM),
have been detected but at low concentrations. The persistence of chloroform and the low
concentrations of daughter products imply relatively low rates of chloroform degradation. Owing
to its relatively high oxidation state, chloroform would be expected to degrade relatively rapidly,
yielding higher concentrations of daughter products such as DCM, under primarily anaerobic
conditions.

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That chloroform daughter products have been detected suggests that conditions are locally
favorable for anaerobic degradation. The presence of carbonaceous material in many of the site
borings and the presence of pyrite in most of the borings suggests that at least local anaerobic
conditions favorable to degradation of chloroform and nitrate exist. The formation hosting the
perched zone was likely anaerobic in the past, and conducive to the preservation of carbonaceous
material and the formation and preservation of pyrite, but, at least some areas of the site, is now
mainly aerobic with pyrite oxidizing to iron oxide. The oxidation of pyrite is likely enhanced
near perched wells which provide a conduit for oxygen to the perched zone.
As a result, wherever conditions may be favorable to anaerobic degradation, the actual
degradation rates of nitrate from either abiotic or biologically mediated degradation may be, in
fact, larger than anticipated, which will be favorable for removal of nitrate from the perched
zone. However, Denison is not relying on either abiotic or biologically mediated degradation as
important removal mechanisms.
Furthermore, nitrate is not expected to be retarded by adsorption onto aquifer materials because
of its high solubility and negative charge. The combination of pumping, hydrodynamic
dispersion, and dilution by recharge are expected to be effective considering that less than an
order of magnitude reduction in concentration is needed to reduce the highest detected nitrate
concentrations within the plume (approximately 69 mg/L) to the target of 10 mg/L. The
downgradient portion of the plume, defined by MW-30 and MW-31, will require reduction in
concentration by only a factor of two to meet the 10 mg/L goal.
In general, Phase II is expected to function in a manner similar to ongoing chloroform removal
from perched water at the site. Construction and operation will be similar to the chloroform
pumping system which consists of five wells (MW-4, MW-26, TW4-4, TW4-19, and TW4-20)
located within the chloroform plume that are pumped as continuously as practical and at rates
that are as large as practical. Water from those wells is disposed in the tailings cells.
The nitrate pumping system will consist of four wells: TW4-22, TW4-24, TW4-25, and TWN-2
(Figure 1-2). Water will be pumped from these wells as continuously as practical and at rates as
high as practical. These wells were selected for pumping because 1) they are located in middle to
upgradient areas of the plume having the highest nitrate concentrations and will minimize the
downgradient migration of these high concentrations, 2) they are expected to have productivities
similar to the chloroform pumping wells, 3) pumping these wells is not expected to enhance the
downgradient migration of chloroform, and 4) they are temporary chloroform (TW4-series) or
nitrate (TWN-series) investigation wells and converting them to pumping wells will not impact

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tailings cell point of compliance monitoring under the Mill’s Groundwater Discharge Permit
(“GWDP”).
Pumping these wells is expected to remove nitrate mass from the perched zone as rapidly as
practical, and flatten hydraulic gradients within the plume to reduce rates of downgradient
migration and allow natural attenuation to be more effective. Furthermore, the depression of the
water table resulting from pumping in the upgradient portion of the plume will reduce interaction
between the perched water and any residual shallow vadose zone sources that may exist. As a
result plume migration is expected to be minimal or cease once Phase II is implemented.
Currently the plume appears to be changing very slowly. Figure 9-2 compares the extents of the
nitrate plume in the third quarters of 2010 and 2011. Over this period, the plume appears to be
relatively stable, having expanded slightly in some areas and contracted slightly in others. The
apparent stability of the plume is likely the result of the generally low hydraulic conductivities of
the perched zone, and ongoing pumping within the adjacent chloroform plume. Implementation
of Phase II is expected to further reduce or halt downgradient migration and to reduce
concentrations within the plume. If ongoing monitoring indicates the plume continues to migrate,
then contingencies will be implemented.
As discussed above, the productivities of the proposed nitrate pumping wells are expected to be
similar to those of the chloroform pumping wells. The transmissivities at proposed nitrate
pumping wells TW4-22, TW4-24, and TW4-25 are estimated to be between those of chloroform
pumping wells MW-26 and TW4-19; and the transmissivity at TWN-2 is estimated to be about
one third that of chloroform pumping well TW4-20 (Table 4). Therefore, the long-term
productivities of TW4-22, TW4-24, and TW4-25 are expected to be between those of MW-26
and TW4-19; and the long-term productivity of TWN-2 is expected to be about one third that of
TW4-20. Although expected pumping rates at TWN-2 will be relatively low, the high
concentrations detected at that well will result in relatively high nitrate removal rates. Pumping
at TWN-2 is expected to reduce or eliminate the apparent residual perched water mound at that
location. As the mound is depleted, the productivity of TWN-2 is expected to diminish.
However, continued operation of TWN-2, even at low average extraction rates, is expected to be
beneficial.
The potential interaction of the chloroform plume with the nitrate pumping system is of concern.
Figure 10 shows the locations of the nitrate and chloroform plumes as of the third quarter of
2011. The chloroform plume is located generally east-southeast of the nitrate plume, but the
plumes mingle in the vicinity of TW4-19, TW4-20 and TW4-22 (northeast corner of tailings Cell
#2). Pumping the proposed nitrate wells will impact chloroform migration to some extent, and
any pumping that enhances downgradient migration of chloroform is undesirable. It is expected

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that pumping the proposed wells will at most draw chloroform cross-gradient to the west-
northwest. However, pumping of any wells to the southwest of the chloroform plume (such as
MW-30 and MW-31) would have the undesirable impact of enhancing the downgradient
migration of chloroform, and is not considered to be an option. Furthermore, converting MW-30
or MW-31 to nitrate pumping wells would degrade the usefulness of these wells for tailings cell
point of compliance monitoring under the GWDP.
Data collected during Phase II monitoring will be used to estimate the extent of the capture zone,
and to calculate nitrate mass removal rates by pumping. Denison will calculate the capture zones
after four quarters of water level measurements have been taken, and will include the
calculations, with figures, in the next quarterly nitrate monitoring report. Numerical and/or
analytical models will be used if needed to assist in evaluating the data and estimating natural
attenuation.
It is expected that the four pumping wells, in combination with the existing chloroform pumping
wells, will adequately capture the nitrate plume, such that concentrations of nitrate in excess of
the 10 mg/L standard are not expected to migrate beyond the current boundaries of the plume.
Based on experience from the chloroform pumping results to date, it is expected that the capture
zone from the four nitrate pumping wells will, by themselves extend upgradient to capture the
entire plume north of TW4-22 and TW4-24 as well as more than 400 feet downgradient of TW4-
22 and TW4-24. For example, the downgradient extent of the combined capture zone of
chloroform pumping wells MW-26, TW4-19, and TW4-20 (Figure 12) extends more than 400
feet downgradient of MW-26. The capture zone from the four nitrate pumping wells alone is
expected to likewise extend at least 400 feet southwest of TW4-22 and TW4-24, encompassing
by themselves approximately three quarters of the plume (Figure 13). However, the proportion of
the nitrate plume under hydraulic capture is expected to be larger than this estimate as the nitrate
capture zone merges and is enhanced by the chloroform capture zone. The result is that either
complete hydraulic capture will be achieved, or if not achieved, concentrations of nitrate in
excess of 10 mg/L are not expected to migrate beyond the current boundaries of the plume.
Hydraulic capture will be considered successful if the concentrations of nitrate in MW-30 and
MW-31 remain stable or decline and concentrations of nitrate in downgradient wells MW-5 and
MW-11 do not exceed the 10 mg/L standard.
The nitrate plume is defined as that portion of the perched aquifer that has a concentration of
nitrate in excess of 10 mg/L. In evaluating whether the pumping system has contained the plume,
the proper parameter to evaluate is therefore whether the 10 mg/L boundary has moved beyond
the currently defined plume boundary. MW-5 and MW-11 presently do not exceed the 10 mg/L
Groundwater Quality Standard; that is, they are outside the currently defined plume, and act as

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bounding wells for the plume. So long as they continue to be less than or equal to 10 mg/L they
will remain as bounding wells outside of the plume, and the plume will not have expanded.
It is possible that there may still be some movement of impacted water (i.e., there may not be
complete hydraulic capture), but so long as that movement of water does not cause the
concentration in any downgradient well to exceed 10 mg/L, the plume itself will not have
expanded and adequate hydraulic control will have been demonstrated. As a result, it is possible
that there may be some future impact on MW-5 and MW-11, even though the plume has not
expanded. However, any impacts on MW-5 and MW-11 will be monitored to ensure that the
concentrations in those wells, if they do increase over time, do not exceed 10 mg/L. If the
concentration of nitrate in either or both of those wells increases above 10 mg/L, then the plume
will have expanded and plume capture will not have been successful. Further actions, such as
modeling or the addition of more nitrate pumping wells, would need to be investigated at that
time. Because numerous monitoring wells currently exist downgradient of MW-5 and MW-11
(i.e., MW-35, MW-36, MW-37, MW-15 and MW-14 as a first line of defense, and beyond that
line, MW-17, MW-03, and MW-20), existing wells would continue to bound the plume, and
there would be no chance that the plume could expand beyond the downgradient edge of the
Mill’s existing tailings cells, without being detected and without ample time to institute further
mitigative actions.
7.2.1 Well Abandonment
Currently there are 19 TWN-series wells that were installed for the investigation of nitrate at the
site. Wells in the vicinity of the nitrate plume will be retained for monitoring. TWN-series wells
located north–northeast of TWN-18 are not needed for this purpose and are therefore selected for
abandonment. Wells proposed for abandonment are TWN-5, TWN-6, TWN-8, TWN-9, TWN-
10, TWN-11, TWN-12, TWN-13, TWN-15, TWN-16, and TWN-17. . Wells to be retained for
nitrate and chloride monitoring are TWN-1, TWN-2, TWN-3, TWN-4, TWN-7, and TWN-18.
The foregoing wells will be abandoned within one year from the date of approval of this CAP, in
accordance with applicable regulations (State of Utah Administrative Rules for Water Wells R655-4-
14). Although not needed for nitrate plume monitoring, wells TWN-14 and TWN-19 will be
retained for water level monitoring only, to provide ongoing water level data for the northeast
portion of the site.
A well abandonment report will be submitted to the Executive Secretary within 15 months after
the date of approval of this CAP.

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7.2.2 Groundwater Pumping System
The Phase II corrective action groundwater pumping system will consist of wells TW4-22, TW4-
24, TW4-25, and TWN-2 (Figure 1-2). Each well will be equipped with a Grundfos Series SQE
1x200-240 Volt, 6.2Amp submersible pump. To prevent damage to the pumps, each will operate
on a cycle that allows pumping only when sufficient water is present in the well. The capacity of
each pump will be greater than the sustainable pumping rate for each well. Therefore, the
average amount of water pumped from each well will be, in general, the maximum practical.
These wells were selected for pumping because they are located in areas of the perched zone
having both high nitrate concentrations and relatively high transmissivities that allow relatively
high rates of mass removal, and because they are not expected to have a negative impact on
chloroform migration from the adjacent chloroform plume.
Water pumped from each well will be routed by ½ inch high-density polyethylene Drisco
discharge lines, comparable to the transfer lines in the chloroform pumping system, to the
tailings cells for disposal. A schematic drawing of the transfer piping system is provided in
Figure 11-5. The discharge line near each wellhead will be equipped with an in-line Carlon ½”
flow meter/totalizer (or equivalent). The flow meter/totalizer will be housed in an insulated
wooden box with a heat source to prevent freezing. Readings from each totalizer will be used to
report quarterly pumped volumes and average pumping rates.
Operation of the nitrate wellfield will be similar to that for the chloroform wellfield. The
contingencies described in Section 8 will be implemented should nitrate mass removal rates drop
significantly due to losses in well productivity.
7.2.3 Water Level Monitoring
Water levels will be monitored weekly in each of the four nitrate pumping wells. Water levels in
the remaining wells listed in Table 3 will be monitored monthly for the first twelve months after
commencement of Phase II pumping, and thereafter quarterly. Depths to water will be measured
using an electric water level meter in the same way they are currently collected. Hydraulic
capture zones will be estimated from water level contour maps generated quarterly from the
water level data, with the first capture zones estimated after twelve months of data have been
obtained. The contingencies described in Section 8 will be implemented should the proportion of
the remaining nitrate plume that is under hydraulic capture shrink significantly.
7.2.4 Water Quality Monitoring
Pumping wells TW4-22, TW4-24, TW4-25, and TWN-2, and the other wells listed in Table 3,
will be monitored quarterly. Sampling and analytical procedures will be the same as currently

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employed for the nitrate monitoring as described in the quarterly monitoring reports submitted
by Denison to DRC. Each well will be sampled for the following constituents with respect to
monitoring the nitrate plume:
• Chloride
• Nitrogen, Nitrate + Nitrite as N
• pH
• Temperature

Dissolved oxygen was not included in the Plan due to unique conditions at White Mesa. The
required three pore volume purge when sampling monitor wells at the site and low hydraulic
conductivity in the perched aquifer causes slow recharge to the well bore after purging. This
slow recharge allows oxygen to diffuse into the groundwater as it enters the well bore rendering
any dissolved oxygen measurement unreliable.
Denison has also assessed the need for analyzing data from selected on site wells for other
groundwater quality parameters that could be relevant to this Plan, and has concluded that the
existing groundwater monitoring in existing GWDP compliance wells is adequate, and that no
further constituents, other than nitrate and chloride in the TWN wells, need be added to any wells
at the site, for the reasons discussed below.
The Mill is the subject of an ongoing groundwater compliance monitoring program, which
monitors the complete list of constituents regulated in Table 2 of the GWDP. If any contaminant
sources, whether or not associated with the nitrate plume, reach levels of concern in
groundwater, they will be detected in the GWDP compliance monitoring program. It is therefore
not necessary for the nitrate corrective action to attempt to monitor the same constituents which
are adequately monitored under the existing GWDP program.
Further, since the Plan provides a nitrate plume pumping program designed to bound and control
the known contamination, any other constituents present within the nitrate plume, related to
nitrate as precursors or byproducts or otherwise, will also be captured by the pumping system.
Quarterly reports will be prepared that contain the same elements of the current chloroform
corrective action monitoring reports submitted by Denison to DRC. Specific information
elements to be included in the reports are listed in Sections 10.2.3 and 10.2.6.
Existing nitrate and chloride monitoring will continue in each other monitoring wells at the site
at the frequency required under the GWDP or the chloroform investigation, as the case may be.

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Maintaining the current quarterly frequency at the closest downgradient well MW-11 and semi-
annual frequency at the next-closest downgradient well MW-5 is reasonable considering the
apparent stability of the plume at MW-30 and MW-31 and the hydraulic conductivity at MW-5
(3.5 x 10-6 cm/s) which is nearly three orders of magnitude lower than at MW-11 (1.4 x 10-3
cm/s)[HGC, 2007]. The sampling frequency for MW-5 and MW-11 was established under the
GWDP based on the velocity of flow in the perched aquifer at these locations. More frequent
monitoring was considered inappropriate due to the low flow rates and the potential to sample
the same water or similar water in consecutive sampling events at each well.
Should concentrations within the plume begin to generally increase (disregarding short-term
fluctuations), or the plume boundaries begin to expand, the contingencies discussed in Section 8
will be implemented.
7.2.5 Reporting
Reporting is proposed to occur quarterly, using a format and content similar to the quarterly
chloroform monitoring reports submitted by Denison to DRC. The quarterly reports will include
the following details:
1. calculation of quarterly nitrate mass removed by pumping,
2. comparison of the current areal extent of the nitrate plume from the latest quarter with the
latest quarter of the previous reporting period, and
3. discussion of any contingencies to be implemented.
7.3 Phase III
Phase III may be implemented at the discretion of Denison at any time if Denison determines
that continuation of Phase II is not necessary or appropriate. If Denison decides to implement
Phase III, Denison will submit a revised CAP to the Executive Secretary for approval, which
incorporates Phase III. Phase II will continue until Phase III is approved by the Executive
Secretary.
If implemented, Phase III will consist of a transport assessment, a hazard assessment, and an
exposure assessment along with a corrective action assessment including an evaluation of best
available remedial technologies. Selection of a technology for implementation will be based on
an evaluation whether the technology will remediate contamination to as low as is reasonably
achievable, if the 10 mg/L standard is not reasonably achievable. One possible outcome of these
evaluations could be an application for alternate corrective action concentration limits (ACACL).
As required by UAC R317-6-6.15(G), the proposed ACACL must be protective of human health,
and the environment, and must utilize best available technologies. If an ACACL is proposed, the

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revised CAP will include the information required, under UAC R317-6-6.15(G), and any
ACACL would require the approval of the Utah Water Quality Board.
The transport assessment will identify any data gaps that exist and develop work plans to collect
any data needed to support hydrologic and geochemical modeling. Such modeling will consist of
appropriate quantitative models to predict flow paths, travel times, and potential points of
exposure of nitrate contaminated groundwater. Any potential geochemical reactions or other
attenuation mechanisms will also be identified. The transport assessment will inform the hazard
assessment and the exposure assessment.
The hazard assessment will identify the risks and hazards to human health and the environment
associated with nitrate to determine whether an ACACL should be proposed, if the subsequent
exposure assessment concludes that an exposure is reasonably likely.
The purpose of the exposure assessment is to evaluate the potential harm to human health and the
environment from the hazards identified in the hazard assessment. The exposure assessment
takes into account site-specific circumstances that may reduce or enhance the potential for
exposure to nitrate. This assessment identifies and evaluates exposure pathways, and provides
forecasts of human and environmental population responses, based on the projected constituent
concentrations, and available information on the chemical toxicity effects of the constituents.
The assessment also addresses the underlying assumptions, variability, and uncertainty of the
projected health and environmental effects. Exposure pathways are identified and evaluated
using water classification and water use standards, along with existing and anticipated water
uses.
The corrective action assessment consists of a review of ground-water corrective action
alternatives in conjunction with the hazard assessment and the exposure assessment. Past,
current, and proposed practicable corrective actions will be identified and evaluated against the
costs and benefits associated with implementing each corrective action alternative. If ACACLs
are identified as the proposed alternative, the corrective action assessment will demonstrate that
the proposed ACACL is as low as is reasonably achievable, considering practicable corrective
actions, and is therefore conservative and cost- effective, and would be granted with good cause.
A principal way of demonstrating this is by estimating and comparing the benefits imparted by a
corrective action measure against the cost of implementing that measure.
7.3.1 Water Level and Water Quality Monitoring
Water level and water quality monitoring plans will be proposed in the revised Phase III CAP
prior to implementation of any proposed corrective action alternative.

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8. ASSESSMENT OF CORRECTIVE ACTION AND PROTECTION OF
PUBLIC HEALTH AND THE ENVIRONMENT AND
CONTINGENCY PLAN
The effectiveness of Phase II of the corrective action will be assessed based on the following
criteria:
1. stability of plume boundaries
2. concentration trends within the plume
3. nitrate mass removal rates resulting from pumping, and
4. stability of capture zones.

Plume boundaries and capture zones will be considered stable if concentrations of nitrate in
excess of the 10 mg/L standard do not migrate beyond the current boundaries of the plume.
Hydraulic capture will be considered successful if the concentrations of nitrate in MW-30 and
MW-31 remain stable or decline and concentrations of nitrate in downgradient wells MW-5 and
MW-11 do not exceed the 10 mg/L standard.
The Contingency Plan schedules for each of the foregoing criteria are set out in the Sections 8.1
through 8.4 as applicable.
The criteria for assessment of the effectiveness of Phase III of the corrective action will be
determined once the elements of Phase III have been developed. As discussed in Section 3.2.3,
Phase III will be undertaken at a later date after public participation and Executive Secretary
approval. Phase III may include, but is not limited to: continuation of Phases I and II activities
alone or in combination with monitored natural attenuation, evaluation of additional remediation
and monitoring technologies/techniques, determination of any additional hydrogeologic
characterization, groundwater contaminant travel times and directions, determination of ultimate
points of exposure to the public and/or wildlife, appropriate risk analysis, a cost/benefit analysis,
and the possible development of and petition to the Board for alternate corrective action
concentration limits pursuant to UAC R317 -6-6 .15 (G).
This CAP does not specify the details of Phase III, at this time. A Phase III preliminary plan and
schedule for the evaluation of alternatives, for the completion of any further studies, analyses,
applications and petitions, and for the ultimate definition of Phase III, may be proposed by
Denison at a later date, after completion of such studies and evaluations, followed by submittal
of a proposed CAP revision to the Executive Secretary.

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8.1 Stability of Plume Boundary (Phase II)
The stability of the plume boundary, based on Phase II CAP monitoring activities discussed in
Sections 7 and 10, will be used to determine the following:
• Whether any additional pumping wells are needed, and
• The need to reevaluate the Phase II strategy.

Under conditions where the plume boundaries remain stable or contract, no additional pumping
wells will be needed, and no reevaluation of Phase II will be needed. Under conditions where the
plume migrates, with the concurrence of the Executive Secretary, one or more additional
pumping wells will be added, if suitable wells are available, to slow the migration rates and/or to
bring more of the plume under hydraulic capture. The installation of additional downgradient
monitoring wells is not anticipated because two lines of wells currently exist downgradient of the
nitrate plume. Any such additional pumping wells will be added in accordance with a schedule to
be approved by the Executive Secretary. If the plume continues to migrate, or suitable additional
pumping well locations are not available, then Phase II will be reevaluated, which may include
commencement of Phase III. Analytical or numerical models will be used if needed in the
reevaluation to develop a response. The reevaluation process will be completed in accordance
with a schedule to be approved by the Executive Secretary.
8.2 Concentration Trends within the Plume (Phase II)
Concentration trends within the plume will be used to determine the need for reevaluation of
Phase II. Concentration trends will be based on analytical data collected from Table 3 wells
through Phase II CAP monitoring.
Under conditions where concentrations within the plume are generally stable or declining
(disregarding short-term fluctuations), no reevaluation will be required. Should concentrations
within the plume begin to generally increase (disregarding short term fluctuations), then
reevaluation of Phase II will be required. Analytical or numerical models will be used in the
reevaluation if needed to develop a response. The reevaluation process will be completed in
accordance with a schedule to be approved by the Executive Secretary. Anticipated responses to
this condition would likely include adding existing or new wells to the pumping network, if
suitable well locations are available, or other measures designed to achieve a more rapid rate of
mass reduction. If suitable well locations are not available, then Phase III will be considered.

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8.3 Nitrate Mass Removal Rates Resulting from Pumping (Phase II)
Under conditions where nitrate mass removal rates by pumping drop substantially as a result of
reduced concentrations within the plume, no action will be taken. Under conditions where nitrate
mass removal rates by pumping drop substantially as a result of lost well productivities, then an
evaluation of the lost productivity will be undertaken. If the lost productivity is determined to be
a well efficiency problem, the inefficient wells will be re-developed or replaced in accordance
with a schedule to be approved by the Executive Secretary. Should the lost productivity be
determined to be due to a general reduction in saturated thickness, analytical or numerical
models will be used to evaluate the potential effectiveness of adding existing or new wells to the
pumping network to improve overall productivity, if suitable well locations are available. If the
analysis indicates that overall productivity will not improve significantly by adding wells, or if
suitable well locations are not available, then no action will be taken.
A loss in productivity due to a general decrease in saturated thickness will likely be offset by the
benefits of the reduced saturated thickness. First, this condition would indicate that removal of a
substantial amount of nitrate laden water had already taken place. Second, the reduced saturated
thickness within the nitrate plume would reduce average hydraulic gradients and reduce the
potential for downgradient migration. These factors will be considered in any reevaluation that
may be performed.
8.4 Stability of the Proportion of the Nitrate Plume under Hydraulic
Capture (Phase II)
Under conditions where concentrations of nitrate in excess of the 10 mg/L standard migrate
beyond the current boundaries of the plume, as evidenced by concentrations of nitrate in MW-30
and MW-31 increasing and/or concentrations of nitrate in downgradient wells MW-5 and MW-
11 exceeding the 10 mg/L standard, an evaluation of the factors resulting in this condition will be
undertaken. If the condition is determined to result from lost productivity of the pumping wells
due to well efficiency problems, the inefficient wells will be re-developed or replaced in
accordance with a schedule to be approved by the Executive Secretary. Should the loss in capture
be determined to result from other conditions, then Phase II will be reevaluated, which may
include commencement of Phase III. Analytical or numerical models will be used in the
reevaluation if needed to develop a response. The reevaluation process will be completed in
accordance with a schedule to be approved by the Executive Secretary.
Anticipated responses to this condition would likely include adding existing or new wells to the
pumping network to bring a larger proportion of the plume within hydraulic capture, it suitable

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well locations are available. If suitable well locations are not available, then Phase III will be
considered.
8.5 Phase III
As discussed in Section 3.2.3, Phase III will be undertaken at a later date after public
participation and Executive Secretary approval. Phase III may include, but is not limited to:
continuation of Phases I and II activities alone or in combination with monitored natural
attenuation, evaluation of additional remediation and monitoring technologies/techniques,
determination of any additional hydrogeologic characterization, groundwater contaminant travel
times and directions, determination of ultimate points of exposure to the public and/or wildlife,
appropriate risk analysis, a cost/benefit analysis, and the possible development of and petition to
the Board for alternate corrective action concentration limits pursuant to UAC R317 -6-6 .15 (G).
This CAP does not specify the details of Phase III, at this time. A Phase III preliminary plan and
schedule for the evaluation of alternatives, for the completion of any further studies, analyses,
applications and petitions, and for the ultimate definition of Phase III, may be proposed by
Denison at a later date, after completion of such studies and evaluations, followed by submittal
of a proposed CAP revision to the Executive Secretary. Until such time, the activities of the
Phase I and Phase II remediation will continue as stipulated in the approved CAP.
8.6 Permanent Effect of Corrective Action
Phase II, Phase III, and the contingencies outlined above (Sections 8.1 through 8.5) are designed
to protect the public health and the environment by containing the nitrate plume within the site
property boundary and reducing nitrate concentrations within the plume to the concentration
limit of 10 mg/L. As concentrations will then continue to be reduced by natural attenuation,
demonstration that the corrective action will have a permanent effect will be based on
appropriate future evaluations.
8.7 In-Place Contaminant Control
As discussed in Section 7, the corrective action relies on active and passive strategies to meet
CAP objectives. The passive strategy includes in-place contaminant control by reducing nitrate
concentrations via natural attenuation.

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9. IMPACTS OF OFFSITE ACTIVITIES
As discussed in Section 7, nitrate will be treated in place by natural attenuation and removed
from the perched zone by pumping. Because all pumped water will be disposed onsite in the
tailings cells, there will be no offsite impacts resulting from CAP implementation.

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10. PROPOSED PLUME CORRECTIVE ACTION ACTIVITIES
Phase II and Phase III corrective action activities and contingencies are discussed in detail in
Sections 7 and 8. These activities are summarized in Sections 10.1 and 10.2 below.
10.1 Phase I
The Phase I source control action was discussed in Section 7.1, above.
10.2 Phase II
Phase II corrective action activities include pumping of wells TW4-22, TW4-24, TW4-25, and
TWN-2, monitoring and maintenance of the pumping system, water level monitoring, monitoring
for nitrate and chloride, estimation of hydraulic capture, implementation of contingencies as
needed, and reporting.
10.2.1 Groundwater Pumping
Wells TW4-22, TW4-24, TW4-25, and TWN-2 (Figure 1-2) will be pumped at the maximum
practical rates. Pumped water will be disposed in the tailings cells. The wellfield will be operated
and maintained in the same fashion as the chloroform removal wellfield. Monitoring will include
pumping rates and volumes for each well.
10.2.2 Water Level Monitoring
Water level monitoring will consist of weekly water level monitoring of pumping wells TW4-22,
TW4-24, TW4-25, and TWN-2, and, for the first twelve months after approval of this CAP,
monthly monitoring of non-pumped wells MW-27, MW-30, MW-31, TW4-21, TWN-1, TWN-3,
TWN-4, TWN-7, and TWN-18 (Figure 1-2). Thereafter, water level monitoring of those non-
pumping wells will continue quarterly. Water level contour maps of the data will be generated
quarterly.
10.2.3 Water Quality Monitoring
Water quality monitoring for pumped wells TW4-22, TW4-24, TW4-25, and TWN-2 and all
other wells listed on Table 3 will be quarterly. Samples will be analyzed for chloride, and for
nitrogen (nitrate and nitrite as N). Field parameters pH and temperature will be recorded.
(Section 6.2.4). Water quality monitoring for chloride, nitrate, and field parameters for all other
wells at the site will continue at the frequency required under the GWDP or chloroform
investigation, as the case may be.

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10.2.4 Estimation of Capture Zones
Hydraulic capture zones will be generated from the quarterly water level contour maps in the
same manner as they are currently generated for the chloroform pumping.
10.2.5 Estimation of Pumped Nitrate Mass
Quarterly estimates of nitrate mass removed by pumping will be made based on cumulative
pumped volumes at each pumped well and nitrate concentrations at each pumped well.
10.2.6 Reporting
Quarterly reports will be prepared that contain the same elements of the current chloroform
corrective action monitoring reports submitted by Denison to DRC and will include the
following:
1. Tabular compilations of groundwater level measured in non-pumped wells over time,
2. Water level data from pumped wells over time,
3. Running and cumulative groundwater volumes removed from each pumping well,
4. Calculations and/or spreadsheets documenting quarterly nitrate mass removed by
pumping,
5. comparison of the areal extent of the nitrate plume from the latest quarter with the latest
quarter of the previous reporting period, and
6. discussion of any contingencies implemented or to be implemented.

10.2.7 Additional Measures
Based on Phase II monitoring, and the criteria discussed in Section 8, contingencies that include
potential installation of additional wells, well rehabilitation or replacement, potential expansion
of the pumping well network, if suitable well locations are available, and reevaluation of the
Phase II strategy and consideration of commencement of Phase III activities will be implemented
as needed. Factors that could trigger the implementation of contingencies include 1) expansion of
the plume boundaries, 2) generally increasing nitrate concentrations within the plume, 3)
reductions in nitrate mass removal rates due to losses in pumping well productivities, and 4)
decreases in the effectiveness of hydraulic capture.
10.3 Phase III
As discussed in Section 3.2.3, Phase III will be undertaken at a later date after public
participation and Executive Secretary approval. Phase III may include, but is not limited to:

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continuation of Phases I and II activities alone or in combination with monitored natural
attenuation, evaluation of additional remediation and monitoring technologies/techniques,
determination of any additional hydrogeologic characterization, groundwater contaminant travel
times and directions, determination of ultimate points of exposure to the public and/or wildlife,
appropriate risk analysis, a cost/benefit analysis, and the possible development of and petition to
the Utah Water Quality Board for alternate corrective action concentration limits pursuant to
UAC R317 -6-6 .15 (G).
This CAP does not specify the details of Phase III, at this time. A Phase III preliminary plan and
schedule for the evaluation of alternatives, for the completion of any further studies, analyses,
applications and petitions, and for the ultimate definition of Phase III, may be proposed by
Denison at a later date, after completion of such studies and evaluations, followed by submittal
of a proposed CAP revision to the Executive Secretary. Until such time, the activities of the
Phase I and Phase II remediation will continue as stipulated in the approved CAP.

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11. REFERENCES
HGC. 2004. Final Report. Long Term Pumping at MW-4, TW4-19, and TW4-15, White Mesa
Uranium Mill Near Blanding, Utah. Submitted to International Uranium (USA)
Corporation, Denver, Colorado.
HGC. 2005. Perched Monitoring Well Installation and Testing at the White Mesa Uranium Mill,
April Through June, 2005. Submitted to International Uranium (USA) Corporation,
Denver, Colorado.
HGC 2007a. Preliminary Corrective Action Plan, White Mesa Uranium Mill Near Blanding,
Utah. August 20, 2007
HGC. 2007b. Preliminary Contamination Investigation Report. White Mesa Uranium Mill Site
Near Blanding, Utah. November 20, 2007.
HGC. 2009a. Site Hydrogeology and Estimation of Groundwater Pore Velocities in the Perched
Zone. White Mesa Uranium Mill Near Blanding, Utah. December 29, 2009
HGC. 2010. Hydrogeology of the Perched Groundwater Zone and Associated Seeps and Springs
Near the White Mesa Uranium Mill Site, Blanding, Utah.
INTERA 2009a. Source Review Report for Nitrate and Chloride in Groundwater at the Mill.
December, 2009.
INTERA 2009b. Nitrate Contamination Investigation Report White Mesa Uranium Mill Site
Blanding, Utah. December 30, 2009.
INTERA. 2011. Nitrate Investigation Revised Phases 2 through 5 Work Plan. August, 2011.
Kirby. 2008. Geologic and Hydrologic Characterization of the Dakota-Burro Canyon Aquifer
Near Blanding, San Juan County, Utah. Utah Geological Survey Special Study 123.
Knight-Piésold. 1998. Evaluation of Potential for Tailings Cell Discharge – Mill. Attachment 5,
Groundwater Information Report, White Mesa Uranium Mill, Blanding, Utah. Submitted
to DRC.
TITAN. 1994. Hydrogeological Evaluation of White Mesa Uranium Mill. Submitted to Energy
Fuels Nuclear.
UMETCO. 1993. Groundwater Study. White Mesa Facilities. Blanding, Utah. Prepared by
UMETCO Minerals Corporation and Peel Environmental Services.

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12. LIMITATIONS STATEMENT
The opinions and recommendations presented in this report are based upon the scope of services
and information obtained through the performance of the services, as agreed upon by HGC and
the party for whom this report was originally prepared. Results of any investigations, tests, or
findings presented in this report apply solely to conditions existing at the time HGC’s
investigative work was performed and are inherently based on and limited to the available data
and the extent of the investigation activities. No representation, warranty, or guarantee, express
or implied, is intended or given. HGC makes no representation as to the accuracy or
completeness of any information provided by other parties not under contract to HGC to the
extent that HGC relied upon that information. This report is expressly for the sole and exclusive
use of the party for whom this report was originally prepared and for the particular purpose that
it was intended. Reuse of this report, or any portion thereof, for other than its intended purpose,
or if modified, or if used by third parties, shall be at the sole risk of the user.

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TABLES
TABLE 1
Nitrate Corrective Action Schedule
STEP OR ACTION DATE
Executive Secretary Issuance of Consent Order Approving Corrective Action
Plan No set date
Commence Corrective Actions within 30 days of CAP approval
Submit Phase 1 Plan and Schedule for Ammonium Sulfate Corrective Action 1/1/2012
Submit Revised Reclamation Plan and Financial Surety Estimate for Phase I 3/4/2012
Submit Evidence of Adequate Surety for Phase 1 within 30 days of approval of
Phase I revised surety estimate
Perform Initial Soil Sampling within 30 days of CAP approval
Perform additional analysis if required within analytical holding time
Construct Ammonium Sulfate Area Cover within 60 days of receipt of data
from additional soil sampling
Submit Revised Reclamation Plan and Financial Surety Estimate for Phase I
and II within 60 days of Consent Order
Submit Evidence of Adequate Surety for Phase I and II
within 30 days of approval of
Phase I and II revised surety
estimate
Submit Nitrate Operations and Maintenance Plan within 30 days of Consent Order
Install Pumps in Wells TW4-22, TW4-24, TW4-25, and TWN-2 within 30 days of Consent Order
Begin Pumping Wells TW4-22, TW4-24, TW4-25, and TWN-2 within 45 days of Consent Order
Cease Sampling of TWN-5, TWN-6, TWN-8, TWN-9, TWN-10, TWN-11,
TWN-12, TWN-13, TWN-14, TWN-15, TWN-16, TWN-17, TWN-19
upon issuance of Consent
Order
Cease Water Level Monitoring of TWN-5, TWN-6, TWN-8, TWN-9, TWN-10,
TWN-11, TWN-12, TWN-13, TWN-15, TWN-16, TWN-17
upon issuance of Consent
Order
Abandon Wells TWN-5, TWN-6, TWN-8, TWN-9, TWN-10, TWN-11, TWN-
12, TWN-13, TWN-15, TWN-16, TWN-17
within 15 months of Consent
Order
Reporting of Monitoring and Pumping Data as part of ongoing quarterly
nitrate monitoring reports
Submit Capture Zone Maps
In quarterly report after four
quarters of monthly
groundwater level data
Submit Well Abandonment Report within 15 months of Consent
Order
To be determined at discretion of Denison - - -
Phase I
Phase II
Phase III
H:\718000\nitrate2011\CAP\Table 1 Nitrate CAP Schedule 02.27.12.xlsx: Table 1 2/24/2012
TABLE 2
Hydraulic Conductivity Estimates for Wells in the Nitrate Plume Area
Well k (cm/s)1 Method
MW-11 1.40E-03 pumping
MW-27 8.20E-05
2slug
MW-30 1.00E-04
2slug
MW-31 7.10E-05
2slug
TW4-19 2.50E-04 pumping
TW4-20 5.90E-05
2slug
TW4-21 1.90E-04
2slug
TW4-22 1.30E-04
2slug
TW4-24 1.60E-04
2slug
TW4-25 5.80E-05
2slug
TWN-1 1.70E-04
2slug
TWN-2 1.49E-05
2slug
TWN-3 8.56E-06
2slug
TWN-18 2.27E-03
2slug
Notes:
1 hydraulic conductivity in centimeters per second
2 KGS slug test solution results for automatically logged data
H:\718000\nitrate2011\PoreVel\perm.xls: Table 2 2/24/2012
TABLE 3
Nitrate Concentrations (mg/L) at Wells Within the Nitrate Plume
Well Q1 2010 Q2 2010 Q3 2010 Q4 2010 Q1 2011 Q2 2011 Q3 2011
MW-30 16.1 15.8 15 16 16 17 16
MW-31 21.7 22.5 21 20 21 22 21
1TW4-19 2 4.4 5.9 2.7 17 12 3
TW4-21 8.4 12 14 7 9 12 14
TW4-22 36.6 19 15 16 18 17 15
TW4-24 33.1 30 31 31 31 35 34
TW4-25 14.4 16 14 15 15 16 16
TWN-2 62.1 69 69 48 43 40 33
TWN-3 25.3 26 27 24 24 26 25
average 24.4 23.9 23.5 20.0 21.6 21.9 19.7
Note:
1 TW4-19 is a chloroform pumping well
H:\718000\nov11\nitrate\NTable2.xls: Table 3 2/24/2012
TABLE 4
Comparison of Chloroform Pumping Well Transmissivities to
Proposed Nitrate Pumping Well Transmissivities
Hydraulic Conductivity Hydraulic Conductivity Saturated Thickness1 Transmissivity
(cm/s)(ft/day)(feet) (ft2/day)
MW-4 chloroform pumping 1.00E-04 0.280 40 11
MW-26 chloroform pumping 8.00E-05 0.224 50 11
TW4-4 chloroform pumping 1.70E-03 4.760 22 105
TW4-19 chloroform pumping 2.50E-04 0.700 62 43
TW4-20 chloroform pumping 5.90E-05 0.165 52 9
TW4-22 proposed pumping 1.30E-04 0.364 59 21
TW4-24 proposed pumping 1.60E-04 0.448 57 26
TW4-25 proposed pumping 5.80E-05 0.162 88 14
TWN-2 proposed pumping 1.49E-05 0.042 76 3
Note:
1 estimated non-pumping saturated thickness
Well Type
H:\718000\nitrate2011\PoreVel\perm.xls: Table 4 2/24/2012

FIGURES
HYDRO
GEO
CHEM, INC.APPROVED DATE REFERENCE FIGURE
CELL NO. 2
CELL NO. 4A
3332
MW-21

3000
BOUNDARY
PROPERTY
SCALE IN FEET
0
CELL NO. 1
MILL SITE
CELL NO. 4B
MW-01
MW-02
MW-03
MW-05
MW-11
MW-12
MW-14
MW-15
MW-17
MW-18
MW-19
MW-20
MW-22
MW-23
MW-24
MW-25
MW-27
MW-28
MW-29
MW-30
MW-31
MW-32
MW-33
MW-34
MW-35
PIEZ-1
PIEZ-2
PIEZ-3
PIEZ-4
PIEZ-5
MW-26
TW4-1
TW4-2
TW4-3
TW4-4
TW4-5
TW4-6
TW4-9
TW4-11
TW4-12
TW4-13
TW4-14
TW4-16
TW4-18
TW4-20
TW4-21
TW4-26
MW-04TW4-7 TW4-8
TW4-10
TW4-19
MW-36
MW-37
(abandoned)MW-16
TWN-1
TWN-3
TWN-4
TWN-5
TWN-6
TWN-7
TWN-8
TWN-9
TWN-10
TWN-11 TWN-12
TWN-13
TWN-14
TWN-15
TWN-16
TWN-17
TWN-18
TWN-19
TW4-23
TW4-24
TW4-25
TW4-22
TWN-2
MW-20
PIEZ-1
perched monitoring well
perched piezometer
temporary perched monitoring well
SITE PLAN SHOWING PERCHED
WELL LOCATIONS AND 3rd QUARTER, 2011
NITRATE PLUME EXTENT
WHITE MESA SITE
H:/718000/
nov11/nitrate/nitplume11v2.srf
TW4-18
EXPLANATION
wildlife pond
SJS
temporary perched nitrate
monitoring well
TWN-1
MW-4 perched chloroform extraction well
approximate area of nitrate > 10 mg/L
1-2
proposed nitrate extraction well
TW4-24
perched monitoring well
installed April, 2011
MW-36
HYDRO
GEO
CHEM, INC.APPROVED DATE REFERENCE FIGURE
3332
3000
SCALE IN FEET
0
CELL NO. 4B
5536
5492
5466
5491
5479
5494
5477
5473
5495
5470
5518
5511
5449
5470
5396
5483
5502
5499
5537
5515
5491
5508
5489
5494
5482
5487
5515
5518
5534
5522
5536
5512
5517
5532
5526
5536
5521
5517
5520
5506
5481
5497
55025509
5525
5521
5516
5517
5552
5536
5558
5501
5477
5544
5534
5542
5519
5507
5536
5545
5507
5552
5562
5543 5560
5518
5528
5525
5561
5536
5502
5555
5521
5522 5517
5494
5513
5511
5544
5534
5542
5519
5507
5536
5545
5507
5552
5562
5543 5560
5518
5528
5525
5561
5536
5502
5555
5491 5481
MW-01
MW-02
MW-03
MW-05
MW-11
MW-12
MW-14
MW-15
MW-17
MW-18
MW-19
MW-20
MW-22
MW-23
MW-24
MW-25
MW-26
MW-27
MW-28
MW-29
MW-30
MW-31
MW-32
MW-33
MW-34
MW-35
MW-36
MW-37
TW4-19
TW4-26
PIEZ-1
PIEZ-2
PIEZ-3
PIEZ-4
PIEZ-5
TW4-2
TW4-6
TW4-11
TW4-12
TW4-13
TW4-14
TW4-16
TW4-18
TW4-1
TW4-10
TW4-20TW4-22
TW4-23
TWN-1
TWN-2
TWN-3
TWN-4
TWN-5
TWN-6
TWN-7
TWN-8
TWN-9
TWN-10
TWN-11 TWN-12
TWN-13
TWN-14
TWN-15
TWN-16
TWN-17
TWN-18
TWN-19
TW4-4
TW4-5
TW4-7
TW4-9
TW4-21
TW4-24
TW4-25
TW4-3
TW4-8
MW-04
MW-22
PIEZ-1
5396
5552
perched monitoring well showing
elevation in feet amsl
perched piezometer showing
elevation in feet amsl
5514 temporary perched monitoring well
showing elevation in feet amsl
H:/718000/nov11/bbel/bbelq211v2.srf
EXPLANATION
SJS
temporary perched nitrate monitoring well
showing elevation in feet amsl
TWN-4
5519
5487
MW-36
KRIGED TOP OF BRUSHY BASIN ELEVATIONS
WHITE MESA SITE
TW4-1
perched monitoring well installed April,
2011 showing elevation in feet amsl
MW-4
3
perched chloroform extraction well
showing elevation in feet amsl5521
HYDRO
GEO
CHEM, INC.APPROVED DATE REFERENCE FIGURE
3332
3000
SCALE IN FEET
0
CELL NO. 4B
5583
5503
5471
5503
5522
5501
5494
5494
5500
5587
5603
5453
5450
5498
5507
5538
5576
5543
5513
5538
5548
dry
5494
5493
5554
5557
5583
5540
5585
5538
5584
5578
5566
5584
5574
5525
5552
5562
5549
55855568
5548
5585
5575
5538
5594
5611
5597
5543
5541
5551
5553 5555
5542
5570
5598
5597
5610
5602
5603
5586
5590
5560
5590
5584
5586
5615 5636
5588
5587
5584
5605
5607
5588
5609
5492 5490
MW-01
MW-02
MW-03
MW-05
MW-11
MW-12
MW-14
MW-15
MW-17
MW-18
MW-19
MW-20
MW-22
MW-23
MW-24
MW-25
MW-26
MW-27
MW-28
MW-29
MW-30
MW-31
MW-32
MW-33
MW-34
MW-35
MW-36
MW-37
TW4-19
TW4-26
PIEZ-1
PIEZ-2
PIEZ-3
PIEZ-4
PIEZ-5
TW4-2
TW4-6
TW4-11
TW4-12
TW4-13
TW4-14
TW4-16
TW4-18
TW4-1
TW4-10
TW4-20TW4-22
TW4-23
TWN-1
TWN-2
TWN-3
TWN-4
TWN-5
TWN-6
TWN-7
TWN-8
TWN-9
TWN-10
TWN-11 TWN-12
TWN-13
TWN-14
TWN-15
TWN-16
TWN-17
TWN-18
TWN-19
TW4-4
TW4-5
TW4-7
TW4-9
TW4-21
TW4-24
TW4-25
TW4-3
TW4-8
MW-04
MW-22
PIEZ-1
5450
5594
perched monitoring well showing
elevation in feet amsl
perched piezometer showing
elevation in feet amsl
5554 temporary perched monitoring well
showing elevation in feet amsl
H:/718000/
nov11/nitrate/wl0911dv2.srf
EXPLANATION
SJS
temporary perched nitrate monitoring well
showing elevation in feet amsl
TWN-4
5603
NOTE: MW-4, MW-26, TW4-4, TW4-19 and TW4-20 are pumping wells
5493
MW-36
KRIGED 3rd QUARTER, 2011 WATER LEVELS
WHITE MESA SITE
TW4-1
perched monitoring well installed April,
2011 showing elevation in feet amsl
5551
MW-4
estimated dry area (kriged
Brushy Basin elevation >
kriged perched water elevation
4perched chloroform extraction well
showing elevation in feet amsl
HYDRO
GEO
CHEM, INC.APPROVED DATE REFERENCE FIGURE
3332
3000
SCALE IN FEET
0
CELL NO. 4B
47
11
6
12
44
7
17
21
dry
30
70
92
4
dry
54
15
5
40
39
28
22
30
58
dry
12
6
40
40
49
18
48
26
51
52
30
63
57
6
45
80
52
8359
24
64
59
21
42
75
39
42
64
30
31 37
48
57
87
53
76
61
84
79
54
16
83
32
24
72 77
70
59
59
44
72
86
54
2 9
MW-01
MW-02
MW-03
MW-05
MW-11
MW-12
MW-14
MW-15
MW-17
MW-18
MW-19
MW-20
MW-22
MW-23
MW-24
MW-25
MW-26
MW-27
MW-28
MW-29
MW-30
MW-31
MW-32
MW-33
MW-34
MW-35
MW-36
MW-37
TW4-19
TW4-26
PIEZ-1
PIEZ-2
PIEZ-3
PIEZ-4
PIEZ-5
TW4-2
TW4-6
TW4-11
TW4-12
TW4-13
TW4-14
TW4-16
TW4-18
TW4-1
TW4-10
TW4-20TW4-22
TW4-23
TWN-1
TWN-2
TWN-3
TWN-4
TWN-5
TWN-6
TWN-7
TWN-8
TWN-9
TWN-10
TWN-11 TWN-12
TWN-13
TWN-14
TWN-15
TWN-16
TWN-17
TWN-18
TWN-19
TW4-4
TW4-5
TW4-7
TW4-9
TW4-21
TW4-24
TW4-25
TW4-3
TW4-8
MW-04
dry/abnd
dry
MW-22
PIEZ-1
54
42
perched monitoring well showing
saturated thickness in feet
perched piezometer showing
saturated thickness in feet
40 temporary perched monitoring well
showing saturated thickness in feet
H:/718000/
nov11/bbelev/sat0911v2.srf
EXPLANATION
SJS
temporary perched nitrate monitoring well
showing saturated thickness in feet
TWN-4
84
NOTE: MW-4, MW-26, TW4-4, TW4-19 and TW4-20 are pumping wells
6
MW-36
3rd QUARTER, 2011 SATURATED THICKNESS
WHITE MESA SITE
TW4-1
perched monitoring well installed April,
2011 showing saturated thickness in feet
30
MW-4
estimated dry area (kriged
Brushy Basin elevation >
kriged perched water elevation
5
perched chloroform extraction well
showing saturated thickness in feet
HYDRO
GEO
CHEM, INC.APPROVED DATE REFERENCE FIGURE
3332
3000
SCALE IN FEET
0
CELL NO. 4B
65
110
83
106
89
108
104
106
76
70
52
87
67
114
114
75
51
77
102
76
69
dry
112
110
64
67
50
73
56
70
54
56
58
40
46
87
74
63
76
5764
81
55
54
64
62
18
41
48
43
71
68 67
65
56
47
51
17
32
39
70
75
89
62
63
81
70 32
46
63
92
48
34
58
52
108 109
MW-01
MW-02
MW-03
MW-05
MW-11
MW-12
MW-14
MW-15
MW-17
MW-18
MW-19
MW-20
MW-22
MW-23
MW-24
MW-25
MW-26
MW-27
MW-28
MW-29
MW-30
MW-31
MW-32
MW-33
MW-34
MW-35
MW-36
MW-37
TW4-19
TW4-26
PIEZ-1
PIEZ-2
PIEZ-3
PIEZ-4
PIEZ-5
TW4-2
TW4-6
TW4-11
TW4-12
TW4-13
TW4-14
TW4-16
TW4-18
TW4-1
TW4-10
TW4-20TW4-22
TW4-23
TWN-1
TWN-2
TWN-3
TWN-4
TWN-5
TWN-6
TWN-7
TWN-8
TWN-9
TWN-10
TWN-11 TWN-12
TWN-13
TWN-14
TWN-15
TWN-16
TWN-17
TWN-18
TWN-19
TW4-4
TW4-5
TW4-7
TW4-9
TW4-21
TW4-24
TW4-25
TW4-3
TW4-8
MW-04
dry/abnd
dry
MW-22
PIEZ-1
67
62
perched monitoring well showing
depth in feet
perched piezometer showing
depth in feet
64 temporary perched monitoring well
showing depth in feet
H:/718000/nov11/
bbelev/dtw0911v2.srf
EXPLANATION
SJS
temporary perched nitrate monitoring well
showing depth in feet
TWN-4
39
NOTE: MW-4, MW-26, TW4-4, TW4-19 and TW4-20 are pumping wells
110
MW-36
3rd QUARTER, 2011 DEPTHS TO WATER
WHITE MESA SITE
TW4-1
perched monitoring well installed April,
2011 showing depth in feet
71
MW-4
6
perchedchloroform extraction well
showing depth in feet
HYDRO
GEO
CHEM, INC.APPROVED DATE REFERENCE FIGURE
3332
3000
SCALE IN FEET
0
CELL NO. 4B
NS
NS
NS
NS
ND
NS
ND
NS
NS
NS
NS
NS
NS
NS
NS
0.41
6
NS
NS
16
21
dry
ND
0.2
6.8
6
4
6.6
7.5
0.3
4
1.9
7.1
6.8
5.2
2.6
2.8
1.7
ND
4.63
6.5
14
15
11
7
0.1
1.8
NS
NS
4.9
4.1 0.1
ND
34
16
0.5
33
25
1.1
0.3
1.1
0.7
ND
11
0.1
0.1 0.6
0.1
3.5
1.6
2.4
8.5
1.8
7.1
NS 2.3
MW-01
MW-02
MW-03
MW-05
MW-11
MW-12
MW-14
MW-15
MW-17
MW-18
MW-19
MW-20
MW-22
MW-23
MW-24
MW-25
MW-26
MW-27
MW-28
MW-29
MW-30
MW-31
MW-32
MW-33
MW-34
MW-35
MW-36
MW-37
TW4-19
TW4-26
PIEZ-1
PIEZ-2
PIEZ-3
PIEZ-4
PIEZ-5
TW4-2
TW4-6
TW4-11
TW4-12
TW4-13
TW4-14
TW4-16
TW4-18
TW4-1
TW4-10
TW4-20TW4-22
TW4-23
TWN-1
TWN-2
TWN-3
TWN-4
TWN-5
TWN-6
TWN-7
TWN-8
TWN-9
TWN-10
TWN-11 TWN-12
TWN-13
TWN-14
TWN-15
TWN-16
TWN-17
TWN-18
TWN-19
TW4-4
TW4-5
TW4-7
TW4-9
TW4-21
TW4-24
TW4-25
TW4-3
TW4-8
MW-04
MW-11
PIEZ-1
ND perched monitoring well showing
concentration in mg/L
6.8 temporary perched monitoring well
showing concentration in mg/L
H:/718000/
nov11/nitrate/nit0911v2.srf
EXPLANATION
SJS
temporary perched nitrate monitoring well
showing concentration in mg/L
TWN-1
NOTE: MW-4, MW-26, TW4-4, TW4-19 and TW4-20 are pumping wells
MW-36
KRIGED 3rd QUARTER, 2011 NITRATE (mg/L)
(NITRATE + NITRITE AS N)
WHITE MESA SITE
TW4-1
perched monitoring well installed April,
2011 showing concentration in mg/L
MW-4
7
0.5
0.2
4.9
perched piezometer showing
concentration in mg/L
7
chlorofrom extraction well
showing concentration in mg/L
MW-18
PIEZ-1
MW-19
PIEZ-2
MW-27
TW4-21
PIEZ-3
TW4-22
TW4-20
TW4-19 TW4-18
TW4-5
TW4-25
TW4-24
TW4-9
TW4-12
TW4-13
TW4-2
TW4-8
TW4-1
MW-04
TW4-11TW4-16
MW-26
MW-32
MW-31
MW-30
TW4-10 TW4-3
Cell No. 1
Cell No. 2
WildlifePond
TW4-7
TWN-8
TWN-5
TWN-7
TWN-18
TWN-3
TWN-2
TWN-4
TWN-1

Frog Pond approx. 1 mile NEWastewater Treatment Plant approx. 2 miles NE
Pip elin e
Pipeline
Lawzy Pipeline
L
a
w
z
y Pip
elin
e
U n d e r g r o u n d S e w e r l i n e
Cell 1 Leach Field [7]1979-1985
CCD [18]
V205 Oxidation Tanks [24]
Fly Ash Pond [8]
Chem Lab [22]
Met Lab [23]
Former OfficeLeach Field [4]
Sewage Vault [2]
Scale House Leach Field [3]1977-1979
Main Leach Field [1]1985-Present
Ammonium SulfateCrystal Tanks [10]
Ammonia Tanks [5]
V205 Mini Lab & V205 Precip [20]
YC Precip Mini Lab [19]SAG Leach Field [6]1998-2009
Lawzy Sump [11]
Wildlife Pond [17]
SX Mini Lab [21]
Former Vault [13] 1992-2009
Lawzy Lake [12]
Truck Shop1979-1985Leach Field [14]
Chlorate Tanks [9]
New CCD/SXLeach Field [15]2009-Present
Historical Pond [16]
Mill Site
GP-41B
GP-46B
GP-47B GP-45B
GP-48B
GP-42B
GP-43B
GP-19B
GP-18B
GP-17B
GP-20B
GP-44BGP-40B
GP-39B
GP-21B
GP-22B GP-35B
GP-36B GP-15B
GP-16B
GP-26BGP-25B
GP-23B
GP-24B
GP-37BGP-38B
GP-05B GP-06BGP-13BGP-14B
GP-11BGP-12B
GP-01B
GP-04B
GP-02B
GP-03B
GP-07BGP-09BGP-10BGP-08B
GP-33B
GP-34B
GP-31B
GP-32B
GP-28BGP-27B
GP-29B
GP-30B
10
15
5
5
10
5
5
1 0
2 0
1 5
30
2
0
1
5
1
0
5
S:\Projects\IUC-001-01-001 Denison Mines\GIS\mapdocs\NitrateReport\20120206_mancosThickness.mxd
Figure 8Potential Nitrate Source Areasand Geoprobe Locations Showingthe Thickness of the Mancos Shale
300 0 300150Feet
Source(s): Aerial – Utah GIS Portal website, dated 2009;Wells – HGC, Inc., May 2008 report.Legend
Geoprobe Boring Location
Monitoring Well
Piezometer
Spring/Seep
Surface Water
Chloroform Monitoring Well
Nitrate Monitoring Well
Leach Field (currently in operation)Sampling Method to be Determined
Potential Mill Site Source –Geoprobe Boring
Other Potential Nitrate andChloride Source – Geoprobe Boring
Inaccessible Potential Mill Site Source –No Geoprobe Boring
Mancos Shale Thickness Contour (feet)
H:\718000\nitrate2011\CAP\Figure 9-1.xls: Figure 9-1
NITRATE CONCENTRATIONS IN MW-30 AND MW-31HYDRO
GEO
CHEM, INC.Approved FigureDateAuthorDate File Name
SJS 2/23/12 9-1FX1-FX22/23/12
Nitrate Concentrations in MW-30
Nitrate Concentrations in MW-31
HYDRO
GEO
CHEM, INC.APPROVED DATE REFERENCE FIGURE
3332
3000
SCALE IN FEET
0
CELL NO. 4B
MW-01
MW-02
MW-03
MW-05
MW-11
MW-12
MW-14
MW-15
MW-17
MW-18
MW-19
MW-20
MW-22
MW-23
MW-24
MW-25
MW-26
MW-27
MW-28
MW-29
MW-30
MW-31
MW-32
MW-33
MW-34
MW-35
MW-36
MW-37
TW4-19
TW4-26
PIEZ-1
PIEZ-2
PIEZ-3
PIEZ-4
PIEZ-5
TW4-2
TW4-6
TW4-11
TW4-12
TW4-13
TW4-14
TW4-16
TW4-18
TW4-1
TW4-10
TW4-20TW4-22
TW4-23
TWN-1
TWN-2
TWN-3
TWN-4
TWN-5
TWN-6
TWN-7
TWN-8
TWN-9
TWN-10
TWN-11 TWN-12
TWN-13
TWN-14
TWN-15
TWN-16
TWN-17
TWN-18
TWN-19
TW4-4
TW4-5
TW4-7
TW4-9
TW4-21
TW4-24
TW4-25
TW4-3
TW4-8
MW-04
MW-20
PIEZ-1
perched monitoring well
temporary perched monitoring well
H:/718000/
nov11/nitrate/nitcompv2.srf
EXPLANATION
SJS
temporary perched nitrate monitoring well
TWN-1
MW-36
COMPARISON OF NITRATE PLUME BOUNDARIES
3rd QUARTER 2010 AND
3rd QUARTER 2011
TW4-1
perched monitoring well installed April, 2011
MW-4
perched piezometer
3rd quarter, 2011 nitrate
plume boundary
3rd quarter, 2010 nitrate
plume boundary
9-2perched chloroform extraction well
HYDRO
GEO
CHEM, INC.APPROVED DATE REFERENCE FIGURE
CELL NO. 2
CELL NO. 4A
3332
MW-21

3000
BOUNDARY
PROPERTY
SCALE IN FEET
0
CELL NO. 1
MILL SITE
CELL NO. 4B
MW-01
MW-02
MW-03
MW-05
MW-11
MW-12
MW-14
MW-15
MW-17
MW-18
MW-19
MW-20
MW-22
MW-23
MW-24
MW-25
MW-27
MW-28
MW-29
MW-30
MW-31
MW-32
MW-33
MW-34
MW-35
PIEZ-1
PIEZ-2
PIEZ-3
PIEZ-4
PIEZ-5
MW-26
TW4-1
TW4-2
TW4-3
TW4-4
TW4-5
TW4-6
TW4-9
TW4-11
TW4-12
TW4-13
TW4-14
TW4-16
TW4-18
TW4-20
TW4-21
TW4-26
MW-04TW4-7 TW4-8
TW4-10
TW4-22
TW4-19
TW4-23
TW4-24
TW4-25
TWN-1
TWN-2
TWN-3
TWN-4
TWN-5
TWN-6
TWN-7
TWN-8
TWN-9
TWN-10
TWN-11 TWN-12
TWN-13
TWN-14
TWN-15
TWN-16
TWN-17
TWN-18
TWN-19
MW-36
MW-37
(abandoned)MW-16
MW-20
PIEZ-1
perched monitoring well
perched piezometer
temporary perched monitoring well
3rd QUARTER, 2011
NITRATE AND CHLOROFORM PLUMES
WHITE MESA SITE
H:/718000/
nov11/nitrate/nitchl11v2.srf
TW4-19
EXPLANATION
wildlife pond
SJS
temporary perched nitrate
monitoring well
TWN-1
MW-36 perched monitoring well
installed April, 2011
MW-4
approximate area of chloroform > 70 ug/L
approximate area of nitrate > 10 mg/L
10perched chloroform extraction well
Sewage Vault [2]
Ammonium SulfateCrystal Tanks [10]
GP-26B
GP-25B
V205 Mini Lab & V205 Precipitation Area
Mill Process Bldg.
Pulp Storage
Tanks
S:\Projects\IUC-001-01-001 Denison Mines\GIS\mapdocs\NitrateReport\20111122ammoniumSulfate_8.mxd
Figure 11-1Ammonium Sulfate Contamination
80 0 8040Feet
Source(s): Aerial – Utah GIS Portal website, dated 2009;Wells – HGC, Inc., May 2008 report.
Legend
Geoprobe Boring Location
Potential Mill Site Source -Geoprobe Boring
HYDRO
GEO
CHEM, INC.APPROVED DATE REFERENCE FIGURE
CELL NO. 2
CELL NO. 4A
3332
MW-21

3000
BOUNDARY
PROPERTY
SCALE IN FEET
0
CELL NO. 1
MILL SITE
CELL NO. 4B
MW-01
MW-02
MW-03
MW-05
MW-11
MW-12
MW-14
MW-15
MW-17
MW-18
MW-19
MW-20
MW-22
MW-23
MW-24
MW-25
MW-27
MW-28
MW-29
MW-30
MW-31
MW-32
MW-33
MW-34
MW-35
PIEZ-1
PIEZ-2
PIEZ-3
PIEZ-4
PIEZ-5
MW-26
TW4-1
TW4-2
TW4-3
TW4-4
TW4-5
TW4-6
TW4-9
TW4-11
TW4-12
TW4-13
TW4-14
TW4-16
TW4-18
TW4-20
TW4-21
TW4-26
MW-04TW4-7 TW4-8
TW4-10
TW4-22
TW4-19
TW4-23
TW4-24
TW4-25
TWN-1
TWN-2
TWN-3
TWN-4
TWN-5
TWN-6
TWN-7
TWN-8
TWN-9
TWN-10
TWN-11 TWN-12
TWN-13
TWN-14
TWN-15
TWN-16
TWN-17
TWN-18
TWN-19
MW-36
MW-37
(abandoned)MW-16
MW-20
PIEZ-1
perched monitoring well
perched piezometer
temporary perched monitoring well
ESTIMATED EXTENT OF CAPTURE OF
CHLOROFORM PUMPING WELL MW-26
3rd QUARTER, 2011
H:/718000/
nov11/nitrate/mw26capv2.srf
TW4-19
EXPLANATION
wildlife pond
SJS
temporary perched nitrate
monitoring well
TWN-1
MW-36 perched monitoring well
installed April, 2011
MW-4
estimated Q3, 2011 extent of capture
of chloroform pumping well MW-26
12
perched chloroform
extraction well
HYDRO
GEO
CHEM, INC.APPROVED DATE REFERENCE FIGURE
3332
3000
SCALE IN FEET
0
CELL NO. 4B
MW-01
MW-02
MW-03
MW-05
MW-11
MW-12
MW-14
MW-15
MW-17
MW-18
MW-19
MW-20
MW-22
MW-23
MW-24
MW-25
MW-26
MW-27
MW-28
MW-29
MW-30
MW-31
MW-32
MW-33
MW-34
MW-35
MW-36
MW-37
TW4-19
TW4-26
PIEZ-1
PIEZ-2
PIEZ-3
PIEZ-4
PIEZ-5
TW4-2
TW4-6
TW4-11
TW4-12
TW4-13
TW4-14
TW4-16
TW4-18
TW4-1
TW4-10
TW4-20TW4-22
TW4-23
TWN-1
TWN-2
TWN-3
TWN-4
TWN-5
TWN-6
TWN-7
TWN-8
TWN-9
TWN-10
TWN-11 TWN-12
TWN-13
TWN-14
TWN-15
TWN-16
TWN-17
TWN-18
TWN-19
TW4-4
TW4-5
TW4-7
TW4-9
TW4-21
TW4-24
TW4-25
TW4-3
TW4-8
MW-04
MW-20
PIEZ-1
perched monitoring well
temporary perched monitoring well
H:/718000/
nov11/nitrate/Ndgcaptrv2.srf
EXPLANATION
SJS
temporary perched nitrate monitoring well
TWN-1
MW-36
ANTICIPATED MINIMUM DOWNGRADIENT EXTENT
OF CAPTURE RESULTING FROM PUMPING
TW4-22, TW4-24, TW4-25, AND TWN-2
TW4-1
perched monitoring well installed April, 2011
MW-4
perched piezometer
3rd quarter, 2011 nitrate
plume boundary
13
anticipated downgradient
extent of capture
perched chloroform extraction well
proposed nitrate extraction wellTW4-22

APPENDIX A

HYDROGEOLOGIC CROSS SECTIONS
HYDRO
GEO
CHEM, INC.APPROVED DATE REFERENCE FIGURE
3332
3000
SCALE IN FEET
0
CELL NO. 4B
SW
NE
SW2
NE2
NW
SE
NS
NS
NS
NS
ND
NS
ND
NS
NS
NS
NS
NS
NS
NS
NS
0.41
6
NS
NS
16
21
dry
ND
0.2
6.8
6
4
6.6
7.5
0.3
4
1.9
7.1
6.8
5.2
2.6
2.8
1.7
ND
4.63
6.5
14
15
11
7
0.1
1.8
NS
NS
4.9
4.1 0.1
ND
34
16
0.5
33
25
1.1
0.3
1.1
0.7
ND
11
0.1
0.1 0.6
0.1
3.5
1.6
2.4
8.5
1.8
7.1
NS 2.3
MW-01
MW-02
MW-03
MW-05
MW-11
MW-12
MW-14
MW-15
MW-17
MW-18
MW-19
MW-20
MW-22
MW-23
MW-24
MW-25
MW-26
MW-27
MW-28
MW-29
MW-30
MW-31
MW-32
MW-33
MW-34
MW-35
MW-36
MW-37
TW4-19
TW4-26
PIEZ-1
PIEZ-2
PIEZ-3
PIEZ-4
PIEZ-5
TW4-2
TW4-6
TW4-11
TW4-12
TW4-13
TW4-14
TW4-16
TW4-18
TW4-1
TW4-10
TW4-20TW4-22
TW4-23
TWN-1
TWN-2
TWN-3
TWN-4
TWN-5
TWN-6
TWN-7
TWN-8
TWN-9
TWN-10
TWN-11 TWN-12
TWN-13
TWN-14
TWN-15
TWN-16
TWN-17
TWN-18
TWN-19
TW4-4
TW4-5
TW4-7
TW4-9
TW4-21
TW4-24
TW4-25
TW4-3
TW4-8
MW-04
MW-11
PIEZ-1
4.9
perched monitoring well showing
concentration in mg/L
6.8 temporary perched monitoring well
showing concentration in mg/L
H:/718000/nitrate2011/
CAP/AppA/nit0911xsv2.srf
EXPLANATION
SJS
temporary perched nitrate monitoring well
showing concentration in mg/L
TWN-1
MW-36
LOCATIONS OF CROSS SECTIONS
AND KRIGED 3rd QUARTER, 2011 NITRATE (mg/L)
(NITRATE + NITRITE AS N)
TW4-1
perched monitoring well installed April,
2011 showing concentration in mg/L
MW-4
7
0.5
0.2
perched piezometer showing
concentration in mg/L
A.1
ND
perched chloroform extraction well
showing concentration in mg/L
NOTE: MW-4, MW-26, TW4-4, TW4-19 and TW4-20 are pumping wells
AP
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4
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6
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0
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0
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elevation (feet amsl)
MW-20
MW-03
MW-14
MW-11
MW-31
TW4-24
MW-27
TWN-2
TWN-3
TWN-18
TWN-8
TWN-6
TWN-10
TWN-15
TWN-16
TWN-12
Fly Ash Pond
Cell 1 Leach Field
CCD/SX Leach Field
Historical Pond
Lawzy Lake
Q1
,
2
0
1
1

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r
o

C
a
n
y
o
n

F
o
r
m
a
t
i
o
n
Br
u
s
h
y

B
a
s
i
n

M
e
m
b
e
r

o
f
Mo
r
r
i
s
o
n

F
o
r
m
a
t
i
o
n
Sh
a
l
e

i
n

D
a
k
o
t
a

/
Bu
r
r
o

C
a
n
y
o
n

F
o
r
m
a
t
i
o
n
Co
n
g
l
o
m
e
r
a
t
e

o
r

C
o
n
g
l
o
m
e
r
a
t
i
c
Sa
n
d
s
t
o
n
e

i
n

D
a
k
o
t
a

/
Bu
r
r
o

C
a
n
y
o
n

F
o
r
m
a
t
i
o
n
Ap
p
r
o
x
i
m
a
t
e

A
r
e
a
>1
0
0

m
g
/
L

C
h
l
o
r
i
d
e

Pi
e
z
o
m
e
t
r
i
c

S
u
r
f
a
c
e
0

5
0
0

1
0
0
0

1
5
0
0

2
0
0
0

2
5
0
0

3
0
0
0

3
5
0
0

4
0
0
0

4
5
0
0

5
0
0
0
di
s
t
a
n
c
e

a
l
o
n
g

c
r
o
s
s

s
e
c
t
i
o
n

(
f
e
e
t
)
54
5
0
54
7
0
54
9
0
55
1
0
55
3
0
55
5
0
55
7
0
55
9
0
56
1
0
56
3
0
56
5
0
56
7
0
56
9
0
57
1
0
57
3
0
57
5
0
elevation (feet amsl)
TWN-18
MW-19
PIEZ-1
TWN-9
TWN-14
TWN-17
TWN-19
Q1
,
2
0
1
1

N
i
t
r
a
t
e
,

C
h
l
o
r
i
d
e

i
n

m
g
/
L
:
Q4
,
2
0
1
0

N
i
t
r
a
t
e
,

C
h
l
o
r
i
d
e

i
n

m
g
/
L
:
Q3
,
2
0
1
0

N
i
t
r
a
t
e
,

C
h
l
o
r
i
d
e

i
n

m
g
/
L
:
Q2
,
2
0
1
0

N
i
t
r
a
t
e
,

C
h
l
o
r
i
d
e

i
n

m
g
/
L
:
1.
4
,

6
1
1.
6
,

5
9
1.
8
,

6
4
1.
8
,

6
3
NS
,

N
S
2.
4
,

2
5
NS
,

N
S
2.
6
,

2
8
7.
0
,

6
0
6.
5
,

6
0
6.
8
,

5
2
7.
2
,

5
2
9.
5
,

2
1
7
8.
0
,

1
7
2
10
.
7
,

2
1
0
7.
7
,

1
7
5
3.
7
,

2
4
4.
2
,

2
8
3.
5
,

2
6
2.
9
,

3
0
8.
6
,

9
0
8.
0
,

6
5
8.
9
,

6
6
11
,

8
7
7.
0
,

1
1
4
7.
0
,

1
0
7
7.
2
,

1
1
3
6.
2
,

1
1
3
Jm
b
b
Jm
b
b
Kd
b
c
Kd
b
c
Qa
f
No
t
e
s
:

(
1
)

a
p
p
r
o
x
i
m
a
t
e
l
y

2
0
0

f
e
e
t

n
o
r
t
h

o
f

c
r
o
s
s

s
e
c
t
i
on

(
2
)

a
p
p
r
o
x
i
m
a
t
e
l
y

2
0
0

f
e
e
t

s
o
u
t
h

o
f

c
r
o
s
s

s
ec
t
i
o
n

Ap
p
r
o
x
i
m
a
t
e

5

m
g
/
L

Ni
t
r
a
t
e

I
c
o
c
o
n
Ap
p
r
o
x
i
m
a
t
e

A
r
e
a

>
1
0

m
g
/
L

N
i
t
r
a
t
e
5
ve
r
t
i
c
a
l

e
x
a
g
g
e
r
a
t
i
o
n

=

8

:

1
5/
2
4
/
1
1
A.
3
SJ
S
AP
P
R
O
V
E
D

D
A
T
E
RE
F
E
R
E
N
C
E
FI
G
U
R
E
HY
D
R
O
GE
O
CH
E
M
,

I
N
C
.
0

2
0
0

4
0
0

6
0
0

8
0
0

1
0
0
0

1
2
0
0

1
4
0
0

1
6
0
0

1
8
0
0

2
0
0
0

2
2
0
0
di
s
t
a
n
c
e

a
l
o
n
g

c
r
o
s
s
-
s
e
c
t
i
o
n

(
f
e
e
t
)
54
6
0
54
8
0
55
0
0
55
2
0
55
4
0
55
6
0
55
8
0
56
0
0
56
2
0
56
4
0
56
6
0
56
8
0
57
0
0
57
2
0
57
4
0
57
6
0
elevation (feet amsl)
TWN-7
TWN-2
TW4-25
TW4-21
TWN-1
PIEZ-3
Historical Pond
Lawzy Sump
SAG Leach Field
Ammonium Sulfate Tanks (1)
Ammonia Tanks (2)
Former Office Leach Field (3)
Main Leach Field (4)
Q1
,
2
0
1
1

N
i
t
r
a
t
e
,

C
h
l
o
r
i
d
e

i
n

m
g
/
L
:
Q4
,
2
0
1
0

N
i
t
r
a
t
e
,

C
h
l
o
r
i
d
e

i
n

m
g
/
L
:
Q3
,
2
0
1
0

N
i
t
r
a
t
e
,

C
h
l
o
r
i
d
e

i
n

m
g
/
L
:
Q2
,
2
0
1
0

N
i
t
r
a
t
e
,

C
h
l
o
r
i
d
e

i
n

m
g
/
L
:
1.
3
,

6
.
0
1.
0
,

4
.
0
1.
6
,

7
.
0
1.
2
,

6
.
0
43
,

9
3
48
,

9
3
69
,

1
0
4
69
,

9
7
15
,

3
1
5
15
,

3
1
2
14
,

2
5
0
16
,

3
0
6
9.
0
,

3
0
3
7.
0
,

2
1
0
14
,

2
7
8
12
,

2
6
6
0.
5
,

1
7
0.
6
,

1
4
0.
6
,

1
9
0.
6
,

2
0
1.
8
,

4
0
1.
8
,

2
5
1.
8
,

3
5
1.
6
,

3
6
Qa
f
Km
Km

K
m
Kd
b
c
Kd
b
c
Kd
b
c
Jm
b
b
Jm
b
b
No
t
e
s
:

(
1
)

a
p
p
r
o
x
i
m
a
t
e
l
y

1
1
5

f
e
e
t

s
o
u
t
h
w
e
s
t

o
f

c
r
o
s
s-
s
e
c
t
i
o
n

(
2
)

a
p
p
r
o
x
i
m
a
t
e
l
y

1
5
0

f
e
e
t

s
o
u
t
h
w
e
s
t

o
f
c
r
o
s
s
-
s
e
c
t
i
o
n

(
3
)

a
p
p
r
o
x
i
m
a
t
e
l
y

3
0
0

f
e
e
t

s
o
u
t
h

o
f

c
r
o
s
s-
s
e
c
t
i
o
n

(
4
)

i
m
m
e
d
i
a
t
e
l
y

s
o
u
t
h

o
f

c
r
o
s
s
-
s
e
c
t
i
o
n
EX
P
L
A
N
A
T
I
O
N
Qa
f
Km
Kd
b
c
Jm
b
b
A
l
l
u
v
i
u
m
/
F
i
l
l
Ma
n
c
o
s

S
h
a
l
e
Da
k
o
t
a

S
a
n
d
s
t
o
n
e
/
Bu
r
r
o

C
a
n
y
o
n

F
o
r
m
a
t
i
o
n
Br
u
s
h
y

B
a
s
i
n

M
e
m
b
e
r

o
f
Mo
r
r
i
s
o
n

F
o
r
m
a
t
i
o
n
Sh
a
l
e

i
n

D
a
k
o
t
a

/
Bu
r
r
o

C
a
n
y
o
n

F
o
r
m
a
t
i
o
n
Co
n
g
l
o
m
e
r
a
t
e

o
r

C
o
n
g
l
o
m
e
r
a
t
i
c
Sa
n
d
s
t
o
n
e

i
n

D
a
k
o
t
a

/
Bu
r
r
o

C
a
n
y
o
n

F
o
r
m
a
t
i
o
n
Pi
e
z
o
m
e
t
r
i
c

S
u
r
f
a
c
e
Ap
p
r
o
x
i
m
a
t
e

A
r
e
a
>1
0

m
g
/
L

N
i
t
r
a
t
e

Ap
p
r
o
x
i
m
a
t
e

A
r
e
a

>
1
0
0

m
g
/
L

C
h
l
o
r
i
d
e

IN
T
E
R
P
R
E
T
I
V
E

N
O
R
T
H
W
E
S
T
-
S
O
U
T
H
E
A
S
T
CR
O
S
S

S
E
C
T
I
O
N

(
N
W
-
S
E
)
WH
I
T
E

M
E
S
A

S
I
T
E

H
:
/
7
1
8
0
0
0
/
n
i
t
r
a
t
e
2
0
1
1
/
CA
P
/
A
p
p
A
/
C
A
P
x
s
n
w
s
e
.
s
r
f
NW
SE
ve
r
t
i
c
a
l

e
x
a
g
g
e
r
a
t
i
o
n

=

3

:

1
5/
2
4
/
1
1
A.
4
SJ
S

APPENDIX B

LITHOLOGIC LOGS FOR
MW-3A, MW-30, MW-31, MW-34, AND MW-37