DRC-2012-001333 - 0901a068802c6c9e

DENISO
MINES
Apnl13 2012
VIA EMAIL AND FEDEX
DRC-2012-001333
Rusty Lundberg Executive Secretary
Utah Radiation Control Board
Utah Department of Environmental Quality
195 North 1950 West
PO 80x144810
Salt Lake City UT 84114 4810
Denison Mines (USA) Corp
105017th Street Suite 950
Denver CO 80265
USA
Tel 30362&-7798
Fax 303389^125
www denisonmines com
Re Plan and Time Schedule under Utah Ground Water Discharge Permit UGW370004 Part
I G 4(d)
Dear Mr Lundberg
Reference is made to the Denison letter dated January 20 2012 Regarding the Plan and Time
Schedule for assessment of pH under Utah Groundwater Discharge Permit UGW370004 Part IG 4(d)
Dunng a conference call held on March 12 2012 Utah Division of Radiation Control ( DRC) staff
reviewed the January 20 2012 Plan and Schedule with Denison personnel and discussed a number of
changes to the Plan and Schedule to address DRC s concerns
The attached pH Plan summanzes Denison s understanding of the changes to the Plan and Schedule
and the regulatory path forward which were agreed upon in pnncipal dunng that conference call
Please contact the undersigned if you have any questions or require any further information
Yours very truly
DENISON MINES (USA) CORP
''Jo Ann Tischler
Director Compliance and Permitting
cc Ron F Hochstem
Harold R Roberts
David C Frydenlund
David E Turk
Stewart J Smith Hydro Geo Chem Inc
Daniel W Erskine INTERAInc
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HYDRO GEO CHEM, INC.
Environmental Science & Technology

PLAN TO INVESTIGATE
pH EXCEEDANCES IN PERCHED
GROUNDWATER MONITORING WELLS
WHITE MESA URANIUM MILL
BLANDING, UTAH

April 13, 2012

Prepared for:

DENISON MINES (USA) CORP.
1050 17th Street, Suite 950
Denver, Colorado 80265

Prepared by:

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

Project Number 7180000.00-2.0

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TABLE OF CONTENTS

1. INTRODUCTION.............................................................................................................. 1
1.1 Purpose....................................................................................................................2
1.2 Previously Submitted Plans....................................................................................2
2. HISTORY........................................................................................................................... 5
2.1 Summary of pH Activities......................................................................................5
2.2 Conclusions from the pH Data Analyses Conducted to Date.................................6
2.3 Summary of Agreements and Actions....................................................................6
2.3.1 Denison Actions.......................................................................................... 6
2.3.1.1 Existing Wildlife Ponds............................................................... 6
2.3.1.2 Statistical Analysis of pH Trends ................................................ 7
2.3.1.3 Assessments Outlined in the Plans and Schedules ...................... 7
2.3.1.4 Analysis of Pyrite at the Site........................................................ 7
2.4 Regulatory Actions .................................................................................................8
3. PH PLAN............................................................................................................................ 9
3.1 Statistical and Geochemical Evaluation..................................................................9
3.1.1 Statistical Analysis of pH Data................................................................... 9
3.1.1.1 Linear Regression to Test for Trends......................................... 10
3.1.1.2 Data Exploration........................................................................ 11
3.1.1.3 Updating Compliance Limits..................................................... 11
3.1.2 Geochemical Analysis of Wells with Significantly Declining pH........... 12
3.1.2.1 Analysis of Indicator Parameters............................................... 12
3.1.2.2 Mass Balance Analysis.............................................................. 13
3.1.2.3 Potential Transport Analysis...................................................... 15
3.1.3 Reporting................................................................................................... 15
3.2 Pyrite Analysis Plan..............................................................................................15
3.2.1 Background............................................................................................... 16
3.2.2 Pyrite Oxidation as a Potential Mechanism for Decreasing pH ............... 17
3.2.3 Rationale................................................................................................... 18
3.2.4 Sampling and Analytical Plan................................................................... 19
3.2.5 Reporting................................................................................................... 21
4. LIMITATIONS................................................................................................................. 23

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TABLE OF CONTENTS (Continued)

TABLES

1 Listing of Groundwater Monitoring Wells Currently in Out-of-Compliance Status and
Groundwater Wells in Accelerated Monitoring
2 Tabulated pH Results from INTERA 2011 GWCL Evaluation
3 Tabulation of Presence of Pyrite, Iron Oxide, and Carbonaceous Fragments in Drill Logs
4 Samples to be Submitted for Visual Examination of Pyrite
5 Samples to be Submitted for Laboratory Analysis of Pyrite

FIGURES

1 White Mesa Site Plan Showing Locations of Perched Wells, Piezometers, and Borings
2 White Mesa Site Plan Showing Locations of Samples to be Visually Verified for Pyrite
3 White Mesa Site Plan Showing Locations of Samples for Laboratory Analysis of Pyrite

APPENDICES

A Lithologic Logs
B Well Construction Diagrams

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1. INTRODUCTION
This document presents the pH Plan and Time Schedule (pH Plan) to address dual exceedances
of pH in eleven perched groundwater monitoring wells at the White Mesa Mill (the Mill) and to
provide information related to the overall decline in groundwater pH that has been observed in
site wells. Sections 1 and 2 were prepared primarily by Denison Mines (USA) Corp (Denison);
Section 3.1 was prepared primarily by INTERA, Inc (INTERA); and Section.3.2 was prepared
primarily by Hydro Geo Chem, Inc (HGC).
The eleven wells currently in out-of-compliance (OOC) status are listed in Table 1. The
Groundwater Discharge Permit UGW370004 (GWDP), Part I.G.2 states that “out-of-compliance
status exists when the concentration of a pollutant in two consecutive samples from a compliance
monitoring point exceeds a GWCL in Table 2 of this Permit”. The GWDP provides an
acceptance range for field pH GWCLs. In all instances, the field pH measurements discussed
herein are slightly below the lower limit of the GWCLs specified in the GWDP. E-mail
correspondence from DRC dated March 13, 2012 provided a list of wells in OOC status that was
partially incorrect. Table 1 lists the wells that are currently in OOC (as of 4th Quarter 2011) and
the consecutive quarters in which those measurements were noted. Table 1 also lists the
groundwater wells which are currently in accelerated monitoring for field pH measurements but
are not in OOC. Accelerated monitoring would be the result of field pH excursions that are one-
time or non-consecutive measurements below the field pH GWCL. The OOC status is limited to
those wells which have experienced two consecutive monitoring periods outside the GWCLs
range.
The decline in pH has been noted in perched wells located upgradient, cross-gradient, and
downgradient of the Mill and tailings cells. This phenomenon may have any number of causes;
however, the widespread nature of the declining pH indicates that, whether recent or longer-term,
it results from a natural phenomenon unrelated to Mill operations.
Reference is made to the following previously submitted documents:
• Plan and Time Schedule Under Part I.G.4(d) for Violations of Part I.G.2 for Constituents
in the First, Second, Third and Fourth Quarters of 2010 and First Quarter of 2011 dated
June 13, 2011 (Initial Plan and Schedule);
• Plan and Time Schedule Under Part I.G.4(d) for Violations of Part I.G.2 for Constituents
in the Second Quarter of 2011 dated September 7, 2011 (Q2 2011 Plan and Schedule);
and

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• Letter dated January 20, 2012 regarding the Plan and Time schedule Under Utah
Groundwater Discharge Permit UGW370004 Part I.G.4(d.)
• Revised Background Groundwater Quality Report: Existing Wells For Denison Mines
(USA) Corp.’s Mill Site, San Juan County, Utah. October 2007, (Existing Wells
Background Report)
• Revised Addendum: -- Evaluation of Available Pre-Operational and Regional
Background Data, Background Groundwater Quality Report: Existing Wells For
Denison Mines (USA) Corp.’s Mill Site, San Juan County, Utah. November 16, 2007,
prepared by INTERA, Inc. (Regional Background Report)
• Revised Background Groundwater Quality Report: New Wells for Denison Mines (USA)
Corp.’s White Mesa Uranium Mill, San Juan County, Utah. Published in April, 2008
prepared by INTERA, Inc. (New Wells Background Report)

The latter three reports are collectively referred to as the “Background Reports”.
During conference calls held on December 5, December 19, 2011, and March 12, 2012 Utah
Division of Radiation Control (DRC) staff discussed issues related to pH and the Denison actions
necessary to address DRC’s concerns.
This document sets out the Plan and Schedule to address the issues related to pH at the Mill site
that was agreed upon in principle during those conference calls.
1.1 Purpose
The purpose of this pH Plan is to describe the activities that will be completed by Denison to
address the eleven wells in OOC status for pH and to determine whether the decline in pH in the
perched groundwater at the Mill is the result of a natural phenomenon unrelated to Mill
operations.
1.2 Previously Submitted Plans
As noted above, Denison has submitted two Plans (the Initial Plan and Schedule and the Q2 2011
Plan and Schedule) to address analytes other than pH in OOC status. Those plans were submitted
June 13, and September 7, 2011.
The assessments for OOC constituents other than pH, proposed by Denison and described in
Section 4 of the Initial Plan and Schedule and Section 4 of the Q2 2011 Plan and Schedule, will
continue to be performed as proposed and in the timeframes set out in those Plans and Schedules.

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Those assessments are intended to determine if the exceedances in question are due to
background influences or Mill activities. If the exceedances are determined to be due to
background influences then, as contemplated by those Plans and Schedules and this pH Plan, it
will not be necessary to perform any further evaluations on the extent and potential dispersion of
the contamination or to perform any evaluation of potential remedial actions. Monitoring will
continue and, if appropriate, revised groundwater compliance limits (GWCLs) will be proposed
to reflect changes in background conditions at the site. Specifics related to these assessments are
discussed in the respective plans referenced above. Similar logic applies to the GWCLs for pH at
the site.

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2. HISTORY
A brief discussion of the history and previous activities is provided in Sections 2.1 and 2.2.
2.1 Summary of pH Activities
During the completion of the 4th Quarter 2010 Quarterly Groundwater Monitoring Report,
Denison noted eleven perched groundwater monitoring wells with pH measurements below the
GWCLs. These wells are located upgradient, cross-gradient, and downgradient of the Mill and
tailings cells. Investigation into the eleven pH GWCLs in question indicated that the GWCLs for
groundwater pH in all wells established in the January 20, 2010 GWDP were erroneously based
on historic laboratory results instead of field measurements as contemplated by Table 2 of the
GWDP. Denison notified DRC in a letter dated February 1, 2011 that the existing GWCLs for
groundwater pH were incorrectly based on laboratory results rather than field measurements and
proposed to submit revised descriptive statistics for field pH to be used as revised pH GWCLs by
the end of the second quarter 2011.
Denison received approval from DRC by e-mail on February 14, 2011 to proceed with the
revision of the pH GWCLs based on field measurements. Denison’s geochemical consultant,
INTERA, Inc., completed the data processing and statistical assessments necessary to revise the
GWCLs based on historic field pH data. The data processing and statistical assessments
completed by INTERA were based on the DRC-approved methods in the logic flow diagram
included as Figure 17 of the New Wells Background Report. Following the statistical evaluation
of pH data by INTERA., Denison compared the Mill’s groundwater pH data from the 2nd
Quarter of 2011, including accelerated sampling results through June 2011, and noted that all of
the June 2011 groundwater results, and many of the other results from the 2nd Quarter, were
already outside the revised GWCLs to be proposed in the June 30, 2011 letter, based on the logic
flow diagram.
INTERA further noted that the historical trend of decreasing pH, which was addressed in the
Background Study Reports, appeared to be present in nearly all wells throughout the Mill site
area, including upgradient, downgradient, and cross-gradient wells in the groundwater
monitoring program. Table 2 presents a summary of the results of the statistical evaluation of
groundwater pH data performed by INTERA in June 2011. As shown in Table 2, as of June
2011, all groundwater monitoring (MW-series) wells demonstrated a downward trend in the field
pH data over time.
Denison notified DRC on June 28, 2011 by telephone and by follow-up letter dated June 30,
2011 that the 2nd Quarter 2011 data exceeded the recalculated GWCLs. Denison advised DRC

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that, as a result of these findings, Denison did not believe it was appropriate to continue with its
efforts to reset the GWCLs for pH based on field pH data, as originally planned, but instead it
appeared that it would be more appropriate to undertake a study to determine whether the
decreasing trends in PH are due to natural influences and, if so, to determine a more appropriate
way to determine GWCLs. Additionally, Denison requested the opportunity for a meeting with
DRC to discuss Denison’s findings to date and to agree upon any further investigations to be
completed, as well as to agree upon the steps and milestone dates to be incorporated in the pH
Plan. The meetings with DRC were conducted via teleconference on December 5, and December
19, 2011. These teleconferences resulted in the January 20, 2012 letter and this revised pH Plan.
A subsequent teleconference on March 12, 2012 led to the development of this pH Plan.
2.2 Conclusions from the pH Data Analyses Conducted to Date
The primary conclusion from the activities conducted to date is that the historical trend of
decreasing pH, which was addressed in the Background Study Reports, appears to be present in
nearly all wells throughout the Mill site area, including upgradient, downgradient, and cross-
gradient wells in the groundwater monitoring program, and there seems to be no abatement of
the trend. The wide-spread nature of the decrease in pH in upgradient, downgradient and cross-
gradient wells, suggests that the pH decrease results from a natural phenomenon unrelated to
Mill operations.
2.3 Summary of Agreements and Actions
The following is a summary list of agreements and actions which resulted from the discussion
with DRC in teleconferences on December 5, December 19, 2011 and March 12, 2012.
2.3.1 Denison Actions
2.3.1.1 Existing Wildlife Ponds
DRC and Denison acknowledge that recharging the existing wildlife ponds at the site may be
adding oxygen to the groundwater, which, on the assumption that sufficient pyrite exists in the
formation, may contribute to the decreasing trends in pH at the site, and to exceedances of
certain metals in wells possibly as a result of decreases in pH.
The Mill has therefore agreed to stop recharging both upper wildlife ponds immediately. No
actions to prevent natural accumulation of water will be taken. However, the ponds are not
designed to gather precipitation from the local drainages, so the net evaporation rate should

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ensure that the ponds do not accumulate any significant precipitation. Recharge at the two upper
wildlife ponds would not resume without approval of the Executive Secretary.
The Mill will continue to recharge the lower wildlife pond (Butch’s Bayou).
DRC and Denison acknowledge that stopping the recharge of the two upper wildlife ponds is
expected to affect the perched water quality and water levels over time, which could result in the
need to reset GWCLs at the site.
2.3.1.2 Statistical Analysis of pH Trends
Denison will provide to DRC a statistical analysis of pH in all wells at the Mill site, which will
quantify the decreasing trends in pH at the site as a whole, and indicate which monitoring wells
have significant decreasing trends in pH. The analyses are discussed in detail in Section 3.1. In
performing this statistical analysis, Denison will follow the Groundwater Data Preparation and
Statistical Process Flow for Calculating Groundwater Protection Standards, White Mesa Mill
Site, San Juan County, Utah, included as Figure 17 in the New Wells Background Report. This
statistical analysis report will be submitted to the Executive Secretary within 90 days after
execution and delivery of a Stipulated Consent Agreement (the “Stipulated Consent Agreement”)
relating to the implementation of this pH Plan.
2.3.1.3 Assessments Outlined in the Plans and Schedules
The assessments proposed by Denison and described in Section 4 of the Initial Plan and
Schedule and Section 4 of the Q2 2011 Plan and Schedule for OOC constituents except pH, will
continue to be performed as proposed and in the timeframes set out in those Plans and Schedules.
In addition, the statistical analysis of indicator parameters discussed in Section 3.1.2.1 below will
also be performed in all wells that have one or more OOC constituents and for which such
analysis is not otherwise being performed under Section 3.1.2.1.
2.3.1.4 Analysis of Pyrite at the Site
The site-wide decline of pH is occurring in perched wells cross-gradient, upgradient, and
downgradient of the Mill suggesting that the potential causes are not related to Mill operation.
Potential causes of the site-wide decline of pH may be the result of physical interactions,
geochemical phenomenon, natural processes, or some combination of all of these factors.
Physical interactions such as over-pumping, over-developing, increased sample frequency and
the associated increased purging of the perched wells may be contributing factors. A
geochemical phenomenon (such as the oxidation of pyrite) is a potential mechanism for the

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decline in pH and could be enhanced by increased oxygen transport resulting from the physical
interactions listed above. Natural processes such as drought conditions which may increase the
rate of oxygen transport in the vadose zone may also be contributing factors. Although not
necessarily the only or primary cause, the oxidation of pyrite (or other sulfides) is expected to
occur site-wide, because pyrite has been noted in borings across the entire site (including borings
located upgradient, cross-gradient, and downgradient of the Mill and tailings cells). Regardless
of the outcome of the pyrite investigation specified in this pH Plan, it appears that the pH decline
is a site-wide phenomenon resulting from one or more non-Mill related factors.
This pH Plan describes the activities that will be conducted to verify the presence of pyrite as
one of the possible causes of the decrease in pH in perched groundwater at the Mill. In summary,
the presence of pyrite will be verified using screening, visual and analytical methods.
A report will be prepared that summarizes the sample selection and submission process, the
methods employed, and the results. The report will include an assessment of the results with
regard to the potential for pyrite oxidation to affect pH at site perched monitoring wells. This
report will be submitted to the Executive Secretary within 120 days after execution and delivery
of the Stipulated Consent Agreement.
A detailed description of the pyrite investigation is included in Section 3.2 of this pH Plan.
Regardless of the results of the pyrite verification study, however, the pH data to date indicate
that the pH decline is a site-wide phenomenon and that if oxidation of pyrite or other sulfides is
not the cause, then another, natural, site-wide phenomenon must be the cause.
2.4 Regulatory Actions
The January 20, 2012 letter was discussed with DRC in a teleconference on March 12, 2012, and
it was agreed that the commitments by Denison and DRC referred to in that letter and the
implementation of this pH Plan will be incorporated into the Stipulated Consent Agreement.

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3. PH PLAN
The pH plan consists of a statistical and geochemical evaluation and a plan to verify the presence
of pyrite as discussed in the following Sections.
3.1 Statistical and Geochemical Evaluation
As discussed in Section 2.1, Denison has been aware of the site wide decline in pH trends for
some time. The New Wells Background Report stated:
“on a review of the pH time plots in all existing wells (see Appendix D of the
Background Report), there appears to be a general decreasing trend in pH in all
wells. Figure 18 shows results of linear regression analyses for all site
monitoring wells over the same time period used for new wells. Regression lines
trend downward in all site monitoring wells and among the existing wells the
trends are statistically significant in MW-3, MW-12, MW-14 and MW-17. The fact
that pH is trending downward in all site monitoring wells indicates that
statistically significant decreasing trends in pH in MW-25, MW-27, MW-28, and
MW-3A are not related to any potential tailings seepage impacts. Instead there is
a systematic process occurring that affects the site as a whole. This process may
be a natural phenomenon related to regional changes or it could be some
systematic change in the way that samples are collected or analyzed.”
In INTERA’s response to the URS Memorandum: Completeness Review for the Revised
Background Groundwater Quality Report: Existing Wells for Denison Mines (USA) Corp.’s
White Mesa Mill Site, San Juan County, Utah, dated July 2, 2008, INTERA predicted that pH in
some wells could fall below GWCLs if methods of calculating GWCLs for pH were not
modified. At this time, Denison proposes to perform a statistical analysis of pH in data collected
from monitor wells across the site and a geochemical analysis of indicator parameters in the 11
pH wells in question in order to obtain a more complete and up to date understanding of pH
trends across the site and any potential relationship to mill operations.
3.1.1 Statistical Analysis of pH Data
Denison will perform a statistical analysis of pH data from all perched monitor wells at the site
for which at least eight rounds of data are available in accordance with statistical methods
described in the Existing Wells Background Report. A test for trends will be particularly
important and will be conducted in accordance with Section 6 (Testing for Trends and
Calculating the GWCL) of the Existing Wells Background Report.

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3.1.1.1 Linear Regression to Test for Trends
As there are no no-detect values in pH data, linear regression is the best test for normally or log-
normally distributed data. The correlation coefficient (R) represents the linear relationship
between two variables. R Square (R2) shows how closely X and Y are related. By taking the
square of the R value, all values of R2 are positive (values of R can range from -1 to +1), and fall
between 0 (no correlation) and 1 (perfect correlation). The R2 value is a measure of the strength
of the predictive capability of the regression line. An R2 value of 0 indicates that the regression
line has no predictive ability at all. An R2 value of 1 indicates that the regression line fits the data
perfectly and, therefore, has the highest possible predictive capability. Generally, an R2 value
less than 0.5 is considered to be a poor correlation, and the linear regression line is not
considered to be a reliable representation of the data (i.e., it explains less than half of the data).
The significance of a correlation coefficient of a particular strength or fit will change depending
on the size of the sample from which it was computed. In this document, linear regression trends
are considered to be statistically-significant if there are enough data points to make a
determination and enough of those points fall within the calculated variance of the data set. Least
squares regression analysis of the data will be performed in order to determine whether the
association between the variables is statistically significant at the 95 percent level.
The statistical significance (p-level) of a result is an estimated measure of the degree to which it
is "true" (in the sense of "representative of the population"). More technically, the value of the p-
level represents a decreasing index of the reliability of a result. The higher the p-level, the less
we can believe that the observed relation between variables in the sample is a reliable indicator
of the relation between the respective variables in the population. Specifically, the p-level
represents the probability of error that is involved in accepting our observed result as valid, that
is, as "representative of the population." For example, the p-level of .05 (i.e.,1/20) indicates that
there is a 5 percent probability that the relation between the variables found in our sample is a
"fluke." In other words, assuming that in the population there was no relation between those
variables whatsoever, and we were repeating experiments like ours one after another, we could
expect that in approximately every 20 replications of the experiment there would be one in which
the relation between the variables in question would be equal or stronger than in ours. In many
areas of research, the p-level of .05 is customarily treated as a "border-line acceptable" error
level (StatSoft, Inc, 2005. STATISTICA [data analysis software system], version 7.1.
www.statsoft.com).

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3.1.1.2 Data Exploration
Some monitor wells at the site have data extending from 1979 to the present while others have
barely eight recent data rounds. To date, decreasing pH trends have been observed most strongly
in data collected from 2005 to the present. Therefore, Denison proposes to explore data sets to
ascertain if there are any particular time periods during which pH data have shown a site wide
decline and if such declines have happened in the past. If such declines have happened in the past
or if they can be tied to a particular period, it may provide evidence for a process or cause of the
declines.
3.1.1.3 Updating Compliance Limits
As mentioned in Denison’s June 13, 2011 response to the Notice of Violation and Compliance
Order, Docket No. UGW11-02, the United States Environmental Protection Agency (EPA) has
recognized the need to update compliance limits periodically to reflect changes to background
conditions.
As stated in EPA 530/R-09-007, March 2009 Statistical Analysis Of Groundwater Monitoring
Data At RCRA Facilities Unified Guidance, Environmental Protection Agency, Office Of
Resource Conservation And Recovery:
“We recommend that other reviews of background also take place periodically.
These include the following situations:
When periodically updating background, say every 1-2 years
When performing a 5-10 year permit review
During these reviews, all observations designated as background should be
evaluated to ensure that they still adequately reflect current natural or baseline
groundwater conditions. In particular, the background samples should be
investigated for apparent trends or outliers. Statistical outliers may need to be
removed, especially if an error or discrepancy can be identified, so that
subsequent compliance tests can be improved. If trends are indicated, a change in
the statistical method or approach may be warranted.”
And
“Site-wide changes in the underlying aquifer should be identifiable as similar
trends in both upgradient and compliance wells. In this case, it might be possible
to remove a common trend from both the background and compliance point wells
and to perform interwell testing on the trend residuals.”

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EPA further states:
“5.3.4 UPDATING WHEN TRENDS ARE APPARENT
An increasing or decreasing trend may be apparent between the existing
background and the newer set of candidate background values, either using a
time series plot or applying Chapter 17 trend analyses. Should such trend data be
added to the existing background sample? Most detection monitoring tests assume
that background is stationary over time, with no discernible trends or seasonal
variation. A mild trend will probably make very little difference, especially if a
Student-t or Wilcoxon rank-sum test between the existing and candidate
background data sets is non-significant. More severe or continuing trends are
likely to be flagged as SSIs by formal intrawell prediction limit or control chart
tests.
With interwell tests, a stronger trend in the common upgradient background may
signify a change in natural groundwater quality across the aquifer or an
incomplete characterization of the full range of background variation. If a change
is evident, it may be necessary to delete some of the earlier background values
from the updated background sample, so as to ensure that compliance testing is
based on current groundwater conditions and not on outdated measures of
groundwater quality.”
3.1.2 Geochemical Analysis of Wells with Significantly Declining pH
If the pH trend data from a monitor well is determined to be statistically significant, a
geochemical analysis will be performed to determine if the declining pH trends can be related to
potential mill processes. The geochemical analysis will consist of:
• an analysis of indicator parameters,
• a mass balance analysis, and
• an analysis of potential for transport.
3.1.2.1 Analysis of Indicator Parameters
Seepage from the tailings impoundments would be indicated by rising concentrations of chloride,
sulfate, fluoride, and uranium because: 1) these constituents are abundant in tailings wastewater
(see Table 15 of the Revised Background Report), and 2) these constituents are relatively mobile
and conservative in the groundwater environment. In contrast, many other constituents are either
not present in relatively high concentrations in tailings wastewater and/or are reactive in the
subsurface environment. Denison will prepare time concentration plots of these four parameters
from data taken from all monitor wells on site that have one or more OOCs, including OOCs for
pH (where such indicator parameter data is available) to determine if there is evidence that
concentrations of any of the OOC parameters can be related to potential mill processes.

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Regression or Mann Kendall analysis will be performed to determine if any such indicator
parameter has a significant upward trend. If a monitor well has a significant upward trend in
some, but not all, indicator parameters, then a further analysis will be performed to determine
whether or not the increasing trends can be related to potential mill processes.
3.1.2.2 Mass Balance Analysis
After the analysis of indicator parameters, if any indicator parameter shows a significant upward
trend, a mass balance calculation will also be performed to determine if there is evidence that
concentrations can be related to potential mill processes. It is possible to estimate the mass of
each indicator parameter in the groundwater beneath the millsite by assuming a saturated
thickness of groundwater in the aquifer matrix, a porosity of the aquifer matrix, an average
concentration of constituents in groundwater, and an area to which the average concentration
applies. Any potential source of indicator parameters will be evaluated to determine if it has the
potential to have caused the mass of the indicator observed in the groundwater beneath the Mill
site. First, the potential source must have a means to reach groundwater such as sufficient water
or other fluid to travel through the vadose zone. Second there must have been sufficient
concentrations of the indicator parameter in the source to account for the mass of indicator
parameter observed in the groundwater. Both conditions can be evaluated by mass balance
calculations.
An example of a mass balance calculation was presented in INTERA, Inc. 2009. Nitrate
Contamination Investigation Report, White Mesa Uranium Mill Site, Blanding Utah, where one
of the suggested possibilities was a groundwater mound from the tailings cells that might cause
elevated nitrate and chloride concentrations upgradient in the area of the nitrate and chloride
plume. A calculation for nitrate to evaluate this possibility (a calculation for chloride would be
similar) suggests that on the order of eleven percent tailings solution (assuming the highest
recently observed nitrate concentration in the tailings of 290 mg/L) would have to mix with
unimpacted groundwater (assuming 1 mg/L) in order to account for the observed mass of nitrate
in groundwater, assuming an average nitrate concentration in the plume above the 20 mg/L
isopleth of 30 mg/L. The details of this example calculation based on nitrate are provided below.
The size of the nitrate plume above 20 mg/L is approximately 40 acres, or approximately
1,740,000 square feet in map area. Assuming 45 feet of saturated thickness (based on Hydro Geo
Chem, Inc 2007. Preliminary Contamination Investigation Report. White Mesa Uranium Mill
Site Near Blanding, Utah. November 20, 2007) and a porosity of 0.2, there are approximately
15,700,000 cubic feet or 117,000,000 gallons of groundwater in that area. Eleven percent of that
is approximately 12,900,000 gallons (approximately 40 acre feet) which is a conservative

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estimate of the volume of tailings solution that would have to be mixed with groundwater to
account for the mass of nitrate in the portion of the plume above 20 mg/L nitrate. The following
calculations support these estimates:
Assume:
• Nitrate Concentration in Tailings Solution 290 mg/L
• Nitrate Concentration in un-impacted Groundwater 1 mg/L
• Average Plume Concentration 30 mg/L

Mixing Equation: Ct*Vt + Cg*Vg = Cm*Vm (eq1)

Where: Ct = Concentration of nitrate in tailings solutions
Vt = Volume of tailings solutions
Cg = Concentration of nitrate in unimpacted groundwater
Vg = Volume of unimpacted groundwater
Cm = Concentration of nitrate in mixture of groundwater and tailings solutions
Vm = Volume of mixture of groundwater and tailings solutions

Another Equation: Vt + Vg = Vm (eq2)

Substituting eq2 in eq1: Ct*Vt + Cg*Vg = Cm* (Vt + Vg) (eq3)

Substitute Nitrate Concentrations in eq3
290*Vt + 1*Vg = 30*(Vt + Vg)
290*Vt + 1*Vg = 30*Vt + 30*Vg
260*Vt = 29*Vg
Vt = 29/260*Vg = 0.11*Vg

Based on the above, the volume of tailings solution would have to be approximately eleven
percent of the volume of un-impacted groundwater in the mixture.
The above mass balance is an example of calculations that would be prepared for, and the
reasoning that would be applied to, indicator parameters in data from wells that are OOC for pH,

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if those wells have rising trends in the indicator parameters. In the case of the indicator
parameters their concentrations would be used instead of nitrate in the above equation(s). These
calculations would provide one line of evidence to test the possibility that any potential rising
trend in indicator parameters and the decreasing pH (in wells that are OOC for pH) could or
could not be related to mill operations.
3.1.2.3 Potential Transport Analysis
In cases where data from OOC wells that have statistically significant decreasing pH trends and
increasing indicator trends, are distant from the Mill’s tailings cells, a transport analysis will be
performed to determine the plausibility of impact from mill related processes. The transport
analysis will consider the geochemical transport properties of each indicator parameter with a
significantly increasing trend and an analytical calculation of potential travel times to the well
from potential mill related sources will be performed to determine if there is evidence that the
indicator parameter could plausibly have arrived at the well during the life of the mill.
3.1.3 Reporting
The Statistical and Geochemical Evaluation Report will detail the results of all of the analysis to
be performed and the conclusions to be drawn from such analyses. Denison will work with DRC
to reset GWCLs to properly reflect the decreasing pH trends. The report will also identify any
further studies that the analysis indicates should be performed, and will propose, for Executive
Secretary review and approval, a plan and schedule for completion of any such additional
studies.
If further analysis is required after completion of the Statistical and Geochemical Evaluation
Report, Denison and the Executive Secretary will agree on the scope of that analysis, based on
the findings in the report, including any further reports that will need to be prepared. The report
will be submitted to the Executive Secretary within 90 days after execution and delivery of the
Stipulated Consent Agreement
3.2 Pyrite Analysis Plan
As discussed in Section 2.3.1.4, oxidation of pyrite (or other sulfides) is a potential cause of the
site-wide decline in pH. Pyrite has been noted in the majority of the borings at the site having
detailed lithologic logs (including borings located upgradient, cross-gradient, and downgradient
of the millsite and tailings cells). The occurrence of the declining pH trend over the entire site
indicates that the trend is not the result of site operations. Otherwise the decreases in pH would
occur primarily within the area of the millsite and tailings cells.

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Although pyrite has not been noted in every boring at the site having a detailed lithologic log, it
has been noted in sufficient borings for pyrite oxidation to be considered a plausible mechanism
for decreasing pH. The lack of visually detected pyrite in the lithologic log of any specific boring
does not necessarily indicate that pyrite is not present in or near that boring nor that pyrite is not
present in close enough proximity to that boring to influence pH in the well completed in that
boring. Verification of the pyrite noted in existing drill cuttings samples from a subset of borings
installed across the entire site is considered sufficient to demonstrate the site-wide occurrence of
pyrite and to support the oxidation of pyrite (or other sulfides) as one plausible mechanism for
the decreasing pH.
The purpose of the Pyrite Analysis Plan is therefore to verify the presence of pyrite as one of the
possible causes of the decrease in pH. Existing drill cuttings and/or core samples stored at the
site will be used for this purpose. The data quality objectives are as follows.
1. To verify the existence of pyrite reported in existing boring logs from a sample of site
borings. The sample will include borings located across the entire site (upgradient, cross-
gradient, and downgradient of the millsite and tailings cells).
2. To verify the existence of and analyze for pyrite in MW-series wells which are in
accelerated monitoring for pH or OOC for pH and which have drill cuttings and/or core
stored onsite.

3.2.1 Background
The 97 perched monitoring wells, temporary perched monitoring wells, and piezometers shown
in Figure 1 are screened in a relatively shallow perched water zone hosted primarily by the Burro
Canyon Formation. Where saturated thicknesses are greater, the perched water rises into the
overlying Dakota Sandstone. The Burro Canyon is underlain by the Brushy Basin Member of the
Morrison Formation, a bentonitic shale that essentially forms the base of the perched water zone.
The permeability of the Burro Canyon is generally low, with a geometric average hydraulic
conductivity on the order of 10-5 centimeters per second (cm/s), but with a range of
approximately 10-8 cm/s to 10-2 cm/s.
Lithologic logs reveal that iron oxides and pyrite are common within the Burro Canyon and
overlying Dakota. Many of the logs indicate the presence of carbonaceous fragments consistent
with reduced conditions and the presence of pyrite. The iron oxides present in many of the
borings may result from oxidization of pyrite or other sulfides.

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Table 3 indicates the presence of visible pyrite, iron oxides, and carbonaceous material from
borings at the site for which detailed and moderately detailed logs are available. Logs for many
of the older wells at the site (MW-1 through MW-15) are not detailed enough to contain this
information and are not included in Table 3. Logs for wells MW-16 through MW-22 are only
moderately detailed. Logs for wells MW-3A, MW-23 through MW-37, temporary wells (TW4-
series and TWN-series wells), and piezometers (PIEZ-series and DR-series) contain the most
detail. Temporary wells and piezometers are included in Table 3 because many of these wells are
in the vicinity of MW-series wells lacking detailed logs (for example, upgradient well MW-1)
and they demonstrate the site-wide occurrence of pyrite.
Lithologic logs for all borings at the site having detailed logs (MW-3A, MW-23 through MW-
37, temporary wells (TW4-series and TWN-series wells), and piezometers [PIEZ-series and DR-
series]) are provided in Appendix A. Pyrite has been noted in approximately 2/3 of the borings
having detailed lithologic logs.
3.2.2 Pyrite Oxidation as a Potential Mechanism for Decreasing pH
Oxidation of pyrite is one potential mechanism for the decreasing pH measured in perched zone
wells. Pyrite oxidizes in the presence of oxygen according to the following equation, producing
hydrogen ions and sulfate in the process:
2FeS2 + 7O2 + 2H2O = 2Fe2+ + 4SO42- + 4H+ (eq4)

This is the same mechanism that results in acidic drainage from mine tailings or waste rock piles
containing pyrite. Oxygen transported into the piles reacts with the pyrite (in the presence of
water) releasing acid and sulfate.
The widespread occurrence of visible pyrite in the Burro Canyon Formation (upgradient, cross-
gradient, and downgradient of the millsite and tailings cells) makes this mechanism plausible.
Sources of oxygen include 1) diffusion through the vadose zone aided by the generally dry
condition of the vadose zone and barometric pumping 2) transport of oxygen from the surface
directly to the formation via perched monitoring well casings, and 3) infiltration of water
containing dissolved oxygen. Significant sources of infiltrating water containing oxygen include
the wildlife ponds as discussed in Section 2.3.1.1. Oxygen transport in the vicinity of perched
wells is expected to be enhanced by fluctuations in the perched water table caused by routine
purging and sampling, the recent redevelopment effort, and changes in pumping. Changes in

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purging and sampling methodology and frequency are also expected to impact oxygen transport
to perched water.
A low rate of pyrite oxidation is likely taking place over the entire site due to diffusion of oxygen
through the vadose zone and via oxygen dissolved in recharge. However, the rates are likely
much larger in the vicinity of the perched zone wells where the well casings are a direct conduit
for oxygen transport to the groundwater. With each well casing acting as a constant source of
oxygen directly to groundwater, gradually expanding volumes of the perched zone near each
well are expected to be impacted over time as oxygen spreads out, more pyrite is oxidized, and
any neutralization capacity in the formation is consumed.
3.2.3 Rationale
Although pyrite has been noted in approximately 2/3 of the borings having detailed lithologic
logs, the DRC has requested verification of pyrite occurrence before considering oxidation of
pyrite as a potential mechanism for decreasing pH.
Drill cuttings and core samples from the installation of numerous perched monitoring wells and
borings have been collected, labeled as to the borehole name/number and depth interval, and
stored on-site. Pyrite present in these existing samples is expected to have undergone small to
negligible degradation since collection. Use of existing samples in the verification process is
therefore considered acceptable.
Pyrite has been detected visually in drill cuttings from the site since at least 1999. Visual
detection of pyrite in a particular sample suggests that the volumetric content of pyrite in the
sample is at least 0.1%. Notations in the logs indicate volumetric pyrite contents may be as high
as three percent in some intervals. Visual re-examination by an experienced geologist or
mineralogist of drill cuttings samples previously identified as having pyrite is considered
sufficient to verify the presence of pyrite. As an additional measure, laboratory analysis of pyrite
is also proposed as discussed below.
The presence of visually detectable pyrite in a sample would increase the sulfur and iron contents
of that sample and yield total iron and sulfur concentrations that are expected to be noticeably
higher than samples without visually detectable pyrite, assuming all other conditions equal.
Analysis of total iron and sulfur would likely identify samples with pyrite. However, gypsum has
also been identified in drill cuttings from the site and gypsum would contribute to the total sulfur
analytical result. Furthermore, high iron content could result from high concentrations of iron
oxide minerals which may or may not be indicative of oxidized pyrite. Therefore, analysis of

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samples for total iron and sulfur would likely yield results that are ambiguous with respect to
pyrite content.
Using an analytical method specific to pyrite is expected to yield more conclusive results.
Scanning electron microscopy coupled with energy dispersive x-ray analysis is one method
capable of detecting pyrite.
3.2.4 Sampling and Analytical Plan
Verification of the presence of pyrite will be accomplished using visual and analytical methods.
Visual verification will rely on examination of samples by an experienced geologist or
mineralogist other than the geologist(s) who originally logged the borings. Analytical
verification will rely on laboratory analysis of selected samples for pyrite and other sulfides. The
locations of borings from which samples are to be submitted for visual or laboratory
identification of pyrite, respectively, are provided in Figures 2 and 3. The sample set provides
site-wide coverage.
Since 1999 drill cuttings samples were typically collected at 2 1/2 foot depth intervals and stored
in zip-seal bags labeled with the boring identification (ID) and the depth interval. Smaller
samples of the drill cuttings were typically washed and stored in plastic cuttings boxes labeled
with the borehole ID and having each sample compartment labeled with the depth interval. When
collected, core samples were logged continuously except for intervals where core recovery was
not possible. Drill core was stored in cardboard core boxes labeled with the borehole ID and
depth interval represented in each box.
Samples to be submitted for visual verification are provided in Table 4. All borings listed in
Table 4 had pyrite noted in the drilling logs. Visual verification will rely on examination of drill
cuttings and/or core samples from selected depth intervals where pyrite was noted in the drilling
logs. The depth intervals will be within the screened intervals of borings completed as wells.
Appendix B contains well completion diagrams for all wells listed in Table 4. Samples listed in
Table 4 were collected from borings installed since 2002 that were upgradient, cross-gradient,
and downgradient of the tailings cells (Figure 2). Borings listed in Table 4 include TWN-19 (the
most upgradient boring at the site) and DR-25 (the most downgradient boring at the site.
Samples submitted for visual verification will consist of zip sealed bags of cuttings from the
desired borings and depth intervals. These samples will be submitted to an experienced geologist
or mineralogist for verification of 1) the presence of, 2) estimated abundance of, and 3) the
estimated grain sizes of pyrite (or other visible sulfides) in each sample. Visual examination will
include microscopic examination to ensure that pyrite too fine-grained to have been identified

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during the logging procedure will be detected. A blank sample consisting of “play sand” placed
in a zip seal bag and labeled similarly to the cuttings samples will also be submitted for visual
analysis.
Samples to be submitted for laboratory analysis are provided in Table 5. Table 5 includes all
MW-series wells under accelerated monitoring with declining pH for which cuttings or core
samples are available. Not all borings listed in Table 5 had pyrite noted in the drilling logs.
Samples submitted for laboratory analysis will consist of zip sealed bags of cuttings from the
desired borings and depth intervals and subsamples of core from the desired borings and depth
intervals, All submitted samples will be from depth intervals within the screened intervals of the
wells. Appendix B contains well completion diagrams for all wells listed in Table 5. Analytical
verification will rely on laboratory analysis for pyrite via scanning electron microscopy coupled
with energy dispersive x-ray analysis or another method that is capable of quantifying sulfides.
Pyrite was not noted in the detailed drilling logs for MW-3A, MW-23, MW-24, MW-28, and
MW-29, all of which are OOC for pH. Samples from these borings will be selected for
laboratory analysis based on a field screening procedure. Existing cuttings and/or core samples
from these borings will be screened visually and for iron and sulfur using a portable XRF. The
XRF will be used in accordance with manufacturer’s instructions. All samples from the screened
depth intervals of the wells (Table 5) will be tested.
The results of the visual examination and the XRF screening will be documented in the field
notebook. Documentation will include the sample color, whether or not pyrite was visible, and
the results of the XRF scan with respect to iron and sulfur.
At least one sample from the screened depth interval of each boring will be submitted for
laboratory analysis. If one or more samples from a particular boring have visually identifiable
pyrite (presumably missed during the original logging procedure) at least one of those samples
will be submitted for analysis. If the XRF screening is unsuccessful at identifying a sample from
a particular boring having both iron and sulfur anomalies (and visual pyrite is not present), at
least one sample will be selected for analysis based on color. A grayish or greenish color
consistent with reduced conditions will be considered favorable for pyrite occurrence.
Each bagged cuttings or core sample selected for laboratory analysis will be photographed. Any
core selected for analysis will be photographed within the core box prior to bagging. Cuttings
selected for analysis will be photographed within the cutting storage box or zip-sealed bag. The
depth interval written on the bag or cuttings storage box must be visible in the photograph.

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Cuttings samples submitted for either visual or laboratory analysis will consist of the entire
bagged cuttings sample. Subsamples from the existing bagged samples will not be submitted
because of the likelihood that subsamples may not be representative due to pyrite having settled
out in the original sample bags. If the original sample bag has deteriorated, the entire original bag
will be placed inside a new labeled bag and submitted for analysis. A blank sample consisting of
“play sand” placed in a zip seal bag and labeled similarly to the cuttings samples will also be
submitted for laboratory analysis. The laboratory will be instructed to return unused sample
material to the site within the original bags.
Core samples submitted for either visual or laboratory analysis will consist of subsamples of the
core from the desired depth interval and placed in zip-sealed bags labeled with the boring
number and the depth interval. The laboratory will be instructed to return unused sample material
to the site within the original bags.
3.2.5 Reporting
A report will be prepared that describes the screening, selection, and submission of samples, the
results of the sample screening process, and the visual and analytical methods employed. The
report will provide the visual and analytical results and will include an assessment of the results
with regard to the potential for pyrite oxidation to affect pH at site perched monitoring wells.
This report will be submitted to the Executive Secretary within 120 days after execution and
delivery of the Stipulated Consent Agreement.

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4. LIMITATIONS
The information and any opinions, recommendations, and/or conclusions 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 the particular
purpose for which 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
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TABLE 1
Listing of Groundwater Monitoring Wells Currently in Out-of-Compliance Status
and Groundwater Wells in Accelerated Monitoring
Wells in Out-of-Compliance ("OOC") Status for Field pH
Well
Quarter/Sampling Events of Initial Consecutive Field pH measurements outside of
the GWCLs
MW-3 Q2 2010 - Q3 2010
MW-3A Q2 2010 - Q3 2010
MW-12 Q4 2010 - Q1 2011
MW-14 Q1 2010 - Q2 2010
MW-23 Q4 2010 - Q1 2011
MW-24 Q4 2010 - Q1 2011
MW-25 Q4 2010 - January 2011 Monthly Sample
MW-26 July 2010 Monthly Sample - August 2010 Monthly Sample
MW-28 Q2 2010 - Q3 2010
MW-29 Q4 2010-Q2 2011 (semi-annual sampling frequency)
MW-32 Q2 2010 - Q3 2010
Wells in Accelerated Monitoring for Field pH**
Well Quarter/Sampling Events of Initial Field pH measurements outside of the GWCLs
MW-18 Q2 2010, Q3 2011 - Accelerated to quarterly from semi-annual
MW-19 Q2 2010, Q3 2011 - Accelerated to quarterly from semi-annual
MW-27 Q3 2011 - Accelerated to quarterly from semi-annual
MW-30 June 2011 Monthly Sample - Accelerated to monthly from quarterly
MW-31 June 2011 Monthly Sample - Accelerated to monthly from quarterly
* - All wells in OOC status are sampled at an accelerated frequency as required by the
Groundwater Discharge Permit UGW370004, Part I.G.1.
** - The field pH measurements were outside on the GWCL on the dates listed above,
however, the measurements were not outside of the GWCL in consecutive sampling
periods. Therefore, these wells are not in out-of-compliance status.

TABLE 2
Tabulated pH Results from
INTERA 2011 GWCL Evaluation*
Well Constituent GWQS N % Detected Distribution (r2)
Regression
Trend Z-Score
Mann-
Kendall
Trend
Mean
Standard
Deviation
()
Lowest
observed
pH value
Highest
observed
pH value
Poisson
Limit
(95%)
Original
Permit
GWCL
Comments
MW-1 pH 6.5-8.5 21 100 Normal or Log-Normal 0.16 downward 7.27 0.28 6.82 7.86 6.5-8.5 Flow Sheet Method
MW-2 pH 6.5-8.5 14 100 Normal or Log-Normal 0.05 downward 7.02 0.26 6.44 7.48 6.5-8.5 Lowest Observed-Flow Sheet
MW-3 pH 6.5-8.5 24 100 Normal or Log-Normal 0.34 downward 6.46 0.25 5.95 6.99 6.5-8.5 Lowest Observed-Flow Sheet
MW-3A pH 6.5-8.5 22 100 Normal or Log-Normal 0.42 downward 6.53 0.38 5.90 7.62 6.5-8.5 Flow Sheet Method
MW-5 pH 6.5-8.5 20 100 Normal or Log-Normal 0.37 downward 7.44 0.16 7.15 7.67 6.5-8.5 Flow Sheet Method
MW-11 pH 6.5-8.5 41 100 Normal or Log-Normal 0.13 downward 7.73 0.28 7.22 8.40 6.5-8.5 Flow Sheet Method
MW-12 pH 6.5-8.5 22 100 Non-Parametric 0.14 -2.85 downward 6.70 0.27 5.86 7.15 11.36 6.5-8.5 Lowest Observed-Flow Sheet
MW-14 pH 6.5-8.5 48 100 Normal or Log-Normal 0.14 downward 6.58 0.20 6.15 7.19 6.5-8.5 Lowest Observed-Flow Sheet
MW-15 pH 6.5-8.5 19 100 Non-Parametric 0.08 -1.72 downward 6.79 0.18 6.24 7.01 11.54 6.5-8.5 Lowest Observed-Flow Sheet
MW-17 pH 6.5-8.5 22 100 Normal or Log-Normal 0.08 downward 6.79 0.30 6.03 7.43 6.5-8.5 Lowest Observed-Flow Sheet
MW-18 pH 6.5-8.5 26 100 Normal or Log-Normal 0.17 downward 6.59 0.37 5.82 7.23 6.5-8.5 Lowest Observed-Flow Sheet
MW-19 pH 6.5-8.5 24 100 Normal or Log-Normal 0.26 downward 6.98 0.31 6.09 7.45 6.5-8.5 Lowest Observed-Flow Sheet
MW-20 pH 6.5-8.5 14 100 Normal or Log-Normal 0.25 downward 7.16 0.12 6.95 7.42 6.5-8.5 Flow Sheet Method
MW-22 pH 6.5-8.5 13 100 Normal or Log-Normal 0.37 downward 5.76 0.20 5.53 6.22 6.5-8.5 Lowest Observed-Flow Sheet
MW-23 pH 6.5-8.5 26 100 Normal or Log-Normal 0.25 downward 6.59 0.33 5.74 7.19 6.5-8.5 Lowest Observed-Flow Sheet
MW-24 pH 6.5-8.5 23 100 Normal or Log-Normal 0.34 downward 6.56 0.50 5.73 7.54 6.5-8.5 Flow Sheet Method
MW-25 pH 6.5-8.5 28 100 Normal or Log-Normal 0.06 downward 6.71 0.21 6.36 7.25 6.5-8.5 Flow Sheet Method
MW-26 pH 6.5-8.5 31 100 Non-Parametric 0.18 -1.90 downward 6.70 0.40 6.06 7.88 11.24 6.5-8.5 Flow Sheet Method
MW-27 pH 6.5-8.5 27 100 Normal or Log-Normal 0.04 downward 7.06 0.30 6.40 7.68 6.5-8.5 Lowest Observed-Flow Sheet
MW-28 pH 6.5-8.5 26 100 Normal or Log-Normal 0.36 downward 6.01 0.23 5.39 6.34 6.5-8.5 Lowest Observed-Flow Sheet
MW-29 pH 6.5-8.5 22 100 Normal or Log-Normal 0.09 downward 6.45 0.27 5.78 6.92 6.5-8.5 Lowest Observed-Flow Sheet
MW-30 pH 6.5-8.5 33 100 Normal or Log-Normal 0.17 downward 6.90 0.21 6.53 7.47 6.5-8.5 Flow Sheet Method
MW-31 pH 6.5-8.5 34 100 Normal or Log-Normal 0.04 downward 7.18 0.22 6.65 7.80 6.5-8.5 Lowest Observed-Flow Sheet
MW-32 pH 6.5-8.5 44 100 Normal or Log-Normal 0.25 downward 6.43 0.25 5.82 7.02 6.5-8.5 Lowest Observed-Flow Sheet
Notes:
Proposed Frequency of Re-Evaluation is based on frequency of sampling for each well at the time of this report and EPA guidance (EPA, 2009) suggesting re-evaluation of background after eight additional data points.
* Note: This Table reflects pH data through the 1st Quarter of 2011. Denison is not proposing these GWCLs at this time. This Table is provided for historic information purposes only.
Revised Groundwater Compliance
Limits for pH in Monitoring Wells
White Mesa Mill Site, Blanding Utah
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TABLE 3
Tabulation of Presence of
Pyrite, Iron Oxide, and Carbonaceous Fragments in Drill Logs
Well Pyrite C Fragments Iron Oxide
MW-3A X
aMW-16 X
aMW-17 X
aMW-18 X
aMW-19 X
aMW-20 X
aMW-21 X X
aMW-22 X
MW-23 X
MW-24 X
MW-25 X X
MW-26 X X
MW-27 X X
MW-28 X
MW-29 X
MW-30 X X
MW-31 X X
MW-32 X X
MW-33 X
MW-34 X X X
MW-35 X X X
MW-36 X X
MW-37 X X
Piez-2 X
Piez-4 X X
Piez-5 X X
DR-2 X X
DR-5 X X
DR-6 X X
DR-7 X
DR-8 X
DR-9 X X
DR-10 X
DR-11 X X
DR-12 X X
DR-13 X
DR-14 X X
DR-15 X X
DR-16 X X
DR-17
DR-18 X X
DR-19 X
DR-20 X X
DR-21 X
DR-22
DR-23 X X
DR-24 X X
DR-25 X X
H:\718000\pHdecrease\apr12revision\
PyriteTable_rev0412.xls: Table 3 Page 1 of 2 4/12/2012
TABLE 3
Tabulation of Presence of
Pyrite, Iron Oxide, and Carbonaceous Fragments in Drill Logs
Well Pyrite C Fragments Iron Oxide
TW4-1 X
TW4-2 X X
TW4-3 X X X
TW4-4
TW4-5 X X
TW4-6 X X X
TW4-7 X X X
TW4-8 X
TW4-9 X X X
TW4-10 X X
TW4-11 X
TW4-12 X X X
TW4-13 X X X
TW4-14 X
TW4-15 X X
TW4-16 X X
TW4-17 X X
TW4-18 X X
TW4-19 X
TW4-20 X
TW4-21 X X
TW4-22 X
TW4-23 X X X
TW4-24 X
TW4-25 X X
TW4-26 X
TWN-1 X
TWN-2 X X
TWN-3 X X
TWN-4 X
TWN-5 X X
TWN-6 X X
TWN-7 X
TWN-8 X X
TWN-9 X
TWN-10 X
TWN-11 X X
TWN-12 X X
TWN-13 X X
TWN-14 X X
TWN-15 X X
TWN-16 X X
TWN-17 X
TWN-18 X X
TWN-19 X X
Notes:
C Fragments = particles of carbonaceous material (plant remains, etc)
a = only moderately detailed log available
H:\718000\pHdecrease\apr12revision\
PyriteTable_rev0412.xls: Table 3 Page 2 of 2 4/12/2012
TABLE 4
Samples to be Submitted for Visual Examination of Pyrite
Well Pyrite Noted Cuttings Core Depth Interval Screen Interval
MW-26 (TW4-15)X X 92.5 - 95 62.5 - 122.5
MW-26 (TW4-15)X X 95 - 97.5 62.5 - 122.5
MW-34 X X 67.5 - 70 69 - 109
MW-36 X X 87.5 - 90 79.9 - 119.9
MW-36 X X 112.5 - 115 79.9 - 119.9
MW-37 X X 110 - 112.5 80.2 - 120.2
TW4-16 X X 95 - 97.5 82 - 142
TW4-22 X X 90 - 92.5 53.5 - 113.5
TW4-22 X X 102.5 - 105 53.5 - 113.5
TWN-5 X X 110 - 112.5 80 - 150
TWN-5 X X 112.5 - 115 80 - 150
TWN-8 X X 117.5 - 120 75.5 - 145.5
TWN-16 X X 87.5 - 90 43 - 93
TWN-19 X X 82.5 - 85 26 - 106
DR-9 X X 105 - 107.5 82.1 - 112.1
DR-12 X X 87.5 - 90 73 - 93
DR-16 X X 97.5 - 100 NA
DR -25 X X 75 - 77.5 NA
Note:
NA = not applicable (boring not completed as a well)
H:\718000\pHdecrease\apr12revision\PyriteTable_rev0412.xls: Table 4 4/12/2012
TABLE 5
Samples to be Submitted for Laboratory Analysis of Pyrite
Well Pyrite Noted Cuttings Core Depth Interval Screen Interval
MW-3A TBD1 TBD1 TBD1 78 - 95
MW-23 TBD1 TBD1 TBD1 109 - 129
MW-24 TBD1 TBD1 TBD1 100 - 120
MW-25 X X 65 - 67.5 65 - 115
MW-26 (TW4-15)X X 90 - 92.5 62.5 - 122.5
MW-27 X X 80 - 82.5 41 - 91
MW-28 TBD1 TBD1 TBD1 66 - 106
MW-29 X TBD1 95 - 125
MW-30 X X 65 - 67.5 67 - 107
MW-31 X X 95 - 97.5 69 - 129
MW-32 (TW4-17)X X 105 - 107.5 80 - 130
Note:
TBD1 = to be determined based on field screening
H:\718000\pHdecrease\apr12revision\PyriteTable_rev0412.xls: Table 5 4/12/2012

FIGURES

APPENDIX A

LITHOLOGIC LOGS

APPENDIX B

WELL CONSTRUCTION DIAGRAMS