DRC-2011-003469 - 0901a0688021a467

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Loren Morton - Denison Mines: Reclamation Plan 4.0 - Round 1A Interrogatory
DRC-2011-003469
From: Loren Morton
To: Harold Roberts
Date: 4/6/11 4:55 PM
Subject: Denison Mines: Reclamation Plan 4.0 - Round lA Interrogatory
CC: Bob Baird - URS; Dave Rupp; David Frydenlund; Jon Luellen; Rusty Lundberg; Tom
Rushing
Attachments: RndlAInterrogatoriesDUSARecPlanProposedAltCover.doc
Harold,
URS has prepared the Round lA Interrogatory, that we promised you back in our 10/5/10 meeting, related to
DUSA Reclamtion Plan 4.0. Sorry for the delay. ^
If you have questions, and a conference call or meeting would help, feel free to ca
arrange.
Also, tomorrow Dave Rupp will be sending you a status report on MOA expenditures to date on the this URS
review project.
Loren
Dave Rupp or myself to
file://C:\Documents and Settings\Lmorton\Local Settings\Temp\XPgrpwise\4D9C9AEDEQ... 4/6/2011
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UTAH DIVISION OF RADIATION CONTROL
DENISON MINES (USA) CORPORATION
RECLAMATION PLAN, REVISION 4.0, NOVEMBER 2009;
SUPPLEMENTAL INTERROGATORIES - ROUND 1A
APRIL 2011
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TABLE OF CONTENTS
INTRODUCTION V
EXHIBIT A. PRELIMINARY INFORMATION DEFINING DUSA'S PROPOSED
ALTERNATIVE COVER SYSTEM pESIGN. 2
SYNOPSIS OF INTERROGATORIES 3
INTERROGATORY White Mesa RecPlan 02/Ola: 10CFR40 Appendix A, Criterion 1:
Permanent Isolation without Ongoing Maintenance 5
INTERROGATORY White Mesa RecPlan 03/01 A: 10CFR40, Appendix A, Criterion 4:
Location and Design Requirements.. 9
INTERROGATORY White Mesa RecPlan 05/OlA: 10 CFR PART 40, Appendix A; UAC R317-
3-1; and UAC R317-3: Construction Quality Control and Assurance 14
INTERROGATORY White Mesa RecPlan 09/01 A: UAC R313-25-7; UAC R313-25-8; UAC
R317-6-1(6)6.1 : Water Balance Design Features in Cover System ..... 18
11
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ACRONYMS AND ABBREVIATIONS
CFR Code of Federal Regulations
DOE U.S. Department of Energy
DRC Utah Division of Radiation Control
DUSA Denison Mines (USA) Corporation
EPA U.S. Environmental Protection Agency
MWH Montgomery Watson Harza
NRC U.S. Nuclear Regulatory Commission
UAC Utah Administrative Code
111
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INTRODUCTION
The Utah Division of Radiation Control (DRC) is reviewing the license renewal application
submitted by Denison Mines (USA) Corp; (DUSA) fbr its White Mesa uranium mill. The DRC
has mobilized the expertise of URS Corporation (URS) by authorizing the latter to review
Revision 4 of DUSA's Reclamation Plan, submitted in connection with the license renewal
application and to prepare interrogatories that solicit information the DRC judges is necessary to
satisfy relevant regulatory requirements.
On October 5,2010, the DRC met with DUSA to review Round 1 Interrogatories that address
Revision 4.0 of the Reclamation Plan for the White Mesa facility. In this meeting, DUSA
proposed to submit details and justification for an altemative cover design that would rely
primarily on evapotranspiration to control and minimize infiltration. DUSA expressed its behef
that such a change could be made in the approach to relicensing and an acceptable final
reclamation tailings cell closure cover could be reached more rapidly than by pursuing the
previously proposed cover design and relicensing course and with no greater exposure to
criticism from the public. The DRC agreed to the consider DUSA's proposed changes with the
expectation that the license renewal process would not be delayed and might even be accelerated.
The DRC, with DUSA's approval (reiterated by email sent by Harold Robert to Loren Morton on
October 7, 2010), instructed URS, the DRC's contractor, to prepare immediately a supplement
set of interrogatories to the Round 1 Interrogatories to address issues that should be pursued and
addressed by DUSA in connection with their proposed altemative cover design.
URS has responded to the DRC's instmctions and considered current NRC guidance on cover
system design in reviewing the bit of defining information provided by DUSA's contractor,
Montgomery Watson Harza (MWH), reproduced as Exhibit A below (MWH 2010); sent as an
attachment to the email transmitted from Harold Roberts to Loren Morton of the DRC on
October 7, 2010.
The result of URS' review is the following set of four supplemental Round 1 interrogatories,
with each interrogatory denoted by the suffix "A" to each interrogatory number (for example,
"INTERROGATORY WHITE MESA RECPLAN 03/01A . . ."); i.e.. Round 1A Interrogatory.
These Round 1A interrogatories supplement the Round 1 Interrogatories that were submitted to
DUSA in September 2010 ("Revision 4.0 Reclamation Plan Round 1 Interrogatories", hereafter
referred to as the "Interrogatory White Mesa Recplan" interrogatories).
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EXHIBIT A. PRELIMINARY INFORMATION DEFINING DUSA'S PROPOSED
ALTERNATIVE COVER SYSTEM DESIGN (MWH 2010).
The proposed alternative conceptual cover design for the White Mesa Mill Tailing Cells will consist of
a monolithic evapotranspiration (ET) cover that will cap the entirety of all tailings cells. The proposed
2.84-meter {9,3-feet) thick monolithic ET cover design (see Figure 1) would consist of (from top to
bottom):
• 15 centimeters (0.5 feet) of a gravel-amended topsoil admixture to promote revegetation and
provide for protection against erosion and frost damage
• 107 centimeters (3.5 feet) of random fill soil (sandy clayey silt) placed at 85 percent of
Standard Proctor dry density to serve as a water storage, biointrusion, and radon attenuation
layer
• 162 centimeters (5,3 feet) of random fill soil (sandy clayey silt) composed of 2.8 feet of
random fill compacted to 95 percent of Standard Proctor dry density over 2.5 feet of random
fill placed at SO percent of Standard Proctor dry density, to serve as grading (platform fill) and
radon attenuation layers.
The proposed cover design replaces the top surface of the cover (the slope will remain at 0,2
percent); the side slope design may include rock armoring, as Included in the original design. An
alternative monolithic ET cover is the preferred conceptual cover design to minimize infiltration and
meet the radon attenuation standard The proposed cover design will be sufficient to prw^
adequate thickness to protect against frost penetration, provide adequate water storage capacity to
minimize the rate of infiltration into the underlying tailings, and provide [ong-term moisture within the
cover to attenuate radon flux.
Frgure 1. Alternative tailings cell cover design.
VEGETATION (PRIMARILYGRASSES)
TOP SOIL VVITH GRAVEL FOR EROSION AHO FROST PROTECTION
SANDY CLAYEY SILT PUCED/vT 85% STAMD/\RD PROCTOR DRY DENSITY
FORVVATER STORAGE/BIOINTRUSION ANOmOON ATTENUAT
SANDY CLAYEY SILT UPPER 2.8fT
COyPACTEO TO 95% STANDARD PROCTOR DRY DENSITY AND
WmR 2.6 FEET PLACED AT 80% SWDARD PROOTDR DRY DENSITY
FOR GRADNG (PLATFORM FILL)MD RADON ATTENUATION
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SYNOPSIS OF ROUND lA INTERROGATORIES
A summary of the supplemental items addressed in the Round 1A interrogatories that comprise
this request for additional information follows below.
Interrogatory White Mesa RecPlan 02/01 A: This interrogatory addresses:
• Information on the specific characteristics of soils proposed for use in constmcting the
proposed altemative cover design to demonstrate that the soil will have properties that are
compatible with the vegetation community that is proposed for establishment in the final
cover.
• Information to demonstrate the capability of the proposed altemative cover design for
long-term prevention of possible ftiture penetration of the tailings by plants or burrowing
animals under the no-active maintenance scenario.
• Information regarding the need for incorporating a filter layer at the interface between the
sideslope and the components of the topdeck portion of the proposed altemative cover
design to limit possible movement of fine soil particles derived from intemal erosion of
the proposed topdeck gravel/topsoil and loosely compacted topdeck soil layers into the
filter and sideslope riprap erosion protection layer in the cover.
Interrogatory White Mesa RecPlan 03/OlA: This interrogatory addresses:
• Procedures that will be used to produce and install the proposed gravel/topsoil adrnixture
layer on the topdeck.
• Key data and material testing results for component materials proposed for use in
constmcting the gravel/topsoil admix layer.
• Information on the types of vegetation proposed to be established and subsequent plant
succession.
• Modeling to project the rate of long-term soil erosion of the gravel/topsoil admix surface
layer due to sheet erosion, overland flow, and gullying.
• Constmction of the proposed altemative cover system, including, but not limited to:
materials, specifications, and constmction equipment and constmction process.
• Revisions to the Reclamation Plan necessary to properly describe the proposed
altemative cover system.
Interrogatory White Mesa RecPlan 05/OlA: This interrogatory addresses the revision and
expansion of the Quality Plan for Constmction Activities:
• Information regarding DUSA's plans and schedule for constmcting, instmmentation, and
monitoring a Test Pad to quantify/verify cover system parameters used in modeling
(short-term and long-term) field performance.
• Justification for monitoring approaches and monitoring devices, including but not limited
to specifications and operations/maintenance requirements.
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• Information on natural analogs from peer-reviewed technical literature sources that might
be used to complement and corroborate the results of the on-site CQAQC Test Pad
testing program/cover performance program.
Interrogatory White Mesa RecPlan 09/OlA: Although no Round 1 interrogatory exists
(namely. Interrogatory White Mesa Recplan 09/01) in the DRC's September 13, 2010 document,
this interrogatory is provided to address issues related to the altemative cover system design that
were not germane to the existing authorized rock cover system design. This supplemental
interrogatory addresses:
• Additional informafion regarding potential long-term conditions in the proposed
altemative cover system and in the liner systems in Cells 2, 3, 4A, and 4B considered in
developing the cover design.
• Additional information regarding the need for including a low-permeability barrier layer
(e.g., a composite HDPE geomembrane and geosynthetic clay liner [GCL] system) in the
altemative cover system for limiting potential long-term long-term bathtubbing of
moisture on the liner systems in the reclaimed tailings embankment and limiting long-
term releases from the reclaimed tailings embankment.
Information regarding the need for including a capillary break or lateral drainage and/or
cobble layer in the cover system to reduce the amount of infiltration into the tailings.
Information on the applicability of published individual or joint NRC-EPA guidance
related to the conceptual design of LLRW disposal facilities that contain low-
permeability liner components to the design of the cover system.
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INTERROGATORY WHITE MESA RECPLAN 02/01 A: 10CFR40 APPENDIX A,
CRITERION 1: PERMANENT ISOLATION WITHOUT ONGOING MAINTENANCE
REGULATORY BASIS:
UAC R313-24-4 invokes the following requirement from 1QCFR40 Appendix A, Criterion 1: "The
general goal or broad objective in siting and design decisions is permanent isolation of tailings
and associated contaminants by minimizing disturbance and dispersion by natural forces, and to
do so without ongoing maintenance. For practical reasons, specific siting decisions and design
standards must involve finite times (e.g., the longevity design standard in Criterion 6), The
following site features which will contribute to such a goal or objective must be considered in
selecting among alternative tailings disposal sites or judging the adequacy of existing tailings
sites:
• Remoteness from populated areas;
• Hydrologic and other natural conditions as they contribute to continued
immobilization and isolation of contaminants from ground-water sources; and
• Potential for minimizing erosion, disturbance, and dispersion by natural forces over
the long term.
The site selection process must be an optimization to the maximum extent reasonably achievable
in terms of these features.
In the selection of disposal sites, primary emphasis must be given to isolation of tailings or
wastes, a matter having long-term impacts, as opposed to consideration only of short-term
convenience or benefits, such as minimization of transportation or land acquisition costs, AWhile
isolation of tailings will be a function of both site and engineering design, overriding
consideration must be given to siting features given the long-term nature of the tailings hazards.
Tailings should be disposed of in a manner that no active maintenance is required to preserve
conditions of the site,''
INTERROGATORY STATEMENT:
1. Refer to Sections 5.2,2, 5.3, Section 5 of Attachment Ay Figures A-5.1-1 through A-5A1-3,
and Table A-5.3.2.1-1 of the Rev 4.0 Reclamation Plany and MWH 2010, In addition to the
information requested in Round 1 Interrogatory White Mesa RecPlan 02/01 (as it remains
applicable to the proposal altemative cover design), please provide the following information
for the proposed altemative tailings cell cover design (MWH 2010):
1. Provide additional information on the specific characteristics of soils (sandy clayey silt
materials) proposed for use in constmcting the proposed altemative cover design to
demonstrate that the soil will have adequate properties (e.g., favorable water relations,
appropriate nutrient capacity and Sodium Absorption Ratio, etc...) that are compatible
with the vegetation community that is proposed for establishment in the final cover.
Provide information demonstrating that the soils would be likely to achieve the goal of
estabhshing "primarily grasses" (MWH 2010) on the cover in a manner which will allow
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the seeded/established grasses to competitively preclude long-term invasion ofthe
vegetated surfaces by deeper-rooted tress and shmbs.
2. Describe assumptions that have been made, with supporting rationale, with respect to the
degree to which any more shallow-rooted plants (e.g., shallow-rooting trees or shmbs)
could colonize the proposed altemative cover during the required design life of the cover
(200-1,000 years) and that might be prone to future tip-up/blow-over, resulting in
physical damage to the cover system over the long term, unless they were removed
through an active maintenance program.
3. Evaluate and provide information to demonstrate the capability of the altemative cover
design for preventing possible future penetration of the tailings by plants or burrowing
animals under the no-active maintenance scenario. Please provide the following as part of
this evaluation:
a. Information on the potential for ftiture deep-rooted plants and deep-burrowing
animals to occur at/frequent the site or site vicinity, including any occurrences that
could result from future climate changes occurring within the required performance
period for the cover (200-1,000 years).
b. Information on the possible need for including a cobble layer, capillary break layer,
and/or later drainage layer in the cover system to mitigate/prevent penetration of the
cover throughout the required performance period (200-1,000 years) by burrowing
animals or root growth, under the no-active maintenance scenario.
2. Refer to Sections 5.2.2, 5.5, Section 5 of Attachment A, Figures A-S,!-! through AS. I-
5, and Table A-5.3.2. I-l ofthe Rev 4.0 Reclamation Plan, and MWH 2010\]n
to the information requested in Interrogatory White Mesa RecPlan 02/01 (as it remains
applicable to the proposal altemative cover design), please provide the following
information for the proposed altemative tailings cell cover design (MWH 2010):
• Provide information regarding the need for incorporating a filter layer at one or more
of the interface(s) between the sideslope cover components and the components of the
topdeck portion of the proposed altemative cover design. Evaluate filter requirements
for hmiting the possible movement of fine soil particles derived from internal erosion
of the proposed topdeck gravel/topsoil unit and loosely compacted topdeck soil layers
into any filter and sideslope riprap erosion protection layer that would be incorporated
into the cover. Provide filter stability criteria and supporting calculations utihzing
applicable filter design criteria (e.g., as described in NUREG-1623), guidance
contained in NUREG/CR-4620 (Nelson, et al. 1986), and other applicable guidance
• documents (e.g., USDA 1994). Altematively, provide detailed information that would
clearly justify why such filter layer would not be required.
BASIS FOR INTERROGATORY:
As discussed in Round 1 Interrogatory White Mesa RecPlan 02/01, maximum burrowing depths
for animals at or near the site should be defined and justification provided as to how the
proposed altemative cover design will prevent potential long-term damage/dismption ofthe
buried tailings by burrowing animals and/or deep plant root penetration. Different pubhshed
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references indicate that Big Sagebmsh in the westem U.S. can exhibit typical average rooting
depths between about 114 and 250 cm [between about 3.7 and 8 ft] (e.g., see Waugh, et al. 1^^^^^
Foxx, et al.l984; Klepper, et al. 1985, Reynolds 1990b); however, at least one reference suggests
that root depths for Big Sagebmsh could be much deeper-possibly extending to up to 914 cm [30
ft] (Foxx, et al. 1984).
The proposed altemative cover design (MWH 2010) does not contain a capillary break layer,
lateral drainage layer, or cobble rock layer. Inclusion of a layer of this type (with any required
filter layers also provided to prevent migration of fines into the voids of this layer) could help
provide a barrier to prevent deep root penetration within the cover. For example, in certain
circumstances, established plant species could undergo agronomic stress (as a result of
unfavorable water relations and/or insufficient nutrient capacity in the cover soils during a dry
weather period). Certain plants could likely extend their roots seeking water and nutrients in
response to such stresses (e.g., see DOE 1989, Section 4.3.4) - SQQ Silso Interrogatory RecPlan
09/OlA: UACR313-25-7; UACR313-25-8; UACR317-6-1(6)6,1: Infiltration through t^^^^
Cover^ below. Additional information needs to be provided that demonstrates the ability of the
proposed altemative cover materials/system to provide and maintain the appropriate nutrient
capacity and favorable water relations required to promote an unintermpted Co
intended/preferred grasses over the cover system throughout the required design life of the
embankment (200-1,000 years). The evaluation should take into consideration the future climate,
soil properties, pedogenesis, and rooting characteristics of the desired plants on the cover (DOE
1989).
Although compacted soil layers in final cover system may offer some protection against root
penetration, plants vary greatly in their ability to penetrate compacted soils (Waugh and
Richardson 1997). At arid and semi-arid sites, root densities can be higher in buried clayey-type
soils and plant roots may concentrate in and extract water from bxiried clayey layers, causing
some seasonal desiccation (Hakonson 1986 and Reynolds 1990a,b). Based on these
considerations, there is likely to be uncertainty as to the degree to which shallower-rooted trees
or shmbs or deeper-rooted plants (e.g.. Big Sagebmsh) mi^t eventually become established in
the cover system during the required design life of the embankment, especially during the future
no-active maintenance period. The potential therefore exists for some degree of penetration of
the cover system by the roots of deeper-rooted plants following final cover constmction. The
range of potential future plant development and animal burrowing conditions for the final cover
environment needs to be adequately defined for use as input in subsequent performance model
assessments.
Inclusion of a rocky layer within the final cover would also provide a deterrent against future
burrowing by animals as the animals would not attempt to move into a rocky, unfavorable layer
in lieu of a more favorable soil medium.
The need for incorporating a filter layer included at critical interfaces between the sideslope
cover components and the components of the topdeck portion of the proposed altemative cover
design. For example, a filter layer should be included to limit the possible movement of fine soil
particles derived from intemal erosion of the proposed topdeck gravel/topsoil and loosely
compacted topdeck soil layers into any filter and sideslope riprap erosion protection layer
included in the final cover design. Without inclusion of an appropriate filter in such instances;
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piping of fines from the top deck portion of the cover system could occur if seepage gradients or
pressures are high enough to initiate erosive discharge velocities at the baseflow. (USDA 1994).
REFERENCES:
Foxx, T.S., G.D. Tiemey, and J.M. Wilhams 1984. Rooting Depths of Plants Relative to
Biological and Environmental Factors, Los Alamos Report LA-10254-MS, November
' 1984.
Hakonson, T.E. 1986. Evaluation of Geologic Materials to Limit Biological Intrusion into Low-
Level Radioactive Waste Disposal Sites, LA-10286-MS. Los Alamos National
Laboratory, Lbs Alamos, New Mexico.
Klepper, E. L., K. A. Gano, and L. L. Cadwell 1985. Rooting Depth and Distributions of Deep-
Rooted Plants in the 200 Area Control Zone of the HanfordSite, PNL-5247, Battelle
Pacific Northwest Laboratory, Richland, Washington.
MWH 2010. "Proposed Preliminary Altemative Cover Design for White Mesa Tailings Cells".
Letter from MHW to Harold Roberts of Denison Mines (USA) Corp. dated October 6,
2010.
NRC (U.S. Nuclear Regulatory Commission) 2003. Standard Review Plan for the Review of a
Reclamation Plan for Mill Tailings Sites under Title II of the Uranium Mill Tailings
Radiation Control Act of 7975. Washington, D.C, June 2003.
Reynolds, T.D. 1990a. Effectiveness of Three Natural Biobarriers in Reducing Root Intmsion by
Four Semi-Arid Plant Species. Health Physics, Vol. 59, pp. 849-852.
Reynolds, T. D. 1990b. "Root Mass and Vertical Root Distribution of Five Semiarid Plant
Species." T/^a/^A PA;;5/c^, Vol. 58, No. 2, pp. 1^
U.S. Department of Agriculture (USDA) 1994. "Chapter 26, Gradation Design of Sand and
Gravel Filters". Part 633 - National Engineering Handbook, Washington, D.C. October
1994,47 pp.
U.S. Department of Energy (DOE) 1989. Technical Approach Document, Revision 2. UMTRA-
DOE/AL 050425.0002, Albuquerque, New Mexico. December 1989.
Waugh, W. J., J C. Charters, G. V. Last, B. N. Bjomstad, S. O. Link, C. R. Hunter 1994, Barrier
Analogs: Long-Term Performance Issues, Preliminary Studies, and Recommendations,
PNL-9004, Pacific Northwest Laboratories, Richland, Washington.
Waugh, W.J., and Richardson, G.N., 1997. "Ecology, Design, and Long-Term Performance of
Surface Barriers: Applications at Uranium Mil Tailings Sites." Barrier Technologies for
Environmental Management, National Academy PvQSS, 1997A
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INTERROGATORY WHITE MESA RECPLAN 03/OlA: 10CFR40, APPENDIX A,
CRITERION 4: LOCATION AND DESIGN RQUIREMENTS
REGULATORY BASIS:
UAC R313-24-4 invokes the following requirement from 10CFR40. Appendix A, Criterion 4: "The
following site and design criteria must be adhered to whether tailings or wastes are disposed of
above or below grade,
(a) Upstream rainfall catchment areas must be minimized to decrease erosion potential and the
size ofthe floods which could erode or wash out sections of the tailings disposal area,
(b) Topographic features should provide good wind protection.
(c) Embankment and cover slopes must be relatively flat after final stabilization to minimize
erosion potential and to provide conservative factors of safety assuring long-term stability. The
broad objective should be to contour final slopes to grades which are as close as possible to
those which would be provided if tailings were disposed of below grade; this could, for example,
lead to slopes of about 10 horizontal to 1 vertical (10h:lv) or less steep. In general, slopes
should not be steeper than about 5h:lv. Where steeper slopes are proposed, reasons why a slope
less steep than 5h:lv would be impracticable should be provided, and compensating factors and
conditions which make such slopes acceptable should be identified.
(d) A full self-sustaining vegetative cover must be established or rock cover employed to reduce
wind and water erosion to negligible levels.
Where a full vegetative cover is not likely to be self-sustaining due to climatic or other
conditions, such as in semi-arid and arid regions, rock cover must be employed on slopes of the
impoundment system. The Executive Secretary will consider relaxing this requirement for
extremely gentle slopes such as those which may exist on the top of the pile.
The following factors must be considered in establishing the final rock cover design to avoid
displacement of rock particles by human and animal traffic or by natural process, and to
preclude undercutting and piping:
• Shape, size, composition, and gradation of rock particles (excepting bedding material
average particles sizemust be at least cobble size or greater);
• Rock cover thickness and zoning of particles by size; and
• Steepness of underlying slopes.
Individual rock fragments must be dense, sound, and resistant to abrasion, and must be free from
cracks, seams, and other defects that would tend to unduly increase their destruction by water
and frost actions, Weak, friable, or laminated aggregate may not be used.
Rock covering of slopes may be unnecessary where top covers are very thick (or less); bulk cover
materials have inherently favorable erosion resistance characteristics; and A there is negligible
drainage catchment area upstream ofthe pile and good wind protection as described in points
(a) and (b) of this criterion.
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Furthermore, all impoundment surfaces must be contoured to avoid areas of concentrated
surface runoff or abrupt or sharp changes in slope gradient. In addition to rock cover on slopes,
areas toward which surface runoff might be directed must be well protected with substantial rock
cover (rip rap). In addition to providing for stability of the impoundrnent system itself overall
stability, erosion potential, and geomorphology of surrounding terrain must be evaluated to
assure that there are not ongoing or potential processes, such as gully erosion, which would lead
to impoundment instability,
(e) The impoundment may not be located near a capable fault that could cause a maximum
credible earthquake larger than that which the impoundment could reasonably be expected to
withstand. As used in this criterion, the term "capable fault" has the same meaning as defined in
section 111(g) of Appendix A of 10 CFR Part 100, The term "maximum credible earthquake"
means that earthquake which would cause the maximum vibratory ground motion based upon an
evaluation of earthquake potential considering the regional and local geology and seismology
and specific characteristics of local subsurface material,
(f) The impoundment, where feasible, should be designed to incorporate features which will
promote deposition. For example, design features which promote deposition of sediment
suspended in any runoff which flows into the impoundment area might be utilized; the object of
such a design feature would be to enhance the thickness of cover over time.''
INTERROGATORY STATEMENT:
1. Refer to Sections 5.2. i, 5.2.2, 3.3, Section 5.1 of Attachment A, Figures A-5.1-1 through A-
5.1-3, and Table A-5.3.2.1-1 of the Rev 4.0 Reclamation Plan, and MWH 2010: In addition
to the information requested in Round 1 Interrogatory White Mesa RecPlan 03/01 (as it
remains applicable to the proposal altemative cover design), please provide and justify the
adequacy ofthe following information for the proposed altemative tailings cell cover design:
a. Provide procedures that will be used to produce and install the proposed gravel/topsoil
admixture layer on the topdeck portion of the proposed altemative cover system. Include
descriptions of rock cmshing/sizing operations (if any); the expected distribution of
particle sizes ofthe gravel materials of constmction; and the processes to be used to mix,
place, and compact the gravel and topsoil materials that will constitute the final admix
layer.
b. Provide key data and material testing results for component materials proposed for use in
constmcting the gravel/topsoil admix layer (e.g., plasticity index of soil; dispersive vs.
non-dispersive nature and organic content of the topsoil; specific gravity of gravel
materials; gravel particle gradation; and percentage of gravel vs. topsoil in admixture).
Provide separate calculation(s) as needed showing how parameter values were
determined (e.g., void ratio, density, and composite gradation of the final admix) for the
admix layer that are used as input into erosion calculations.
c. Provide information on the types of vegetation proposed to be established (e.g., type of
rangeland grass and/or other plant species) and the type(s) of plant communities that are
anticipated to evolve in the final altemative cover system over the long term (i.e.,
describe likely plant succession scenarios). Assess the abilities of both planned and
successive plants to protect against erosion and support transpiration.
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d. Provide an analysis of rate of soil erosion of the gravel/topsoil admix surface layer due to
sheet erosion using USLE or MUSLE (Modified Uniform Soil Loss Equation based on
Utah Water Research Laboratory MUSLE [Apt and Ruff 1978]).
e. Provide calculations demonstrating the adequacy of the proposed gravel/topsoil admix
layer to protect against erosion from overland flow (e.g., a calculation of allowable
effective stress on the admix layer surface using the tractive forces method) expected to
occur across the cover surface. Acceptable analysis methods include those described in
NUREG-1623 (NRC 2002) and include the Temple et al. 1987 tractive force (allowable
shear stress) method and the "permissible velocity" method as discussed by Chow
(1959). If the latter method is used, justify the selection of Manning's "n" values used in
the calculations for a conservative range of potential vegetation conditions (e.g., from an
essentially bare "desert pavement" type condition to a well vegetated or grassy
condition).
f Provide information on and justification for values of all parameters used in erosion
calculations for assessing stability of the gravel/topsoil admix layer. Demonstrate that
such layer properties are representative ofthe expected as-built gravel/topsoil admix
layer, as opposed to simply relying on values estimated in the literature..
g. Provide information to justify the value of the maximum allowable slope necessary to
prevent initiation of gullying in the topdeck portion of the altemative cover design.
Acceptable analysis methods include those described in NUREG-1623 (NRC 2002),
including the Horton/NRC equation and the Corps of Engineers Method (NRC 2002).
Provide appropriate Manning's "n" values for a conservativb range of potential
vegetation conditions that would be considered/used in the calculation (i.e., an essentially
bare "desert pavement" type condition to a well vegetated or grassy condition).
h. Redefine the proposed altemative cover design shown in Exhibit A following the
Introduction to these Round lA interrogatories to:
• Include information regarding vegetation seed type and seeding process for the
upper soil layer; and
• Define characteristics of rock riprap that will be included on the sideslope portions ,
of the altemative cover design, or, altematively, state that no rock armoring would
be used on the sideslopes and provide detailed justification for not including such
armoring in the cover system.
2. Refer to Section 3.3.3 (Infiltration Analysis), Section 3.3.7 (Soil Cover-Animal Intrusion),
and Attachment A, Section 5.3.2.1 (Methods) and Table 5.3.2.1-1 of the Rev 4.0
Reclamation Plan and MWH 2010: In addition Xo ihQxni^
Interrogatory White Mesa RecPlan 03/01 (as it remains applicable to the proposal altemative
cover design), please provide the following information for the proposed altemative tailings
cell cover design:
a. Provide additional information regarding how the gravel/topsoil admix layer will be
constmcted in the altemative cover system. Discuss whether the composite admixture
will be prepared away from the disposal unit and then transported to the topdeck surface
with low ground pressure equipment, or, altematively, created in place as the cover is
11
f ^^"^^ ^^^^' ^ Round 1A Interrogatones ^ypjg
constructed. In either case, describe and justify the construction equipment and process.
Also provide additional information regarding the proposed loose-lift thicknesses,
moisture conditioning, and placement and compaction methods (e g., equipment to be
used and number of passes to be made by such equipment when constructing the sandy
clayey silt layers in the altemative cover system. Demonstrate that installation procedures
will result in soil systems that are compacted to a degree to less than or equal to the
estimated "Growth Limiting Bulk Density" ofthe soil system, as described by Goldsmith,
et al. (2001) and Gray (2002), e.g., less than or equal to approximately 80 to 85 %
standard Proctor density for the soils used, in order to not inhibit vegetative growth in the
topdeck portion of the cover system.
b. Please revise Sections 3.3.3, 3.3.7 of the text in the Reclamation Plan, and Section 5.3.2.1
and Table 5.3.2.1-1 in Attachment A to the Reclamation Plan, to reflect the final
compaction criteria selected for the final proposed topdeck cover system, e.g., as
referenced in the proposed Preliminary Altemative Cover Design for the White Mesa
Tailings Cells (MWH 2010).
BASIS FOR INTERROGATORY
The proposed altemative cover design includes a gravel/topsoil admix layer on the topdeck
portion ofthe cover system, rather than a layer of rock riprap. This layer needs to be evaluated
for adequacy with respect to long-term erosion protection, consistent with NRC guidelines and
recommendations for evaluating erosion protection (e.g., NRC 2002). Erosion protection
calculations provided in Appendix F of the Reclamation Plan, Rev. 4 need to be revised to
address the proposed new cover system design.
The gravel/topsoil admix layer will be unique in its characteristics, depending on the specific
composition ofthe components used in its constmction and the specific procedures used tomix,
place, and compact the layer. For this reason, specific layer properties for this admix layer (e.g.,
admix layer void space and density), as they are used in erosion protection evaluations/ '
calculations, should be specifically calculated for the layer (i.e., rather than using literature-
derived or assumed values for these layer properties).
Information that needs to be provided, for review, for the proposed altemative cover design also
includes information on the types of vegetation proposed to be established (e.g., type of
rangeland grass and/or other plant species) and plant communities that are anticipated to develop
m the final altemative cover system over the long term, hi other words, plant succession miist be
addressed. This information will be used as input in separate modeling simulations and will
support certain erosion analyses, including determination of appropriate Manning's "n"
roughness coefficients for use in design analyses.
Work conducted by Goldsmith and others (2001) and Gray (2002) suggests that a compaction V
between 80% and 85% of the standard Proctor maximum dry density provides many of the
stabilizingbenefits of higher soil compaction without jeopardizing the viability of vegetation
development and growth. Use of excessive compactive effort and/or ineffective techniques when
installing the gravel/topsoil admix layer and use of too-small loose-lift thicknesses and/or
excessive compactive effort during constmction of the portion ofthe underiying sandy clayey silt
12 - ; A
Denison Mines (USA) Corp - Rev, 4,0 Reclamation Plan Round lA Interrogatories WWW^^SL
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layers that is intended to serve as the vegetative growth medium could result in excessive
amounts of compaction in these layers, thus deterring vegetation growth. Additional information
should be provided demonstrating that these potential concems will be adequately addressed in
the design and constmction specifications.
The sideslope portions ofthe final cover system will be susceptible to long-term erosion.
Applicable erosion protection design criteria (e.g., NRC 2002) suggest that rock armoring of .
sideslope areas could likely be required to ensure adequate long-term erosion protection of these
sideslope areas.
REFERENCES:
Apt, S.R., and Ruff, J.F. 1978. "Three Procedures for Estimating Erosion from Constmction
AvQas." Symposium on Uranium Mill Tailings Management, Volume II, Geotechnical
Engineering Program, Civil Engineering Department, Colorado State Univetsity,
November 20 and 21, 1978, pp. 87-102. ^
Chow, V.T. 1959. Open-Channel Hydraulics, McGraw-Hill Company, Inc., New York, NY.
Goldsmith, W., Silva, M., and Fischenich, C. 2001. Determining Optimal Degree of Soil
Compaction for Balancing Mechanical Stability and Plant Growth Capacity, Report
ERDC-TN-EMRRP-SR-26., U.S. Army Engineer Research and Development Center,
Vicksburg, MS. May 2001, 9 pp. URL: http://el.erdc.usace.army.mil/elpubs/pdf/sr26.pdf
Gray, D. H. 2002. "Optimizing Soil Compaction and Other Strategies," Erosion Control,
Volume9,No. 5, September-October2002. URL;
http://www.erosioncontrol.com/september-october-2002/optimizing-soil-
compaction.aspx.
MWH 2010. "Proposed Preliminary Altemative Cover Design for White Mesa Tailings Cells".
Letter from Melanie Davis of MHW to Harold Roberts of Denison Mines (US A) Corp.
dated October 6, 2010.
Nelson, J.D., Abt, S.R., Volpe, R.L, van Zyl, D., Hinkle, N.E., and Staub, W.P. 1986.
Methodologies for Evaluating Long-Term Stabilization Designs of Uranium Mill Tailings
Impoundments. Prepared for Nuclear Regulatory Commission, Washington, D.C.
NUREG/CR-4620, ORNL/TM-10067. June 1986, 151 pp.
Temple, D.M., Robinson, K.M., Ahring, R.M., and Davis, A.G. 1987. Stability Design of Grass-
Lined Channels. U.S. Department of Agriculture, Agricultural Handbook No. 667, U.S.
Govemment Printing Office, Washington, D.C, 167 pp.
Nuclear Regulatory Commission (NRC) 2002. Design of Erosion Protection for Long-Term
5raZ?///0;, NUREG-1623, September 2002.
13
Denison Mines (USA) Corp - Rev, 4, 0 Reclamation Plan Round lA Interrogatories T |^'U^ 6[ .
ApriUOll %#jm
INTERROGATORY WHITE MESA RECPLAN 05/01 A: 10 CFR PART 40, APPENDIX
A; UAC R317-3-1; AND UAC R317-3: CONSTRUCTION QUALITY CONTROL AND
ASSURANCE
REGULATORY BASIS:
Refer to R317-3-1 (1.7), 1.7, Construction Supervision. The applicant must demonstrate that
adequate and competent inspection will be provided during construction. It is the responsibility
of the applicant to provide frequent and comprehensive inspection of the project
Refer to R317-3-10(4)(E), E, Construction Quality Control and Assurance, A construction
quality control and assurance plan showing frequency and type of testing for materials used in
construction shall be submitted with the design for review and approval. Results of such testing, ,
gradation, compaction, field permeability, etc, shall be submitted to the Executive Secretary,
INTERROGATORY STATEMENT:
1. Refer to Section 7.0 of Attachment A and Attachment B to the Rev. 4.0 Reclamation Plan,
and MWH 2010: In addition to the information requested in Round 1 Interrogatory White
Mesa RecPlan 05/01 (as it remains apphcable to the proposed altemative cover design),
please include information in the CQAQC Plan regarding DUSA's plans for constmcting and
monitoring a Test Pad to quantify field/constmction parameters that are specifically pertinent
to demonstrating the (short-term and long-term) performance of the altemative tailings cell
cover design. Address, as part of the Test Pad program, testing of parameters (e.g.. National
Research Council 2007; Albright, et al. 2007) including, but not necessarily limited to:
• In-situ water content testing (e.g., soil moisture profile monitoring) and monitoring for
potential changes in water content according to depth through time. i
• In-situ flux rate testing (e.g., through use of one or more pan lysimeters) and monitoring
to assess potential changes in flux rates through time,
• Physical sampling and laboratory testing for index properties, including Plasticity Index
and saturated hydraulic conductivity, and other pertinent parameters (organic matter
content, compaction properties, etc.) and monitoring to assess potential changes in these
properties through time.
• Testing for determining soil water characteristic curves (SWCCs, e.g., according to
ASTM D6836 [ASTM 2008]) and monitoring for potential changes in SWCCs through
time. This also includes, but is not limited to determination of individual soil total
porosity, field capacity, wilting point, and residual saturation, etc.
• Relevant climatological parameters (precipitation and evaporation rates, etc.).
2. Provide justification for monitoring approaches and monitoring devices (e.g., use of TDR
probes, heat dissipation probes, pan lysimeters, and/or neutron probe access tubes, etc.)
proposed for use in the cover performance verification monitoring program. -
3. Describe how information on natural analogs (existing plant communities and existing
natural soil profiles at the borrow source site(s) or other sites that exhibit characteristics
similar to those of the final cover system at various times in its design hfe) will be used to
14
Denison Mines (USA) Corp - Rev. 4.0 Reclamation Plan Round 1A Interrogatories WTBJ^
ApriUOll Uamigp
complement the results of the CQAQC Test Pad testing program/cover performance program
discussed above. Describe possible future changes in climate states and extreme precipitation
events that were considered as part of the design of the proposed altemative cover and in
selecting analog sites for inspection/investigation.
4. Provide a Constmction Quality Assurance Constmction Quality Control (CQACQC) plan
containing detailed information on constmction procedures and equipment to be used for
constructing the proposed altemative final cover system and the Test Pad cover system;
Describe the acceptable tolerances that will apply when measuring final grades during
constmction of the cover and the Test Pad cover system. Identify testing frequencies,
equipment, and methods for testing of constmcted final grades. Provide information
demonstrating that the specified grading tolerances for the final cover and Test Pad cover
constmction can be reliably, accurately, and consistently measured in the field throughout the
cover constmction effort. Provide case studies/examples from peer-reviewed literature that
clearly demonstrate that a final cover system constmcted to a similar scale and under similar
site conditions and using similar soils and equipment as the proposed cover system having a
topdeck slope of (only) 0.2 % can be effectively constmcted with a positive slope inclination
maintained throughout the entire cover surface area. Provide information demonstrating that
long term, post-constmction settlement and/or subsidence within the reclaimed tailings
embankment will not result in any areas that could allow ponding of water to occur on the
cover surface and/or result in increased percolation into the cover system.
5. Provide information on seed/seeding application rates and acceptable germination levels for
promoting vegetation (grass) growth on the final cover. Provide information in the CQAQC
Plan on application rates and procedures to be used for measuring/confirming that specified
apphcation rates are achieved
BASIS FOR INTERROGATORY
A cover system Test Pad capable of assisting in confirming the performance of the proposed
altemative cover system should be constmcted and monitored. The proposed altemative cover
design incorporates more loosely compacted soil layers, and a surficial rock riprap layer is no
longer to be included. The altemative cover system appears to be intended to serve as a water
balance cover system (an evapotranspiration [ET]-type cover where the cover is designed to act
not as a barrier, but as a sponge or "reservoir" for storing moisture generated during precipitation
events, fpr subsequent release back to the atmosphere as ET, with plants established on the cover
surface designed that survive on the naturally-occurring precipitation capable of promoting
vegetation growth to enhance evapotranspiration).
Characteristics of the proposed altemative cover will inevitably change in the long term in
response to climate, pedogenesis, and ecological succession (Albright, et al. 2007; Benson, et al.
2007). Use ofa less compacted gravel/topsoil admixture layer and more loosely compacted
underlying soil layers in the cover without the riprap layer could render the altemative cover
susceptible to post-constmction changes in certain physical and hydraulic properties of the cover.
For example, relatively large changes in moisture content (wetting and drying cycles) in the
cover system and plant root development would be expected to occur through time during the
15
Denison Mines (USA) Corp - Rev, 4,0 Reclamation Plan Round lA Interrogatories WHWit^^^
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post-closure period (200-1,000 years) which could eventually lead to changes in some hydraulic
properties ofthe soil cover system. Changes could include creation of larger pore spaces and a
broader pore size distribution as a result bf wet-dry cycles (desiccation) and reductions in soil
density due to frost heave action, which could ultimately lead to changes in hydrauhc properties.
By comparison, the conditions associated with the cover design presented in the Rev. 4.0
Reclamation Plan could have been expected to reduce evaporation and enhance water storage in
the cover (e.g., Groenevelt, et al. 1989; Kemper, et al. 1994), and thus provide some degree of
buffering (insulating) benefit against larger moisture fluctuations in the upper portion of the
underlying soil layer(s) in the cover.
Comparisons of data collected from a depth of 30 cm (1 foot) within water balance covers
constmcted at different field sites in the Altemative Cover Assessment Program at the time of
constmction and data collected 2 to 4 years following constmction of those covers indicate
potentially large changes in saturated hydraulic conductivity (increases by as much as 10,000
times); increases in the van Genuchten parameter a (an increase by as much as 1,000 times was
observed); and increases in the saturated volumetric water content and the van Genuchten
parameter n (e.g., Benson, et al. 2007). Results of such studies indicated that, depending on the
specific materials and constmction methods, actual as-built conditions, and actual climatic
conditions present, the largest changes in soil cover properties (at least in the upper 1-foot zone)
were observed in those water balance covers that are comprised of denser, fine-textured soils that
have more uniform pore space distributions. Less is known about how changes in hydraulic
properties vary with depth in ET cover systems evaluated.
Plasticity Index can be a useful indicator for assessing volume changes. Soil Water Characteristic
Curves for soils used in the cover system could be expected to change.with time, based on post-
constmction changes that may occur in the controlling soil parameters of the soil layers. Such
changes could modify soil moisture storage/retention, and other hydrauhc properties.
Monitoring the proposed altemative cover system or monitoring of a Test Pad simulating the
cover system components and geometry) to assess the long-term performance of the altemative
cover is needed to verify the characteristics and infiltration performance of the constmcted cover
system as well as to gain confidence in understanding long-term changes that may occur in the
physical/hydraulic properties of the altemative cover system over time following its constmction.
REFERENCES:
Albright, W.H., Waugh, W.J., and Benson, CH. 2007. "Altemative Covers: Enhanced Soil
Water Storage and Evapotranspiration in the Source Zone." Enhancements to Natural
Attenuation: Selected Case Studies, Early, T.O. (ed), pp 9-17. Prepared for U.S. Dept. of
Energy by Washington Savannah River Company, WSRC-STI-2007-00250. URL:
http://vmw.dri.edii/images/stories/research/programs/acap/acap^piiblica^^
ASTM (American Society for Testing and Materials) 2006. ASMTD6836 - 02(2008)e2:
Standard Test Methods for Determination ofthe Soil Water Characteristic Curve for
Desorption Using a Hanging Column, Pressure Extractor A Chilled Mirror Hyg^^^^
and/or Centrifuge. ASTM, West Conshohocken, Pennsylvania.
16
Denison Mines (USA) Corp - Rev, 4,0 Reclamation Plan Round 1A Interrogatories W¥IJ ^5
ApriUOll
Benson, C.H., Sawangsuriya, A., Trzebiatowski, B., and Albright, W.H. 2007.. "Postconstmction
Changes in the Hydraulic Properties of Water Balance Cover Soils", Journal of
Geotechnical and GeoenvironmentalEngineering, 133:4, pp. 349-359.
Groenevelt, P.H., P. van Straaten, V. Rasiah, and J. Simpson 1989. "Modification in Evaporation
Parameters by Rock Mulches'', 5b//TecAwo/ogy 2:^
Kemper, W.D., A.D. Nicks, and A.T. Corey 1994. "Accumulation of Water in Soils under
Gravel and Sand Mulches", Soil Science Society of America Journal 58:56-63 (1994).
MWH 2010. "Proposed Preliminary Altemative Cover Design for White Mesa Tailings Cells".
Letter from MHW to Harold Roberts of Denison Mines (USA) Corp. dated October 6,
2010.
National Research Council 2007. Assessment of the Performance of Engineered Waste
Containment Barriers. Board of Earth Sciences and Resources. The National Academies
Press, Washington, D.C, 2007, 134 pp.
17
Denison Mines (USA) Corp - Rev, 4,0 Reclamation Plan Round 1A Interrogatories "ffJfnf^S
April 2011 li^J^llJ
INTERROGATORY WHITE MESA RECPLAN 09/OlA: UAC R313-25-7; UAC R313-25-
8; UAC R317-6-l(6)6.1 : WATER BALANCE DESIGN CONTROL FEATURES IN
COVER SYSTEM
REGULATORY BASIS:
UAC R317-6-1 (6)(61)(A) Implementation, Unless otherwise determined by the Executive
Secretary, the application for a permit to discharge wastes or pollutants to ground water shall
include the following complete information:
UAC R317-6-1 (6)(6.1)(G) Implementation, Information which shows that the discharge can be
controlled and will not migrate into or adversely affect the quality ofany other waters ofthe
state, including the applicable surface water quality standards, that the discharge is compatible
with the receiving ground water, and that the discharge will comply with the applicable class
TDS limits, ground water quality standards, class protection levels or an alternate concentration
limit proposed by the facility,
INTERROGATORY STATEMENT:
Although no Round 1 interrogatory was developed that focused specifically on design features
included in the final cover system for controlling the water balance within the reclairned taiUngs
embankment following closure (namely, no Interrogatory White Mesa Recplan 09/01 exists) this
interrogatory is provided to address certain issues related to the design of the altemative cover
system design that were not germane to the existing authorized rock cover system design. In
addition, it is acknowledged that review of a Revised Infiltration and Contaminant Transport
(ICTM) Report is being conducted separately and is still in progress and that additional issues
and/or interrogatory items may arise from further review and discussions with DUSA as an
outcome of that review. Nonetheless, the following items are provided here since the issue of
long-term water balance within the closed tailings embankment is integrally connected to details
of the final cover system design.
1. Refer to Sections 3.2.2, 3.3, Section 5 of Attachment A, Figures A-5.1-1 through A-5.1-3,
and Table A-5.3.2.1-1 ofthe Rev 4.0 Reclamation Plan, and MfFi? 2 WO: Please provide
the following information:
• Provide information regarding potential long-term conditions in the proposed altemative
cover system that has been considered in developing the cover design. Include
information on the saturated hydraulic conductivity values expected to be achieved for
the as-built soil layer components in the proposed altemative cover system. Also provide
information on the estimated range of long-term hydraulic conductivity values projected
to occur within each of the soil layer components in the cover (e.g., under long-term,
degraded cover conditions). Describe the assumptions that have been made with respect
to key variables that influence the cover design, including, but not limited to: (I) Absence
of ongoing maintenance of the cover system and lack of maintenance/removal of leachate
from tailings cell sumps in the future; (2) nature and extent of degraded conditions
projected to occur in the cover (and cell liner systems) over the required design hfe of the
18
I
Denison Mines (USA) Corp - Rev, 4,0 Reclamation Plan Round lA Interrogatories W I'DlC
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embankment [200-1,000 years]; (3) magnitude of potentially wetter future precipitation
conditions that may occur at the site over the embankment's required design life; (4)
presence and distribution of different plant species/communities and animal-induced
burrowing that could occur in the cover system over the long term; and (5) other
degraded conditions that could develop within the cover system (and liner system) as a
result of other degradation mechanisms. Describe and quantify, to the extent practicable,
uncertainties that are associated with assumptions made with respect to these variables.;
• Evaluate and provide information regarding the need to include a low-permeability
barrier component (e.g., an HDPE geomembrane and a geosynthetic clay liner [GCL]) in
the altemative cover system for limiting long-term vertical movement of moisture
through the cover. Altematively, provide detailed information that clearly demonstrates
why such a low-permeability barrier layer, which NRC recommends, be included in final
tailings cell reclamation covers (NRC 2003, Section 2.7), is not warranted or necessary.
Provide information demonstrating that the proposed altemative cover system would
provide an adequate level of long-term xQducXion of vertical moisture movement through
the cover to both minimize the potential for long-term "bathtubbing" of liquid within the
closed tailings embankment and restrict the transport of contaminants from the closed
tailings embankment to subsurface groundwater throughout the design life [200-1,000
years] of the embankment to levels equivalent to, or better than, a final cover system that
includes such a low-permeability component.
Evaluate and provide information regarding the need for including a capillary break or
lateral drainage and/or cobble layer in the topdeck portion of the proposed altemative
cover, for further limiting vertical downward movement of moisture through the cover
system and into the tailings. Provide information demonstrating that omitting such a
design feature - which could provide a means of virtually precluding "breakthrough" of
excess moisture levels in the cover into the tailings at a semi-arid to arid site as is the case
for the White Mesa Site - will not j eopardize the capacity of the altemative cover for
minimizing long-term downward vertical movement of moisture through the cover
system throughout the required postclosure performance period (200-1,000 years). See
dX^o Interrogatory RecPlan 02/01 A: 10CFR40 Appendix A, Criterion 1: Permanent
Isolation without Ongoing Maintenance, above. If further analysis indicates that a lateral
drainage layer is needed in the final cover system, based on the proposed final cover
grading configuration and cover topdeck slope lengths, evaluate and provide information
regarding the need for including intermediate discharge/drain outiets and/or higher
transmissivity lateral drains in the drainage layer design in the cover in order to reduce
the water budget (infiltration) that could come into contact with the tailings during the
postclosure performance period.
Evaluate and provide information on the applicability of published individual or joint
NRC-EPA guidance related tp the conceptual design of LLRW disposal facilities that y
contain low-permeability liner components to the design of the cover system for the
tailings cells at the White Mesa Mill Facility. Provide information that clearly
demonstrates that the proposed altemative cover system will not lead to potential
bathtubbing of liquid within the tailings embankment during the postclosure period when
19
Denison Mines (USA) Corp - Rev. 4,0 Reclamation Plan Round lA Interrogatories WWS^^^
April 2011 :r ILIJI^^
no active maintenance would be performed at the facihty and Under the scenario
involving long-term (degraded) conditions present in the cover system. Provide
quantitative estimates of potential long-term leachate head buildup amounts on liner
systems for each disposal cell where the liner system characteristics (e.g.,
PVC/compacted subgrade, double composite HDPE/GCL liner systems, etc.) differ
between the various disposal cells. Provide calculations (e.g., using methods in Giroud
1997) of leakage rates through each type of liner system that consider the range of
uncertainties associated with: (1) the long-term hydraulic performance of each liner
system; (2) the long-term hydraulic performance of the cover system at limiting
downward vertical movement of moisture within the tailings embankment, given
potential long-term degradation of the cover system materials; and (3) extent and duration
of dewatering occurring within the various tailings disposal cells, during the
embankment's required performance period.
• Provide information evaluating potential worst-case/abnormal long-term leakage rates
through the various cell liner systems that consider: (1) the uncertainties associated with
the potential (progressive) changes in the number, size, and types of defects in the
geosynthetic liner systems that might occur during the required performance period of the
tailings embankment, including circular defects and linear [e.g., stress] cracks, etc.) as
described in the peer-reviewed literature; (2) uncertainties associated with the extent and
duration of dewatering operations that may occur within the various tailings cells active
life, and during the embankment's required performance period; and (3) uncertainties
associated with potential long-term infiltration rates through the (degraded) final cover
system,
2, In developing a response to this interrogatory, prior review comments and Requests for
Additional Information (RFIs) previously submitted to DUSA by the UDEQ DRC on the
ICTM report should also be considered and addressed as they apply to the proposed
altemative cover design depicted in Exhibit A. These documents include, but are not
limited to: DRC's Request for Additional Information (RFI) letter dated Febmary 2,
2009, and DRC's email dated September 3, 2009 (DRC 2009a and 2009b, respectively).
BASIS FOR INTERROGATORY:
The proposed altemative cover design does not include a low-permeabihty component/low-
permeability barrier. In that regard, the proposed altemative cover does not appear to be
consistent with NRC guidelines and recommendations relating to standard acceptance criteria for
evaluating tailings reclamation cover designs. NUREG-1620 (NRC 2003), Section 2.7, specifies
that a goal of a tailings reclamation plan/decommissioning plan is to ensure that the disposal cell
cover has a component having minimal hydraulic conductivity, and provides the complimentary
functions of both limiting radon emissions from (also see Rd I Interrogatory White Mesa
Recplan 04/01 addressing radon emissions), and limiting water infiltration m/o, [the] stabilized
mill tailings. The discussion in Section 2.7 of NRC 2003 suggests that NRC contemplates that a
cover system containing a low-permeability component having a properly field-and-laboratory-
testing-verified saturated hydraulic conductivity value of 1 x 10'^ cm/sec or less is sometimes
considered to be generally acceptable.
20
Denison Mines (USA) Corp - Rev. 4,0 Reclamation Plan Round lA Interrogatories
ApriUOll A %iMWm3
Recent studies (e.g., Scalia and Benson 2011) describe results of testing of exhumed GCLs that
were previously installed in final cover systems immediately above a compacted soil subgrade
and immediately beneath a polyethylene synthetic geomembrane that had been left in place in the
covers between about 5 and 7 years. Results of laboratory testing of exhumed GCL samples that
had hydrated rapidly to at least 50% water content and had experienced osmotic swell indicate
that the GCL samples essentially retained their initial low hydraulic conductivity. These results
provide evidence that including a composite GCL/geomembrane low-permeability barrier in the
final cover and ensuring that it would rapidly achieve this level of hydration and swell would
likely be beneficial in helping to achieve the objective (per NUREG-1620) of reducing (long-
term) downward movement of moisture through the final cover into the tailings. Such a
reduction would help minimize the potential for bathtubbing within the closed tailings
embankment and minimize potential long-term releases from the base of the embankment during
the post-closure post-maintenance period following final cover placement.
Inclusion of a capillary break or lateral drainage layer and/or cobble layer (accompanied by
appropriate filter layers as needed) in a final cover would help contribute toward achieving the
desired water balance in the cover, i.e., the promotion of evapotranspiration relative to the
downward movement of water into the tailings (e.g., see DOE 1989; Stormont and Morris 1998),
as well as help provide a barrier to deep root penetration and minimize upward movement of
contaminants (within the cover) via capillary forces- See also Interrogatory RecPlan 02/01 A:
10CFR40 Appendix A, Criterion 1: Permanent Isolation without Ongoing Maintenance, above.
These benefits would be achieved by virtue of the incorporated capillary/drainage/cobble layer,
only allowing significant quantities of water to drain out of and move downward from the
overlying soil layer component when the overlying soil is completely saturated. Additionally,
research results (e.g., Soong and Koemer 1997; Thiel and Stewart 1993, etc.) indicate that
conventional model predictions have often underestimated percolation rates into lateral drainage
layers that have been incorporated into final cover systems, leading to slope failures at some
facilities.
Some ofthe tailings cells (e.g., Cells 4A and 4B) contain composite of very low-permeability
liners under the tailings, including GCL and geomembrane components (having as-built
saturated hydraulic conductivities less than I x 10"^ cm/sec). Use of a cover system that does not
include a very low-permeability component of equal or lower permeability than the liner
components could create the potential for future buildup of liquids within the tailings
embankment following closure due to net infiltration rates through the cover exceeding net
leakage rates through the liner system over the long term. Information needs to be provided that
demonstrates that the selected final cover design will not result in the creation of this bathtub ;
effect within the closed embankment.
Pubhshed information (e.g., EPA 2002, Hsuan et al. 2004; Rowe and Rimal 2008; others)
suggests that the potential exists for cracks (e.g., stress cracks) to occur in the HDPE
geomembrane liners (in Cells 4A and 4B) and/or the PVCliners (in Cells 2 and 3) in the tailings
disposal cells during the tailings embankment's required performance period. Cracking might
occur as a result of one or more factors including: (1) the stress crack resistance and the yield
stress ofthe HDPE geomembrane liner used in each cell depending on its age and manufacturing
source; (2) degree of long-term antioxidant depletion and/or embrittiement that may occur in the
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Denison Mines (USA) Corp- Rev. 4.0 Reclamation Plan Round 1A Interrogatories W^^jj^^l^
April 2011
various HDPE geomembrane liners over the liner's service life; (3) tensile stresses and wrinkles
that might be present in each cell liner system; (4) type and amount of plasticizers and rate of
post-installation plasticizer loss that may occur in the PVC geomembrane liners (Cells 2 arid 3);
and (5) other possible factors. Similar factors could also lead to changes in size and/or shape,
over time, of any circular defects that may be present in the liners as a result of installation or
subsequent long-term degradation processes occurring in the liner material.
REFERENCES:
DOE (U.S. Department of Energy) 1989. Technical Approach Document. Revision //. UMTRA-
DOE/AL 050425.0002. Albuquerque, New Mexico.
DRC 2009a. "White Mesa Uranium Mill, Ground Water Discharge Permit No. UGW370004.
Infiltration and Contaminant Transport Modeling Report: DRC Review Comments,
Request for Additional Information," Febraary 2, 2009 Letter ^om Tom Rushing to
David Frydenlund, 9 pp. ;
DRC 2009b. "Denison Mines: Further Thought on Meeting Yesterday - Radon Control Issiies",
September 3,2009 Email from Loren Morton to Harold Roberts, 1 p.
EPA 2002. Assessment and Recommendations for Improving the Performance of Waste
Containment System. EP A/600/R-02/099, 2002; Compiled by Bonaparte, R., Daniels, D.,
and Koemer, R.M.
Giroud, J.P. 1997. "Equations for Calculating the Rate of Liquid Migration Through Composite
Liners Due to Geomembrane Defects." Geosynthetics Intemationai, Vol. 4, Nos. 3-4,
pp. 335-348.
Hsuan,Y.G., Schroeder, H.F., Rowe, K., Greenwood, J., Cazzufi, D., and Koemer, R. M. 2008.
Long-Term Performance of Geosynthetics. EuroGeo4 Keynote Paper, 40 pp.
MWH 2010. "Proposed Preliminary Altemative Cover Design for White Mesa Tailings Cells".
Letter from MHW to Harold Roberts of Denison Mines (USA) Corp., dated October 6,
2010.
NRC (U.S. Nuclear Regulatory Commission) 2003. Standard Review Plan for the Review of a
Reclamation Plan for Mill Tailings Sites under Title II of the Uranium Mill Tailings
i?ac?ja^ion Confro/^c/0//975, Rev. 1. Washington, D.C., June 2003.
Rowe, R. K., and Rimal, S. 2008. "Aging and Long-term Performance of Geomembrane
Liners," Geoawenca5 2008, Cancun, Mexico, March. 2-5, 2008., 10 pp.
Scalia, J., and Benson, CH. 2011. "Hydraulic Conductivity of Geosynthetic Clay Liners
Exhumed from Landfill Final Covers with Composite Barriers", Journal of Geotechnical
and Geoenvironmental Engineering, Vol. 137, No.l, January 1, 2011: pp. 1-13.
22
Denison Mines (USA) Corp - Rev. 4.0 Reclamation Plan Round lA InterrogatorieA W YfO^^
April 2011 ; , . - ".WjilJ
Soong, T.Y., and Koemer, R.M. 1997. The Design of Drainage Systems over Geosynthetically
Lined Slopes. GRl Report #\9.
Stormont, J. And Morris, C. 1998. "Method to Estimate Water Storage Capacity of Capillary
Barriers," Journal of Geotechnical and Geoenvironmental Engineering 124: pp.
297-302. URL: http://ro.uow.edu.au/engpapers/208/.
Thiel, R.S., and Stewart, M.G. 1993. "Geosynthetic Landfill Cover Design Methodology and
Constmction Experience in the Pacific Northwest", Proceeding: Geo '93, Vancouver,
B.C. IFAI. Pp. 1131-1144.
U.S. EPA (Environmental Protection Agency) 1987. Joint NRC-EPA Guidance on a Conceptual
Design Approach for Commercial Mixed Low-Level Radioactive and Hazardous Waste
Disposal Facilities - Action Memorandum. U.S. EPA, Washington, D.C, August 18,
1987. URL: nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=100018ZA.txt.
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