DRC-2009-006626 - 0901a06880151202

J:)i>C. - J-LC<( CO ^i^^/. Page 1 of 1
Sonja Robinson - Revised minutes for March 31, 2009 meeting between Denison Mines, DRC, and
MWH concerning White Mesa ICTM
From: "Douglas Oliver Jr." <[e-mail]>
To: Loren Morton <[e-mail]>
Date: 11/18/2009 12:40 PM
Subject: Revised minutes for March 31, 2009 meeting between Denison Mines, DRC, and
MWH concerning White Mesa ICTM
CC: Thomas Rushing ii <[e-mail]>, David Frydenlund
<DFr}'[e-mail]>, Harold Roberts <[e-mail]>
Attachments: Minutes for 31 Mar09 meeting revised 18Nov09.docx; Minutes for 31 Mar09
meetingrevised 18Nov09 redlined version.docx
Loren,
At Dave Frydenlund's request, I am sending you the revised minutes for the March 31, 2009 meeting between
Denison Mines, DRC, and MWH concerning the White Mesa Infiltration and Contaminant Transport Model
(ICTM). Draft minutes were originally submitted to the DRC on April 23, 2009. The attached revised minutes
reflect changes that were made in response to DRC's comments sent to Denison on April 28, 2009 by Tom
Rushing. I have included both a final copy and a redlined version of the minutes so you can readily see the
changes we made. Ifyou have any questions or comments, please contact Dave Frydenlund.
Thanks,
Doug
Douglass. Oliver, P.G.
Principal Hydrogeologist
MWH Americas, Inc.
10619 South Jordan Gateway, Ste. 100
SaltLakeCity, UT 84095
email: douRlas.ollver(S>mwhelobal.com
Phone: [phone]
Fax; 801-617-4224
This e-ma>l is intended for exclusive use the person(s) mentioned as the recipient(s). This message and any attached files with it are confidential and may contain
privileged or propneiary informaiion If you are not the intended recipient(s) please delete thrs message and notify the sender. Vou may not use. distribute prim or
copy this message if you are nol the intended fecipient{s).
file:/.C:\Documents and Settings\Sdrobinson\Local Settings\Temp\XPgrpwise\4B05259BE... 12/9/2009
1

MINUTES FROM MEETING WITH UTAH DIVISION OF RADIATION
CONTROL (DRC) TO DISCUSS COMMENTS ON THE WHITE MESA
INFILTRATION AND CONTAMINANT TRANSPORT MODELING REPORT
Date: March 31, 2009
Time: l:00-6:00pm MDT
Location: Utah DRC Office (168 North, 1950 West, Salt Lake City, Utah)
Attendees: Utah DRC: Loren Morton and Thomas Rushing
Denison Mines (USA) Corp: Harold Roberts and Dave Frydenlund
MWH Americas: Doug Oliver, Ryan Jakubowski and Phil Crouse
The purpose of the meeting was to discuss the DRC's comments (dated February 2, 2009)
on the Infiltration and Contaminant Transport Modeling (ICTM) Report that was prepared
by MWH for Denison and submitted to the DRC in November 2007. These minutes are
intended to summarize the primary discussions and key decisions made during the
meeting. The order of items presented in this summary is not necessarily in the order
discussed at the meeting.
DISCUSSION ITEMS
Background
MWH presented an overview of the project including:
• Site description
• Project background / permit requirements
• Timeline
• Modeling overview
Many of the DRC's comments were discussed during this presentation.
Key Issues
Based on their review of the ICTM Report, the DRC identified the following list of "key"
issues:
1. Vegetation details to support the proposed evapotranspiration (ET) cover.
2. Sorption and retardation of contaminants of concern.
3. Source term concentrations for tailings fluids.
4. Modeling of potential leakage through liners.
2

5. Coupling of models and how output from one model is input into the next model.
6. Effects of storm intensity, ponding, and 2-D effects of runon/runoff on infiltration
through the ET cover.
7. Cell 1.
Primary matters discussed and decisions made regarding these key issues are presented
below.
ET Cover Design and Vegetation
The cover design as presented in the ICTM Report was preliminary and conceptual in
nature. The ET concept was adopted because it is more effective than the conventional
cover proposed in the reclamation plan. The Ground Water Discharge Permit specifically
allowed for design changes to improve cover performance. After the modeling is
completed, the cover design and reclamation plan can be revised, but the modeling should
come first. The cover can be engineered to meet the required performance standards.
The ICTM will be based on site-specific data where possible, and will rely on literature
values where necessary (Note: since the time of this meeting, additional site-specific data
have been collected). The DRC will review all final engineering designs and materials
specifications to ensure conformance with the modeled performance capabilities.
The DRC would like the report to include additional details concerning the vegetation
such as the proposed seed mix (plant species). Details that need to be justified and
supported for the modeling include rooting depth and root density distribution, percent
cover, vegetation density and LAI (leaf area index). Other considerations include soil
properties (e.g., soil types, salinity, organic content), longevity and competition with
woody species. A sensitivity analysis should be performed on vegetation parameters to
evaluate the effects these have on the model results. The DRC raised the need for cited
references from botanists and range scientists and the sensitivity analysis needs to
simulate long-term vegetation establishment (Note: the September 2, 2009 meeting
involved extensive discussion concerning long-term vegetation establishment, which will
be incorporated in the revised ICTM report).
Sorption and Retardation
The results of the materials testing (soil-water characteristic curves) need to be discussed
in more detail in the Report. Specifically, the Report needs to describe the samples that
were used and why these sample locations were selected and what they represent in the
model. During the meeting, MWH presented a simplified cross section showing the
sample locations relative to the tailings cells. This figure will be added to the ICTM
Report.
In regard to sorption and retardation, MWH provided DRC with the NRC/USGS
reference NUREG/CR-6820 (Davis and Curtis, 2003) which describes the approach used
to calculate sorption and retardation for the uranium mill tailings site at Naturita. The
NRC/USGS reference also describes a methodology used to measure the mass of HFO
(hydrous ferric oxide). We incorporated a similar approach for White Mesa. The
3

amount of ANP (acid neutralizing potential) and methodology used to measure the ANP
were discussed.
The DRC was concerned that there was not enough ANP and HFO data to adequately
represent the distribution in the vadose zone. Furthermore, the DRC thought that the
ANP values (which are relatively low), don't appear to match the geochemical modeling
that shows significant acid neutralization. During the meeting it was noted that MWH
will look into this. Following the meeting we noted that this discrepancy may be
explained by the normalization procedure incorporated as part of the PHREEQC
modeling.
Options to consider include:
• collecting more HFO and ANP data to better represent vadose zone materials, or
• doing a sensitivity analysis (reduce sorption by one or more orders of magnitude)
to evaluate the effects of this uncertainty/variability on the model results.
The geochemical modeling used to calculate the sorption coefficients needs to be
described more clearly in the Report (details were provided in Appendix B). The Report
needs to state the prerequisite geochemical conditions necessary for sorption onto HFO
(e.g., pH ranges and resulting effects on sorption).
Tom suggested collecting samples and doing batch sorption tests with tailings fluids to
corroborate values calculated with HFO data (Note: This was discussed in more detail in
the September 2, 2009 meeting).
Source Term Chemistry
The source term concentrations for tailings fluids used in the model were discussed. The
DRC would like a statistical analysis performed on the data. Denison collected and
analyzed tailings fluids in 2007 and 2008 to address questions regarding mill process
water (DRC has not received this data because the data were collected for internal
purposes). Data from the University of Utah study were not used in this modeling effort
because the University of Utah study was not published until 2008, while the ICTM
report was submitted in 2007.
A sensitivity analysis will be performed with different source terms to evaluate the
effects of source concentrations on the overall predictions.
Modeling of Potential Leakage Through Liner
MWH discussed the approach used to model potential leakage through the liner. MWH
described the pseudo layer that was required in HYDRUS in order to simulate leakage
through the HDPE and PVC liners. The Giroud and Bonaparte method was used to
calculate leakage for a given head through the liner. The hydraulic conductivity was
adjusted in the pseudo layer until the flux was matched using the same head as was used
in the Giroud and Bonaparte calculations. These calculations need to be included in the
report (appendix). Given that the model considers the PVC and HDPE liners to be thin
4

for modeling purposes (30 mil and 60 mil, respectively) and have extremely low hydraulic
conductivity, the large contrasts in hydraulic conductivity over short distances, would
cause the model to be unstable and the solution would not converge. As a result, a thicker
layer (“pseudo layer”) with higher hydraulic conductivity was assumed. The layer
thickness used was 30 cm, but this was arbitrary. This layer could be any thickness, but
there is a corresponding hydraulic conductivity that is required for a given thickness to
match the calculated flux for a given head. As the thickness of the pseudo layer is
increased, the corresponding hydraulic conductivity must be increased to match the flux
for a given head on the liner. This layer was assumed to include no sorption so as not to
retard contaminants. (Note: As discussed in the September 2, 2009 meeting, we decided
to model leakage through the liners differently, and as a result, this pseudo layer is no
longer in the model).
Coupling of Models
MWH presented an overview of the modeling approach and linkage of models. The
DRC would like to see the modeling approach streamlined/simplified, if possible. This
would make it easier for DRC to explain to the public that the model results are
conservative, protective, and robust.
A flow chart will be added to the Report to clarify the purpose of each model and how the
inputs and outputs are related/coupled. Different models were required because there is
no single model that can simulate all required processes. Furthermore, the different time-
scales that act on different parts of the system resulted in much greater efficiency by
modeling the distinct parts of the system separately (e.g., cover model requires extremely
short time steps while the vadose zone model has longer time steps). Models that were
used simply to develop initial conditions (e.g., initial soil moisture distribution of the
tailings and bedrock vadose zone) will be moved to the appendices of the report to
improve readability. The report should clearly state how the output of one model is used
as the input to the next.
Another way to simplify the modeling would be to assume steady-state (average) flux rates
into the tailings as input into the lower HYDRUS model of the tailings/cell liner/bedrock
vadose zone.
The sensitivity analysis needs to be expanded to determine the parameters that are most
sensitive. This work should be documented in the appendices to keep the body of the
report streamlined.
Effects of Storm Intensity, Ponding, and Runon/Runoff
The effects of storm intensity, ponding, and 2-D/3-D effects of runon/runoff on
infiltration were discussed. The Report must explain why a 1-D model is sufficient rather
than a 2-D or 3-D model.
A series of sensitivity runs were discussed to evaluate storm intensity and ponding. To
test storm intensity, a short period of time should be modeled with hourly (or less)
precipitation and compared to the same precipitation entered as a daily value (as we have it
5

modeled). The water content and flux at specific nodes in the profile can be used to
compare the results. To evaluate ponding, a similar analysis can be performed. The
results of these sensitivity tests should be documented and included in the appendices.
Cell 1
Currently the plan is to place D&D materials from the decommissioning of the mill in
Cell 1. However, these materials could be placed in Cell 4A or 4B. Prior to placing the
D&D materials, the liner and any contaminated underlay (foundation) material from Cell
1 would be removed and placed in Cell 4A or 4B. A rad survey (with field
instrumentation and lab data for correlation) would be completed and any contamination
remaining would be remediated with the end goal being clean closure (soil cleanup
standard based on radium-226 and natural uranium). The Cell 1 area would be opened to
the west for surface water drainage. Then the 10-acre area on the southern side of Cell 1,
adjacent to the Cell 2 berm, would be lined with compacted clay. The D&D materials
(dry) would be placed on the clay liner and covered with an ET cover (extension of the
cap that will extend across the other cells). This needs to be included in the ICTM Report
and can be modeled by simulating Cell 1 with relatively dry tailings and a clay liner. We
could assume that the material would behave as a high permeability porous media (e.g.,
sand) at a concentration equivalent to the values used for the tailings. We could vary the
initial moisture content (i.e., -500 cm to -5,000 cm) as part of the sensitivity analysis.
Because the purpose of this model is to evaluate the effectiveness of the cover for the
closure period, the current pond in Cell 1 will not be simulated.
Other Items Discussed
The operational phase was not included in the HYDRUS simulations because the purpose
of the infiltration and contaminant transport modeling was to evaluate the effectiveness of
the cover. However, including the operational phase in the modeling was discussed.
The operational phase includes the period that the cells were in operation prior to
closure, which is assumed to run from 1980 (startup of Cell 2) through 2016 (completion
of Cell 4B filling). This may affect water and contaminant fluxes through the vadose
zone and to groundwater. After the operational period, an additional 200 years will be
simulated following closure of the cells.
The slimes drains in Cells 2 and 3 are "burrito drains", meaning sand has been placed in
an envelope over the drains, rather than in a continuous layer across the bottom of the
tailing cells. The 1-ft thick sand layer in the MODFLOW model did not extend across
the entire tailing cell area, but did cover the entire 400 ft by 600 ft drain area. The
MODFLOW model will be modified to simulate the drain system more accurately.
PATH FORWARD
We agreed that the path forward would involve preparing these minutes summarizing the
meeting (issues discussed and path forward/actions) and a draft response to the DRC's
comments. For comments that require additional work, the draft response can simply
include a statement as to how we will address the comment.
6

MWH will submit meeting minutes and a draft response to Denison in one week, then
Denison will submit these to DRC on April 23 (which date was later extended to April 30
for the draft response). We will have conference calls to discuss any items that are not
clear in our responses, rather than going back and forth with formal letters. Once DRC
agrees on our responses, we can revise the responses and submit a final response. The
ICTM Report will then be revised in accordance with the final response.
1

MINUTES FROM MEETING WITH UTAH DIVISION OF RADIATION
CONTROL (DRC) TO DISCUSS COMMENTS ON THE WHITE MESA
INFILTRATION AND CONTAMINANT TRANSPORT MODELING REPORT
Date: March 31, 2009
Time: l:00-6:00pm MDT
Location: Utah DRC Office (168 North, 1950 West, Salt Lake City, Utah)
Attendees: Utah DRC: Loren Morton and Thomas Rushing
Denison Mines (USA) Corp: Harold Roberts and Dave Frydenlund
MWH Americas: Doug Oliver, Ryan Jakubowski and Phil Crouse
The purpose of the meeting was to discuss the DRC's comments (dated February 2, 2009)
on the Infiltration and Contaminant Transport Modeling (ICTM) Report that was prepared
by MWH for Denison and submitted to the DRC in November 2007. These minutes are
intended to summarize the primary discussions and key decisions made during the
meeting. The order of items presented in this summary is not necessarily in the order
discussed at the meeting.
DISCUSSION ITEMS
Background
MWH presented an overview of the project including:
• Site description
• Project background / permit requirements
• Timeline
• Modeling overview
Many of the DRC's comments were discussed during this presentation.
Key Issues
Based on their review of the ICTM Report, the DRC identified the following list of "key"
issues:
1. Vegetation details to support the proposed evapotranspiration (ET) cover.
2. Sorption and retardation of contaminants of concern.
3. Source term concentrations for tailings fluids.
4. Modeling of potential leakage through liners.
2

5. Coupling of models and how output from one model is input into the next model.
6. Effects of storm intensity, ponding, and 2-D effects of runon/runoff on infiltration
through the ET cover.
7. Cell 1.
Primary matters discussed and decisions made regarding these key issues are presented
below.
ET Cover Design and Vegetation
The cover design as presented in the ICTM Report was preliminary and conceptual in
nature. The ET concept was adopted because it is more effective than the conventional
cover proposed in the reclamation plan. The Ground Water Discharge Permit specifically
allowed for design changes to improve cover performance. After the modeling is
completed, the cover design and reclamation plan can be revised, but the modeling should
come first. The cover can be engineered to meet the required performance standards.
The ICTM will be based on site-specific data where possible, and will rely on literature
values where necessary (Note: since the time of this meeting, additional site-specific data
have been collected). The DRC will review all final engineering designs and materials
specifications to ensure conformance with the modeled performance capabilities.
The DRC would like the report to include additional details concerning the vegetation
such as the proposed seed mix (plant species). Details that need to be justified and
supported for the modeling include rooting depth and root density distribution, percent
cover, vegetation density and LAI (leaf area index). Other considerations include soil
properties (e.g., soil types, salinity, organic content), longevity and competition with
woody species. A sensitivity analysis should be performed on vegetation parameters to
evaluate the effects these have on the model results. The DRC raised the need for cited
references from botanists and range scientists and the sensitivity analysis needs to
simulate long-term vegetation establishment (Note: the September 2, 2009 meeting
involved extensive discussion concerning long-term vegetation establishment, which will
be incorporated in the revised ICTM report).
Sorption and Retardation
The results of the materials testing (soil-water characteristic curves) need to be discussed
in more detail in the Report. Specifically, the Report needs to describe the samples that
were used and why these sample locations were selected and what they represent in the
model. During the meeting, MWH presented a simplified cross section showing the
sample locations relative to the tailings cells. This figure will be added to the ICTM
Report.
In regard to sorption and retardation, MWH provided DRC with the NRC/USGS
reference NUREG/CR-6820 (Davis and Curtis, 2003) which describes the approach used
to calculate sorption and retardation for the uranium mill tailings site at Naturita. The
NRC/USGS reference also describes a methodology used to measure the mass of HFO
(hydrous ferric oxide). We incorporated a similar approach for White Mesa. The
3

amount of ANP (acid neutralizing potential) and methodology used to measure the ANP
were discussed.
The DRC was concerned that there was not enough ANP and HFO data to adequately
represent the distribution in the vadose zone. Furthermore, the DRC thought that the
ANP values (which are relatively low), don't appear to match the geochemical modeling
that shows significant acid neutralization. During the meeting it was noted that MWH
will look into this. Following the meeting we noted that this discrepancy may be
explained by the normalization procedure incorporated as part of the PHREEQC
modeling.
Options to consider include:
• collecting more HFO and ANP data to better represent vadose zone materials, or
• doing a sensitivity analysis (reduce sorption by one or more orders of magnitude)
to evaluate the effects of this uncertainty/variability on the model results.
The geochemical modeling used to calculate the sorption coefficients needs to be
described more clearly in the Report (details were provided in Appendix B). The Report
needs to state the prerequisite geochemical conditions necessary for sorption onto HFO
(e.g., pH ranges and resulting effects on sorption).
Tom suggested collecting samples and doing batch sorption tests with tailings fluids to
corroborate values calculated with HFO data (Note: This was discussed in more detail in
the September 2, 2009 meeting).
Source Term Chemistry
The source term concentrations for tailings fluids used in the model were discussed. The
DRC would like a statistical analysis performed on the data. Denison collected and
analyzed tailings fluids in 2007 and 2008 to address questions regarding mill process
water (DRC has not received this data because the data were collected for internal
purposes). Data from the University of Utah study were not used in this modeling effort
because the University of Utah study was not published until 2008, while the ICTM
report was submitted in 2007.
A sensitivity analysis will be performed with different source terms to evaluate the
effects of source concentrations on the overall predictions.
Modeling of Potential Leakage Through Liner
MWH discussed the approach used to model potential leakage through the liner. MWH
described the pseudo layer that was required in HYDRUS in order to simulate leakage
through the HDPE and PVC liners. The Giroud and Bonaparte method was used to
calculate leakage for a given head through the liner. The hydraulic conductivity was
adjusted in the pseudo layer until the flux was matched using the same head as was used
in the Giroud and Bonaparte calculations. These calculations need to be included in the
report (appendix). Given that the model considers the PVC and HDPE liners to be thin
4

for modeling purposes (30 mil and 60 mil, respectively) and have extremely low hydraulic
conductivity, the large contrasts in hydraulic conductivity over short distances, would
cause the model to be unstable and the solution would not converge. As a result, a thicker
layer (“pseudo layer”) with higher hydraulic conductivity was assumed. The layer
thickness used was 30 cm, but this was arbitrary. This layer could be any thickness, but
there is a corresponding hydraulic conductivity that is required for a given thickness to
match the calculated flux for a given head. As the thickness of the pseudo layer is
increased, the corresponding hydraulic conductivity must be increased to match the flux
for a given head on the liner. This layer was assumed to include no sorption so as not to
retard contaminants. (Note: As discussed in the September 2, 2009 meeting, we decided
to model leakage through the liners differently, and as a result, this pseudo layer is no
longer in the model).
Coupling of Models
MWH presented an overview of the modeling approach and linkage of models. The
DRC would like to see the modeling approach streamlined/simplified, if possible. This
would make it easier for DRC to explain to the public that the model results are
conservative, protective, and robust.
A flow chart will be added to the Report to clarify the purpose of each model and how the
inputs and outputs are related/coupled. Different models were required because there is
no single model that can simulate all required processes. Furthermore, the different time-
scales that act on different parts of the system resulted in much greater efficiency by
modeling the distinct parts of the system separately (e.g., cover model requires extremely
short time steps while the vadose zone model has longer time steps). Models that were
used simply to develop initial conditions (e.g., initial soil moisture distribution of the
tailings and bedrock vadose zone) will be moved to the appendices of the report to
improve readability. The report should clearly state how the output of one model is used
as the input to the next.
Another way to simplify the modeling would be to assume steady-state (average) flux rates
into the tailings as input into the lower HYDRUS model of the tailings/cell liner/bedrock
vadose zone.
The sensitivity analysis needs to be expanded to determine the parameters that are most
sensitive. This work should be documented in the appendices to keep the body of the
report streamlined.
Effects of Storm Intensity, Ponding, and Runon/Runoff
The effects of storm intensity, ponding, and 2-D/3-D effects of runon/runoff on
infiltration were discussed. The Report must explain why a 1-D model is sufficient rather
than a 2-D or 3-D model.
A series of sensitivity runs were discussed to evaluate storm intensity and ponding. To
test storm intensity, a short period of time should be modeled with hourly (or less)
precipitation and compared to the same precipitation entered as a daily value (as we have it
5

modeled). The water content and flux at specific nodes in the profile can be used to
compare the results. To evaluate ponding, a similar analysis can be performed. The
results of these sensitivity tests should be documented and included in the appendices.
Cell 1
Currently the plan is to place D&D materials from the decommissioning of the mill in
Cell 1. However, these materials could be placed in Cell 4A or 4B. Prior to placing the
D&D materials, the liner and any contaminated underlay (foundation) material from Cell
1 would be removed and placed in Cell 4A or 4B. A rad survey (with field
instrumentation and lab data for correlation) would be completed and any contamination
remaining would be remediated with the end goal being clean closure (soil cleanup
standard based on radium-226 and natural uranium). The Cell 1 area would be opened to
the west for surface water drainage. Then the 10-acre area on the southern side of Cell 1,
adjacent to the Cell 2 berm, would be lined with compacted clay. The D&D materials
(dry) would be placed on the clay liner and covered with an ET cover (extension of the
cap that will extend across the other cells). This needs to be included in the ICTM Report
and can be modeled by simulating Cell 1 with relatively dry tailings and a clay liner. We
could assume that the material would behave as a high permeability porous media (e.g.,
sand) at a concentration equivalent to the values used for the tailings. We could vary the
initial moisture content (i.e., -500 cm to -5,000 cm) as part of the sensitivity analysis.
Because the purpose of this model is to evaluate the effectiveness of the cover for the
closure period, the current pond in Cell 1 will not be simulated.
Other Items Discussed
The operational phase was not included in the HYDRUS simulations because the purpose
of the infiltration and contaminant transport modeling was to evaluate the effectiveness of
the cover. However, including the operational phase in the modeling was discussed.
The operational phase includes the period that the cells were in operation prior to
closure, which is assumed to run from 1980 (startup of Cell 2) through 2016 (completion
of Cell 4B filling). This may affect water and contaminant fluxes through the vadose
zone and to groundwater. After the operational period, an additional 200 years will be
simulated following closure of the cells.
The slimes drains in Cells 2 and 3 are "burrito drains", meaning sand has been placed in
an envelope over the drains, rather than in a continuous layer across the bottom of the
tailing cells. The 1-ft thick sand layer in the MODFLOW model did not extend across
the entire tailing cell area, but did cover the entire 400 ft by 600 ft drain area. The
MODFLOW model will be modified to simulate the drain system more accurately.
PATH FORWARD
We agreed that the path forward would involve preparing these minutes summarizing the
meeting (issues discussed and path forward/actions) and a draft response to the DRC's
comments. For comments that require additional work, the draft response can simply
include a statement as to how we will address the comment.
Deleted: This will be addressed in the
response.
6

MWH will submit meeting minutes and a draft response to Denison in one week, then
Denison will submit these to DRC on April 23 (which date was later extended to April 30
for the draft response). We will have conference calls to discuss any items that are not
clear in our responses, rather than going back and forth with formal letters. Once DRC
agrees on our responses, we can revise the responses and submit a final response. The
ICTM Report will then be revised in accordance with the final response.