DRC-2011-002829 - 0901a068802120ef

State of Utah
GARY R. HERBERT
Governor
GREGBELL
Lieutenant Governor
March 21, 2011
Department of
Environmental Quality
Amanda Smith
Executive Director
DIVISION OF RADIATION CONTROL
Rusty Lundberg
Director
RC-2011-0028
CERTIFIED MAIL
(Return Receipt Requested)
David C. Frydenlund, Vice President, Regulatory Affairs and Counsel
Denison Mines (USA) Corp.
1050 17'*^ Street, Suite 950
Denver, CO 80265
Subject: February 18, 2011 Denison Mines (USA) Corporation, "Work Plan and Schedule for
SupplementarContarninant Investigation Report for White'Mesa Mill Nitrate "
Investigation": DRC Review Comments
Dear Mr. Frydenlund:
DRC Review comments regarding the February 18, 2011 Denison Mines (USA) Corporation (DUSA)
"Work Plan and Schedule for Supplemental Contaminant Investigation Report for the White Mesa Mill
Nitrate Investigation (Work Plan), are enclosed. The review and comments were prepared by URS
Corporation per contract agreement with the DRC.
Please note that the comments present a dynamic approach to completing the work plan, including the
development of a conceptual site model (CSM) and a phased approach to contaminant source investigation,
including water and sediment sampling. This dynamic approach was not anticipated by the DRC/DUSA
tolling agreement signed and executed on 12/15/2010.
Item 6 of the 12/15/2010 tolling agreement states, "This Agreement shall terminate on the earlier of (a)
April 30, 2011 ("Automatic Termination Date") unless extended by prior written agreement executed by
the parties; and (b) the date of execution and delivery of the revised or replacement Consent Agreement
contemplated by paragraph 5 above." Therefore, a meeting (or telephone conference call) amongst DRC,
DUSA and URS staff is necessary, and needs to be arranged as soon as possible to determine a schedule
for DUSA revision of the Work Plan and anticipated timelines to execute a revised Consent Agreement.
We suggest this meeting or call take place during the week of April 4, 201,1. Please contact me at (801)
536-0080 to arrange a time for the meeting or call.
Since^fify,
Tf^m Rushing,
'^Geotechnical Services Section
F:\DUSA\Nitrale Contamination hivesligation\URS Nitrate Work Plan Comments\WorkplanReviewCommentsTransmittalLtr.doc
t95 North 1950 West • Sait Lake City, UT
Mailing Address: P.O. Box 144850 • Salt Lake City, UT 84114-4850
Telephone [phone]'Fax [phone] 'T.D.D. [phone]
www.deq.utah.gov
Printed on 100% recycled paper
URS
MEMORANDUM
To: Tom Rushing (DRC), Loren Morton (DRC), Phil Goble (DRC)
Fi^om: Paul Bitter (URS), Jeremy Cox (URS), Michael J. Singleton (SC)
cc: i Robert Baird (URS)
ijate:^;' 21 March 2011
Re: Comments on Work Plan and Schedule for Supplemental Contaminant Investigation
Report for White Mesa Mill Nitrate Investigation dated Feb. 18, 2011
This memorandum contains the URS and DRC comments on the Work Plan and Schedule for
Supplemental Contaminant Investigation Report for White Mesa Mill Nitrate Investigation (Work
Plan) dated Feb. 18, 2011, which was prepared for Denison Mines USA (DUSA) by Intera
Corporation. This review has been performed as a deliverable for Contract No. 116259 issued
through the Utah Department of Environmental Quality, Division of Radiation Control (DRC).
This review also is in accordance with the Memorandum of Understanding (MOU) between the
DRC and DUSA dated February 17, 2011. For purposes of expediency, the URS and state
comments are edited for conciseness and combined into one memo.
The review of the Work Plan has been informed by the following documents:
Summary of work completed, data results, interpretations and recommendations for the
July 2007 Sampling Event at the Denison Mines, USA, White Mesa Uranium Mill Near
Blanding, Utah, prepared by T. Grant Hurst and D. Kip Solomon of the Department of
Geology and Geophysics at the University ofUtah, subinitted May 2008.
Nitrate Contamination Investigation Report, White Mesa Uranium Mill Site, Blanding,
Utah, prepared by Intera Corporation, dated December 30, 2009.
- The "Notice of Additional Required Action Letter" (NOTICE) dated October 5, 2010
from DRC to DUSA regarding DRC review of the 2009 report.
- The letter dated November 15, 2010 from DUSA to DRC responding to the NOTICE
listed above.
A spreadsheet of monitoring well construction data (DUSA WELLCOMP.xls) and as-
built reports for monitoring wells provided to URS by DRC on February 28, 2011.
DRC and URS have reviewed the Work Plan with the support of Michael Singleton, Ph.D., of
Singleton Consulting. Dr. Singleton has approximately 14 years of experience in stable isotope
and geochemical data analysis, including the application of this experience to the assessment of
recharge and impacts to groundwater from human and animal waste. Dr. Singleton is the author
or co-author of 17 published papers. His qualifications are available upon request.
Page 1 of 13 URS
The comments regarding the Work Plan are presented below.
In summary, our reviews siiggest the following: 1) a dynamic conceptual site model should be
produced in the work plan based on current information; 2) the model should be updated during
the investigation to include results of samples analyzed in accordance with the work plan, 3) more
potential sources should be analyzed to test the hypotheses regarding nitrate sources, 4) isotopic
analyses for sulfur and oxygen in sulfate should supplement the proposed isotopic analyses of
nitrate and water to better distinguish potential sources, and 5) the sampling be conducted in more
than one phase so the results can be discussed during a conference call with DRC, URS, and
Michael Singleton for the purpose of conducting further phase(s) of investigation with focus arid
efficiency.
1. General Comment: The 2009 Nitrate Contamination Investigation Report (CIR) attempted to
present a conceptual site model (CSM) to explain the presence of elevated levels of nitrate
and chloride in the groundwater beneath the mill. Although it was not referred to as a "CSM"
in that report, the CSM displays the possible formation of the nitrate/chloride plume in the
center of the property due to one potential source. Since submittal of the CIR, DUSA has
brought forward two other explanations and potential sources of the nitrate and chloride
contamination in meetings with the DRC. Other potential sources (see comment #2 below)
were not fully evaluated in the CSM in the 2009 Nitrate CIR. Ideally, a CSM that comprises
plan and cross section depictions of potential sources should provide the following evaluation
structure, documentation and conclusions regarding potential sources of the plume:
a. Each potential source, described in text and shown on one or more figures; the figure(s),
should be supplemented with site-specific chemical, lithological, hydrogeological, and
physical data that affect the fate and transport of source material.
b. The physical and chemical means and pathways by which the potential source could be
conveyed to the present location of contamination, described in text and displayed in the
conceptual drawings.
c. Discussion of the analytical and geological data that are available and displayed ori one or
more of the figures to support the potential source of the nitrate and chloride
contaminants in groundwater; data that do not support the potential source of the
contaminants also can be displayed to eliminate a potential source.
d. Discussion of the analytical and geological data that are lacking (i.e., data gaps) in the
evaluation of the potential source's fate and transport.
e. Description ofthe data that will be generated during the investigation that will be used to
update the CSM.
The Work Plan should present the CSM with the attributes discussed above, near the
beginning of the document, with all of the successive sections discussed in terms of how the
sections contribute to the structure ofthe CSM. The details of the CSM are discussed in the
following coniments.
2. General Comment: All potential sources, for the nitrate and chloride contamination in the
groundwater beneath the mill site must be addressed by the CSM. It is noted and accepted
Page 2 of 13 URS
that one potential source of the nitrate and chloride, the Frog Pond, was dismissed by DRC in
the October 2010 NOTICE and that Denison did not produce any additional evidence for that
potential source in the November 2010 letter responding to the NOTICE. An additional
source, upgradient of the DUSA property, was also dismissed in the 2009 Nitrate
Contamination Investigation Report as being too far from the plume at the center of the
property to possibly be the source of the plume due to the time required for groundwater to
travel from the northem boundary of the site to the center of the property. The DRC requires
that the CSM identify three (or more if practical) potential sources for the elevated
concentrations of nitrate and chloride that were outlined in the 2009 Nitrate CIR and the
November 2010 DUSA memo: namely, (1) naturally-occurring deposits of nitrate and
chloride in the vadose zone mobilized by recharge from the wildlife ponds or other locations,
such as Lawzy Lake (the "New Theory"), (2) possible soil / groundwater contamination
caused by the US Army missile activities on or near White Mesa, and (3) activities in or
around the mill site, including the leach fields, historical stock watering ponds, and other
potential source areas. The latter would be sub-divided into multiple potential source areas,
as listed in the source review report in the 2009 Nitrate CIR. The three potential sources
could be contributing individually or in combination to the current nitrate and chloride
plumes.
Throughout the work plan, figures, maps and cross sections discussed in comment #1, should
be cited as appropriate. The figures must provide the current hydrogeologic understanding of
contaminant sources and their fate and transport at the site. Specifically, DUSA needs to
provide the following regarding the development of maps and cross sections:
a. All potential sources.
b. For cross-sections, the soil types at each depth interval in the subsurface along the path of
the cross-section, based on the available boring logs for at least five wells or sampling
locations.
c. For cross-sections, the depth to groundwater and the direction of groundwater flow; for
maps, the direction of groundwater flow.
d. All relevant analytical data for soil at the locations shown on the maps and cross-sections.
e. All relevant analytical data for groundwater at the locations shown on the maps, with the
current plume boundaries depicted on the cross-section.
f All relevant site features at the surface along the path of the cross-sections or in the view
of the map.
g. A minimum of two cross-sections should be generated: one roughly north to south, and
one roughly east to west.
General Comment: The Work Plan should be structured in such a way that each component
of the Work Plan presents a hypothesis relative to proving or disproving each potential source
of nitrate contamination, methods and measurements to test each hypothesis, including the
purpose of sample collections and analysis, and specific criteria to determine whether each
hypothesis has been verified. A "weight of evidence" approach using multiple data to test or
support a hypothesis should be employed whenever possible when evaluating hypotheses.
Page 3 of 13 URS
5. General Comment: DUSA must provide DRC with written notice at least two weeks prior to
the beginning of each phase of field work associated with the investigation to allow for DRC
observation of field work. The cost of the DRC observation of field work will be borne by
DUSA.
6. Section 4.1, third paragraph: Figures 12 through 14, which are referenced in this paragraph,
identify a historical stock watering pond that, upon comparison to Figure 15, is located on the
south end of the investigation area, approximately half a mile southeast of MW-20 (near
MW-22). The Work Plan should explain the purpose of identifying this pond. If this pond is
illustrated in these figures as part of a response to DRC's discussion of nitrate concentrations
in groundwater downgradient of the site in the October 2010 NOTICE, then such a response
should be presented in the framework of the CSM and in the context of a hypothesis (e.g., a
historical stock watering pond is the source of the elevated nitrate concentrations in MW-20).
Then data that support or refute the hypothesis, and DUSA's conclusion, based on the weight
of evidence, should be identified in the work plan.
7. Section 4.1, last paragraph and Section 4.2, last paragraph: The assertion of a "strong
potential for military operations on White Mesa that may have led to some or all of the
observed present-day groundwater contamination problems" is a statement that should be
presented as a hypothesis in the work plan and analytical methods should be identified to test
the hypothesis, as discussed above. A calculation of the mass of nitrate in the groundwater
beneath the mill, as discussed in the 2009 Nitrate CIR, demonstrates that a significant mass of
nitrate is present in the saturated zone beneath the mill. It is not clear that launching rockets
from the property is likely to have contributed a significant mass of ammonium or nitrate to
the subsurface. Unlike static rocket motor testing with quenching through waiter jets, there
would be no mechanism to transport the contaminants to the saturated zone during rocket
launches. Further, the presumed location of the launches is reported to be downgradient of
the current location of the plume. There currently is no historical evidence that would
identify the location or nature of support activities associated with the rocket launches. If
DUSA wishes to test the hypothesis that missile operations may have served as source of
nitrate contamination, then the DRC requests that the groundwater at the site be analyzed for
perchlorate. The Pershing rocket motors likely would have contained some amount of
perchlorate that would have been transported to the saturated zone with the other components
of the rocket fuel. The determination as to whether this potential source will be examined
needs to be included in the Work Plan now. If it is to be included, full details regarding the
examination must be provided. If DUSA elects to eliminate past military activities as a
source of nitrate and chloride, this decision will be considered final by the DRC.
8. Section 5.0, last paragraph: The 2005 study that is referenced supposedly cites
concentrations with units of milligrams per liter. The text characterizes the concentrations as
concentrations in soil, which should be in units of mass only. The units and results more
likely reflect the leachable concentrations of nitrogen measured during the leachate tests
conducted on the soil samples. Please resolve the discrepancy, and clarify what the
concentrations of nitrate represent in this and other leachate-test discussions in the work plan.
Page 4 of 13 URS
9. Section 5.1, first paragraph: DRC agrees that some Geoprobe sampling of a naturally-
occurring source of nitrate in the vadose zone is warranted for undisturbed areas during the
investigation, providing that the number of samples is^sufficient to characterize a potential
source and its fate and transport. The proposed number of samples has not been explained or
justified in the work plan. DRC requests that DUSA provide a statistical basis for the number
of Geoprobe sample locations in the undisturbed areas in this section ofthe work plan.
10. Section 5.1, Step 7: If multiple soil lithologies are visible within the one-foot core, one
sample shall be collected and analyzed from each lithology. Please revise the sampling
procedure accordingly.
11. Section 5.1, Step 10: Please provide the source (i.e., agency) of the SPLP procedure and
method number and repeat this information in the footnote to Table 2.
12. Section 5.2: The expected minimum number of borings must be listed in this section. Table
1 indicates that up to four borings are planned. The work plan should be constructed such
that the number and depth of bedrock borings will be based on the number and results of
Geoprobe sampling locations finally determined necessary to test the nitrogen reservoir
hypothesis, and subject to DRC approval prior to commencement of further drilling.. .
13. Section 5.2, first paragraph: Background for the facility shall be determined by the 95%
upper confidence level on the mean (95% UCL) of all 20 "background" samples collected
from soil sampling locations in undisturbed areas (not altered by anthropogenic activities)
and will be subject to DRC approval. Admittedly, some flexibility should be incorporated
into the decision to core into consolidated material based on the overall results of the
Geoprobe investigation. However, decisions to drill should be made jointly with DRC and
should be reflected in the process flow diagram included in the work plan. The decision to
bore further may benefit from a calculation of the concentration of nitrate in the soil that is
expected to result in a groundwater concentration exceeding the compliance standard for
nitrate (i.e., a soil to groundwater screening level).
14. Section 5.2, fourth and fifth paragraphs: DUSA desires to test the hypothesis that naturally-
occurring deposits of nitrate and chloride in the unsaturated zone are contributing to the
elevated concentrations of these compounds in the saturated zone beneath the mill. DRC
requests that an additional sample be collected in the unconsolidated interval that contains the
highest concentration of nitrate, as determined by the results of the Geoprobe investigation,
for each drilling location. The additional sample should be analyzed for nitrate isotopes
(nitrogen and oxygen) in addition to the nitrate and chloride analyses via the synthetic
precipitation leaching procedure (SPLP) prescribed in the work plan. The characterization of
the nitrate isotopes in these deposits, if present, will assist in determining whether the nitrate
in the groundwater may have originated from the deposits.
15. Section 5.2: DRC requests that DUSA ensure that enough soil is collected from each interval
to allow for the SPLP analyses for nitrate and chloride and for isotope analyses for sulfate
and nitrate (see comments regarding isotope analyses below). DUSA must confirm the
required sample volumes with the contract laboratory and list the required volumes in this
section of the Work Plan.
Page 5 of 13 URS
16. Section 6.1: Geoprobe sampling around the potential source areas in themill area is
warranted. However, two of the potential source areas listed with a high priority for
investigation in the source review report (Attachment 2 of the 2009 Nitrate CIR) were not
included in the list of source investigation areas. These two areas are the historical stock
watering pond (near the current location of the sulfuric acid tank) and the northem wildlife
pond. DRC requests that these two areas be added to the list of potential source areas in
Section 6.1, and included in the CSM discussion.
17. Section 6.1: Including the chlorate tanks as a potential source of nitrate may be incorrect.
^ Based on the information in the source review report, the tanks hold sodium chlorate. Ifthe
tanks are being investigated as a source of chloride in groundwater, they should be
characterized as a potential source of chloride. If the tanks have historically held ammonium
chlorate, then this should be noted with the entry for the chlorate tanks as a potential source
for nitrate. If the tanks have never held ammonium chlorate and are not considered a potential
source for nitrate in the groundwater based on operating records, then this potential source
area should be deleted from the list of investigation areas.
18. Figure 21: The red line for a potential nitrate or chloride source and the red outline for a leach
field scheduled for investigation are indistinguishable. As a result, it is not possible to
determine from Figure 21 which areas were potential sources that have been determined not
to warrant any investigation. DRC requests that the coloring for these two categories of areas
in Figure 21 be revised to make the figure legible.
19. Section 6.1, fourth and fifth paragraphs: DRC disagrees with the assertion that no subsurface
soil sampling is necessary at the two active leach fields if the current influent to the leach
fields is sampled. The current content of the influent to the leach fields could be very
different from the influent to the leach fields twenty or thirty years ago. DRC requests that
subsurface soil sampling should occur at these locations and should be supplemented by, not
replaced by, analyses of the influent to the leach field. Performing direct push sampling in
several locations within the unconsolidated (shallow) interval in the active leach fields will
not create preferential pathways for waste water to reach the groundwater table, particularly if
the boreholes are sealed with bentonite as stated in the work plan. DRC agrees with the
sampling of the waste water and the use of a mass balance as outlined in this paragraph.
20. Section 6.1, fourth paragraph and Section 6.2 first paragraph: The text in these sections
appears to differ regarding which leach fields (SAG leach field or CCD/SX leach field) are
active. Please cl£irify.
21. Section 6.1: The minimum number of proposed mill site"Geoprobe borings should be listed
in this secfion. Table 1 indicates that as many as 13 borings are planned. As discussed
above, the number of mill site borings must be statisfically proportionate with the number of
shallow borings drilled in undisturbed areas to determine background nitrate / chloride soil
content. The current maximum of 13 appears to correspond to one boring per inactive
potential source area. One boring per potential inactive source area is inadequate
characterization of these areas. In addition, the active areas should be sampled (see comment
#19). DRC requests two Geoprobe sample locations for each potential source area that was
Page 6 of 13 URS
rated as a low priority in the source review report (Attachment 2 ofthe 2009 Nitrate CIR) and
four Geoprobe sample locations for each of the sources rated as a high priority or those
regarded as likely contributors to the nitrate contamination in the source review report. This
corresponds to two Geoprobe sampling locations in each of nine areas (sewage vault/lift
stafion, former vault/lift station, ammonia tanks. Cell 1 leach field, fly ash pond, chlorate
tanks [assuming this area is retained], ammonium sulfate tanks, truck shop leach field, and
CCD/SX leach field), and four Geoprobe sampling locations in each of eight areas (scale
house leach field, former office leach field, northem wildlife pond, Lawzy Lake, Lawzy
sump, the historic pond in the location of the sulfuric acid tank, the SAG leach field, and the
main leach field) for a total of 50 Geoprobe locations at potential source areas in and around
the mill site. In addition, the list of sampling locations shall include, but not be limited to, all
of the potenfial sources listed on Figure 21 of the Work Plan. The proposed sampling
locations must be shown on a figure in the Work Plan.
22. Secfion 6.1, Step 3: The number of samples analyzed from each Geoprobe sample locafion
within the mill site differs from the number of samples proposed for each Geoprobe sampling
location in the undisturbed areas. Please jusfify the difference in the number of samples per
location between the two areas. If the current text for Step 3 is not changed to match the
procedure for the undisturbed area, please specify the criteria for which two intervals within
the alluvial material are to be sampled for the Geoprobe sampling locafions at the mill site for
review by the DRC.
23. Section 6.2, first paragraph: It is unclear whether the procedure for determining whether
nitrate concentrations are "elevated" is the same as that stated in Secfion 5.2. This section
specifies that the procedures for drilling and sampling are idenfical to those described in
Secfion 5.2, but does not explicitly state that the criteria for drilling at a location are the same.
Please clarify.
24. Section 6.2, first paragraph: DRC disagrees with the categorical exclusion of coring in the
active leach fields. This exclusion seems to be based on the theory (presented in Secfion 6.1)
that the drilling would create preferenfial pathways for wastewater fluids to reach the
saturated zone. DRC agrees that the deep drilling within the vadose zone underneath active
leach fields could potentially create contaminant transport pathways to groundwater.
However, the creation of pathways may be minimized by the procedures for backfilling the
borings described in Section 5.2. DRC requests that the decision whether to drill in the active
leach fields (if elevated concentrations of nitrate are discovered in the unconsolidated
material) should be deferred pending further discussion with DRC after analyfical data are
available from the Geoprobe sampling and are assessed, rather than pre-emptively ruling out
drilling in these areas The Work Plan must present the process for evaluating the analytical
data from the Geoprobe sampling and determining whether deep coring is required.
Consultation with, and approval of, the DRC regarding the decision to drill and the drilling
locations must be part of the process presented in the work plan. The general planned
locations for coring, if required, must be included in the work plan.
Page 7 of 13 URS
25. Section 6.2, first paragraph: In order to test the hypothesis that elevated concentrations of
nitrate and chloride in the unsaturated zone due to milling acfivifies are contributing to the
elevated concentrafions of these compounds in the saturated zone beneath the mill, DRC
requests that an addifional sample be collected in the unconsolidated interval with the highest
concentrafion of nitrate, as determined by the results of the Geoprobe investigafion, for each
drilling locafion, and that a nitrate isotope analysis (nitrogen and oxygen) be performed on
these samples in addifion to the nitrate and chloride analyses via the SPLP. The
characterization of the nitrate isotopes in these locafions, if elevated concentrations are
present, will assist in determining whether the nitrate in the groundwater may have originated
from these acfivities.
26. Secfion 6.2: DRC requests that DUSA ensure that enough soil is collected from each interval
to allow for the SPLP analyses for nitrate and chloride and for isotope analyses for sulfate,
nitrate, and water (see comments regarding isotope analyses below). DUSA must confirm the
required sample volumes with the contract laboratory and list the required volumes in this
secfion of the Work Plan.
27. Secfion 6.2, first paragraph: DRC agrees that drilling of 13 bedrock drilling locations should
be sufficient to characterize the concentrations of nitrate and chloride in the deeper vadose
zone. Although many potential source areas have been idenfified, DRC anticipates that many
of the potenfial source areas will not contain elevated concentrafions of nitrate and chloride.
Accordingly, the decision of how many bedrock drilling sites selected at the mill site must be
determined after consultation and approval of the DRC.
28. General comment: The work plan must state that all Geoprobe and drilling locafions will be
logged by a qualified, Utah Licensed Professional Geologist. Photographs of soil cores are
recommended. The boring logs should be recorded on a form similar to that used for borehole
WMMW-16 that was included in the as-built reports for the wells around the tailings ponds.
The lithological (boring) logs for the installafion of the nitrate wells in October 2009 did not
provide all of the necessary information or may not have a location to provide necessary
informafion, such as sampling intervals, survey data, and other details, and appear to
inconsistently show whether the alluvial materials are consolidated or unconsolidated. This
problem in record keeping is unacceptable. Please revise the field forms to provide a
complete and comprehensive record of field activities and the information required.
29. Section 7: DRC and URS request the identification of addifional locations for isotope
analysis in order to better characterize the source(s) of the nitrate contaminafion in
groundwater. Only six wells are scheduled to be sampled for stable isotopes of nitrate and
water. Only two of these are within the Mill Site - too few to assess the nitrate sources in
this area. Please revise the location and number of groundwater isotope samples to be
' collected on the mill site to provide statistical power, and be representafive of the
groundwater quality. There may be multiple sources and locafions contributing to the nitrate
plume below the Mill Site. In addifion, only one of the wells (MW-31) scheduled to be
sampled for stable isotopes was also sampled in the Hurst and Solomon (2008) study.
Additional wells should be sampled for stable isotopes that were part of the Solomon study in
Page 8 of 13 URS
order to leverage the valuable groundwater age data from that study in identifying nitrate
sources. Wells MW-19 and MW-27 are especially important to include since they are
presumed to represent recharge from the Wildlife Ponds. Well MW-30 should also be
included to increase the coverage of high nitrate groundwater below the Mill Site where
groundwater age is known. Well TW4-24 should be included because it has contained the
highest recorded concentrations of nitrate and chloride in groundwater at the site and is
located adjacent to the mill site. Addifionally, stable isotope analysis should be performed at
TW4-4, which is located in a separate "lobe" of the nitrate plume and is also located within
the chloroform plume. Finally, the influent to the sewage vaults and the acfive leach fields,
like the slimes drain of tailings cell 2, should be sampled to characterize the isotope signature
of any nitrogen compounds used in mill processing acfivities and released into wastewater
streams. Therefore, DRC requests that MW-19, MW-27, MW-30, TW4-4, TW4-24, contents
of sewage vaults, the influent to the main leach field, and the influent to all other acfive leach
fields be added to the list of locafions in Section 7 for stable isotope analyses of nitrate and
water. The list of acfive leach fields and sewage vaults shall include, but not be limited to, all
acfive leach fields and sewage vaults shown on Figure 21 ofthe Work Plan.
30. Section 7: In addition to the stable isotope analyses for groundwater, nitrate from samples of
vadose zone soils, from both undisturbed areas and potential source areas within the mill site,
should be analyzed for stable isotope composition as discussed in comments #14 and #25
above; i.e. nitrogen and oxygen isotopes of nitrate found in the soil / rock matrix and/or pore
fluids / groundwater. Such samples are critical for establishing the isotopic signature of
nitrate sources in the vadose zone at this site. Isotope analyses should also be conducted on
1:1 disfilled water leaches of core samples.
31. Secfion 7 and Table 2: (a) Two methods are currently used to determine oxygen and
nitrogen isotope compositions in dissolvedjiitrate. The first methodL(Ion Exchange Method)
uses ion exchange columns to separate nitrate from cations present in the sample, and then
uses chemical treatments to remove sulfate and organic compounds before producing a silver
nitrate salt that is then analyzed by combustion/pyrolysis of the salt to produce N2 and CO
gas which is analyzed by isotope rafio mass spectrometry (Silva et al., 2000). The lab
identified in the work plan (Isotech) uses this Ion Exchange Method. A more recent method
(Denitrifier Method) uses a particular strain of denitrifying bacteria to produce N20 gas
from nitrate in the water sample, which is then analyzed by isotope ratio mass spectrometry
(Sigman et al., 2001; Caciotfi et al., 2002). The study proposed for DUSA would benefit
from using a lab capable of carrying out the Denitrifier Method to determine oxygen and
nitrogen isotope compositions in dissolved nitrate for two reasons. 1) The Denitrifier Method
requires much less sample volumes and lower concentrations than the lon Exchange Method.
This will make it possible to analyze the small samples collected from disfilled water leached
from sediment core samples. 2) The Ion Exchange method can give erroneous results for
oxygen isotope compositions in nitrate if the sulfate is not completely removed from the
sample before producing the silver nitrate salt. If this occurs, both nitrate and sulfate oxygen
contribute to the oxygen isotope composition of the salt produced, thus incorrectly identifying
Page 9 of 13 URS
the nitrate source. Interference from sulfate is a particular concem at this study site, since
sulfate concentrations are much higher than typical groundwaters. Please resolve this
problem in the work plan.
References Cited:
Silva, S.R., Kendall, C, Wilkison, D.H., Ziegler, A.C., Chang, C.C, and Avanzino, R.J,
2000. A new method for collection of nitrate from fresh water and the analysis of
nitrogen and oxygen isotope ratios, J. of Hydrology, 228: 22-36.
Sigman, D.M., Casciotfi, K.L., Andreani, M., Barford, C, et al. (2001) A bacterial
method for the nitrogen isotopic analyses of nitrate in seawater and fresh water. Anal.
Chem., 73, 4145-4153.
Casciotfi, K.L., Sigman, D.M., Hastings, M.G., Bohlke, J.K. et al. (2002) Measurement
of the oxygen isotopic composition of nitrate in seawater and freshwater using the
denitrifier method, Anal. Chem., 74, 4905-1226.
(b) Some laboratories that may perform isotopic analyses for nitrate may not be able to
perform isotopic analyses for ammonium. Wastewater samples (see corriment #29) may
contain primarily ammonium rather than nitrate. Please determine whether the majority of
the nitrogen in the wastewater streams is in the form of ammonium or nitrate. Ifthe majority
is present as ammonium, confirm that the laboratory has the ability to perform isotopic
analyses for ammonium, and adjust the work plan to indicate that the wastewater samples will
have isotopic analyses for ammonium rather than nitrate.
32. Secfion 7: It is not clear which sources will be differenfiated using the isotope compositions
of nitrate. There is a possibility that isotopic signatures of nitrate from ammoniuiri
compourids used in processing at the Mill Site may be similar to those of nitrate derived from
septic effluent and treated waste water effluent. Typically, these ammonium sources have
higher delta-15N values than natural pools of nitrate in the soil zone, but as noted, the ranges
for these sources can also overlap in both nitrogen and oxygen isotope corinposifion. It is
likely that stable isotope analyses of nitrate may be useful for testing the hypothesis that
nitrate below the Mill Site is due to mobilization of a natural pool of nitrate in the unsaturated
soil zone vs. contamination by an ammonium source. However, there are numerous potential
ammonium sources (wastewater effluent, septic effluent, ammonium processing chemicals),
which lead to nitrate with similar isotopic signatures. It is unlikely that stable isotope
analyses of nitrate will allow for differentiation of the various ammonium sources.
Denitrificafion can further complicate the use of nitrate isotope compositions for idenfifying
source compositions by enriching residual nitrate in the isotopically heavier nitrogen and
oxygen. The recharge from the Wildlife Ponds idenfified by Hurst and Solomon (2008) may
carry organic carbon into the groundwater system where it acts as an electron donor to
support denitrificafion.
Per the study conducted by Hurst and Solomon, it was noted that sulfate isotopic study is
useful to differenfiate sulfur sources from the tailings ponds (tailings sulfate) and natural
deposits (gypsum). This is because of fracfionafion processes occurring in the ore refining
process, and the use of sulfuric acid from an outside source in ore refinement. DRC requests
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that stable isotope analysis of sulfur (sulfur- 32 and 34) and oxygen (oxygen-16 and 18) in
sulfate be included with the analysis of every groundwater and wastewater sample analyzed
for nitrate isotopic ratio in Secfion 7 and Table 2 of the work plan to assist in interpretation
and differentiation of the nitrogen sources. Please confirm that the contract laboratory can
perform this analysis. It is unlikely that a sufficient volume of leachate could be produced
from the soil cores (see comment #30) to analyze the isotopic signatures of both nitrate and
sulfate in the soil samples. For this reason, DRC is not requesfing isotopic analysis of sulfur
and oxygen in sulfate in the soil cores. Analysis for sulfate by Method 300.0 shall
accompany the sulfate isotopic analysis on every groundwater and wastewater sample to
provide an additional level of comparison, similar to the 2008 study.
33. Table 2: Usually one sample container can be used for oxygen and hydrogen isotopes in
water. One liter is probably more than the analytical lab will need for O and H in water.
Table 2 may need to be revised based on input from the analyfical lab(s).
34. Section 7.0: Please add analysis for ammonia-nitrogen by Method 350.2 to the fist of
convenfional laboratory analyses for groundwater and wastewater samples.
35. Section 7.1: Standard reference materials used by the analyfical lab to calculate isotopic
values shall be reported. Section 7.1 addresses the need to assess the precision of isotope
measurements, but does not address accuracy. DRC requests that split samples of
groundwater and wastewater samples be collected at a frequency of at least 10% of samples
for isotope analyses; the split samples will be analyzed by a second, independent laboratory
to provide some additional support for the accuracy of isotope analyses. The laboratories
selected by DUSA are subject to approval by DRC prior to collection of any samples for
isotope analysis. The collection of split samples for soil isotope analysis will not be required
by DRC due to the limited sample volume.. In. order to ensure consistent QA/QC procedures
for the laboratories, commercial laboratories, rather than university laboratories, shall be used
for all stable isotope analyses, unless DUSA demonstrates that a commercial laboratory is
unavailable to perform a particular isotope analysis and the DRC then waives the
requirement. All non-isotope laboratory analyses shall be performed by a laboratory certified
by the State of Utah.
The work plan needs to include more narration and additional tables (flow charts) outlining
the process for collecting Denison (in-house) QA/QC samples to self assess laboratory
performance (in addifion to the laboratory QA/QC protocols). Such planning needs to
include specific sample types [e.g. blind duplicates, field collected spiked blanks, and field
collected spiked matrix (spiked duplicates)] to allow full evaluafion of precision and
accuracy. The tables need to include specific wells where the Denison field QA/QC will be
collected as well as specific reference to the matrix used for spike analysis. The justifications
for QA/QC protocols should be included in the narrative (with references where applicable)
and all sample collecfion (water and soil) should be summarized on appended tables (see
comment 41 below).
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36. Secfion 8: DRC agrees with the conceptual approach of using mass balances as a line of
evidence for potential source areas. However, the comparison of the estimated mass of
nitrate in the groundwater beneath the mill site to the required amount of leachate from the
tailings pond is drawn directly from the 2009 Nitrate CIR. Since leakage from the tailings
ponds has been ruled out, it would be preferable to compare the mass of nitrate in the
groundwater beneath the mill site to the mass of nitrate that could have been delivered from
naturally-occurring nitrate deposits. In addifion, an estimafion of the mass of chloroform in
the groundwater beneath the mill site would be helpful for comparing the mass of nitrate or
waste water that could have been delivered to the groundwater through leach fields.
37. Figure 1: DRC requests that the figure number be inserted into the fifie. The use of a
decision logic diagram is helpful, and could be included in the framework of a CSM. The
current logic diagram (Figure 1 flow chart) included in the work plan is not sufficient as
clarified in comments above. The work plan is required to contain a comprehensive logic
diagram. Also as stated above, the logic diagram could be included as part of a larger
conceptual model structure, but at minimum this element needs to include specific hypothesis
statements for each activity undertaken for the study in order to definitively accept or reject
idenfified potential sources. Refer to comments #1, 2, and 4 for addifional details.
38. Figure 3: the legibility of the values and label on the x-axis could be improved.
39. Figure 20: The word "Missile" is misspelled on the legend.
40. Figure 21: Please explain why the number of leach fields shown on this figure differs from
previous reports.
41. Table 2: DRC requests that the planned sampling be summarized in a table showing the
sample locations; number, and types of samples for each location; the types of analyses and
the associated container type, holding time, and preservative; and the planned QA/QC
samples at pre-determined locations. Some of these details are present in Table 2, but
insufficient detail is currently presented in the tabled Sampling and arialysis should conform
to the existing Quality Assurance Plan for the mill, but the work plan will need to specify the
QA/QC measures for isotopic analysis. Specifically, DUSA needs to clarify the QA/QC
protocols which will be used for each sample type and list the proposed sample locations with
an idenfifier. For example, at least 10% of the groundwater and wastewater samples must be
spht, with analysis of the split samples by a second, independent laboratory. The locafions of
the split samples must be idenfified in the Work Plan. The work plan needs to clarify which
samples will conform with the facility QAP plan, as identified in the section 7.1 narrative,
and which samples will require additional QA/QC validafion based on inadequacy or
inapplicability of the QAP requirements. The laboratories selected by DUSA for isotope
analyses are subject to approval by DRC, based on a review of their intemal QA/QC
procedures, prior to collection of any samples for isotopic analysis.
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Thank you.
URS Corporation
Paul R. Bitter, P.E.
Senior Remediafion Engineer
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