DRC-2010-002742 - 0901a0688017876c

DENISOh^i
MINES
OsnlsonHHinid (
1090 ITthStrset, Suite
OMivor, CO 80268
USA
Tel: [phone]
Fax:30338»412S
www.d«nisonintfie&com
JP^A Receive
April 2, 2010
SENT VIA PDF AND FEDERAL EXPRESS
Mr. Dane L. Finerfrock
Executive Secretary
Utah Radiation Control Board
State ofUtah Department ofEnvironmental Quality
168 North 1950 West
Salt Lake City, Utah 84114-4850
Re: White Mesa Uranium Mill ~ Plan of Action and Schedule for Modification of
Groundwater Monitoring Quality Assurance Plan to Address Turbidity Stabilization and
Conversion to Low-Flow Sampling and Request for Interim Variance
Dear Mr. Finerfrock:
As a follow up to the telephone call of February 22, 2010 with Mr. Loren Morton and Mr. Phil
Goble of the State of Utah Department of Environmental Quality, Division of Radiation Control
("DRC"), this letter proposes a Plan of Action and Schedule for modification of certain sampling
procedures documented in Denison Mines (USA) Corp.'s ("DUSA's") White Mesa Uranium
Mill Ground Water Monitoring Quality Assurance Plan (QAP) (Revision 5, dated February 9,
2010) (the "QAP") under State ofUtah Groundwater Discharge Permit No. UGW3 70004 (the
"Permit"), and requests an interim variance of certain of those sampling procedures pending
completion of those modifications.
1.0 Site Information and Relevant Factors
There are currently 23 groundwater compliance monitoring wells at the White Mesa Mill (the
"MiU") site that are monitored under the Permit. A dedicated pump, with a pumping rate of
approximately 0.20 gpm, is installed in each of those wells. Those pumps are used to purge
water from the wells prior to sampling and to withdraw water for samples.
There are also 26 chloroform investigation wells and 19 nitrate investigation wells at the site.
None of those wells currently have dedicated pumps. Those wells are purged prior to sampling
in accordance with the requirements ofthe QAP by use ofa non-dedicated pump at the rate of
approximately 6.0 gpm. In the case of chloroform investigation wells, the pump is removed
from the well after purging is complete, and sampling is performed by disposable bailer in
accordance with the requirements of the QAP. In the case of nitrate investigation wells, the
pump is retained in the well to draw the sample and then is removed from the well after the
sample has been taken. In both cases, the pump is decontaminated between wells, in accordance
with the requirements ofthe QAP.
The QAP states the following under 6.2.7 (d) (v):
"Take measurements of field parameters (pH, specific conductance, temperature, redox potential
and turbidity) during well purging, using Field Parameter Meter and turbidity measuring
instrument. These measurements will be recorded on the Field Data Worksheet. Purging is
completed after two casing volumes have been removed and the field parameters pH,
temperature, specific conductance, redox potential (Eh) and turbidity have stabilized to within
10% over at least two consecutive measurements. The groundwater in the well should recover to
within at least 90% of the measured groundwater static surface before sampling. In addition,
turbidity measurement in the water should be < 5 NTU prior to sampling (DTG Well
Development 6.7, page 6-48) unless the well is characterized by water that has a higher
turbidity. A flow-cell needs to be used for field parameters. If the well is purged to dryness or is
purged such that full recovery exceeds two hours, the well should be sampled as soon as a
sufficient volume of groundwater is available to fill sample containers (DTG, Well Purging,
7.2.4, page 7-9)."
Although dedicated low flow pumps are installed in each ofthe 23 groundwater monitoring wells
at the site, low flow procedures have not been developed, hence do not apply to those wells.
Rather, sampling in those wells is required to follow the foregoing procedures.
2.0 Problems Identified
Section 6.2.7 (d)(v) ofthe QAP as currently drafted gives rise to three problems. The first is that
it applies to all wells on site, including the groundwater monitoring wells with the dedicated low
flow pumps. This results in an inordinate amount of time required to purge two casing volumes
for most of those wells at the low flow rate of approximately 0.20 gpm.
The second problem is that the requirement for stabilization of turbidity within 10% over at least
two consecutive measurements has proven to be difficult or impossible in a number of
chloroform and nitrate investigation wells at the site that use the non-dedicated 6 gpm pump.
For example, during 1^* quarter 2010 sampling of TW4-22 and TW4-23, two casing volumes
were purged and the four turbidity readings over the last four minutes of purging were 29.5, 36.9.
111.3 and 70.4 nephelometric turbidity units ("NTUs") for TW4-22 and 136.2, 152, 95.7 and
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68.9 NTUs for TW4-23. In both cases the other parameters had stabilized during those four
minute periods. See the attached Field Data Sheets.
The third problem is that the requirement that turbidity should be less than or equal to 5 NTUs
("unless the well is characterized by water that has a higher turbidity") has also been found to be
unattainable in several wells, as is evident from the foregoing examples. To date, natural
background turbidity of the water has not been formally characterized in any of the groundwater
monitoring wells, chloroform investigation or nitrate investigation wells at the site. As a result,
Denison is not in a posifion at this time to demonstrate that the inability to achieve turbidity less
than or equal to 5 NTU in any well is due to the natural turbidity ofthe water in the well.
3.0 Plan and Schedule to Remedy the Issues
3.1 Proposed Plan: Conversion to Low-Flow Sampling Method and QAP Revisions
DUSA has contracted with a technical expert in sampling methods and protocols to evaluate the
current sampling program and make recommendations for improvements. DUSA's ultimate goal
is to revise sampling methods so that representative samples will consistently be obtained from
all monitoring wells at the site, EPA-approved criteria will be met, and the QAP will comply
with this best-practice methodology for the specific groundwater conditions at the Mill site.
Upon receiving these recommendations, DUSA will propose amendments to the QAP to reflect
recommended changes in the sampling methods.
Based on evaluations to date, DUSA believes that there are a number of acceptable ways to
collect samples that are representative of ground water conditions and to minimize changes in
ground water chemistry during sample collection and handling, in accordance with approved
EPA guidance. The most appropriate procedures will often depend on the specific conditions
applicable to each well. For wells that are amenable to low flow sampling, low-flow sampling
with a dedicated pump is generally regarded as one of the best ways to consistently obtain
representative ground water samples. Low-flow pumping rates will generally reduce or
eliminate the problem of elevated turbidity and will also result in more consistent, repeatable,
and defensible groundwater samples. "Sampling-induced turbidity problems can often be
mifigated by using low-flow purging and sampling techniques." (Puis and Barcelona, 1996). We
understand that DRC has approved the use of this method at other facilities and has
recommended in the past that DUSA consider low flow sampling at the Mill site. Use of low
flow sampling methodologies, instead of requiring the evacuation of two casing volumes, in
' DUSA realizes that Section 6.2.7 (d)(v) states that the turbidity level "should" be <.5 NTU, not "shall" be <.5
NTU. However, in recent discussions, DRC staff has indicated a desire to change the wording from "should" to
"shall", thereby making it a requirement that the turbidity level be <.5 NTU prior to sampling. This issue is
included here as a problem, to the extent the wording is changed in the future as indicated by DRC staff.
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wells that currently have dedicated low flow pumps will also, for many of the wells, eliminate
the inordinate amount of time required to evacuate two casing volumes with those pumps.
However, not all wells are suited for low flow sampling. The method is typically not employed
in wells with extremely low yield (less than approximately 0.5 liter/minute) because one of the
criteria for low-flow is minimal drawdown ofthe water column during the purge. For wells with
extremely low yield, the well should be evacuated to dryness and the groundwater allowed to
recover before sampling, according to EPA protocol (Yeskis and Zavala, 2002). Other methods,
such as purging some number of casing volumes, establishing stable parameters, or other
methods are accepted for wells that do not have dedicated low flow pumps.
Currently all of the 23 groundwater monitoring wells at the site are equipped with dedicated
pumps that are amenable to low-flow sampling, although low flow sampling procedures are not
documented in the QAP and are therefore not being implemented in those wells. As a part ofthe
sampling program evaluafion, DUSA proposes to evaluate the suitability of low flow sampling
techniques for all groundwater, chloroform and nitrate wells at the site for the low flow sampling
method.
In order to assess the suitability of implementing low-flow sampling for each well on site, the
following steps will be taken:
• Review well construction specifications to determine total depth, screen interval, etc.; and
• Review historical purge and sample data to determine depth to groundwater, past purge
rate, amount of drawdown, etc.
From this information it will be possible to select those wells which are candidates for low-flow
sampling. An assessment of the groundwater monitoring wells which currently utilize dedicated
low flow pumps will provide a guide to the well specifications and behaviors that are best suited
for the low flow method. This information will be used to select possible additional low flow
wells. For those wells that do not have dedicated low flow pumps or where low flow sampling is
not suitable, other sampling procedures will be identified.
Specific procedures and equipment to be used for low flow sampling, and the wells in which low
flow sampling is to be employed, will be detailed in proposed amendments to the QAP. Such
amendments will also address specific altemative procedures and equipment to be used for
sampling wells that are not amenable to low flow sampling or which do not have dedicated
pumps at this fime.
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As part of DUSA's evaluation of the current sampling program, DUSA will evaluate the
practicality and appropriateness of maintaining this turbidity requirement in light of current EPA
guidance and recent research.
3.2 Implementation Schedule
The evaluation process and the approval and implementation of revised sampling procedures is
expected to require approximately six months (two quarters) from the time of the approval ofthis
letter. Proposed amendments to the QAP, tied closely to EPA guidance and sampling protocols,
will be submitted to the Executive Secretary for review and approval.
The following is a proposed schedule for implementation ofthe revised sampling program:
Upgraded Sampling Program Implementation Steps
1. Conduct a study of the current sampling methods and
identify the wells that are causing the need for the turbidity
variance based on historical well data
2. Evaluate the suitability of those wells (those with
historically high turbidity measurements during sampling) for
conversion to low flow sampling with dedicated pumps
3. Identify all other wells suitable for low flow sampling with
dedicated low flow pumps
4. Identify methods other than low flow sampling that are
suitable for wells that are not amenable to low flow sampling or
which do not have dedicated pumps at this fime
5. Submit proposed amendments to the QAP to reflect the
amended sampling protocols and the most current EPA sampling
guidance
6. Obtain Executive Secretary approval for the revised QAP
7. Implement the new procedures during the third quarter
sampling event
Milestone Dates (2010),
complete by:
April 30
April 30
April 30
April 30
May 28
June 30
September 30
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4.0 Request for Interim Variance
In order to implement the proposed Plan and Schedule in Secfion 3.0, above, DUSA hereby
requests that the Executive Secretary waive the requirement in Section 6.2.7(d)(v) of the QAP
for turbidity to stabilize in all groundwater monitoring wells, chloroform investigation wells and
nitrate investigation wells, until such time as revised sampling procedures are approved in a
revised QAP, provided that DUSA adheres to the schedule specified in Secfion 3.0 above.
DUSA interprets the phrase "In addition, turbidity measurements in the water should be <_5 NTU
prior to sampling . . ." in Section 6.2.7 of the QAP to be permissive, not mandatory. DUSA
confirmed our understanding of this language during our telephone discussion with DRC on
February 24, 2010. As a result of that discussion, the agreed-upon QAP submittal for approval
on March 22, 2010 maintains the word "should" with that understanding. However, to the extent
the Executive Secretary interprets that phrase to be a mandatory requirement, DUSA hereby
requests a waiver from that requirement as well, on the same terms and conditions as the
foregoing waiver.
5.0 Discussion and Justification of Proposed Plan and Variance
As discussed during the February 22 phone call, DUSA's sampling objective, in compliance with
EPA guidance, is to "collect samples that are "representative" of in-situ ground water conditions
and to minimize changes in ground water chemistry during sample collecfion and handling."
(Yeskis and Zavala, 2002). The QAP provides detailed guidance for obtaining representafive
samples. However, in the case of the turbidity requirements, the QAP does not adequately
account for the potential natural variations in aquifer material which can lead to wide-ranging
turbidity level measurements and turbidifies that consistently exceed 5 NTU. "Sampling-induced
turbidity problems can often be mitigated by using low-flow purging and sampling techniques."
(Puis and Barcelona, 1996). DUSA therefore believes that low flow sampling will be
appropriate for most wells at the Mill site and believes that revisions to the QAP to accommodate
low flow sampling are appropriate. Denison also believes that other EPA approved methods will
be appropriate for wells that are not amenable to low flow sampling or which are not equipped
with dedicated low flow pumps at this time, and that revisions to the QAP to accommodate such
other methods will be appropriate.
DUSA fiirther believes that representative groundwater samples will be obtained under the terms
of the interim variance requested above, while the amended sampling regime is being
implemented at the site. EPA ground water sampling guidance indicates that ambient turbidity
levels may not be achievable under some circumstances but that representative groundwater
samples may be obtained in spite of elevated turbidity, given stabilization of the other field
parameters and/or compliance with other purge criteria such as a specified purge volume. "The
USEPA recognizes that in some hydrogeologic environments, even with proper well design.
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installation, and development ... the sample turbidity cannot be reduced to ambient levels."
(Yeskis and Zavala, 2002). Further, this sampling guidance states that under a low-stress (low
flow) sampling approach, "the turbidity reading is desired to stabilize at a value below 10
Nephelometric Turbidity Units (NTUs)" (double the current QAP requirement value of 5 NTU)
and that for the well-volume approach, the stabilization criteria may be based on "the
stabilization of water-quality-indicator parameters or on a pre-determined well volume." Note
that EPA guidance allows parameter stabilization or a pre-determined volume such as some
number of well volumes. The general order of stabilization is typically pH, temperature, specific
conductance, followed by oxidation-reduction potential, dissolved oxygen and turbidity.
According to Puis and Barcelona (1996), "natural turbidity levels in ground water may exceed 10
nephelometric turbidity units (NTU)." At present, DUSA lacks the data needed to determine the
ambient turbidity level in each well. The apparent turbidity levels may be due to several factors
including the aquifer grain size, aquifer composition, the natural turbidity of the formation water
(resulting from colloidal transport and deposition. Puis and Barcelona, 1996) and the purge
pumping rate. The result is that it is not always possible to purge and sample in compliance with
the QAP requirements using the current sampling protocols. DUSA believes the cause of the
higher turbidity measurements may be a combination of the fine aquifer grain size within some
sections of the aquifer and the pumping rate of the type of pump used (a portable, electric
submersible pump with a flow rate of approximately 6 gpm) in the wells not already equipped
with dedicated low-flow pumps.
In summary, the main objective of any groundwater sampling program should be to obtain
representative samples, and there are a variety of ways to achieve this goal. The compliance
with specific stabilization criteria is not the objective; rather, parameter stabilization is one
indicator that representative groundwater has been obtained. There are limitations to the benefits
of strict adherence to specific parameter criteria, and DUSA believes that even with turbidity
measurements which exceed the current QAP requirements, the groundwater samples should be
considered valid. "If parameter stabilization criteria are too stringent, then minor oscillations in
indicator parameters may cause purging operations to become unnecessarily protracted. It
should also be noted that turbidity is a very conservative parameter in terms of stabilization.
Turbidity is always the last parameter to stabilize. Excessive purge times are invariably related
to the establishment of too stringent turbidity stabilization criteria." (Puis and Barcelona, 1996).
Any long term changes proposed by DUSA would maintain or improve compliance with the
appropriate EPA best practice ground water sampling guidance. DUSA has conducted a review
ofthe most current EPA guidance and suggests that the QAP variance proposed in this letter, as
well as implementation of a low flow sampling approach where appropriate, is supported in
general by the scientific sampling literature and specifically by the following references:
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1. Yeskis, D. and Zavala, B., 2002, U.S. Environmental Protection Agency, Ground-Water
Sampling Guidelines for Superfund and RCRA Project Managers, Ground Water Forum Issue
Paper, EPA-542-S-02-001, Office of Solid Waste and Emergency Response.
This EPA Ground Water Forum Issue Paper from 2002 provides the most recent, nationally
recognized ground water sampling guidance from EPA, according to DUSA's EPA Region 8
point of contact, Mr. Andrew Schmidt. This document covers both "low-stress" sampling and
the "well-volume" approach.
2. Puis, R.W. and Barcelona, M.J., 1996, U.S. Environmental Protection Agency, Low-Flow
(Minimal Drawdown) Ground- Water Sampling Procedures, EPA Ground Water Issue, Office of
Research and Development, EPA 540-S-95-504, Office of Solid Waste and Emergency Response.
This EPA Ground Water Issue paper is the standard regulatory and scientific guidance for low-
flow ground water sampling procedures and is cited repeatedly in the 2002 Yeskis and Zavala
guidance.
If you have any questions or require any ftirther information, please contact the undersigned.
Yours very truly.
Jo Ann Tischler
Director, Compliance and Permitting
cc: Ron F. Hochstein
Harold R. Roberts
David E. Turk.
Attachments
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