DRC-2011-001650 - 0901a068801fea5e

ORG"2011-00165
DENISO
MINIS
February 1, 2011
VIA E-MAIL AND OVERNIGHT DELIVERY
Mr. Rusty Lundberg
Co-Executive Secretary
Utah Water Quality Board
Utah Department of Environmental Quality
195 North 1950 West
P.O. Box 144810
Salt Lake City, UT 84114-4820
Denison (Mines (USA) Corp.
1050 17th Street, Suite 950
Denver, CO 80265
USA
Tel: [phone]
Fax:[phone]
www.denisonmlnes.com
Re: State of Utah Groundwater Discharge Permit ("GWDP") No. UGW370004
Proposed Correction of Groundwater Control Limits ("GWCL's") for pH ,
Dear Mr Lundberg:
The currently approved version of the GWDP in Part 1.0. Table 2, provides, for each well in the White Mesa
Mill's (the "Mill's") point of compliance program, a range of pH values to serve as its respective GWCL. This
letter proposes a plan to revise the incorrectly-established GWCLs, as discussed below.
Background
The US Environmental Protection Agency ("EPA") in the RCRA Ground-Water Monitoring Technical
Enforcement Guidance Document ("TEGD") of September 1986 states that several parameters, including pH,
are physically and/or chemically unstable and must be tested in the borehole, or at the field sampling location,
with a field test kit. Fieid samples may undergo evolution (degassing) of naturally-present CO2 during,
packaging, shipment, and re-opening of sample containers at the laboratory. In the case of pH, the sampie
measured by the laboratory will tend to have generally lower CO2 levels and generally higher pH than the
corresponding measurement made in the field. Hence, field pH measurements are therefore more correctly
representative of electrochemical conditions at the point and time of sampling. Consistent with the EPA,
TEGD, the Mill's GWDP, in Part I.C. Table 2, establishes a requirement for "Field pH" in standard pH units.
Denison agrees with EPA's TEGD, indicating that measuring pH in the field, that is, closest to the point and
time of sampling, is more representative of chemical conditions in the sample than an equivalent
measurement made in an analytical laboratory several days later. Denison agrees with the GWDPs
requirement of field pH, rather than lab pH, as the choice of measurement.
The current GWCLs are based on the evaluation reported in INTERA, Inc.'s April 30, 2008 Revised Report, \
Background Groundwater Quality Report: New Wells for Denison Mines (USA) Corp. 's Wtiite Mesa Mill Site, .
San Juan County, Utati (the "Background Study Report'). All pH data used in the Background Study Report
were produced by the Mill's off-site contract analytical laboratory. That is, the GWCLs were not developed
from background field data measured at the sampling location. In addressing the statistically significant
decreasing trends in time plots for all the site wells, the Background Study Report states in Section 2.5.6:
N:\Field pH GWCL study\01.31.11 pH letter to Rusty Lundberg.docx
Letter to Mr. Rusty Lundberg
February 1, 2011
Page 2
"Since 2004, DUSA has been improving its sampling and analysis protocols at the request of
the UDEQ. The pH measurements recorded during this period were all laboratory
measurements. This period also coincides with the observed decreases in pH suggesting a
potential connection with some laboratory process."
That is, although GWCLs were established to control, and should be based on, field pH data, the numeric
GWCL values established in the GWDP were based on laboratory pH data. For the reasons described
above, laboratory pH data should be expected to yield consistently higher mean values and higher GWCLs
than would be developed from corresponding field data. It has become apparent, over time, that the ongoing
comparison of pH data measured monthly, quarterly or semi-annually in the field, to GWCLs established from
statistical analysis of data measured in a laboratory, is meaningless, and cannot be used as a basis for
determining compliance with the GWDP. In order to establish a basis for determining compliance, it will be
necessary to develop corrected GWCLs for pH based on field pH data. I
Proposed Approach
To develop a corrected set of GWCLs, Denison proposes to employ the field pH data developed from the timej
of initiation of the GWDP and its associated Quality Assurance Plan in 2005 to the present. A sufficient'
number of continuous periods of quarterly data are available from this period to provide more than the
minimum of eight continuous periods of data for analysis as recommended by the TEGD.
Denison has collected the field pH measurements with three flow-through multi-meter instruments, one of|
which is no longer in service, over the period since 2005. All three have been calibrated consistent withj
manufacturer's recommendations and the requirements of the QAP. As a result, data generated from any of:
the instruments is expected to be suitable for purposes of statistical analysis.
The GWCLs proposed by Denison will be based on the method depicted in the process flow diagram in
Figure 17 of the Background Study Report, including box and whisker plots, statistical distribution analyses'
and trend analyses, to the extent each step in the process is applicable. However, some components of the,
diagram, such as tests to determine the percentage of the total number of values which are non-detects, are
not applicable to logarithmic parameters like pH data, and will not be applied.
As discussed above, comparison of ongoing field data to GWCLs established from laboratory data is
meaningless, as are any apparent "exceedances" identified as a result of such a comparison. Denison
proposes to evaluate all field pH results from the proposed period of the 2005 GWDP to the present via the
process in Table 17, whether or not any result was apparently in "exceedance" of the incorrectly established
existing GWCLs for pH.
Based on the requirements of the QAP, during each sampling event, multiple repeated measurements are
made of each field parameter, including field pH, in each well up until the time the sample is taken, and the
multiple measurements are recorded on the field data sheet for each well. For the purposes of chemical
representativeness, only the last field pH measurement (the one made closest to the time of sampling and
which should be most representative of the conditions at the time of sampling) and most representative of
formation/aquifer water will be used in the statistical evaluation.
Path Forward
For consistency and accuracy, Denison intends to propose revised the GWCLs for pH in all. on-site wells.:
Denison also proposes that development of GWCLs for new monitoring wells (MW-34, 35 and any additional-
DENISON
MINES
Letter to Mr. Rusty Lundberg
February 1, 2011
Page 3
wells which may be established as point of compliance wells) also be based on evaluation of background field
pH data, not lab pH data, as discussed above.
Please advise us whether the above proposal is acceptable to DRC. Upon your agreement, Denison will
initiate the re-evaluation of pH background data. Denison hopes to submit proposed revised pH GWCLs by
the end of the second quarter of 2011.
Please contact the undersigned if you have any questions or require any further information.
Yours very truly,
DENISON MINES (USA) CORP.
Jo Ann Tischler
Director, Compliance and Permitting
cc: David C. Frydenlund
Harold R. Roberts
David E. Turk
K. Weinel
OENISO
MINES