DRC-2009-007085 - 0901a0688015a1ed

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DENISOh^i
MINES
December 31, 2009
VIA PDF AND FEDERAL EXPRESS
Mr. Dane L. Finerfrock
Co-Executive Secretary
Utah Water Quality Board
State of Utah Department of Environmental Quality
168 North 1950 West
P.O. Box 144850
Salt Lake City UT 84114-4850
Denison Mines (USA) Corp.
105017th Street, Suite 950
E)enver, GO 80265
USA
Tel: [phone]
Fax: [phone]
www.clenisonmines.cofn
Dear Mr. Finerfrock:
Re: Chloroform Contamination Investigation. Chloroform Concentrations Exceeding the
Groundwater Quality Standard in Monitor Well TW4-6. Request for a Submittal of a Plan of Action
and Work Schedule. Confirmatory Action Letter.
Recent chloroform concentrations in monitor well TW4-6 at the White Mesa Mill (the "Mill") have
exceeded the 70 ug/l State of Utah groundwater quality standard, requiring an adjustment to the hydraulic
containment program relating to the chloroform contamination plume at the Mill.
This letter is in response to your Confirmatory Action Letter dated November 9, 2009, which confirms
Denison Mines (USA) Corp's ("Denison's") agreement to submit on or before December 31 a plan of
action and work schedule to achieve hydraulic containment at TW4-6.
Enclosed please find a letter report dated December 28, 2009 from Hydro Geo Chem, Inc. that addresses
the recent detection of chloroform concentrations at TW4-6, and discusses potential response options
and recommends a course of action.
In accordance with the recommendations in Hydro Geo Chem's letter report, Denison proposes the
following plan of action and work schedule to achieve hydraulic containment at TW4-6:
1. On or before January 31, 2009, Denison will commence pumping at TW4-4, which is immediately
upgradient of TW4-6, using similar pumping equipment and procedures as currently utilized for the other
chloroform pumping wells at the Mill site.
2. Pumping of TW4-4 will continue until at least the analytical results of the third quarter 2010
chloroform sampling event have been received and analyzed. This will allow for the pumping to have
taken place for two full quarters and a review of the quarterly chloroform monitoring results to determine
whether or not the concentration of chloroform in TW4-6 is declining. If the chloroform concentration in
TW4-6 is declining as a result of the pumping of TW4-4, then the pumping of TW4-4 will continue.
3. If at any time the chloroform concentration in TW4-6 has not been reduced to below 70 ug/l and
the chloroform concentration in TW4-6 does not decrease for any two consecutive quarters (not counting
the first quarter of 2010), then, within 60 days after the end of such second consecutive quarter, Denison
will commence pumping TW4-6, in addition to TW4-4, using similar pumping equipment and procedures
as currently utilized for the other chloroform pumping wells at the Mill site.
4. The pumping of both TW4-4 and TW4-6 will continue until the analytical results for three quarters
of chloroform sampling have been received and analyzed. This will allow for the pumping of both wells to
have taken place for two full quarters and a determination of whether or not the concentration of
chloroform in TW4-6 is declining as a result of the pumping of both TW4-4 and TW4-6. If the chloroform
concentration in TW4-6 is declining, then pumping in both TW4-4 and TW4-6 will continue until the
chloroform concentration in TW4-6 has been reduced to below 70 ug/l.
5. Once chloroform concentrations in TW4-6 have been reduced to below 70 ug/l, Denison will
continue pumping either or both of TW4-4 or TW4-6 as it determines necessary to maintain chloroform
concentrations in TW4-6 below 70 ug/l.
6. If, after commencement of pumping in both TW4-4 and TW4-6, the chloroform concentrations in
TW4-6 have not been reduced to below 70 ug/l and the chloroform concentrations in TW4-6 do not
decrease for any two consecutive quarters (not counting the quarter in which pumping in TW4-6
commences), then, within 60 days after the end of such second consecutive quarter, Denison will install a
new chloroform monitoring well downgradient of TW4-6, and will continue to pump either TW4-4 or TW4-
6, as Denison, with the concurrence of the Executive Secretary, determines necessary in order to
hydraulically contain the chloroform plume.
If you have any questions or require any further information, please contact the undersigned.
Yours very truly,
DENISON MINES (USA) CORP.
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David C. Frydenlund
Vice President, Regulatory Affairs and Counsel
cc: Ron F. Hochstein
Harold R. Roberts
Steven D. Landau
David E. Turk
DENISOr^i
MINES
HYDRO GEO CHEM, INC.
Environmental Science & Technolo^ry
December 28, 2009
Mr. Steven Landau
Denison Mines (USA) Corporation
1050 17th Street, Suite 950
Denver, Colorado 80265
Dear Steve,
This letter addresses the recent detection of chloroform concentrations exceeding 70 ^g/L at
TW4-6, a temporary perched zone monitoring well located at the White Mesa Uranium Mill near
Blanding, Utah (the "Mill" or the "site"). Chloroform concentrations exceeding 70 |Lig/L places the
well within the perched zone chloroform plume at the site. Background conditions, a discussion of
potential response options, and a recommendation are provided below.
Background
TW4-6 was installed in the second quarter of 2000 to serve as a downgradient well for
monitoring perched zone chloroform that most likely originated from the abandoned scale house and
former office leach fields. These leach fields received both laboratory and lavatory wastes in the
early years of Mill operation as described in the Preliminary Corrective Action Plan (Hydro Geo
Chem [HGC], 2007^). Between the time of installation and the fourth quarter of 2008, TW4-6
bounded the chloroform plume which is defined by concentrations that equal or exceed 70 >ig/L.
Chloroform concentrations remained non-detect at TW4-6 between the time of installation and the
first quarter of 2005. Concentrations then maintained a slow, somewhat erratic, but upward trend
until concentrations exceeded 70 j^g/L in the first quarter of 2009. The rate of chloroform migration
at TW4-6 is clearly slower than at TW4-4, the closest well upgradient of TW4-6. Concentrations at
TW4-4 increased from non-detect to more than 2,200 jag/L within only 2 quarters whereas 16
quarters were required for concentrations in TW4-6 to increase from non-detect to only 81 |ig/L.
Hydro Geo Chem, Inc. 2007. Preliminary Corrective Action Plan. White Mesa Uranium Mill Near Blanding, Utah
Ttr^
51 West Wetmore, Suite 101 Tucson, Arizona 85705-1678 11'" 520.293.1500 520.293.1550-Fax [phone]-Toll Free
Mr. Steven Landau
December 28, 2009
Page 2
Since 2003, chloroform has been removed from the perched zone by pumping. Pumping
initially began at MW-4. TW4-19, MW-26 (TW4-15) and TW4-20 were later added to the pumping
network. The purpose of the pumping is to reduce total chloroform mass in the perched zone as
rapidly as is practical. These wells were chosen for pumping because 1) they are located in areas of
the perched zone having relatively high permeability and saturated thickness, and 2) high
concentrations of chloroform were detected at these locations. The relatively high transmissivity of
the perched zone in the vicinity of the pumping wells results in the wells having a relatively high
productivity. The combination of relatively high productivity and high chloroform concentrations
allows a high rate of chloroform mass removal.
Downgradient pumping has also been considered. The primary reason that downgradient
wells such as TW4-6 have not been pumped is that the perched zone has a relatively low
permeability in the downgradient portion of the chloroform plume. Although it would be desirable to
pump at downgradient locations from the standpoint of reducing fiirther downgradient plume
migration, any wells completed in this portion of the plume would likely have a very low
productivity (< 0.5 gpm). Furthermore, the rate of chloroform migration in the downgradient portion
of the plume is slow due to low permeability conditions.
Options
As discussed in the Preliminary Corrective Action Plan (PCAP), should concentrations at a
downgradient well such as TW4-6 exceed 70 ng/L, a new downgradient well is to be installed with
the concurrence of the Utah Department of Environmental Quality (UDEQ). This is Option 1.
Pumping at downgradient wells such as TW4-6 has not been implemented in the past due to low
perched zone permeabilities in the downgradient portion of the plume and the low expected rates of
well productivity.
A second option (Option 2) not presented in the PCAP would be to delay installation of a
well downgradient of TW4-6 and to pump upgradient well TW4-4 at a rate as high as practical.
Should chloroform concentrations continue to increase at TW4-6, then TW4-6 would also be
pumped at a rate as high as practical. Should chloroform concentrations continue to increase at TW4-
6 while bothTW4-4 and TW4-6 are pumped, a new well would be installed downgradient of TW4-6.
Should concentrations at TW4-6 drop below 70 jig/L while TW4-4 is pumped, or while both
TW4-4 and TW4-6 are pumped, an additional downgradient well will not be installed unless
concentrations at TW4-6 should again increase to 70 \ig/L or more. Pumping at either or both wells,
once implemented, will continue to the extent practical.
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Mr. Steven Landau
December 28, 2009
Page 3
Recommendation
Although the productivities of TW4-4 and TW4-6 are likely to be low, Option 2 is
recommended. Pumping of either or both of these wells would provide additional mitigation of
chloroform in the perched zone, and may help reduce the rate of downgradient chloroform migration.
Pushing back the installation of an additional monitoring well downgradient of TW4-6, while
initiating pumping and continuing to monitor concentrations, is justified by the slow rate of
downgradient chloroform migration in this area and by the additional benefits expected from the
pumping. Option 1 would provide for quicker installation of an additional downgradient well but
would not provide the potential benefits of pumping TW4-4 (and TW4-6, if implemented).
Sincerely,
Stewart J. Smith
Associate Hydrogeologist
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