DRC-2010-002767 - 0901a0688017a5c0

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Slate of Utah
G.ARVR, HERBERT
Gii\'tii\(iy
GREG DELL
l.kujfwmW Gfivfrnnr
Department of
Environmental Qualily
Anuiid.i Smith
Eu-i-uTi)e l)iy?ftni-
DIVISION or RADLATION CONTROL
Ojnd L, Fintrf^rix-fi
Dire {-ft It-
ffRC-2010-002767
MEMORANDUM
TO:
FROM:
DATE:
SUBJECT:
9^10
Loren Morton
Dean Henderson
April 8,2010
Review of the Chloroform Coniamination Investigation. Chloroform
Concentrations Exceeding the Groundwater Quality Standard in Monitor Well
TW4-6. Submittal of a Plan of Aciion and Work Schedule.
Dennison Mines (USA) Coi-p.
While Mesa Uranium Mill, near Blanding, Utah.
This a review ofthe Plan of Action and Work Schedule (hereafter "Plan") that wiis submitled by
Dennison Mines (USA) Corp. (hereafter '^DUSA") to have hydraulic containmeni ofthe
chloroform concentrations at TW4-6. A copy of the Plan Is included in Attachment I. The
review will consist of a statement of a proposed action item in the Plan (in italics) followed by a
DRC response.
REVIEW
DUSA Plan Item 1:
'^On or before Januaiy 31, 2009. Denison commenced pumping at TW4-4, which is immediately
upgradient ofTW4-6, using similar pumping equipment and procedures as currently utilized for
the other chlorofonn pumping wells at lhe Mill site. "
DRC Re.sponse
DRC accepis actions in Plan Item 1.
DUSA Plan Item 2:
"Dcnisfm will expand lhe chlorofonn capture zone and grouiuiwater contour maps to include
groundwater head daia at well MW-17 und piezometers P-5. These revised maps will be
contained in the quarterly chloroform monitonng reports, commencing wilh the repon for the l""
quarter of 2010."
(68 Nurili 1950 We,-! -S.ilt UicCity. UT
Mailine Address P O, Boi; I44R50 • SJII Uikc City, UT 84ll44H:iO
Tclcphi)iie(S[H)5'i6-42^0'FLIX (801 )53,'t40')7.Tn 0 (SdO 536^1414
nit-M,//fr/,Ji/t7'; Vl"-
Pri met] nn !Q0^. rcL-^L-lcti piipci
Page 2
DRC Response
DRC accepts aclions in Plan Item 2.
DUSA Plan Item 3:
"Deni.stm will install new chloroform monitoring well TW4-26 at The location indicated on Figure
I atiached to Hydro Geo Chem's Febmary 16, 2010 letter report. This wel! will be pennanent
and constructed in accordance with UAC R 317-6-6.3{1}{6). The well will be installed and
developed by August /, 2010. T\V4-26 will be sampled quarterly for the same amstiluents as the
olher chlorofonn monitoring wells."
DRC Response
Modify Item 3 to read (added wording is underlined deleted wording is strikeout):
Denison will install new chloroform moniloring well TW4-26 at the localion indicated rm Figure 1
attached to Hydro Geo Chem's February 16, 2010 letier report. This well and all oiher new
monitorins wellis) will be pennanent and c<mstrucied in accordance wilh UAC R 317-6-
6.3( l)( 6 )and shall complv wiih Part LF.6 ofthe DUSA Ground Waler Discharge Permit No.
UGW370004.
TW4-26 and any other monitoring! wellis) in.stalled downnradienl ofTW4-6 will he sampled
quarterly for The analyiicai parameters listed in seclion 4 in Appendix A ofthe White Mesa
Uranium Mill Ground Water MoniToring Qualify Assurance Plan, same constituents as ihe olhcr
chloroform monitoring wells.
With this modification DRC will accept aclions in Plan Item 3.
DUSA Plan Item 4:
"Denison will aquifer test TW4-4, TW4-6, and TW4-26, on or before August J, 2010, To
a) Calculate penneabilities and hydraulic conductivities;
b) Calculate local groundwater velocities; and
c) Detennine an ejficient pumping syslem af each pumping well location.
Such aquifer testing will be described in a report that will be submitted to the Executive Secretary
on or before Sepiember 30, 2010."
DRC Response
Modify Item 4 lo read (added wording is underlined deleted wording is strikeout):
Denison will aquifer test TW4-4, TW4-6, and TW4-26, on or before August I, 20J0, to
a) Calculate penneabilities and hydraulic ctmductivities;
b) Calculate local groundwaler velocities: and
c) Detennine an efficient pumping system at each pumping well location.
Such aquifer lestijig will be described in a report that will be submitted to the Executive Secretary
on or before September 30, 2010. Should lhe Execufive Secretai-\' require additional new monlTor
well(s) he installed down sradieni ol'TW4-6 an aauifer test to calculate items in a and b ahove
will he described in a report that will be submitled to the Executive Secretarv within 60 calendar
da\-s after well inslallation.
Page 3
With this modification DRC will accept actions in Plan Item 4.
DUSA Plan Item 5:
"Analyiicai re.'^ults for chlorofonn samples from TW4-4 TW4-6, and TW4-26 will be reported in
the Quanerly Chlorofonn Monitoring Reports that are filed wilh the E.xecutive Secreiary."
DRC Response
DRC accepts actions In Plan Item 5.
DUSA Plan Item 6:
"On or before December 31, 2010, Deni.srm will review the analytical results for TW4-6 for the
f, 2'" and 3'^' quarter 2010 .sampling events and make a detenniiuifion whether or not the
cfmcenfraiion of chlorofonn in TW4-6 is declining as a result ofthe pumping ofTW4-4. The
chlorofonn concentration in TW4-6 will be considered lo have declined as a result ofthe pumping
ofTW4-4 if the concentration of chloroform in T\V4-6 in the 3'^'' quarter of 2010 is less than the
concentration of chlorofonn in TW4-6 in eilher lhe f' quarter or 2'"' quarter of 2010. Based on
the results of fhis detennination, Denison will take the following actions:
a) If the chlorofonn concentration in TW4-6 is detennined to be declining as a result of
the pumping ofTW4-4, then the pumping ofTW4-4 will continite. Pumping aT TW4-6
will not commence at that time; and
b) If the chlorofonn concentration is TW4-6 is determined not to have declined as a result
of pumping TW4-4, then on or before March 1, 201L Denison will commence pumping
TW4-6, in addition to TW4-4, using similar pumping equipment and procedures as
currently uTilizedfor the other chlorofomi pumping w^ells at the Mill site. "
DRC Response
Removal all wording and modify Item 6 to read:
After submlUal of the 4^'' quarter, 2010 chlorofonn monitoring repori, if the Executive Secretary
determines for any reason that pumping TW4-4 is not effectively reducing the chloroform
concentration in TW4-6 DUSA will begin pumping TW4-6 with in 30 days of written nolice from
the Executive Secretary.
DUSA Plan Item 7:
''For so long as the concentration of chloroform in TW4-6 exceeds 70 pg/l and TW4-6 is tiot
being pumped, Denison will make a detenninaticm on or before December 31 ofeach year,
commencing with December 31, 2011, whether or not the concentration of chlorofonn in TW4-6
has declined over the previous four quaners. llie chlorofonn concentration in TW4-6 will be
considered to have declined at any December 31 detennination date ifihe chloroform
concentration in TW4-6 for the mosl recent 3"^ quarter is less than the chloroform concentration
measured in the 4^'' quarter prior thereto. If the chlorofonn concentration in TW4-6 is determined
not fo have declined at any detennination date then, within in 60 days afier the end of such
December 31 date. Denison will commence pumping TW4-6, in addition to TW4-4, using similar
pumping equipment and procedures as currently utUized for the chlorofonn pumping wells at the
Mill site."
Page 4
DRC Response
Remove actions in Item 7 as a result of the wording changes in Item 6.
DUSA Plan Item 8:
"The pumping ofTW4-4, or, if required under paragraphs 6 or 7 above, both TW4-4 and TW4-6,
will continue until the chlorofonn concentration in TW4-6 has been reduced to below 70 pg/L. "
DRC Response
DRC accepts actions in Plan Item 8.
DUSA Plan Item 9:
"Once chloroform concentrations in T^\^4-6 have been reduced to below 70 pg/L, Denison will
conTinue pumping either or bolh ofTW4-4 or TW4-6 as if deicnnines necessaiy to mainiain
chlorofonn concentrations in TW4-6 helow 70 pg/L. "
DRC Response
Remove actions in Item 9 as a result of (he wording changes in Item 6.
DUSA Plan Item 10:
"If, after review ofal leasl two quarters of sample results from TW4-26 il is detennined that the
chloroform concentratirm in TW4-26 exceeds 70 pg/L. then Denison will install an additional
moniToring well, at a location agreed To by The ExecuTive Secretary, within 60 days after the
localion has been agreed lo by the E.xecutive Secreiary. if at least tv^'o quarters of samples results
for this additional well Indicate a chlorofonn crmcentralion in excess of 70 pg/L in that well, this
process of adding an addilional moniloring well will be repealed until such time as the sample
results for an added iiumitpring well are le.ss than 70 pg/L chlorofonn. "
DRC Response
DRC accepis actions in Plan Item 10.
DRC RECOMMENDATIONS
It is recommended that DRC conditionally approve the Plan so long as the Plan includes the
modifications above.
Page 6
Attachment 1
Chlorofonn Contamination Investigation. Chloroform Concentrations Exceeding the Groundwater
Quality Standard in Monitor Well TW4-6. Submittal of a Plan of Action and Work Schedule.
Dennison Mines (USA) Corp.
White Mesa Uranitmi Mill, near Blanding, Utah.
Denison Mines (USA) Corp.
1050 17tbSlieel,SuilE 350
Denver. CO 80265
USA
Tei: 303 628-7798
Fax:303 3B9-4125
wvrw.denl&onmines.com
February 18,2010
VIA PDF AND FEDERAL EXPRESS
Mr. Dane L. Finerfrock
Co-Executive Secretary
Utah Water Qualily Board
State t)t Utah Departinent of Environmental Qualily
168 North 1950 Wesl
P.O. Box 144850
Salt Lake City. UT 84114-4850
Dear Mr. Finerfrock:
Re: Chloroform Contamination Investigation. Chloroform Concentrations Exceeding the
Groundwater Quality Standard in Monitor Well TW4-6. Submittal of a Revised Plan of
Action and Work Schedule. Confirmatory Action Letter.
Recent chloroform concentration:^ in monitor well TW4-6 a\ lhe White Mesa Mill (the "Mill")
have exceeded the 70 ug/I State of Ulali groundwater quality standard, requiring an adjuslnienl to
the hydraulic containment program relating lo the chlorofonn coniamination plume at the Mill.
On December 31, 2009 Denison Mines (USA) Corp. ("Denison") submitted a plan of aciion and
work schedule to achieve hydraulic containment at TW4-6 as vetiuived by lhe Confirmiilovy
AcLi<m Letter dated November 9, 2009.
On February 11, 2010 Division of Radiation Control ("DRC") aud Deni.son staff had a
conference call tu discuss Denison's propo.scd plan of action and schedule, at which time
Denison agreed lo make several modificalions to the plan and schedule. The conclusions
reached during that conference call were confirmed in an email dated February 11, 2010 from
DRC Staff lu Denison.
Enclosed please find:
a) a copy of the Iciter report dnlod December 28. 2009 from Hydro Geo Chcni, Inc., lhat
was previously submiUed wifh Denison's December 31, 2009 plan and schedule; and
h) a leUer rcport dated February 16. 2010 from Hydro Geo Chem, Inc., that addresses
certain of the modifications to the plan and schedule discussed with DRC on February 11,
2010.
7. For so iong as the concentration of chloroform in TW4-6 exceeds 70 ug/l and TW4-6 is
not being pumped. Denison will make a detenninaiion on or before December 31 of each year,
commencing with December 31, 2011, whether or not the concentration of chloroform in TW4-6
has declined over the previous four quarters. The chloroform concentration in TW4-6 will he
considered to have declined al any DeecnAbcv 31 deternnnaUon date if the chlorofoim
concentration in TW4-6 fur [he most recent 3"' quarter i.s le.^s dian the chloroform coneentraiion
measured in the 4"' quarter prior ihereio. If the chloroftmn concentration in TW4-6 is
determined not to have declined at any deiermination dale then, wilhin 60 days after the end of
such December 31 dale, Denison will commence pumping TW4-6, in addition to TW4-4. using
similar puinping equipmeni and proceduies a.s currejirJy ulilized for lhe other chlorofonn
pumping wells at the Mill site.
8. '1 he pumping of TW4-4, or, ii required under paragraph^^ 6jJ>r7' above, both TW4-4 and
TW4'6. will continue until the chloroform concentration in TW4-6 has been reduced to below 70
ug/l.
9, Once chloroform coneeniraiions in TW4-6 have heen reduced to below 70 ug/l, Denison
will continue pumping eilher or both of TW4-4 or TW4-6 as it determines necessary to maintain
chlorofomi concentrations in TW4-6 below 70 ug/l.
10. If. after review of at least Iwo quarters of sample resuhs from TW4-26 il is dclcvmincd
that the chloroform concentration in TW4-26 exceeds 70 ug/l, then Denison will install an
additional monitoring well, al a location agreed lo by the Executive Secretary, within 60 days
after the location ha.s been agreed to by the Executive Secretary. If al least two quarters of
sample rcsults tor this additional well indicate a chloroform concentration in excess of 70 ug/l in
dial well, this process of adding an addilional monitoring well will bc repeated until such time as
die .sample icsulls for au added moniloring well are less than 70 ug/l chloroform.
If you have any questions or require any further infonnation, please contacl the undersigned.
'N'ours very truly.
DENISO:SJ ^IINES (USA) CORP*
David C. Fryacnlund
Vice President, Regulatory Affairs and Counsel
cc: Ron F. Hochstein
Harold R. Roberts
David E. Turk
Stewart Smith
DENISON
MINES
ilYDKt) (iliOCMbjVI, [N(
Jiili'lnun/iniin/ .'j/:iniri. i!-" i'rihunluav
December 28, 2009
Mv. Steven Landau
Denison Mines (USA) Corporation
1050 17th Slreel, Suite 950
Denver, Colorado 80265
Dear Steve,
This letter addresses the recent detection of chlorofonn concentrations exceeding 70 fig/L at
TW4-6, a toiYiporavy perched zone monitoring well locaied al the While Mesa Uranium MiU near
Blanding, Utah (the '^Mill" or the "site"). Chloroform concentrations exceeding 70 ^g/L places the
weli within the perched zone chloro fonn plume at tho site. Background conditions, a discussion of
potential response options, and a recommendation arc provided below.
Backtzround
TW4-6 was installed in the second quarter of 2000 lo scivc as a downgrudict\t well lor
monitoring perched zone chloroform that most likely originated fi'om the abandoned .scale house and
fonner office leach fields. These leach fields received bolii laboratory anij lavatory wastes in the
early years of Mill operation as described in the Preliminary Corrective Action Plan (Hydro Gco
Chem [HGC], 2007'), Between lhe lime of installation and the fourth quarter 012008, TW4-6
bounded the chloroform plume which is defined by concentrations that equal or exceetl 70 [i^L.
Chloroform concentrations remained non-detect at TW4-6 between the time of installation and the
Hrst quarter of 2005. Concentrations then maintained a slow, somewhat erratic, but upward trend
until concentrations exceeded 70 ^ig/L in the fiist quarter of 2009. The rate of chloro foi'm migralion
at TW4-6 is cleariy slower than at TW4-4, die closest well upgradient of TW4-6. Concentralions at
TW4-4 incrcjised from non-detect lo more dian 2,200 ^g/L within only 2 quarters whereas 16
quarters were required for concentrations in TW4-6 to increase from non-detect to only 81 ^g/L.
I'tydro Gco Clicin, Inc. 2007, Prcliniiiiiiry Correciive Acfion Plan. While Mesji Uftaniuiii Mill Near niaiKiing, Utah
x„:
-lU'i-M U-\:(i.iin> .Siiiu- IH! rik-MjM, Ai-i/,ini,i Hli70S Ui7& I i .^^0,^>.v I.SOO S20,39.M^r)(M-.i\ UM).'/1 / .W:^-V/ r^^l^-•|•t,-.
Ml". Stcven f^nd.iu
December 28, 2009
)*figc 2
Since 2003, chlorofonn has been removed from the perched zone by pumping. Pumping
initially began at MW-4. TW4-19, MW-26 (TW4'-15) andTW4-20 were later added to the puinping
network. The purpose ofthe pumping i.s 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 penneability and saturated thickness, and 2) high
concentrations ofclilorofonn were detected at these locations. The relatively high transmissivity of
the perched zone in the vicinity of the pumping wells results in tbe wells having a relatively high
productivity. The combination of relatively high productivity and high chlorofoim concentralions
allows a high rate of chlorofonn mass removal.
Downgi'adient pumping has also been considered. The primaiy reason that downgradient
wells such as TW4-6 have nol been pumped is that the perched zone has a relatively low
peimcability in the downgradicnl portion ofthe chlorofonn plume. Although it would be desirable to
pump at downgradient locadons from the standpoint of reducing further downgi'adient plume
migration, any wells completed in this portion of the plume would likely have a veiy low
productivity (< 0.5 gpm). Fui-thcnnore, the rate of chloroform inigralion in the downgradient portion
ofthe plume is slow due lo low permeability conditions.
Options
As discussed in the Preliminary Conective Action Plan (PCAP), should concenti-ations at a
downgradient well such asTW4-6 exceed70/ig.'L, a new downgi'adient well is lobe installed with
the concurrence ofthe Utah Department ofEnvironmental Quality (UDEQ). This is Option 1.
Pumping at downgi-adieni wells such as TW4-6 has not been implemented in tlie past due to low
perched zone permeabilities in the downgradient portion ofthe piume and the lov/ expected rales of
well productivity.
A second option (Option 2) nol presented in the PCAP would be to delay installation ofa
well downgradient of TW4-6 and to pump upgratlient well TW4-4 a( a rate as high as practical.
Should chloi'ofomi concentrations continue to increase at TW4-6, then TW4~6 would also be
pumped at a rate as high as practical. Should chloroform concenlrations continue to increase at TW4-
6 while boihTW4~4 and TW4-6 are pumped, a new well would be installed downgj-adient of TW4-6.
Should concentrations at TW4-6 dixip below 70 (ag/L while TW4-4 is pumped, or while both
TW4-4 and TW4-6 are pumped, an addilional downgradient well will not be installed unless
concentrations at TW4-6 should again increase to 70 |xg/L or more. Pumping at either or both wells,
once implemented, will continue to the extent practical.
Ci^DtKiiiiicjilsiiFkl Sci(iiig';\iiroberiK\lJ3L-nlSciiinft»Vrciiip<iiaiy ]iucn)ClFitCb-\.Contciu.Oul!oc)k\WXQQAlPXV0'n22ilsi tlr(5),cloc
Mr. Steven [„aii(iiHj
December 2f>, 2009
Recoinmcndation
Although the productivities of TW4-4 and TW4-6 are likely to bc low, Option 2 is
recommended. Pumping of either or both of these wells would provide additional mitigation of
chloroform in the pei'ched zone, and tnay help reduce the rate of downgi'adient chlorofonn migration.
Pushing back the instaUation of an additional monitoring well downgradicnl of TW4-6, while
initiating pumping and continuing to nionitor concentrations, is justified by the slow rate of
downgradictit chlorofonn migration in this area and by die additional benefits expected from the
pumping. Option 1 would provide for quicker installation ofan additional downgradient well but
would not provide the potential bcnefUs of pumping TW4'4 (and TW4-6, if implemented).
Sincerely,
Stewartj. Smith
Associate Hydrogeologist
C:\niH;iiiin;[i1sandSciiiriiis\Iii-oL^;jisUjrj«::il ScUiii&.VrL-m|xit:ii>i Intcnici Fil(;s\Coiilciil,OiilUKJk\WX09All'XW9l228slUrt.^).(ltJC
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En I'! IVH IHi >l! lit SilftlCf C-." "ii'ih}llitiil}\
lar
Februar/ 16,2010
David Frydenlund, Fsq.
Denison Mines (USA) Coi-poration
1050 17lh Street, Suite 950
Denver, Colorado 80265
Dear Mr. Frydenlund.
This is a folluw-up to Hydro Gco Chem, Inc's (HGC's) December 28, 2009 letter to Mr.
Sievcn Landau, Denison Mines, Uiat addressed the detection of chloroform al concentrations
exceeding 70 micrograms per Liter (pg/L) at perched wel! TW4-6 at the White Mesa Uranium Mill
(the 'Site"). As discu.s.sed in die Preliminary Conecdve Action Plan (PC.AP) for the sile, should
coneeniraiions at a downgradient wel 1 such as TW4-6 exceed 7fl (.it/L.'' "*^w downgradient well Is (o
bL' installed with the concurrence of the Utah Department of Enviinnmental Qualitv (UDHQj. HGC
iiiconimcndcd an altcrnulive lhat consisted of pumping TW4-4, the well located immediately
njigradieni of TW4-6, and delaying ilic insiallation of a new downgradient well to scc if the
upgradient pumping would reduce coneeniraiions at TW4-6 below 70 pg/L, Puinping of TW4-6 was
also recommended if concentrations ut TW4-6 did not decrease as a rcsull of pumping TW4-4.
Underthe alternative, a new weli would bc in.stalled downgradieni of TW4-6 should concentrations
at TW4-6 continue to increase during pumping of both welis.
As indicated in ytiur February 12, 2010 e-mail, UDEQ requests tlic installation uf a new
downgradieni well before the inipact of pumping on concent! atiuns al TW4-6 can be detennined by
monitoring. UDL-Q also requests thar hydraulic tests be pertbrmed on the new well, and existing
wells TW4-4 and TW4-6, U) allow calculation ofthe hydi':iullc conductivities, perched waler pore
velocities, and efficient puinping schemes at each location.
The proposed location forthe new wel I, designated TW4-26, is provided on Figure 1, which
is a water level contour map based on Decetnber 2009 measurements. The water level contours
indicate lhat conditions soudi ot'TW4-6 are complicated hy the presence oflhc southern wildlife
pond do the south-soulhwcst) and rhe persistently low waler level at TW4-14 (lo the northea.st).
These features result in a change IVom a generally .southerly hydraulic gradieni north of TW4-6 lo an
appaiemly more easterly gradient south ot TW4-6. The proposed well is therefore located south-
sun thca.si of TW4-6. at about ef|ual distances fromTW4-14 (tothe northeast) and TW4-23 (tothe
west-norlhwesi).
VV<-,i VV,,-iiii.i|-f, Siiir.- 101 lm-i..ii. An/i.ii.i Uri'uF. U.7.'; |-^ .^:0 ?'-n I A[U) ,-^?|) )})?, ISfSO-h.iv .Slid :'2~ y^A'!- Icll l-rir
David FiydcnluiKj. Esq.
February 16,2010
Page 2
HOC' proposes to perfonn the hydraulic tests on the new well, and existing wells TW4-4 and
TW4-6, after installation and development of the new well. Testing procedures will be die same as
described in HGC, 2005'.
Please feel free to contact me if you have any questions or need additional information.
Sincerely,
Stewai'tJ, Smith
Associate Hydrogeologist
Attachment: Figure (1)
^ HGC, 2005 Perched Monitoiing Well Installiition and Tesling at ttie White Mc'm Uranium Mill, April througli
June 2005. Submitted to Iniemational Uranium (USA) Corporation.
H'i7|gCOWlwiri*l(TilMZ[5dr llndHT
ATTACHMENT
FIGURE
Kriged December 2009 Water Levels Showing Extent of Chloroform > 70 pg/L and
Location of Proposed Well TW4-26, White Mesa Silc
FIGURE
PROPERTY
BOUNDARY
TWH.li* v'*'"-'SL/ t
EXPLANATinw
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'•^' Mi-^.milf stio*rgeir/»iDJi ir 'fl*i »nitl
ti£3 52
HYDRO
GEO
CHEM. INC.
KRIGED DECEMBER 2009 WATER LEVELS
SHOWING EXTENT OF CHLOROFORM > 70 U(^L
AND LOCATION OF PROPOSED WELL TW4-26
WHITE MESA SITE
SjS H :/71 BOOCVIwSlcb 1 CVtw26pn3p. sM
In accordance witli the reconunendations in Hydro Geo Chcin's two IcUer reports, and the
discussions wilh DRC staff on February 11, 2010, Denison proposes the following revised plan
of action and work schedule to achieve hydraulic coniaLtiinenl at TW4-6:
1. On or before January 31, 2009, Denison commenced pumping at TW4-4, which is
inunediately upgradient of TW4-6, using similar pumping equipment and procedures as currently
ulili/ed for die other chloroform pumping weils al (he Mill site.
2. Denison will e.\]rand the chloroform capture zone and groundwater contour maps lo
include groundwater head data at well MW-17 and piezometer P-5. These revi.sed maps will be
contained in the quarterly chlorofomi monitoring reports, commencing with the report for the T*
quarter of 2010.
.^. Denison will install new chloroform monitoring well TW4 26 at the location indicaled on
Figure I attached to l-Iydro Ceo Chem's February \b, 2010 Icllcv report. This well will be
pennanent and constmcted in accordance with UAC R317-6-6.3(1X6). The well will be in.stalled
and developed by August 1. '2010. TW4-26 will be sampled quarterly for the same constittients
as \he other chloioform monitoring wells.
4. Denison will aquitcr lest TW4-4. TW4-6 and TW4-26, on or before August I, 2010, lo
a) Calculate permeabilities and hydraulic conductivities;
b) Calculate local groundwater velocities; and
c) Determine an efficient pumping syslem at each puinping wcli location.
Such aquifer testing wili be described in a rcport that will bc submitted lo die Executive
Secretary on or before September 30, 2010.
5. Analytical results for chlorofonn samples from TW4-4, TW4-6 and TW4-26 will be
reported in the Quarterly Chlorofoim Monitoring Reports that are filed with the Executive
Secretary.
6. On or before December 31, 2010, Deni.son w-ili review lhe analytical results for TW4-6
for the P\ 2'"^ and 3^'^ quarter 2010 sampling events and make a deiermination whether or not the
concentration of chloroform in TW4-6 is declining as a result of the puinping of TW4-4. The
chloroform concentration in TW4-6 will be considered to have declined as a result of the
puinping of TW4-4 Ifihe conceniralion of chloroform in TW4-6 in the 3"^ quarter of 2010 is less
than lhe concentration of chlorofonn in TW4-6 in either rhe Isl ciuarter or 2'^^ quarter of 2010.
Based tin the rcsults of this deiermination. Denison wdll lake the following actions:
a) Tf the chloroform concentration in TW4-6 is determined to bc declining as a result oi
the pumping of rW4-4, then the pumping of TW4-4 will continue. Pumping at TW4-6 I
will not commence at lhat lime; and i^W ^^'^/-^
b) If the chlorofonn concentration in TW4-6 is determined not to have declined as a rcsull
of pumping TW4-4. then, on or before March 1, 2011, Denison will commence
puinping TW4-6. in addition lo TW4-4, using similar pumping equipmeni and
procedures as currenlly utilized for the other chloroform pumping wells at the Mill site.
/ DENISOI
MINES