DRC-2008-002243 - 0901a0688070e18f

February 28, 2008
VIA FEDERAL EXPRESS
Mr. Dane L. Finerfrock
Executive Secretary
Utah Radiation Control Board
State of Utah Department of Environmental Quality
168 North 1950 West
Salt Lake City, UT 84114-4850
Dear Mr. Finerfrock:
Denison Mines (USA) Corp.
1050 17th Street, Suite 950
Denver, CO 80265
USA
Tel : [phone]
Fax: [phone]
www.denisonmines.com
Re: Transmittal of 4th Quarter 2007 Chloroform Monitoring Report for the White Mesa
U rani urn Mill
Enclosed are two copies of the White Mesa Uranium Mill Chloroform Monitoring Report for the 4th
Quarter of 2007, as required under State of Utah Notice of Violation and Groundwater Corrective
Action Order UDEQ Docket No. UGQ-20-01.
Yours very truly,
/.L�� <�;MINES (USA) CoRP.
Steven D. Landau
Manager of Environmental Affairs
cc: Ron F. Hochstein
Harold Roberts (wo/enclosure)
David Frydenlund
David Turk
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White Mesa Uranium Mill
Chloroform Monitoring Report
State of Utah
Notice of Violation and Groundwater Corrective Action Order UDEQ
Docket No. UGQ-20-01
4th Quarter (October through December)
2007
Prepared by:
Denison Mines (USA) Corp. (DUSA)
1050 17th Street, Suite 950
Denver CO 80265
February,2008
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1. INTRODUCTION
This is the Quarterly Chloroform Monitoring Report, as required under State of Utah
Notice of Violation and Groundwater Corrective Action Order State of Utah Department
of Environrnental Quality ("UDEQ") Docket No. UGQ-20-01 for the 4th Quarter of 2007
(the "Quarter") for Denison Mines (USA) Corp.'s ("DUSA's") White Mesa Uranium
Mill (the "Mill"). This Report also includes the Operations Report for the Long Term
Pump Test at MW-4, TW4-19, TW4-15 (MW-26) and TW4-20 for the Quarter.
2. SAMPLING AND MONITORING PLAN
2.1. Description of Monitor Wells Sampled During the Quarter
During the Quarter, the following chloroform contaminant investigation groundwater
samples and measurements were taken:
2.1.1. Groundwater Monitoring
Groundwater Monitoring was performed in all of the chloroform monitoring wells, being
the following wells:
• MW-4 • TW4-13
• TW4-A • TW4-14
• TW4-1 • TW4-15 (MW-26)
• TW4-2 • TW4-16
• TW4-3 • TW4-17 (MW-32)
• TW4-4 • TW4-18
• TW4-5 • TW4-19
• TW4-6 • TW4-20
• TW4-7 • TW4-21
• TW4-8 • TW4-22
• TW4-9 • TW4-23
• TW4-10 • TW4-24
• TW4-11 • TW4-25
• TW4-12
The locations of these wells are indicated on the map attached under Tab A.
Wells sampled during this reporting period were analyzed for the following constituents:
• Chloroform
• Chloromethane
• Carbon tetrachloride
• Methylene chloride
• Chloride
• Nitrogen, Nitrate + Nitrite as N
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As UDEQ is aware, Denison has in the past experienced difficulty in obtaining
chloroform samples from well TW4-14. The difficulty arose from the very limited
recovery rate encountered at that location. More specifically, it is generally necessary
that there be at least 1.5 feet of water within the well in order to obtain a sample which is
not influenced by sedimentation from the bottom of the well. At the request of UDEQ,
the recovery rate from the TW 4-14 location was evaluated by bailing and routine water
level measurements in order to determine the necessary time between purging and sample
collection. Such an evaluation was undertaken between September 21 and October 20,
2006 with limited success in water recovery experienced during this study period.
Nonetheless, quarterly samples were able to be collected from well TW4-14 during the
4th Quarter of 2006 (November 8, 2006), this has continued in all Quarters of 2007.
2.1.2. Groundwater Head Monitoring
Depth to groundwater was taken in the following wells and/or piezometers during the
Quarter:
a) All of the chloroform contaminant investigation wells listed in paragraph 2.1.1
above on October 10, 2007;
b) All of the point of compliance monitoring wells under the Mill's Groundwater
Discharge Permit ("GWDP") on 10-31-07.
c) Piezometers-P-1, P-2, P-3, P-4 and P-5 on November 2, 2007
In addition, weekly depth to groundwater measurements were taken in MW-4, TW4-15
(MW-26), TW4-19 and TW4-20, as part of the long term pumping test for MW-4.
2.2. Sampling Methodology, Equipment and Decontamination Procedures
The sampling methodology, equipment and decontamination procedures that were
performed for the chloroform contaminant investigation during the Quarter can be
summarized as follows:
2.2.1. Well Purging and Depth to Groundwater
a) A list is gathered of the wells in order of increasing chloroform contamination.
The order for purging is thus established. Mill personnel start purging with all of
the non-detect wells and then move to the more contaminated wells in order of
chloroform contamination, starting with the wells having the lowest chloroform
contamination; and
b) Before leaving the Mill office, the pump and hose are rinsed with de-ionized
("DI") water. Mill personnel then proceed to the first well which is the well
indicating the lowest concentration of chloroform based on the previous quarters
sampling results. Well depth measurements are taken and the two casing
volumes are calculated (measurements are made using the same instrument used
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for the monitoring wells under the Mill's GWDP). The Grundfos pump (a 6 gpm
pump) is then lowered to the bottom of the well and purging is begun. At the
first well, the purge rate is established for the purging event by using a calibrated
5 gallon bucket. After the evacuation of the first well has been completed, the
pump is removed from the well and the process is repeated at each well location
moving from least contaminated to most contaminated. All wells are capped and
secured prior to leaving the sampling location.
2.2.2. Sampling
a) Following the purging of all chloroform investigation wells, the sampling takes
place (usually the next morning). Prior to leaving the Mill office to sample, a
cooler along with blue ice is prepared. The trip blank is also gathered at that time
(the trip blank for these events is provided by the Analytical Laboratory). Once
Mill Personnel arrive at the well sites, labels are filled out for the various samples
to be collected. All personnel involved with the collection of water and samples
are the outfitted with rubber gloves. Chloroform investigation samples are
collected by means of dedicated bailers and the wells are purged by means of a
dedicated portable pump. Each quarterly pumping and sample collection event
begins at the location least affected by chloroform (based on the previous
quarters sampling event) and proceeds by affected concentration to the most
affected location. The dedicated portable pump is appropriately decontaminated
prior to each purging sampling event and the QA rinsate sample is collected after
said decontamination but prior to the commencement of the sampling event.
b) Mill personnel use a disposable bailer to sample each well. The bailer is attached
to a reel of approximately 150 feet of nylon rope and then lowered into the well.
After coming into contact with the water, the bailer is allowed to sink into the
· water in order to fill. Once full, the bailer is reeled up out of the well and the
sample bottles are filled as follows;
(i) First, a set of VOC vials is filled. This set consists of three 40 ml vials
provided by the Analytical Laboratory. The set is not filtered and is
preserved with HCL;
(ii) Second, a 500 ml sample is collected for Nitrates/Nitrites. This sample is
also not filtered and is preserved with H2S04 (the bottle for this set is
also provided by the Analytical Laboratory);
(iii) Third, a 500 ml sample is collected for Chloride. This sample is not
filtered and is not preserved; and
c) After the samples have been collected for a particular well, the bailer is disposed
of and the samples are placed into the cooler that contains blue ice. The well is
then recapped and Mill personnel proceed to the next well.
DUSA completed (and transmitted to UDEQ on May 25, 2006) a revised Quality
Assurance Plan ("QAP") for sampling under the Mill's GWDP. The GWDP QAP was
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reviewed by UDEQ and has been approved for implementation. The QAP provides a
detailed presentation of procedures utilized for groundwater sampling activities under the
GWDP. While the water sampling conducted for chloroform investigation purposes has
been conformant with the general principles set out in the QAP, some of the requirements
in the QAP were not fully implemented prior to UDEQ's approval for reasons set out in
correspondence to UDEQ dated December 8, 2006. Subsequent to the delivery of the
December 8, 2006 letter, DUSA discussed the issues brought forward in the letter with
UDEQ and has received correspondence from UDEQ about those issues. In response to
UDEQ's letter and subsequent discussions with UDEQ, DUSA has incorporated changes
in chloroform QA procedures in the form of a separate document. The chloroform QA
document describes the differing needs of the chloroform investigation program, and is
and attachment to the GWDP QAP where QA needs other than those described in the
chloroform QA document are addressed.
2.3 Field Data Worksheets
Attached under Tab B are copies of all Field Data Worksheets that were completed
during the Quarter for the chloroform contaminant investigation monitoring wells listed
in paragraph 2.1.1 above and sampled August 15, 2007.
2.4 Depth to Groundwater Sheets
Attached under Tab Care copies of the Depth to Water Sheets for the weekly monitoring
of MW-4, TW4-15 (MW-26), TW4-19 and TW4-20 as well as the monthly depth to
groundwater monitoring data for chloroform contaminant investigation wells measured
during the quarter. Depth-to-groundwater measurements collected on October 10, 2007
were utilized for groundwater contours are included on the Field Data Worksheets at Tab
B of this report.
3. DATA INTERPRETATION
3.1. Interpretation of Groundwater Levels, Gradients and Flow Directions.
3 .1.1. Current Site Groundwater Contour Map
Included under Tab D is a water table contour map, which provides the location of all of
the wells and piezometers listed in item 2.1.2 above for which depth to groundwater was
taken during the Quarter, the groundwater elevation at each such well and piezometer,
measured in feet above mean sea level, and isocontour lines to delineate groundwater
flow directions observed during the Quarter's sampling event. The contour map uses the
October 10, 2007 data for the wells listed in paragraph 2.1.2 (a) above, October 31, 2007
data for the wells listed in paragraph 2.1.2 (b), and November 2, 2007 for the piezometers
listed in paragraph 2.1.2 (c) above.
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Also included under Tab D is a groundwater contour map of the portion of the Mill site
where the four chloroform pumping wells are located, with hand-drawn stream tubes, in
order to demonstrate hydraulic capture from the pumping
3 .1.2. Comparison of Current Groundwater Contour Maps to Groundwater Contour
Maps for Previous Quarter
The groundwater contour maps for the Mill site for the third quarter of 2007, as submitted
with the Chloroform Monitoring Report for the third quarter of 2007, dated November
30, 2007, are attached under Tab E.
A comparison of the water table contour maps for the Quarter to the water table contour
maps for the previous quarter indicates similar patterns of drawdown related to pumping
of MW-4, MW-26 (TW4-15), TW4-19 and TW4-20. Water levels and water level
contours for the site have not changed significantly since the last quarter, except for a few
locations.
An increase in water level of nearly 8 feet occurred in MW-31 and a decrease of nearly 4
feet occurred at MW-27. A water level increase of approximately 7 feet occurred at MW-
4, and a decrease of approximately 8 feet occurred at TW4-20. Water level fluctuations
in these pumping wells are due in part to fluctuations in pumping conditions just prior to
and at the time the measurements are taken. A water level change of approximately 20
feet reported for TW 4-6 is considered erroneous, and the third quarter, 2007 water level
for this well is reported in the Figures.
3 .1.3. Hydro graphs
Attached under Tab F are hydrographs showing groundwater elevation m each
chloroform contaminant investigation monitor well over time.
3.1.4. Depth to Groundwater Measured and Groundwater Elevation
Attached under Tab G are tables showing depth to groundwater measured and
groundwater elevation over time for each of the wells listed in Section 2.1.1 above.
3.1.5. Evaluation of the Effectiveness of Hydraulic Capture
Perched water containing chloroform has been removed from the subsurface by pumping
MW-4, TW4-19, MW-26 (formerly TW4-15), and TW4-20. 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
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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.
The impact of pumping these wells is indicated by the water level contour maps attached
under Tabs D and E. Cones of depression have developed in the vicinity of the pumping
wells which continue to remove significant quantities of chloroform from the perched
zone. The water level contour maps indicate that effective capture of water containing
high chloroform concentrations in the vicinity of the pumping wells is occurring. As
noted in Section 3 .1.2, little change in measured water levels occurred at pumping wells
between the second and third quarters of 2007, except for the increase in water level
(decrease in drawdown) at MW -4 and the decrease in water level (increase in drawdown)
at TW4-20. Overall, the combined capture of TW4-19, TW4-20, MW-4 and MW-26
(TW4-15) has not changed significantly since the last quarter.
Although high chloroform concentrations exist at some locations downgradient of the
pumping wells (for example, near TW4-4), the low permeability of the perched zone at
these locations would prevent significant rates of chloroform mass removal should these
wells be pumped. By pumping at the more productive, upgradient locations, however,
the rate of downgradient chloroform migration will be diminished because of the
reduction in hydraulic gradients, and natural attenuation will be more effective.
3.2. Interpretation of Analytical Results
3.2 .1. Copy of Laboratory Results
Included under Tab H of this Report are copies of all laboratory analytical results for the
groundwater quality samples collected under the chloroform contaminant investigation
on October 10, 2007 along with the laboratory analytical results for a trip blank.
3.2.2. Electronic Data Files and Format
DUSA has provided to the Executive Secretary an electronic copy of all laboratory
results for groundwater quality monitoring conducted under the chloroform contaminant
investigation during the Quarter, in Comma Separated Values (CSV). A copy of the
transmittal e-mail is included under Tab I.
3 .2.3 Current Chloroform Isoconcentration Map
Included under Tab J of this Report is a current chloroform isoconcentration map for the
Mill site.
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3 .2.4 Data and Graphs Showing Chloroform Concentration Trends
Attached under Tab K is a table summarizing chloroform and nitrate values for each well
over time. TW4-14 had a small amount of water just sufficient for sampling (see the
discussion in Section 2.1.1 above)
Attached under Tab L are graphs showing chloroform concentration trends in each
monitor well over time. As TW4-14 was previously dry, a trend graph for that well has
not been included.
3.2.5 Analysis of Analytical Results
Comparing the analytical results to those of the previous quarter, as summarized in the
table included under Tab K, the following observations can be made:
a) Chloroform concentrations have increased by more than 20% in the following
wells, compared to last quarter: TW4-2, TW4-8, TW4-15 (MW-26), and TW4-
20.
b) Chloroform concentrations have decreased by more than 20% in the following
wells, compared to last quarter: TW4-10, TW4-16, and TW4-24;
c) Chloroform concentrations have remained within 20% in the following wells
compared to last quarter: MW-4, TW4-1, TW4-4, TW4-5, TW4-6, TW4-7,
TW4-9, TW4-11, TW4-18, TW4-19, TW4-21, and TW4-22;
d) Chloroform concentrations at TW4-8 increased slightly from 1.5 to 3.5 J.lg/L; and
e) TW4-3, TW4-12, TW4-13, TW4-14, MW-32 (TW4-17), TW4-23, and TW4-25
remained non-detect.
In addition, between the third and fourth quarters of 2007, the chloroform concentration
in well TW4-2 increased from 340 J.lg/L to 3,200 J.lg/L, the concentration in well TW4-20
increased from 5,200 J.lg/L to 9,000 J.lg/L, the concentration in TW4-21 decreased from
140 J.lg/L to 120 J.lg/L, and the concentration in TW4-22 decreased from 530 J.lg/L to 440
J.lg/L. Wells TW4-23 and TW4-25 remained non-detect for chloroform, and the
concentration in well TW4-24 decreased slightly from 2.2 to 1.5 J.lg/L. TW4-24, located
west of TW4-22, and TW4-25, located north of TW4-21, bound the chloroform plume to
the west and north.
Chloroform concentrations in TW 4-6, which was the most downgradient temporary
perched well prior to installation of temporary well TW4-23, remained at 18 J.lg/L. This
well has likely remained outside the chloroform plume due to a combination of 1) slow
rates of downgradient chloroform migration in this area due to low permeability
conditions and the effects of up gradient chloroform removal by pumping, and 2) natural
attenuation. Both TW4-6 and TW4-23 bound the chloroform plume to the south.
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3.3. Quality Assurance Evaluation And Data Validation
Quality assurance evaluation and data validation procedures in effect at the time of
sampling were followed. These involve three basic types of evaluations: field QC
checks; Analytical Laboratory checks; and checks performed by DUSA personnel, as
described below.
3.3.1 Field QC Checks
Field Quality Control samples for the chloroform investigation program consist of a field
duplicate sample, a field blank and a trip blank. These check samples are to be generated
for each quarterly sampling episode. During the 4th Quarter of 2007 duplicates (TW4-65,
duplicate of TW4-20 and TW4-70, duplicate of TW4-15), a DI blank (TW4-60), an
equipment rinsate sample (TW4-63) and a trip blank were collected and analyzed. The
results of these analyses are included with the routine analyses under Tab H.
3.3.2 Analytical Laboratory QA/OC Procedures
The Analytical Laboratory has provided summary reports of the analytical quality
assurance/quality control (QA/QC) measurements necessary to maintain conformance
with NELAC certification and reporting protocol. The Analytical Laboratory QA/QC
Summary Report, including copies of the Mill's Chain of Custody and Analytical
Request Record forms, for the November sampling event, are included under Tab H.
3.3.3 Mill QA Manager Review
The Mill QA Manager, which, for these sampling events was DUSA's Manager of
Environmental Affairs, performed four types of reviews: a determination of whether Mill
sampling personnel followed Mill sampling procedures; a review of the results from the
Field QC Checks; a review of analytical reports for holding times and qualifying
indicators for the data; and a review of the Analytical Laboratory QA/QC analysis. The
results of the QA Manager's review are discussed below.
a) Adherence to Mill Sampling SOPs
On a review of adherence by Mill personnel to the sampling procedures summarized in
Section 2.2 above, the QA Manager concluded that such procedures had been followed.
b) Results From Field QC Checks
The duplicate samples of TW4-15 and TW4-20 indicated a relative percent difference
(RPD) outside the prescribed standard of 20% for methylene chloride at TW4-15 and for
chloroform and carbon tetrachloride analyses at TW4-20. This is somewhat improved
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over the previous quarter, however, it is noted that these sample results are outside of the
prescriptive limitation. The results of the QC evaluation of duplicate samples for this 4th
Quarter, 2007 event is provided in the table below:
While the prior quarters results did not indicate the presence of chloroform in the field
blank, this quarters field blank TW 4-60 and the equipment rinsate blank TW 4-63 found
chloroform in minor concentrations at 5. 7 and 1.4 ug/L.
In response to these conditions, the QA Manager has previously investigated possible
causes of Quality Assurance anomalies in the chloroform sampling data. The areas of
inquiry have included possible sources of chloroform from the DI distribution system and
methods of sample duplication. As was observed for the prior 3rd Quater period, the DI
blank and equipment rinsate sample results (TW4-60 and TW4-63) were non-detect
suggesting that the installation of a carbon filtration unit in the DI water generation
process was successful. In reviewing the results of chloroform duplicate data, the QA
manager has discussed this matter with sampling personnel and it is believed that
collecting sequential duplicate samples from pumping wells may be resulting in
differences between samples. Accordingly, the sampling staff has been instructed to
collect duplicate samples only from non-pumping wells however, subsequent to this
sampling event. The QA Manager has discussed the issue of matrix interference in
chloroform analyses with the contract laboratory but this complexity in the analytical
system remains at issue. As a means of better understanding the issue and the
Laboratory's culpability for low concentration findings of chloroform in equipment
rinsate and field blanks, the Mill staff have prepared blind samples of bottled water for
analyses by the Laboratory. The results of this QC check are not yet available but will
aid in further identification of the error term. These results will be included in the next,
1st Quarter, 2007 Chloroform Report.
c) Review of Analytical Laboratory QA/QC Analysis and Analytical Reports
The QA Manager reviewed the Analytical Laboratory's QA/QC Summary Reports and
made the following conclusions;
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(i)
(ii)
(iii)
(iv)
Check samples were analyzed for each method used in analyzing the
Chloroform investigation samples. These methods were:
Parameter
Nitrogen, (Nitrate+ Nitrite as N)
Chloroform,
Carbon tetrachloride
Chloromethane
Methylene chloride
Chloride
Method
E353.2
E624
E624
E624
E624
A4500-CL B
The check samples included at least the following: a method blank, a
laboratory control spike (sample), a matrix spike and a matrix spike
duplicate;
All qualifiers, if any, and the corresponding explanations in the summary
reports are reviewed by the QA Manager. The qualifiers reported were
for matrix interference in chloroform analyses in some of the analyzed
monitoring location samples.
The laboratory holding time for all analyses was within chloroform
specification and sample temperature was acceptable upon receipt.
4. LONG TERM PUMP TEST AT MW-4, TW4-15 (MW-26), TW4-19 AND
TW4-20, OPERATIONS REPORT
4.1. Introduction
As a part of the investigation of chloroform contamination at the Mill site, DUSA has
been conducting a Long Term Pump Test on MW-4, TW4-19, TW4-15 (MW-26) and
TW4-20. The purpose of the test is to serve as an interim action that will remove a
significant amount of chloroform-contaminated water while gathering additional data on
hydraulic properties in the area of investigation. The following information documents
the operational activities during the Quarter.
4.2. Pump Test Data Collection
The long term pump test for MW-4 was started on April 14, 2003, followed by the start
of pumping from TW4-19 on April 30, 2003, from TW4-15 (MW-26) on August 8, 2003
and from TW4-20 on August 4, 2005. Personnel from Hydro Geo Chern, Inc. were on
site to conduct the first phase of the pump test and collect the initial two days of
monitoring data for MW-4. DUSA personnel have gathered subsequent water level and
pumping data.
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Analyses of hydraulic parameters and discussions of perched zone hydrogeology near
MW-4 has been provided by Hydro Geo Chern in a separate report, dated November 12,
2001, and in the May 26,2004 Final Report on the Long Term Pumping Test.
Data collected during the Quarter included the following:
a) Measurement of water levels at MW-4, TW4-19, TW4-15 (MW-26), and TW4-
20 on a weekly basis, and at selected temporary wells and permanent monitoring
wells on a monthly basis (See Section 3.1 and Tabs B and C for a discussion of
the water levels);
b) Measurement of pumping history:
4.3.
(i) pumping rates
(ii) total pumped volume
(iii) operational and non-operational periods;
c) Periodic sampling of pumped water for chloroform and nitrate & nitrite analysis
and other constituents, as discussed in detail in Section 3.2 above.
Water Level Measurements
Beginning August 16, 2003, the frequency of water level measurements from MW-4,
TW4-15 (MW-26), and TW4-19 was reduced to weekly. From commencement of
pumping TW4-20, water levels in that well have been measured weekly. Depth to
groundwater in all other chloroform contaminant investigation wells is monitored
monthly. Copies of the weekly Depth to Water monitoring sheets for MW-4, TW4-15
(MW-26), TW4-19 and TW4-20 are included under Tab C. Monthly depth-to-water
measurements for October are recorded in the Field Data Worksheets included under Tab
B.
4.4. Pumping Rates and Volumes
4.4.1. MW-4
Approximately 90,830 gallons of water were pumped from MW -4 during the Quarter.
The average pumping rate from MW -4, when the pump was pumping, was approximately
4.0 gpm throughout the Quarter. The well is not purging continuously, but is on a delay
device. The well purges for a set amount of time and then shuts off to allow the well to
recharge. Water from MW -4 was transferred to the Cell 1 evaporation pond through a
pipeline installed specifically for that purpose. At the end of the 3rd Quarter, 2007, and
since commencement of pumping on April 14, 2003, an estimated total of approximately
1,498,010 gallons of water have been purged from MW-4.
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4.4.2. TW4-19
Approximately 334,350 gallons of water were pumped from TW4-19 during the Quarter.
The average pumping rate from TW 4-19, when the pump was pumping, was
approximately 3.1 gpm throughout the Quarter. The pump in this well is operating on a
delay. It pumps for approximately one and a half minutes and then is off for two to three
minutes. Water from TW4-19 was directly transferred to the Cell 1 evaporation pond
through a pipeline installed specifically for that purpose. At the end of the 1st Quarter,
2007, and since commencement of pumping on April 30, 2003, an estimated total of
approximately 7,419,416 gallons of water have been purged from TW4-19.
4.4.3. TW4-15 (MW-26)
Approximately 61,750 gallons of water were pumped from TW4-15 (MW-26) during the
Quarter. The average flow rate from TW4-15, when the pump was pumping, was
approximately 5.5 gpm throughout the Quarter. The well is not purging continuously, but
is on a delay device. The well now purges for a set amount of time and then shuts off to
allow the well to recharge. The water is directly transferred to the Cell 1 evaporation
pond through a pipeline installed specifically for that purpose. At the end of the 1st
Quarter, 2006, and since commencement of pumping on August 8, 2003, an estimated
total of approximately 1,064,340 gallons of water have been purged from TW4-15.
4.4.4. TW4-20
Approximately 63,630 gallons of water were pumped from TW4-20 during the Quarter.
The average flow rate from TW4-20, when the pump was pumping, was approximately
6.0 gpm throughout the Quarter. The well is not purging continuously but is on a delay
device. The well pump is set on a water elevation device. When the water reaches a set
point, the pump turns on until the water level drops to another set point. The water is
directly transferred to the Cell 1 evaporation pond through a pipeline installed
specifically for that purpose. Since commencement of pumping on August 4, 2005, an
estimated total of approximately 776,280 gallons of water have been purged from TW4-
20.
4.5 Daily Inspections
Denison has submitted an Operations and Maintenance Plan, Chloroform Pumping
System, White Mesa Mill, Blanding, Utah, Revision 1.0 to UDEQ for approvaL Upon
approval of that plan, the Mill will commence documenting its daily inspections of the
operational status of the chloroform pumping wells on the daily inspection form, an
example of the form of which is attached as Tab M.
4.6 Operational Problems
No significant operational problems were encountered during the the 4th Quarter of 2007.
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4.7 Conditions That May Affect Water Levels in Piezometers
No water was added to any of the three wildlife diversion ponds during the Quarter.
4.8 Chloroform Analysis
Monthly chloroform sampling ceased on November 8, 2003. From that time all
chloroform contaminant investigation wells were sampled on a quarterly basis. The
sample results are discussed above in Section 3.2.
5. CONCLUSIONS AND RECOMMENDATIONS
The water level contour map for the Quarter indicates that effective capture of water
containing high chloroform concentrations in the vicinity of the pumping wells is
occumng.
Between the second and third quarters of 2007, the chloroform concentration in
temporary well TW4-20 increased from 5,200 J.lg/L to 9,000 J.lg/L, the concentration in
TW4-21 decreased from 140 J.lg/L to 120 J.lg/L, and the concentration in TW4-22
decreased from 530 J.lg/L to 440 J.lg/L. Fluctuations in concentrations in these wells are
likely related to variations in pumping in TW4-20 and nearby wells, and their location
near the suspected former office leach field source area. Regardless of these measured
fluctuations in chloroform concentrations, sampling of temporary wells TW4-24 (located
west of TW4-22) and TW4-25 (located north of TW4-21), indicated these wells remain
outside the chloroform plume and thus bound the plume to the west and north.
Chloroform was not detected at TW4-25 and was detected at a concentration of less than
2 J.lg/L at TW4-24. The chloroform concentration in TW4-2 increased from 340 J.lg/L to
3,200 J.lg/L between the third and fourth quarters. This increase brings the concentration
in TW4-2 back to historically more typical values (for example, the 3,000 J.lg/L measured
during the second quarter of 2007).
Continued pumping of TW4-19, TW4-20, MW-4, and MW-26 is recommended.
Pumping these wells, regardless of any short term fluctuations in concentrations detected
at the wells (such as at TW4-20), helps to reduce downgradient chloroform migration by
removing chloroform mass and reducing average hydraulic gradients, thereby allowing
natural attenuation to be more effective.
The chloroform concentration at downgradient well TW 4-6 remained at 18 J.lg/L.
Although fluctuations in concentrations have occurred, this well has likely remained
outside the chloroform plume due to a combination of 1) slow rates of downgradient
chloroform migration in this area due to low permeability conditions and the effects of
upgradient chloroform removal by pumping, and 2) natural attenuation. Chloroform
remained non detect at downgradient temporary well TW4-23. Both TW4-6 and TW4-23
bound the chloroform plume to the south.
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