DRC-2007-001444 - 0901a0688070e193

DENISONMINES
VIA FEDERAL EXPRESS
January 31, 2007
Dane L. Finerfrock, Executive Secretary
Utah Radiation Control Board
Utah Department of Environmental Quality
168 North 1950 West
P.O. Box 144810
Salt Lake City, UT 84114-4810
Dear Mr. Finerfrock:
Re: Transmittal of 4th Quarter Chloroform Monitoring Report for the White Mesa
Uranium Mill
Enclosed are two copies of the White Mesa Uranium Mill Chloroform Monitoring Report for the
4th Quarter of 2006, as required under State of Utah Notice of Violation and Groundwater
Corrective Action Order UDEQ Docket No. UGQ-20-01.
Yours very truly,
AiJ;;;LL
DENISON MINES (USA) CORP.
Steven D. Landau
Manager-Environmental Affairs
Cc. Ron Hochstein
Harold Roberts
David Frydenlund
David Turk
Tel: [phone]
Fax: [phone]
1050 17th Street, Suite 950
Denver, CO, USA 80265
www.denisonmines.com
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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)
2006
Prepared by:
INTERNATIONAL URANIUM (USA) CORPORATION
1050 17th Street, Suite 950
Denver CO 80265
January 31,2007
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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 Environmental Quality ("UDEQ") Docket No. UGQ-20-01 for the 4rd quarter of 2006
(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-A
• TW4-1
• TW4-2
• TW4-3
• TW4-4
• TW4-5
• TW4-6
• TW4-7
• TW4-8
• TW4-9
• TW4-10
• TW4-11
• TW4-12
• TW4-13
• TW4-14
• TW4-15 (MW-26)
• TW4-16
• TW4-17 (MW-32)
• TW4-18
• TW4-19
• TW4-20
• TW4-21
• TW4-22
The locations of these wells are indicated on the map attached under Tab A.
Each of these wells was sampled for the following constituents on November 8-9, 2006:
• Chloroform
• Chloromethane
• Carbon tetrachloride
• Methylene chloride
• Chloride
• Nitrogen, Nitrate + Nitrite as N
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As UDEQ is aware, IUSA has experienced difficulty in obtaining chloroform samples
from well TW4-14. The difficulty arises 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
with limited success in water recovery experienced during this study period.
Nonetheless, a quarterly sample was able to be collected from TW4-14 on November 8,
2006. Because of the limited data base, trend analyses is not possible for TW 4-14 at this
time and, as such, is not included in the graphic display at Tab L of this report. The
chloroform concentration in this well was less than the detection limit for the November
8, 2006 sampling at this location.
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 November 7, 2006;
b) The following point of compliance monitoring wells under the Mill's
Groundwater Discharge Permit ("GWDP") during the period November 24-30,
2006: MW-1, MW-2, MW-3, MW-3A, MW-5, MW-11, MW-12, MW-14, MW-
15, MW-17, MW-18, MW-19, MW-23, MW-24, MW-25, MW-26, MW-27,
MW-28, MW-29, MW-30, MW-31 and MW-32;
c) Piezometers-P-1, P-2, P-3, P-4 and P-5 on October 31, 2006,; and
d) Existing monitoring wells-MW-20 and MW-22 on October 31,2006
In addition, weekly depth to groundwater was 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
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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. Well depth
measurements are taken and the two casing volumes are calculated
(measurements are made using the same instrument used 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. Purging then begins. 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 placed in DI water and rinsed prior to leaving the well area. After the
rinsing is completed, the well is capped, and Mill personnel then move to the
next well for purging.
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 thes� 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 then outfitted with rubber gloves;
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.
This manner of sampling has been employed by Mill personnel for chloroform
contaminant investigation sampling, including for split sampling undertaken with UDEQ
personnel, since the inception of the chloroform contaminant investigation.
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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
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 for reasons set out in correspondence to UDEQ
dated December 8, 2006. Subsequent to the delivery of the December 8, 2006 letter,
DUSA has discussed the issues brought forward in the letter with UDEQ and has
received correspondence from UDEQ about those issues at the time of this writing. In
response to UDEQ's letter, DUSA is incorporating changes in chloroform QA procedures
in the form of a separate document. The chloroform QA document describes the
differing needs of the chloroform program and attaches the GWDP QAP to that
document for QA needs other than those described in the chloroform QA document.
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 on November 8-9, 2006. The Field Data
Worksheets for the Quarter do not include all of the information required under the
revised GWDP QAP and this was an item of discussion in DUSA's December 8, 2006
correspondence regarding Chloroform QAP requirements, the subsequent oral
communications with UDEQ and UDEQ's letter regarding the matter. Future chlorofom
samplings will be accompanied by the completion of the field data parameters that have
been incorporated into the chloroform QA program.
2.4 Depth to Groundwater Sheets
Attached under Tab C are 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 for all of the chloroform contaminant investigation wells.
Monthly depth-to-groundwater measurements for November, 2006 are included on the
Field Data Worksheets included under Tab B.
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
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November 8-9, 2006 data for the wells listed in paragraph 2.1.2 (a) above, November 24-
30, 2006 data for the wells listed in paragraph 2.1.2 (b) above, October 31, 2006 data for
the piezometers listed in paragraph 2.1.2 (c) above, and October 31, 2006 data for the
wells listed in paragraph 2.1.2 (d) above.
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 2006, as submitted
with the Chloroform Monitoring Report for the fourth third of 2006, dated October 30,
2006, 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, TW4-15(MW-26), TW4-19 and TW4-20. Water levels and water level
contours for the site have not changed significantly since the last quarter. Any
fluctuations in water levels in the pumping wells are due in part to fluctuations m
pumping conditions just prior to and at the time the measurements are taken.
3.1.3. Hydrographs
Attached under Tab F are hydrographs showing groundwater elevation in 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
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.
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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 between the fourth
quarter and the previous quarter. Therefore, the combined capture of TW4-19, TW4-20,
MW-4 and MW-26 (formerly 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 November 8-9, 2006, along with the laboratory analytical results for a trip blank.
3.2.2. Electronic Data Files and Format
IUSA 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.
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)
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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: TW4-6, TW4-10, TW4-20 and TW4-21.
b) Chloroform concentrations have decreased by more than 20% in the following
wells, compared to last quarter: TW4-15 (MW-26) and TW4-22;
c) Chloroform concentrations have remained within 20% in the following wells
compared to last quarter: MW-4, TW-4-1, TW4-2, TW4-4, TW4-5, TW4-7,
TW4-10, TW4-11, TW4-18 and TW4-19;
d) Chloroform concentrations at TW4-14 were non-detect; and
e) TW4-3, TW4-8, TW4-9, TW4-12, TW4-13, and TW4-17 (MW-32) remained
non-detect.
In addition, the chloroform concentration in recently installed well TW4-20 increased
from 5,300 Jlg/L in the third quarter 2006 to 11,000 Jlg/L in the fourth quarter 2006 and
the concentration in TW4-22 decreased from 884 Jlg/L in the third quarter 2006 to 350
Jlg/L in the fourth quarter 2006. Chloroform concentrations in TW4-6, which is the most
downgradient temporary perched well, increased from 11 to 43 Jlg/L after two quarters of
reduction in concentration. The increase in concentration is likely due to continued slow
rates of downgradient chloroform migration. Chloroform migration rates in this area are
slow due to low permeability conditions and the effects of upgradient chloroform
removal by pumping.
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
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for each quarterly sampling episode. During the 4th Quarter of 2006 duplicates (TW4-
65, duplicate of TW4-20) and TW4-70, duplicate of TW4-5), a blank (TW4-60) and a
trip blank (TW4-70) were collected and analyzed. The results of these analyses are
included with the routine anlalyses under Tab H.
3.3.2 Analytical Laboratory QA/QC 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 l\fill 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 sample (TW4-65) of TW4-20 indicated a relative percent difference
slightly above the prescribed standard of 20% at 21.8 % (i.e. TW4-20 = 11,000 ug!L,
TW4-65 = 13,700 ug!L). Given that this result is very close to the QA standard of 20%,
and because duplicate sampling is currently under review by DUSA, follow-up regarding
this sample discrepancy will be included in DUSA's current review of duplicate sampling
techniques. Due to the sample holding time contstaint for chloroform analyses, a re­
analysis cannot be requested for this sample set. Regarding duplicate sample TW4-70
(duplicate of TW4-5) the nitrate result exhibited a -79% relative percent difference (i.e.
2.9 mg!L vs 6.7 mg/L). As a result, and in conformance with DUSA's QAP, the nitrate
result for MW4-5 is disqualified and a root cause analysis will be undertaken with regard
to this matter.
Regarding the field blank and trip blank some parameter measurements warrant follow­
up. More specifically, chloromethane was indicated slightly above the detection limit at
1.3 ug/L (RL=l.O ug!L) in the field blank sample TW4-60. Because the chloromethane
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was sufficiently close to the reporting limit and most likely "noise" within the analytical
method further follow-up in this instance is not warranted.
c) Review of Analytical Laboratory QAJQC Analysis and Analytical Reports
The QA Manager reviewed the Analytical Laboratory's QA/QC Summary Reports and
made the following conclusions;
4.
(i) 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
(ii) The check samples included at least the following: a method blank, a
laboratory control spike (sample), a matrix spike and a matrix spike
duplicate;
(iii) All qualifiers, if any, and the corresponding explanations in the summary
reports are reviewed by the QA Manager. The only qualifiers reported
were for matrix interference in some of the analyzed monitoring location
samples, however, the reporting limit was maintained below the
parameter standard in these instances.
(iv) The laboratory holding time for all analyses was within chloroform
specification and sample temperature was acceptable upon receipt.
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, IUSA 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.
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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. IUSA personnel have gathered subsequent water level and
pumping data.
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:
(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.
4.3. 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 and the October and December monthly Depth to Water
monitoring sheets for all of the chloroform contaminant investigation wells are included
under Tab C. Monthly depth to water measurements for November are recorded in the
Field Data Worksheets included under Tab B.
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4.4. Pumping Rates and Volumes
4.4.1. MW-4
Approximately 89,030 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 4th Quarter, 2006, and
since commencement of pumping on April 14, 2003, an estimated total of approximately
1,225,880 gallons of water have been purged from MW-4.
4.4.2. TW4-19
Approximately 730,240 gallons of water were pumped from TW4-19 during the Quarter.
The average pumping rate from TW4-19, when the pump was pumping, was
approximately 6.0 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 4th Quarter,
2006, and since commencement of pumping on April 30, 2003, an estimated total of
approximately 6,163,586 gallons of water have been purged from TW4-19.
4.4.3. TW4-15 (MW-26)
Approximately 30,560 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 1.5 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 4th
Quarter, 2006, and since commencement of pumping on August 8, 2003, an estimated
total of approximately 876,110 gallons of water have been purged from TW4-15.
4.4.4. TW4-20
Approximately 96,100 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
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estimated total of approximately 478,770 gallons of water have been purged from TW4-
20.
4.5 Daily Inspections
IUSA 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
Operational problems for the 4th Quarter of 2006 were limited to the replacement of the
flow meter at MW-26 (TW4-15) on October 31, 2006. This well continues to experience
sedimentation problems
4. 7 Conditions That May Mfect 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. During
the Quarter, samples from MW-4, TW4-19, TW4-15 (MW-26) and TW4-20 were taken
from a small valve and tee placed in the discharge line downstream from the pump
control valve for each well. 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
occurrmg.
The chloroform concentration in recently installed temporary well TW4-20 increased
from 5,300 flg/L to 11,000 ug!L between the third quarter of 2006 and the fourth quarter
of 2006. This fluctuation in concentration is likely related to variations in pumping in
this well and nearby wells, and its location immediately downgradient of the suspected
former office leach field source area. The decrease in chloroform in TW4-22 from 884 to
350 flg/L between the third and fourth quarters of 2006 is also likely related to changes in
nearby pumping rates and its location close to the suspected source area. Regardless of
these measured fluctuations in chloroform concentrations, pumping 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.
Continued pumping of wells that are currently pumping is recommended.
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The increase in chloroform concentrations at downgradient well TW 4-6 from 11 to
43 �giL after decreasing from 31 to 11 ug/L between the first and third quarters is
consistent with the generally slow migration of chloroform to the south in this area, and
the impact of upgradient pumping. Migration rates in this area are low primarily due to
low-permeability conditions, although the overall rate of chloroform migration is also
slowed as a result of pumping at upgradient locations. Upgradient pumping likely
contributed to the measured decreases in TW 4-6 chloroform concentrations over previous
two quarters.
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