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HomeMy WebLinkAboutDRC-2010-005401 - 0901a068801ca026DENISO MINES September 30, 2010 VIA PDF AND EXPRESS DELIVERY Rusty Lundberg, Executive Secretary Utah Division of Radiation Control Utah Department of Environmental Quality 195 North 1950 West P.O. Box 144810 Salt Lake City, UT 84114-4820 C- 2010-005401 ison Mines (USA) Corp. 1030 17th Straet, Suite 9S0 Denver, CO 802S5 USA Tel: 303 628-7798 Fax: 303 389-4125 www.donl8onmlne9.coffl Dear Mr. Lundberg: Re: State of Utah Ground Water Discharge Permit ("GWDP") No. UGW370004 White IVIesa Uranium Mill - Update on Findings on Cell 1 Leak Detection system ("LDS") This letter report responds to the Utah Division of Radiation Control's September 22, 2010 Conditional Approval and Confirmatory Action Letter regarding the White Mesa Mill (the "Mill") Cell 1 leak detection system ("LDS") and Denison Mines (USA) Corp's ("Denison's") telephone conversations with DRC on August 23, September 15, and September 21, 2010. Description of the LDS Standpipe and Blow Pipe System. The Cell 1 design and LDS has been described in the GWDP and the June 1979 D'Appolonia Engineering Report Appendix A drawings. The above-ground monitoring portion of the LDS consists of a 14-inch covered Drisco pipe (the "standpipe") containing a movable calibrated interior Vt-'mch PVC tube (the "blow tube"). The standpipe lies along the sideslope of the Cell 1 dike beneath the flexible liner, and exits through an opening in the flexible liner at the top of the south dike. The blow tube can be moved (slid) up or down within the standpipe cover opening. Prior to August 2010, the top of the standpipe was nearly flush with the ground (dike) surface. At that time, the length to the bottom of the standpipe and blow tube was 63 feet 4 inches (63.33 feet) along the slope of the dike. Liquid ievel measurements are performed by use of the calibrated blow tube within the standpipe. To perform a liquid depth measurement, the environmental technician blows into the blow tube and listens for a bubbling response indicating the bottom end of the tube is in contact with liquid. He withdraws the tube in increments and repeats the blowing process until the response sound indicates that the tube is no longer in contact with liquid. He then records the measurement from the graduated blow tube, which indicates the depth of empty tube/pipe, that is, how far down the standpipe/blow tube column does the liquid level begin. The height of liquid in the sloped column is calculated by subtracting the empty blow tube depth from the full length of the standpipe. All measurements made within the standpipe and blow tube are measurements along the sloped incline and do not represent vertical head, per se. Letter to Rusty Lundberg - Cell 1 LDS Update Report September 30, 2010 Page 2 The volume of liquid accumulated in the system (infiltration volume) is estimated by pumping the entire column to dryness, collecting the pumped fluid into a series of four calibrated 5-gallon buckets, and recording a collected volume measurement. As indicated in the Discharge Minimization Technology ("DMT") Plan, the measured volume is divided by the elapsed time since the standpipe was last pumped dry to determine the rate of influent flow (infiltration rate or accumulation rate) into the LDS system. As mentioned above, prior to the modifications discussed in the next section, the length ofthe LDS standpipe was 63 feet 4 inches (63.33 feet). History of Extensions to the Pipe System Prior to the August 2010 LDS liquid detection, at the request of David Rupp and Dean Henderson of DRC, Mill personnel added a 2-inch collar and cover to the end of the standpipe and drilled a close-fitted opening in the standpipe cover. The blow tube was extended by the same amount and was fitted through the opening in the cover. Following this modification, the blow tube could still be moved up or down for measurement, and no change to the measurement process was required. At this point, the length of the standpipe and blow tube reached 63 feet 6 inches (63.5 feet). This change was indicated in the revisions to Table 1 provided to DRC on August 30, 2010. On August 10, 2010 at the request of David Rupp and Dean Henderson of DRC, Mill personnel again extended the exposed (and now covered) end of the LDS standpipe and blow pipe. The blow pipe and standpipe were both extended to a new length of 69 feet 6 inches (69.5 feet). This change was indicated in the revisions to Table 1 provided to DRC on August 30, 2010. Investigation of the System and Measurement Process As committed in the phone conversation of September 15, 2010 I visited the Mill and inspected the Cell 1 LDS measurement system equipment on Friday September 24, 2010 and observed a demonstration of the use of the blow tube and measurement process. During that visit, I also reviewed with the environmental technician the methods of collecting and recording LDS data, and the meaning of each of the field notes taken during the measurement processes in June and August 2010. The environmental technician also provided supplementary measurement data coiiected during the June 2010 period, when the Cell 1 level was lowered to keep the LDS system dry and allow for repairs. During the period that the Cell 1 level was lowered, the Cell 1 LDS level was monitored daily except on weekends. That data has been included in Attachment 1 to this letter report. I performed a quality check and standardization of the data previously reported to DRC and revised the data in Table 1 for both events to use the same format and presentation. Any changes to reported data resulting from the quality check are highlighted in bold and yellow in the standardized table in Attachment 1 to this report. Findings and Reason for Confusion in DRC Interpretation of Table 1 The versions of Table 1 provided to DRC for the two different detection events were presented in two different formats. The differences resulted from two different, but accurate, recording styles used by field personnel to record and report the data to Denver Corporate personnel. The table attached to the August 18, 2010 letter summarizing the June 2010 detection showed both the blow pipe and total pipe measurements in the same column. In this table, the word "dry," included from the field notes, indicated that the second depth was the "dry depth reached at bottom of the pipe". The August 30, 2010 letter added a second table with the level data from the August 7, 2010 detection. The second table was in a format that showed only the blow pipe measurements with the word "dry" included from the field notes, which indicated that the tube was "pumped drv after this DENISO MINES Letter to Rusty Lundberg - Cell 1 LDS Update Report September 30, 2010 Page 3 measurement". In this table, the dry depth at the bottom of the pipe was not indicated, but was reached in every pumping event. The revised tables provided to DRC on August 30 and September 14, 2010 did not explain this difference in presentation of the field data. The updated tables in Attachment 1 to this letter report for the two occurrences have been rectified so that both tables report the dry depth at the bottom of the tube each time dryness was achieved. The attachments also clarify what "dry" indicated. The data has been reformatted so that all data for both detection events is presented on the same basis. One minor subtraction error by the Mill personnel affected one liquid level value on August 7, 2010. The liquid height reported as 1.70 feet has been corrected to 1.83 feet in the updated attachment to this letter report as a result of the recalculation. One minor error resulted from conversion of data for presentation in the Table 1 attachments. The error affected only one influent rate to the second decimal point on August 11, 2010. The rate of 0.01 gpm has been corrected to 0.02 gpm in the attachment to this letter report as a result of the recalculation. The corrected influent rates remain well below the leakage rate of 1 gpm as required by the Mill's License Condition 11.3. The errors had no effect on confirming that the LDS was pumped dry after each pumping effort, or on determination of when influent into the LDS ceased. In every case of pumping, the pipe was pumped dry to the bottom of the LDS pipe. During the August detection, prior to August 10, 2010, this bottom depth was consistently 63 feet 6 inches (63.5 feet). After August 10, this bottom depth was consistently 69 feet 6 inches (69.5 feet). On August 18, 2010, one inch of solution was measured at the bottom of the LDS. One inch is not a sufficient fluid level to allow priming and operation of the downhole pump; hence the inch of solution was not pumped. The inch of solution had evaporated to dryness (69.5 feet) by the time of the next day's monitoring on August 19, 2010 and has remained dry since that date. The environmental technician performing the measurements is consistently able to reach the same depth at the bottom of the standpipe with the blow tube. That is, there is no apparent object or deposition creating any obstruction in measurement. Sedimentation, if any exists, may lie along the side of the sloped standpipe or the bottom, but does not interfere with the ability to take measurements of liquid to the same depth in the standpipe each time. Conclusions 1. Based on my review of the LDS measurement process and reported data, there were no apparent errors in liquid level measurement. 2. Based on my review of the LDS measurement process and reported data, there were no apparent errors in liquid volume measurement or time measurement - the two factors entering into the estimation of LDS infiltration rate. 3. One minor subtraction error by the Mill personnel affected one liquid height value on August 7, 2010. The error did not affect estimation of pumped volume or ability to monitor when influent into the LDS ceased. DENISO MINES Letter to Rusty Lundberg - Cell 1 LDS Update Report September 30, 2010 Page 4 4. One minor error resulted from Denver Corporate conversion of data for presentation in the Table 1 attachments. The error affected only one reported influent rate to the second decimal point on August 11, 2010. The rate of 0.01 gpm has been corrected to 0.02 gpm in the attachment to this letter report as a result of the recalculation. The corrected influent rate remains well below the leakage rate of 1 gpm as required by the Mill's License Condition 11.3. The errors had no effect on confirming that the LDS was pumped dry after each pumping effort, or on determination of when influent into the LDS ceased. 5. Based on the ability to read a liquid level to the bottom of the liquid standpipe, there does not appear to be any obstruction or significant deposition in the bottom of the standpipe sufficient to affect monitoring. In any event, the actual depth to the bottom of the standpipe is not significant as long as it is a constant point of reference for liquid depth, as it appears to be. 6. The measurement system approved in the license is being appropriately implemented. 7. The variations noted by DRC were due to the difference in presentation of data in the two notices to DRC. Data reporting has been standardized, and the attached revisions to Table 1 from both the June and August 2010 detection notices have been modified in format and presentation to address the sources of confusion. Please contact the undersigned if you have any questions or require any further information. Yours very truly, DENISON MINES (USA) CORP. '\io Ann Tischler Director, Compliance and Permitting cc: Rich Bartlett David C, Frydenlund Ron F. Hochstein Harold R. Roberts David E. Turk Kathy Weinei DENISO MINES Estimation of Cell 1 Leakage Rate from Date of Fluid Detection Until System Achieved Dryness June and August 2010 Approximate Approximate Depth to Liquid Level (Empty Depth to Liquid Level (Empty Height of Elapsed time since end of Calculated Time of Conditions at portion of pipe or portion of pipe Liquid previous Volume Leakage detection or Time of Level blow tube) (feet or blow tube) (decimal pumping Pumped Rate Date measurement Measurement and inches) (decimal feet) feet) (min) (gallons) (gpm) 6/2/2010 55'10" 55.83 7.50 . .•• -i ' -J j 6/3/2010 8:25 Pump start 55'6" 55.50 7.83 83 6/3/2010 8:42 Pump end when dry 63'4" 63.33 0.00 , • ' "•" , 6/3/2010 9:30 Pump start 61'9" 61.75 1.58 48 23 0.48 6/3/2010 9:33 Pump end when dry 63'4" 63.33 0.00 6/3/2010 14:10 Pump Start 58'8" 58.67 4.67 277 49 0.18 6/3/2010 14:16 Pump end when dry 63'4" 63.33 0.00 6/4/2010 7:53 Pump start 57'0" 57.00 6.33 1057 52 0.05 6/4/2010 7:59 Pump end when dry 63'4" 63.33 0.00 6/4/2010 14:11 Pump Start 57'5" 57.42 5.92 372 43 0:12 6/4/2010 14:17 Pump end when dry G3'4" 63.33 0.00 6/7/2010 10:25 Pump Start 56'6" 56.50 6.83 4088 51 0.01 6/7/2010 10:31 Pump end when dry 63'4" 63.33 0.00 6/8/2010 14:45 Pump Start 56'10" 56.83 6.50 1694 51 0.03 6/8/2010 14:51 Pump end when dry 63'4" 63.33 0.00 6/9/2010 11:31 Pump Start 57'9" 57.75 5.58 1240 43 0.03 6/9/2010 11:36 Pump end when dry 63'4" 63.33 0.00 6/10/2010 11:53 Pump start 57'7" 57.58 5.75 1457 44 0.03 6/10/2010 11:58 Pump end when dry 63'4" 63.33 0.00 6/11/2010 10:29 Pump start 58'0" 58.00 5.33 1351 38 0.03 6/11/2010 10:33 Pump end when dry 63'4" 63.33 0.00 6/14/2010 9:07 Pump start 58'7" 58.58 4.75 4234 37 0.01 6/14/2010 9:11 Pump end when dry 63'4" 63.33 0.00 6/15/2010 8:45 Pump start 58'10" 58.83 4.50 1414 35 0.02 6/15/2010 8:50 Pump end when dry 63'4" 63.33 0.00 6/16/2010 9:05 Pump Start 58'11" 58.92 4.41 1455 32 0.02 6/16/2010 9:09 Pump end when dry 63'4" 63.33 0.00 6/17/2010 8:37 Pump Start 59'6" 59.50 3.83 1408 28 0.02 6/17/2010 8:41 Pump end when dry 63'4" 63.33 0.00 6/18/2010 12:04 Pump Start 59'2" 59.17 4.16 1643 30 0.02 6/18/2010 12:08 Pump end when dry 63'4" 63.33 0.00 6/21/2010 7:11 Pump Start 59'3" 59.25 4.08 4023 25 0.01 6/21/2010 7:14 Pump end when dry 63'4" 63.33 0.00 6/22/2010 7:43 Pump Start 6r2" 61.17 2.16 1469 14 0.01 6/22/2010 7:45 Pump end when dry 63'4" 63.33 0.00 0 0 6/23/2010 63'4" 63.33 0.00 Pumping not requi reel 0 0 Estimation of Cell 1 Leakage Rate from Date of Fluid Detection Until System Achieved Dryness June and August 2010 NOTES.81712010 Mill personnelcalculated 1.7 feet(2O inches). Should be 1.83" (22 inches)**Calculated leak rate is worst case estimate based on time of initial detection.*** Blow tube use was suspended for one day whle PVC cement was allowed to set. Date Time of detection or measurement Conditions at Time of Level Measurement Approximate Depth to Liquid Level (Empty portion of pipe or blow tube) (feet and inches) Approximate Depth to Liquid Level (Empty portion of pipe or blow tube) (decimal feet) Height of Liquid (decimal feet) Elapsed time since end of previous pumping (min) Volume Pumped (gallons) Calculated Leakage Rate (gpm) *gl712010 21:30 Not pumped 61'8"61 .67 1.83 "*81812010 13:30 Pump start 60'8"60.67 2.83 958 5 0.01 81812010 13:32 Pump end when dry 63'6"63.50 0.00 81912010 9:00 Pump start 60'2"60.17 3.33 1 168 22 0.02 81912010 9:03 Pump end when dry 63'6"63.50 0.00 **"8/1 012010 14.21 Pump start unable to measure 1758 30 0.02 ***g/1 012010 14:24 Pump end when dry unable to measure 8t11t2010 13:15 Pump start 63'9"63.75 5.75 137 1 32 0.02 8111t2010 13:19 Pump end when dry 69'6"69.50 0.00 8t12t2010 15:00 Pumo start 64'.2"64.17 1541 25 0.02 811212010 15:13 Pump end when dry 69',6"69.50 0.00 8t1312010 10:40 Pump start 65'0"65.00 4.50 1 167 19 0.02 811312010 10:42 Pump end when dry 69'6"69.50 0.00 811412010 14:20 PumD start 66'2"66.17 3.33 1 658 12 0.01 811412010 14:21 Pump end when dry 69'6"69.50 0.00 8t15t2010 16:1 5 Pumo start 66'4"66.33 3.17 1554 11 0.01 811512010 16:17 Pump end when dry 69'6"69.50 0.00 811612010 14:50 Pump start 67'5"67.42 2.08 1 353 7 0.01 8t16t2010 14:51 Pump end when dry 69'6"69.50 0.00 811712010 13:45 Pumg start 68'5"68.42 1.08 1374 3 0.002 811712010 13:46 Pump end when drl 69'6"69.50 0.00 811812010 0'1 "0.08 0.08 rumprng nor required 0 0 811912010 0'0"0.00 0.00 rumprng nor required 0 0