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HomeMy WebLinkAboutNC0022406_Interim GW Extraction System Status Memo_20181101 MEMORANDUM P:\Duke Energy Carolinas\20. BELEWS CREEK\14.CCP Accelerated Remediation GW Extraction System\IAP Effectiveness Monitoring Report\DEQ Comments Response Date: October 31, 2018 File: 1026.20.14 To: Melonie Martin (Duke Energy, LLC) From: Craig Eady Cc: Ashley Albert and Bill Lantz (SynTerra Corporation) Subject: Interim Groundwater Extraction System Status – Belews Creek Steam Station Interim Groundwater Extraction System Status This memo is intended to provide an update to the ongoing efforts to maximize the performance of the groundwater extraction system to achieve the interim action goals. It is also intended to provide an interim reply to the latest response from NCDEQ, dated September 17, 2018. Extraction System Status  Except for minor individual pump outages to address mechanical issues, the entire system operated during the month of September.  Between 8/27/2018 and 9/24/2018, the system extracted approximately 500,000 gallons of water. The total volume extracted since system start up is over 6 million gallons.  During the last week of August, controls for all of the pumps were adjusted to increase the drawdown levels in each of the extraction wells. Additional adjustments were made to several wells (EX-1, EX-5, and EX-7) in September.  Observation well transducer data was collected on September 19, 2018.  The dramatic levels of rainfall due to the Hurricane Florence affected groundwater levels in the observation wells. Adjustments in extraction well drawdown programming and effects of the changes are summarized below. Interim Groundwater Extraction System Status October 2018 Belews Creek Steam Station Page 2 of 6 P:\Duke Energy Carolinas\20. BELEWS CREEK\14.CCP Accelerated Remediation GW Extraction System\IAP Effectiveness Monitoring Report\DEQ Comments Response Date Setpoint Weekly Water Setpoint Weekly Water Flow Level Flow Level (on/off) (gpm) (feet) (on/off) (gpm) (feet) EX-1 EX-2 8/20/2018 25.0/19.0 2,910 15.7 26.4 18,700 20.1 8/27/2018 19.0/11 2,650 15.8 16.1/8.0 21,690 12.7 9/1/2018 19.0/11 1,940 16.2 16.1/8.0 18,280 12.1 9/7/2018 19.0/11 2,430 17.2 16.1/8.0 23,090 12.1 9/14/2018 19.0/11 1,020 17.23 16.1/8.0 9,850 13.52 9/17/2018 19.0/11 2,630 16.5 16.1/8.0 26,140 12.2 9/24/2018 14.0/7 2,800 16.8 16.1/8.0 26,720 12 EX-3 EX-4 8/20/2018 19.4 7,900 17.6 27.0/21.9 13,890 21.3 8/27/2018 13.1/8.0 8,350 9.5 14.0/6.0 12,310 10.5 9/1/2018 13.1/8.0 6,930 10.3 14.0/6.0 9,500 10.1 9/7/2018 13.1/8.0 8,850 13.8 14.0/6.0 11,850 9.2 9/14/2018 13.1/8.0 3,770 12.01 14.0/6.0 5,040 9.64 9/17/2018 13.1/8.0 9,990 13 14.0/6.0 12,970 12.7 9/24/2018 13.1/8.0 10,170 13.9 14.0/6.0 13,040 9.7 EX-5 EX-6 8/20/2018 24.1 5,880 18.8 19.6 22,950 15.2 8/27/2018 15.9/7.1 6,960 11.5 13.9/6.0 20,950 10.7 9/1/2018 15.9/7.1 5,830 12.4 13.9/6.0 16,510 11 9/7/2018 15.9/7.1 7,290 10.7 13.9/6.0 20,690 11.3 9/14/2018 15.9/7.1 3,090 13.42 13.9/6.0 8,110 11.25 9/17/2018 15.9/7.1 7,960 12.7 13.9/6.0 23,070 10.5 9/24/2018 11.0 / 5.0 8,050 12.9 13.9/6.0 24,000 11 EX-7 EX-8 8/20/2018 29.9 4,708 24.8 29.9 4,810 21.9 8/27/2018 19.9/13.9 4,632 17.3 24.0/10.0 5,050 17.2 9/1/2018 19.9/13.9 3,630 16.8 24.0/10.0 3,780 17.4 9/7/2018 19.9/13.9 4,310 17.4 24.0/10.0 4,920 15.8 9/14/2018 19.9/13.9 1,740 17.29 24.0/10.0 2,100 16.68 9/17/2018 19.9/13.9 4,830 17.7 24.0/10.0 5,950 16.7 9/24/2018 17 / 7 5,170 17.8 24.0/10.0 5,530 17 EX-9 EX-10 8/20/2018 30.6 3,450 24.4 30.6 480 25.1 8/27/2018 24.0/10.0 7,910 17.5 24.0/10.0 500 14.9 9/1/2018 24.0/10.0 5,830 17.4 24.0/10.0 390 10.9 9/7/2018 24.0/10.0 7,010 15.8 24.0/10.0 490 17 9/14/2018 24.0/10.0 2,850 19.17 24.0/10.0 210 22.43 9/17/2018 24.0/10.0 8,540 15.5 24.0/10.0 650 21.8 9/24/2018 24.0/10.0 6,930 17.4 24.0/10.0 540 17.9 Interim Groundwater Extraction System Status October 2018 Belews Creek Steam Station Page 3 of 6 P:\Duke Energy Carolinas\20. BELEWS CREEK\14.CCP Accelerated Remediation GW Extraction System\IAP Effectiveness Monitoring Report\DEQ Comments Response HydroVu online, real-time extraction well transducer data documents the following lower pump-on groundwater elevations for the extraction well pumps. These lower pump-on elevations are intended to result in greater drawdown along the system axis. Extraction Well Number Decrease in GW Elevation (ft) EX-1 5 EX-2 8 EX-3 3 EX-4 12 EX-5 9 EX-6 3 EX-7 11 EX-8 6 EX-9 7 EX-10 9 Observation Well Elevation Data These graphs include the most recent water level elevation data, collected on 9/17/2018. The positive effects of lowering the extraction well pumping levels can be seen in the significant negative slopes of the graphs over the last several weeks in the wells in proximity to the extraction wells. The effects of the substantial rainfall from the Hurricane Florence can be seen at the latter end of the graphs. It is anticipated that once the effects of the hurricane subside, the increase in drawdown will continue. Additional data collection in October will be complete d to monitor water levels in the observation wells. Interim Groundwater Extraction System Status October 2018 Belews Creek Steam Station Page 4 of 6 P:\Duke Energy Carolinas\20. BELEWS CREEK\14.CCP Accelerated Remediation GW Extraction System\IAP Effectiveness Monitoring Report\DEQ Comments Response Interim Groundwater Extraction System Status October 2018 Belews Creek Steam Station Page 5 of 6 P:\Duke Energy Carolinas\20. BELEWS CREEK\14.CCP Accelerated Remediation GW Extraction System\IAP Effectiveness Monitoring Report\DEQ Comments Response Response to DEQ comments of September 17, 2018 Response 1 As noted in the response, observed drawdown in the observation wells has not yet reached target levels. As indicated in previous communications, this condition is predominantly due to unusually high amounts of rainfall. To address this issue, continuing ef forts are being made to increase the drawdown in the extraction wells with adjustments to pump controls, which were made in August and September and appear to be having a positive effect. The groundwater flow model will be revised with additional field observations and recalibrated target pump metrics and provided in the system startup completion report (Response 12). Response 2 It is agreed that more data is needed to determine if the extraction system performance has been optimized. There are a number of possible reasons why optimal drawdown has not yet been achieved, but, as indicated above, the focus of the ongoing efforts is to maximize drawdown. With continued data collection after completion of continuing adjustments, optimization of the system can be completed. The figures associated with reporting, including Figure 2-3, will be revised to reflect additional data as described below and provided in the system startup completion report (Response 12). Response 3 It is agreed that more frequent collection of observation well groundwater elevations will improve the ability to optimize the extraction system and evaluate its effectiveness. Observation well data will be collected on a monthly basis until completion of the startup phase and evaluation of the system effectiveness is complete. Table 2-1 will be revised and provided in the system startup completion report (Response 12). Response 7 There have been several attempts to describe the performance of the system thus far and it is agreed, as noted above, that speculation about the specific localized flow conditions will be much less necessary once there is additional data that reflects more optimized system performance. As noted above, data collection and system evaluation will be more frequent. Also, once the startup phase has been completed, more effective modeling and reporting of site conditions will be possible. An anticipated schedule of optimization and reporting are provided below in Response 12. Interim Groundwater Extraction System Status October 2018 Belews Creek Steam Station Page 6 of 6 P:\Duke Energy Carolinas\20. BELEWS CREEK\14.CCP Accelerated Remediation GW Extraction System\IAP Effectiveness Monitoring Report\DEQ Comments Response Response 8 The variability of constituent concentrations in groundwater, particularly iron, may be due to any number of factors associated with the variability of startup conditions. Understanding of these concentrations will be better once steady state conditions have been reached and there is more data available. Response 11 It is agreed that there are some unexpected differences between individual extraction well performances. This may be due to differences in the transition zone heterogeneities or to variability in individual pumping regimes that have occurred during this startup phase. The pumping rates and target drawdowns continue to be adjusted to maximize drawdown. Response 12 It is agreed that while ongoing efforts are being made to optimize the system and evaluate its effects, it is important to establish reasonable time frames and reporting frameworks. During the remainder of the startup phase:  Extraction well data will continue to be collected on a weekly basis  Observation well transducer data will be downloaded and evaluated monthly  Extraction well transducer data will be evaluated monthly  A brief evaluation of this data, along with descriptions of all optimization measures will be included in the monthly reports It is proposed that over the next several months, close monitoring of the syst em will enable optimization and evaluation of system capabilities to be determined. However, this time frame will approach the end of the year, which will be coincident with the upcoming time frame for initiation of free water decanting in the ash basin. It is expected that reductions in water level in the ash basin will significantly affect conditions at the extraction system location. Evaluation of the system and startup operations should take into account the impacts of the decanting as they may be significant. It is proposed that completion of the startup phase be targeted for the end of March 2019. At that point in time, it should be possible to fully evaluate the effectiveness of the system and to determine if any additional interim measures are necessary. It is also agreed that within two months of completion of the startup phase, that a summary report will be submitted. This report will include all updated figures and tables, updated modeling results, an evaluation of system performance and capabilities, and a recommendation for any future interim actions that may be necessary.