ARCHIVED REPORTS_XR0011856 - Laserfiche WebLink

Home Browse Search

Interim Remediation Plan and Second Quarter 2001 Groundwater Monitoring Report Moore Petroleum Bulk Plant,5491 F Street,Banta,California Page 6 Recent groundwater monitoring events have detected concentrations of MTBE at well MW-12, which is the down-gradient, sentinel well providing early warning for the domestic well located ar 5451 F Street(Figure 2). During the pumping test and as shown on Table C-1 in Appendix C and on Figure C-1, water levels dropped in well MW-12 from 12.64 feet above mean sea level (msl)to 12.60 feet above msl (a decrease of 0.04 feet). This drop in groundwater elevation illustrates that well MW-12 is within the radius of influence of recovery well RW-2. But, due to the low hydraulic conductivity of the silts and clays present at the site, one extraction well alone could not reverse the hydraulic gradient near well MW-12. Well MW-9 was the monitoring point that was the furthest distance from the recovery well. During the pumping test and as shown on Figure C-2 and Table C-2 in Appendix C, water levels dropped in well MW-9 from 12.56 feet above msl to 12.54 feet above msl (a decrease of 0.02 feet. This drop in groundwater elevation illustrates that well MW-9 is also within the radius of influence of recovery well RW-2. All the monitoring locations showed an influence from dewatering recovery well RW-2. Monitoring well MW-8 located next to the former UST excavation and 20-feet from recovery well RW-2 showed the greatest influence as shown on Figure C-3 and Table C-3. Water levels decreased in well MW-8 from 12.65 feet above msl to 12.57 feet above msl (a decrease of 0.08 feet. Figure C-4 located in Appendix C illustrates the hydraulic influence the pumping test had on monitoring location MW-3. During the pumping test and as shown on Figure C-4 and Table C-4 in Appendix C,water levels dropped in well MW-3 from 12.74 feet above msl to 12.68 feet above msl (a decrease of 0.06 feet). It should be noted that the pressure transducer installed in well MW-3 was functioning erratically and these water elevations are estimates. Water levels recorded in recovery well RW-2, the location with the pump, showed a steady decrease throughout the pumping test(Table 1) even when pumping at the low flow rate of 2- gpm. Recovery data compiled after the pump was turned off provides further evidence that flow into the well was slow. Full recharge at recovery well RW-2 was not achieved 40-minutes after the pump was turned off(Table 1). Total draw down at recovery well RW-2 during the 48-hour pumping test was 13.70 feet. Groundwater analytical results from the pumping test showed decreasing concentrations throughout the test. As shown on Table 3, concentrations of TPHg decreased from 3,600 micrograms per liter to 89 micrograms per liter during the test. This was due to the dilution of groundwater during extraction, suggesting that the draw-down of the aquifer was capturing mostly clean water and not the hydrocarbon plume. Table 4 presents the amount in pounds of recovered TPHg, TPHd, and MTBE during the pumping test. As shown on Table 4, 0.012 pounds of TPHg were recovered when extracting 5,730 gallons of groundwater during the pumping test. Less than 0.01 pounds of TPHd and MTBE were recovered during the pumping test. f