ARCHIVED REPORTS_XR0009165 - Laserfiche WebLink

Home Browse Search

Third Quarter 1999 Monitoring and Sampling Report 2 7-Eleven Inc Store No 17334 4501 North Pershing Avenue Stockton CA October 4 1999 ' Pnor to purging, dissolved oxygen (DO) levels were recorded in each well Dissolved oxygen levels ranged from 1 0 milligrams per Inter(mg/L) in the deeper well MW-513 to 0 8-0 9 mg/L in the other groundwater monitoring wells(Table 1) The overall DO distribution indicates depletion of DO ' Monitoring Well Sampling and Analytical Results Quarterly groundwater samples were collected after purging at least 4 well-casing volumes of ' groundwater from each monitoring well, unless the well was purged dry The groundwater samples were collected using disposable bailers Groundwater samples were placed in analysis-specific containers with analysis-specific preservative The samples were then sealed ' using Teflon septum caps, labeled with the job identification number, the sample number,date, time, and type of laboratory analysis required The samples were stored on ice and transported with a chain-of-custody record to a state-certified laboratory for analysis Groundwater samples ' were analyzed for BTEX and TPH-G using Environmental Protection Agency(EPA) methods 8020/modified 8015, and for oxygenates MTBE,TBA, DIPE, ETRE, and TAME using EPA method 8260 Analytical results for the quarterly sampling event are presented in Table 1 and Figure 1 and historical laboratory analytical results are summarized in Table 2 Highest dissolved benzene and TPH-G concentrations were reported in well MW-5A at 6,420 micrograms per liter(pg/L) and 87,600 pg/L, respectively MTBE was detected in groundwater from wells MW-3, MW-4, MW-5A and MW-513 at concentrations of 7 73 pg/L, 2,940 pg/L, 11,700 pg/L and 55 3 pg/L, respectively Dissolved benzene, TPH-G, and MTBE concentrations are plotted on Figure 2 The laboratory analytical reports are included in Attachment 4 ' Quarterly data obtained during this sampling event are consistent with previous findings, indicating stable hydrocarbon concentrations in the source area (the former underground storage tank pit) ' Concentrations of MTBE in downgradient well MW-4 are about 40% lower than those observed in this well during the previous quarter Purgewater Disposal All purgewater generated during this quarterly monitoring and sampling event was stored in 55-gallon Department of Transportation (DOT)-approved drums, pending proper transport and disposal Waste disposal documentation will be forwarded once received 1733483 qmr 1 1