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-t T u Quik Stop Markets,Inc. October 23, 1991 project No. 3-49132-32 Page 2 detectable levels of toluene, ethyl benzene, and total xylenes. MW-1 was subsequently destroyed in October 3, 1991 due to concerns that it could connect two water bearing units which appear to represent separate shallow aquifers. On September 11, I2 and 13, 1990,Exceltech(RESNA)drilled five additional exploratory borings at the site and converted three of them to groundwater monitoring wells. They were designed to monitor groundwater in the lower aquifer. The results of the analyses of the soil samples from these borings revealed little or no petroleum hydrocarbon contamination. Analyses of groundwater samples collected from monitoring wells MW-3 and MW-4 did not find any petroleum hydrocarbon related contaminants but samples from MW-2 were found to contain 1 ppb benzene and detectable levels of ethyl benzene and total xylenes(Exceltech,September 1990). During the above investigations, a leak was discovered in the subsurface piping for the fueling system at the site. Excavations to remove the contaminated soils revealed that the ill and possibly the soil beneath the tank backfill. contamination had affected the tank backf Upon issuance of the proper permits,the overhead canopy, pump islands concrete surface, and three underground storage tanks (USTs) were removed in October and November 1990. Following tank removal, excavation and soil sampling was continued until laboratory analyses of soil samples indicated that petroleum hydrocarbon contaminated soil above the water table in the vicinity of the storage tank excavation had been removed. All contaminated soil was removed from the station and properly disposed of (Exceltech November 1990). New double-walled fiberglass USTs were installed at the site and the remaining excavation was backfilled with clean fill. The canopy, pumps, and concrete surface were replaced and the station put back in operation in March 1991. On April 2, 1990, Exceltech (RESNA), Inc. replaced the destroyed groundwater mcritoring well,MW-1,with two monitoring wells,designated MW-1R and MW-5. MW- 1 R was designed to monitor the lower aquifer and MW-5 to monitor the upper or"perched" aquifer. Analyses of all subsurface and analytical data indicated the presence of two aquifers beneath the site. It was found that the lower aquifer had no detectable TPHG or BTEX and the upper aquifer contained TPHG and some BTEX components (Exceltech, July 1991). Well Pumping and Sampling On August 30, 1991, RESNA personnel visited the site for the purpose of pumping 200 _ gallons of groundwater from monitoring well MW-5. The purpose of this purnping was to see the effect in contaminant levels caused by the pumping. if the contaminant levels remained low, it could indicate a very localized source of contamination. If the level increased,it would suggest that the source of contamination was upgradient and continuing to affect this area. Prior to this,RESNA personnel measured the depth to groundwater and checked for the presence of floating product at each well using an optical interface probe. A clear acrylic bailer was used to collect a water sample from the wells to check for the presence of floating product, surface sheen, or odor: none was detected. Groundwater sa 'les for laboratory analysis were then collectedfrom the well following the procedures =. outlined in our groundwater sampling protocol(Appe ridix A). Approximately four well- casing - casing volumes of groundwater were removed before sampling. Groundwater removed ' ,sRRRL,RRARAm� �.� R,R1Rl�R1AEIR�AA RAR �117YRf1 R171ARW III� �AIg�' �.