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Working to Restore Nature ' September 1993 Quarterly Groundwater Sampling & Analysis December 1, 1993 Quik Stop Market No 132, Stockton, California F7132 93 APPENDIX A SITE BACKGROUND Quik Stop Market No. 132 3555 West Hammer Lane Stockton, California Quik Stop Market No 132 formerly utilized three underground fuel-storage tanks onsite which consist of two 10,000-gallon tanks contained regular unleaded and formerly leaded gasoline, and one 8,000-gallon tank contained super unleaded gasoline In 1987 at the request of Quik Stop Markets, Inc (Quik Stop), RESNA Industries Inc (RESNA), (formerly Exceltech, Inc [Exceltech]), installed a vadose monitoring system around the tanks at the site This system detected hydrocarbon contamination in July 1990 An investigation revealed the possibility of a leak in the product delivery lines Gasoline affected backfill was found and removed from the product line trenches and samples of the native soil at the bottom of the trenches were collected and analyzed for gasoline components The results of the analysis revealed that hydrocarbons had penetrated the soil adjacent to the east half of the product line trench which serves the north pump island On August 23, 1990, RESNA dulled four exploratory borings.g at the site and converted one boring to a groundwater monitoring well The results of laboratory analyses of soil samples ' from three borings detected gasoline hydrocarbons in one boring but not in the other two borings Soil samples from one boring, near the northwest portion of the northern pump island (13-3) contained 460 parts per million (ppm) total petroleum hydrocarbons as gasoline t (TPHg) The groundwater sample from monitoring well MW-1 contained 470 parts per billion (ppb) TPHg, 21 ppb benzene, and detectable concentrations of toluene, ethylbenzene, ' and total xylenes (Exceltech, September 1990) On September 11, 12, and 13, 1990, Exceltech drilled five additional exploratory borings at ' the Site and converted three of them to groundwater monitoring wells MW-2, MW-3 and MW-4 The results of the analyses of the soil samples from these borings indicated that either minor or no petroleum hydrocarbon were present Analyses of groundwater samples ' collected from monitoring wells MW-3 and MW-4 did not detect any TPHg or BTEX, however, samples from MW-2 contained 1 ppb benzene and detectable concentrations of ethylbenzene and total xylenes (Exceltech, September 1990) iDuring the above investigations, Quik Stop discovered a leak in the subsurface piping for the fueling system at the site Excavations to remove the affected soils revealed that the gasoline had affected the tank backfill and possibly the soil beneath the tank backfill Upon issuance of the proper permits, the overhead canopy, pump islands, concrete surface, and ' A-1