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URS Ms Margaret Lagorio Page 2 San Joaquin County Environmental Health Department June 27,2003 water level during the June 2003, sampling event was approximately 58 feet bgs Generalized geologic cross-sections are included in Attachment B Boring logs are included in Attachment C and well construction diagrams are included in Attachment D Previous Investigations Initial Leak/Release In December 1986, an in-tank leak detector at the site indicated product loss had occurred Subsequent investigations identified that the loss had resulted from a leak in the product lime from the unleaded gasoline UST to the dispenser The leaking pipe was replaced Inventory control data for November and December 1986 showed a total inventory loss of approximately 786 gallons of unleaded gasoline (Brown and Caldwell [B&C], 1987a) April 1987 Site Investigation The initial site investigation included drilling three borings and converting these borings into groundwater monitoring wells (W-1, W-2, and W-3) Four soil samples were collected from each boring and one groundwater sample was collected from each well and analyzed for total fuel hydrocarbons, fuel-related volatile organic compounds, and lead Soil samples identified contamination only in boring W-2, but not above reported action limits Groundwater samples identified contamina- tion in all wells and free product in wells W-2 and W-3 Groundwater contamination was identified at the following maximum concentrations total fuel hydrocarbons, 180 milligrams per liter (mg/L), benzene, 30,000 micrograms per liter(pg/L), toluene, 38,000 gg/L, xylenes, 14,000µg/L (B&C, 1987x) The location of the wells is shown on the map in Attachment E Analytical laboratory results are in Attachment F Municipal Well 12, located approximately 240 feet southeast of the site, was shut down after notification of the release Sampling of this well identified benzene, toluene, and xylenes, but not over the reported action level (B&C, 1987a) July 1987 Site Investigation The follow-up site investigation included drilling five borings and converting three of the borings into groundwater monitoring wells (13-1, B-2, W-4, W-5, and W-6) (Attachment E) During drilling activities, the regular and super unleaded product lines and the super unleaded vapor line were ruptured causing between 0 and 68 gallons of regular and/or unleaded gasoline to be released These product and vapor lines were replaced, pressure tested, and put back into service The appropriate agencies were notified of this additional release (B&C, 1987b) i K 1WprocessU5 BP ARCOI004341Closure Request\Station 434 Closure Doc doc