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T c t Fc 4 i 1.0 INTRODUCTION : t This report presents the results of a subsurface investigation for hydrocarbon contamination on the property located at 308 Grant Street in Stockton, California (Figure 1) _ The property was formerly occupied by De Rollo Mazda, an automobile sales and service business. The site previously had three underground (u/g) storage tanks, two of which dispensed gasoline, and one used for storage of waste motor oil (Figure 2). On April 21, L2V, a 1000 gallon underground u/g gasoline storage tank (Tank A) was removed from the subject property (Figure 2). Field inspection during tank removal noted holes in the tank. A soil sample was collected from beneath the tank at a depth of 14 feet below grade. The laboratory results for the sample recorded benzene, toluene, xylenes and total trnlpuM_-hydrocarbon (BTX/TPH) concentrations of 120, 470, 520, and 24_x. parts per million ( ppm) , respectively (Table 1) . r On October 19, 1988, a 5000 gallon u/g gasoline tank (Tank B) and a 300 gallon u/g waste oil tank (Tank C) were removed from the project site (Figure 2 ) . Soil samples were collected from each end of the gasoline tank pit at a dept�i of. approximately 15 feet below grade. The samples were analyzed for benzene, toluene, ethylbenzene, xylenes (BTEX); total petroleum hydrocarbons as gasoline (TPH); ethylene dibromide (EDB) and tetra ethyl lead (TEL) . Laboratory results for the sample indicated concentrations of TPH and ►'® TEL above State designated levels (Marshack, 1986) in the E north end of the former tank pit. The laboratory results } are summarized in Table 2. A soil sample was also recovered from beneath the waste oil tank at a depth of approximately 6 feet below grade. The sample was analyzed for BTEX, TPH, chlorinated hydrocarbons, metals and PCB ' s. Laboratory results for these rA constituents, summarized in Table 3, recorded concentrations less than method detection limits for all constituents except ch1D2ioXDxlp at 7 parts per billion (_pp_ ) and richloroethane . at 30 ppb, These levels are significantly C. below the state designated levels to protect groundwater at a hypothetical average site (Marshack 1986). A May 10, 1989 correspondence from the San Joaquin County Public Health Services Environmental Health Division (SJCPHSEHD) required assessment of chloroform and trichloroethane in addition to the subsurface hydrocarbon contamination. ' 3 This investigation' was conducted in accordance with WaterWork' s proposal dated July 10, ' 1989, which was submitted to the SJCPHSEHD for prior approval This proposal was drafted and the investigation conducted in Regional accordance with the Tri Re Guidelines ,..f g' prepared by the Regional Water Quality Control Board. 1 i 1