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` t 3246 East Fremont Street, Stockton, California September 16, 1993 Chevron USA Products Company Page 1 1.0 INTRODUCTION 1 ' This report is a summary of environmental assessment work conducted at the Chevron service station #9-7780 located at 3246 East Fremont Street, Stockton, California (Figure 1). The work included drilling ' two soil borings, installation of a monitoring well in each boring, excavations in the vicinity of the former product lines and septic tank, soil and groundwater sampling, laboratory analyses of the samples, and Preparation of this report. The scope of work was designed to collect the data required to fulfill the ' requirements of the San Joaquin County Public Health Services, Environmental Health Division (SJPHS/EHD), and the California Regional Water Quality Control Board, Central Valley Region ' (CRWOCB-CVR). 2.0 BACKGROUND According to San Joaquin County records, four underground storage tanks (USTs), including a 6,000-gallon leaded gasoline tank, a 5,000-gallon unleaded gasoline tank, a 2,000-gallon premium unleaded gasoline tank, and a 550-gallon waste oil tank were removed on January 30, 1987. Two septic ' tanks had been identified as being on site prior to 1987. Eight soil samples were collected from beneath the USTs. Only four were submitted for laboratory analysis. Soil samples were collected at 14 feet ' below grade beneath the tank pit area. Concentrations ranged up to 5,300 parts per million (ppm) total petroleum hydrocarbons-as-gasollne (TPH-G) and 19 ppm benzene. The tank pits were backfilled with ' soil excavated during the tank removal. The county records did not indicate that the product piping was removed or sampled at that time. Figure 2 shows the locations of the former USTs and associated piping. On March 19, 1987, three monitoring wells (MW-1, MW-2, and MW-3) were installed to investigate .' possible hydrocarbon impact on the groundwater beneath the site. Concentrations of hydrocarbons were detected while drilling MW-1. Hydrocarbons were also detected in the groundwater at a depth of approximately 40 feet below grade. However, the detection limits used for laboratory analysis were above the detection limits currently acceptable to the SJPHS and the CRWOCB-CVR. On February 22, 1989, all the wells were reported dry. 3 .RaT =�=GROUNDWATER g85EAR ' TECHNOLOGY