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I ' EXECUTIVE SUMMARY SSB Environmental Consultants, Inc , was authorized by Ultramar Inc and the property owners to conduct an investigation to assess the subsurface soils and ground water underlying Beacon Cardlock Station Number 610 located at 3300 Waterloo Road in Stockton, California Previously, four ground-water monitoring wells had been installed at the site beginning in April of 1987 Two of the wells are now dry due to a lowered ground-water table The remaining wells, drilled to similar depths, could not be opened and are presumed dry I The purpose of this investigation was to evaluate the presence of gasoline range hydrocarbons in soil and ground water, to calculate the direction of ground-water flow and gradient to reestablish a monitoring well system, and to provide recommendations based on evaluation of the collected ' data I During this investigation, three monitoring wells (MW-4, MW-5, and MW-6) were installed to a maximum depth of approximately 90 feet below surface Soil samples were obtained at 5 foot intervals from each of the three monitoring well borings to 70 feet below surface Each sample was field analyzed for gasoline range hydrocarbons using a phototonization detector (PID) Six soil samples from each monitoring well boring were submitted to a State certified laboratory for analysis ' of selected gasoline constituents No gasoline range hydrocarbons were detected in soil samples obtained from any of the three borings, except for one soil sample collected from a depth of 25 feet from boring B-8 Chemical analyses of soil sample S-25-B8 indicated xylene concentrations at 0 0059 mg/kg, slightly above the method detection limit of 0 005 mg/kg Additional soil samples collected at 40, 55, 65, and 70 feet in boring B-8 did not contain detectable concentrations of analytes Due to the closeness of the xylene concentration to the method detection limit, SSB does not feel the sample S-25-B8 indicates the presence of hydrocarbons in the soil at the sample location. After installation, the new monitoring wells were developed and purged Ground-water samples were collected for Iaboratory analysis The analytical results of the ground-water samples indicate Ithe presence of gasoline range hydrocarbons in ground water only from monitoring well MW-5 Analysis of the sample from monitoring well MW-5 indicated concentrations of toluene and xylenes at 0 60 ug/l and 0 73 ug/l, respectively The concentrations indicated are slightly above the method detection limit of 0 50 ug/1 These trace amounts of analytes may have been caused by surface runoff from heavy rainfall penetrating the boring during well construction Due to the closeness of the analyte concentrations to the method detection Iimit, monitoring well MW-5 was purged and resampled on April 16, 1993 No detectable concentrations of gasoline range hydrocarbons were found in the ground-water resample