ARCHIVED REPORTS_XR0009729 - Laserfiche WebLink

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OCT 1 11993 1 0 EXECUTIVE SUMMARY • ENVIRONMENTAL HEALTH In March, 1991 three underground fuel storage tanks were Pj%_VWVfff1b the Thiemann's Service site located at 106 West Second Street in the City of Ripon, California Laboratory analyses revealed soil beneath the former tank cluster was impacted with petroleum hydrocarbons, with the highest concentrations detected in the eastern portion of the tank cluster As a result, the San Joaquin County Environmental Health Department requested a site characterization on the basis of these findings In July, 1993 AquaGeosciences, Inc. performed a Site Characterization to assess the extent of impacted soils The study consisted of advancing and sampling eight soil borings, and completing three soil bonngs as groundwater monitoring wells Two bonngs were advanced beneath the former gasoline tank cluster where the highest levels of petroleum hydrocarbons were found during the tank removal The remaining six bonngs were advanced at the purposed margins of the impacted area to assess the lateral limits of hydrocarbon migration from the former tank cluster Laboratory analyses of selected soil samples from the soil borings indicated the soil in the vicinity of the eastern porton of the tank cluster is impacted with elevated concentrations of petroleum hydrocarbons The hydrocarbon constituents range in concentration between 440 to 4700 mg/kg for TPHg to a depth of 30 feet below the surface grade Drilling encountered groundwater at a depth of approximately 29 feet below surface grade • Concentrations of petroleum constituents were non-detect to 510 mg/kg TPHg in soil samples collected from the peripheral soil borings The highest concentrations in the peripheral bonngs were detected in soil boring TH-3 Laboratory analyses of the selected soil samples collected from the remaining borings resulted in concentrations of TPHg ranging between non-detect to 4 5 mg/kg Soil samples from soil borings TH- 2, TH-4b, and TH-6b all indicated non-detectable concentrations, for all hydrocarbon constituents analyzed, with the exception of 0 007 mg/kg toluene in TH-6b at 30 feet (bsg) An interpretation of these data collected in this assessment study characterize the site as impacted with hydrocarbon fuels, centered in the vicinity of the eastern portion of the former tank cluster In the vadose or unsaturated zone, the impacted soil extends laterally with a radius of approximately 22 feet at a depth of 25 feet below surface grade At a depth of 29 feet, the hydrocarbon plume intercepts groundwater and spreads laterally in the water saturated soil to a radius of approximately 35 feet Laboratory analysis of groundwater samples collected from the monitoring wells indicate groundwater is impacted with hydrocarbons in the vicinity of the northwest and northeast limits of the property No petroleum constituents were detected to the southwest Analytical results indicated concentrations of total petroleum hydrocarbons as gasoline reaching a maximum of 210,000 ug/I in monitoring well MW-3, located in the vicinity of the northeast corner of the site The groundwater gradient flows to the 2of17