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Envnonmantal Assessment Report 3 • San Joaquin Catholic CetnMery,C,emetery, Lane and Harding Way,Stockton,CA , June 20,190 30 SITE CONDITIONS 31 Results of Soil Sampling Table 1 summarizes the historical laboratory analytical results for soil samples collected at the site including samples collected on April 18-20, 1995 Benzene was detected at a maximum concentration of 0 61 mg/kg (milligrams per kilogram,equivalent to parts per million, or ppm) in the sample collected at 30 5 feet BGS from boring VW-3,while the highest TPH-G concentration of 1,800 mg/kg was detected in the sample collected at 15 5 feet BGS from that boring BTEX and TPH-G were below laboratory detection limits in analyzed samples from boring VW-1 Soil encountered while drilling consisted of alternating beds of silt, clay and silt/clay mixtures Groundwater was encountered at approximately 58-60 feet BGS Copies of laboratory analyses reports and chain-of-custody manifests for the soil samples collected April 18-20, 1995 are included in Appendix C 32 Extent of Hydrocarbon-Impacted Material Figure 4 shows the estimated lateral extent of hydrocarbon-impacted soils based on data collected . during each investigation The lateral extent of hydrocarbon-impacted soil is well defined to the north and east and south with inferred boundaries to the west underneath the mausoleum The estimated area encompasses approximately 2,000 square feet The vertical extent of hydrocarbon-impacted sod is estimated to be approximately 60 feet, extending between 10 and 70 feet BGS Based on an average concentration within the impacted area of 450 mglkg,the total estimated mass of hydrocarbons in sod is estimated to be approximately 6,500 pounds (1,000 gallon equivalent) Table 2 is a summary of historical groundwater monitoring and analytical data Figure 5 shows the downgradient extent of hydrocarbon-impacted groundwater Currently the upgradient boundaries are unclear due to lack of data beneath the mausoleum Based on concentrations observed in MW-s 1,2 and 3, hydrocarbons dissolved in groundwater make up less than one percent of the total mass of hydrocarbons that exist in the subsurface 40 SOIL_VAPOR EXTRACTION TEST 41 Methodology Soil vapor extraction testing was conducted at the site on May 9, 1995 Testing was performed to determine the following attainable radius of influence, attainable flow rates, hydrocarbon concentration in the extracted soil vapor, and approximate hydrocarbon dissipation rates Vapors were SJCCEAii rpdMrsc 17i ❑❑`i GROUNDWATER E110 TECHNW)GY