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01 lib Environmental Assessment Report 3 . Chevron U 5 A Products Company,508 Charter Way,Stockton CA —May Ill 1995 Completed wells were surveyed by Morrow Surveying for horizontal position and elevation relative to Mean sea level datum using a City of Stockton benchmark as a reference (Appendrx C) Elevations Were obtained for top -of -well -casings and the well box rims On March 23, 1995, wells MW -1, MW -2 and MW -3 were developed by Groundwater Technology using a PVC bailer Prior to development activities, depth to water was measured in each well relative to top -of -well -casing to determine the static water level (Table 3) Wells were manually developed using a surge block and bailer in order to remove fine-grained sediment Approximately 20 gallons of water (equivalent to 7 well volumes) was extracted from each of the wells All water generated during development was pumped into a DOT -approved purge water trailer and transported to the Chevron refinery in Richmond, California for recycling 30 RESULTS OF SOIL SAMPLE ANALYSES Tables 1 and 2 summarize the laboratory analytical results for soil samples collected on March 15 and 16, 1995 Table 1 presents data on BTEX and petroleum hydrocarbons The highest concentrations of BTEX and TPH-G were detected in the sample collected at 35 feet BGS from boring MW -3 at concentrations of 10, 4 6, 1 1, 8 3, and 250 milligrams per kilogram (mg/kg, equivalent to parts per million, or ppm), respectively BTEX and TPH-G were below laboratory detection limits in samples selected for these analyses from boring MW -2 TPH-D and total oil & grease were also below laboratory detection limits in samples analyzed for these compounds from boring MW -1 Concentrations of purgeable halocarbons (EPA method 8010), extractable organics (EPA method 8270), and cadmium to samples collected from the 10- and 35 -foot depths from boring MWA were below laboratory detection limits (Table 2) Levels of lead, nickel and zinc detected in these samples were all below comparable Soluble Threshold Limit Concentration (STLC) limits Total chromium was detected to sample MWA-10 at a concentration of 31 mg/kg, which is less than the STLC limit of 50 ppm for chromium Vl Copies of laboratory analyses reports and chain -of -custody manifests for the sod samples collected March 15 and 16, 1995 are included to Appendix D 40 GROUNDWATER GRADIENT Potentfometnc surface elevations in the three monitoring wells, calculated from gauging data collected March 23, 1995, indicate groundwater flow to the east-northeast at a gradient of 0 004 (Figure 2, Table 3) • 0071 EAFi ,ptlChv 1081 �19 GROUNDWATM ❑❑ TECHNOLOGY .