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Mr George Takemon Project OF90-002 04 October 26, 1995 • Page 2 Between December 1987 and December 1994, following the removal of the tanks, soil borings were drilled and ten groundwater monitoring wells were installed to characterize the lateral and vertical extent of soul and groundwater impact (EMCON, Problem Assessment Report and Final Remediation Plan, December 16, 1992) Dissolved hydrocarbons were detected in the vicinity of the USTs Well MW-I was damaged, and well MW-2 was destroyed during removal of this soil In October 1993, EMCON performed a soil vapor extraction (SVE) test (EMCON, Problem Assessment Report and Final Remediation Plan, December 16, 1992) Results of the test indicated that soil remediation using SVE is feasible In December 1994, a remediation system, consisting of a (Environmental instruments [Ell 250- cubic-foot-per-minute [cfm]) thermal oxidizer, was started up The system was designed to extract soil vapors from wells MW-13 and MW-14 On May 8, 1995, EMCON observed the installation of one air sparge well (AS-1) Well AS-I was installed to increase removal of dissolved hydrocarbons and increase the efficiency of the remediation system In .Tune 1995, a 3/4 horsepower conde blower was installed and connected to well AS-1 Air sparging commenced on.Tune 19, 1995 • GROUNDWATER MOMTOMNGa T! !Rl) QUARTFR '1995 On August 30, 1995, a technician from EiUICCN measured depth to water, performed subjective analyses of groundwater, and collected groundwater samples from monitoring wells MW-9 through MW-11 and MW-14 for laboratory analyses Well MW-9 is partially obstructed and well purging cannot be performed, therefore, a groundwater grab sample was collected Wells MW-3 through MW-5 and MW-13 were dry during the site visit Floating product was not observed in any of the monitoring wells Well locations are shown on Figure 2 Sampling and analysis procedures are presented m Appendix A The surveyed elevations and the depth to groundwater measurements, summarized in Table 1, were used to evaluate the potentiometnc surface beneath the site The potentiometnc groundwater surface on August 30, 1995, was toward the northeast with a hydraulic gradient of 0 003 (see Figure 3) Groundwater elevations decreased approximately 0 88 feet from the previous sampling event(May 1995) Analytical Methods and Results Water samples collected from wells MW-9 through MW-I I and MW-14 were analyzed for TPHG using modified Environmental Protection Agency (EPA) Method 5030/DHS LUFT and for BTEX using EPA Method 5030/8020 Samples were analyzed at Columbia Analytical Services, Inc , in San Jose, California (California Department of Health Services Hazardous Waste Testing Laboratory Certification No 1426) Copies of the chain-of-custody records and laboratory analysis reports are presented in Appendix B Analytical results are summarized in Table 1 SACUV Pi010F9010F900020 4DS-95 PAS i