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. Mr George Takemori Project OF90-002 04 May 30, 1996 Page 3 increased approximately 2 60 feet from the previous sampling event (November 1995) in wells MW-9 through MW-12 and MW-14, but decreased approximately 0 52 foot in well MW-13 Analytical Methods and Results Groundwater samples collected from wells MW-9 through MW-11, MW-13, and MW-14 were analyzed for TPHG using modified U S Environmental Protection Agency (USEPA) Method 5030/DHS LUFT and for BTEX using USEPA Method 5030/8020 The 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 The results of laboratory analyses indicate that TPHG and BTEX were not detected in groundwater samples collected from wells MW-9 and MW-10 Dissolved hydrocarbons were detected in wells MW-11, MW-13, and MW-14 TPHG concentrations ranged from • 6,800 parts per billion (ppb) in well MW-11 to 32,000 ppb in well MW-13 Benzene concentrations ranged from below laboratory detection lutists in well MW-11 to 84 ppb in well MW-13 Concentrations of TPHG and benzene are shown on Figure 2 OPERA—ION AND MAIN-rENANCE: FIRST QUARTER L996 In April 1995, EMCON began overseeing the operation and maintenance of the remediation system The remediation system consists of an EI 250 thermal oxidizer fitted with a catalytic insert and rated at 250 cfrn, and a vacuum blower The remediation system operates under a permit-to-operate issued by San Joaquin Valley Unified Air Pollution Control Distnct, No N-841-2-0 The blower extracts sort vapors from wells MW-13 and MW-14 Extracted sort vapors are combusted in either thermal or catalytic mode prior to discharge to the atmosphere The remediation system is currently operating in the catalytic mode An air sparge blower was installed and started up on June 19, 1995, to remediate dissolved hydrocarbons in the groundwater Air is being injected into well AS-1 at the rate of 5 cfrn into the groundwater Due to low soil vapor concentration during the fourth quarter of 1995, the remediation system was not operated dunng the first quarter 1996 The low soil vapor concentrations • resulted in high supplemental fuel costs, and therefore it was deemed economically judicious to shut the remediation system down for one quarter The shutdown allows the SAC\N TJMF9ftF900020 4HS-9Spas l