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k • Mr George Takemori Project OF90-002 04 May 30, 1996 Page 2 i (BTEX) BTEX was not detected in the other sample, and total petroleum hydrocarbons as gasoline (TPHG) were not detected in either sample In September 1988, the area was overexcavated Confirmation soil samples were collected from the bottom of the excavation Petroleum hydrocarbons were not detected in any of the confirmation soil samples collected during this overexcavation activity 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 soil and groundwater impact ("Problem Assessment Report and Final Remediation Plan," EMCON, December 16, 1992) Dissolved hydrocarbons were detected in the vicinity of the USTs Well MW-1 was damaged and is inaccessible, and well MW-2 was destroyed during removal of this soil In October 1993, EMCON performed a soil vapor extraction (SVE) test ("Problem Assessment Report and Final Remediation Plan," EMCON, December 16, 1992) Results of the test indicated that soil remediation using SVE is feasible In December 1994, a remediation system, consisting of an Environmental Instruments (EI) • 250-cubic-foot-per-nunute (cfm) thermal oxidizer was started up The system was designed to extract soil vapors from wells M-W-13 and MW-14 i On May 8, 1995, EMCON observed the installation of one air sparge well (AS-1), which was installed to increase removal of dissolved hydrocarbons and increase the efficiency of I the remediation system In June 1995, a 314-horsepower conde blower was installed and connected to well AS-1 Air sparging commenced on June 19, 1995 j GROUNDWATER MONITORING: FIRST QUARTER 1996 On February 2, 1996, a technician from EMCON measured depths to groundwater and performed subjective analyses of groundwater from monitoring wells MW-9 through MW-14 In addition, groundwater samples were collected from monitoring wells MW-9 through MW-11, MW-13, and MW-14 for laboratory analyses Well MW-9 was partially obstructed and well purging could not be performed, therefore, a groundwater grab sample was collected Wells MW-3 through MW-5 were dry during the site visit Floating product was not observed in any of the monitoring wells Well locations are shown on Figure 2 EMCON's sampling and analysis procedures are presented in Appendix A The surveyed elevations and the depth to groundwater measurements, summarized in Table 1, were used to evaluate the potentiometric surface beneath the site The potentiometric groundwater surface on February 2, 1996, was toward the northeast to southeast with a hydraulic gradient of 0 003 (see Figure 3) Groundwater elevations SAGS[Y\PJMF9"F9000204Hs-95\pas 1