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in Table 1 Copies of certified analytical reports and chain-of-custody records for each soil sample submitted to the laboratory during this phase of work are contained in Appendix B Soil samples analyzed from both confirmation soil borings CB-1 and CB-2, did not contain detectable concentrations of TPHg, benzene, toluene, or MTBE in any of the soil samples analyzed The only detectable hydrocarbon constituents reported by the laboratory were concentrations of ethylbenzene and xylenes in five of the ten soil samples submitted The highest ethylbenzene concentration was 74 parts per billion (ppb) in the soil sample collected from CB-1 at 50 feet bgs The lughest xylene concentration reported was 7800 ppb m the soil sample collected from CB-2 at 25 feet bgs 4.0 DISCUSSIONFOR CLOSURE The former Econo Gas Station is located at the northwest corner of the intersection of Washington and Sinclair Streets in Stockton, California. It is bounded on the east by Sinclair Street, on the south by Washington Street, and the north and west by private residences The only remaining structure on the site is the former cashier's office The pump islands, canopy, underground storage tanks and lines were removed in 1987 To date, a total of 48 wells have been drilled on and near the site to investigate and remediate soil and groundwater impacted by petroleum hydrocarbons Thirty-one of these wells were originally drilled • as groundwater monitor wells, three were drilled as "bio" wells and fourteen were drilled as vapor extraction wells The monitor wells at the site which were originally screened below the water table began going dry in July of 1989 The bottom of the screen interval in these wells ranges from 50 to 70 feet bgs By January o€ 1990, all of the groundwater monitor wells had gone dry due to a declining water table Four additional monitor wells (MW-27 to MW-30) were installed to depths between 90 and 98 feet bgs in October 1991 Groundwater samples collected from these wells have had no detectable concentrations of TPHg or BTEX since May 1993 MTBE was detected under 5 micro-grains per hter(ug/L,) during the June 1996 sampling event A vapor extraction and thermal oxidation treatment system was installed at the site to remediate the vadose zone which increased in volume as a consequence of the declining water table The remediation system operated at the site from August 1989 to February 1996 During this time, approximately 106,000 pounds (17,000 gallons) of gasoline were removed and treated 4325iNV RPT SBCOR 10700 019 02 3 March 17 1997