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SIEcC0R QUARTERLY SUMMARY REPORT Fourth Quarter 2004 Former 76 Service Station#6981 , 4707 Pacific Avenue, Stockton, CA City/County ID # Stockton County San Joaquin ; PREVIOUS ASSESSMENT In May and June 1988, RESNA Industries collected soil samples during the replacement of the USTs and from test pits excavated adjacent to the product dispenser islands Petroleum hydrocarbons were detected in soil samples collected from the UST pit, product lines, and test pits Approximately 1,600 cubic yards of hydrocarbon- impacted soils were excavated and removed from the site Due to the proximity of roads and structures, overexcavation was terminated before all hydrocarbon- impacted soils could be removed A soil vapor survey was performed to assess the extent of residual hydrocarbons in the soil beneath the site Thirteen groundwater monitoring wells (MW-1 through MW-13), six vapor extraction wells (VW-1 through VW-6), and one groundwater extraction well (PTW-1) were installed on or near the site between January 1990 and August 1992 A vapor extraction test (VET) was performed in March 1992 to evaluate the feasibility of vapor extraction as a remedial option for soils beneath the site An aquifer pump test was performed in August 1992 to evaluate the feasibility of utilizing groundwater ° extraction to remediate hydrocarbon-impacted groundwater A VES utilizing a catox unit was in operation at the site from September 1994 through the second quarter of 2001 By the end of the second quarter of 2001, approximately 14,794 pounds of total petroleum hydrocarbons calculated as gasoline (TPHg) and 183 pounds of benzene were extracted and treated The remediation method was revised in late 2001 from full-time VES using the catox unit to ozone sparging In February 1996, wells MW-3, MW-10, MW-12, and MW-13 were abandoned at the request of the City of Stockton This work was performed to facilitate reconstruction of the intersection and widening of Pacific Avenue In August 1999, Gettler Ryan (GR) installed three groundwater monitoring wells (MW-14 through MW-16), one groundwater sparging well (VW-7) and advanced one soil boring (VW-9) These groundwater monitoring wells replaced the wells that were abandoned in February 1996 In April 2000, the service station building and all related facilities were removed from the site, including two 12,000-gallon double-wall steel gasoline USTs Soil samples were collected from beneath the USTs, product lines, and dispenser islands Soil thought to be potentially impacted was overexcavated A total of approximately 200 cubic yards of soil was excavated from beneath the northwest and southeast dispenser islands and product lines immediately north of the west UST In addition, the UST pit was excavated to a depth of 21 feet bgs All of the soil samples contained no detectable levels of gasoline components except for 2 73 parts per million (ppm) of TPHg beneath the northeast dispenser island at 4 75 feet bgs and 38 3 ppm of TPHg and 0125 ppm of xylenes beneath the product lines northeast of the northwest dispenser island at a depth of 4 feet bgs In November 2001 GR installed ozone wells SPA through SP-10 to approximately 65 feet bgs and ozone wells SPA 1 through SP-13 to approximately 40 feet bgs The wells were connected to an ozone sparge system and the ozone sparge system was placed into operation on December 19, 2001 The system cycles ozone/air injection between ten sparge points (SP-1 through SP- 10) Since the ozone microsparge panel can only supply ten points, wells SPA 1 through SPA