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S E C 0 R QUARTERLY SUMMARY REPORT FOURTH QUARTER 2003 Former 76 Service Station #6981 4707 Pacific Ave, Stockton, CA City/County ID# Stockton County San Joaquin BACKGROUND In May and June 1988, RESNA Industries collected sod samples during the replacement of the USTs and from test pits excavated adjacent to the product dispenser islands Petroleum hydrocarbons were detected in sod 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 sods could be removed A sod vapor survey was performed to assess the extent of residual hydrocarbons in the sod 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 ,p evaluate the feasibility of vapor extraction as a remedial option for sods beneath the site An aquifer pump test was performed in August 1992 to evaluate the feasibility of utilizing groundwater extraction to ag remediate hydrocarbon-impacted groundwater A VES utilizing a catox unit has been in operation at the site since September 1994 As of 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 has been extracted and treated The VES was being operated in a pulse mode During the second quarter of 2001, the VES extracted and treated <0 10 pounds of TPHg and <0 001 pounds of benzene The data appears to indicate that asympotic levels were reached in February 2000 No petroleum hydrocarbon concentrations have been detected in the influent since December 2000 The system was shut down in the third quarter of 2001 due to equipment failure Because of the planned remedial system modifications,the catox unit was not repaired 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, 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 Sod samples were collected from beneath the USTs, product Imes, and dispenser islands Any potentially impacted sod was overexcavated A total of approximately 200 cubic yards of potentially impacted sod 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 sod samples were reported as not detected __. 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 0 125 ppm of xylenes beneath the product lines northeast of the northwest dispenser island at a depth of 4 feet bgs