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4 S E C ® R .Y • QUARTERLY SUMMARY REPORT Second Quarter 2004 i y �F Former 76 Service Station #6981 4707 Pacific Avenue, Stockton, CAR s 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 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 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 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 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 , t 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 Any potentially impacted sod was overexcavated A total of approximately 200 cubic yards of potentially impacted 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 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 1 Groundwater has been monitored on a quarterly basis since 1990 and sampled at the site on a Y quarterly or semi-annual basis since April 1993 Floating product or sheen has never been observed in any of the wells Historically, petroleum hydrocarbon concentrations in the . groundwater have ranged from not detected to 78,000 parts per billion (ppb) of TPHg (well VW- h 2), not detected to 28,000 ppb of benzene (well MW-5), and not detected to 4,900 ppb of MtBE 4 (well VW-3) Groundwater data for the third quarter 2001 sampling event on September 12 and z� 1 J