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Remedial Action Plan Canepa's Car Wash. 6230 Pacific Avenue. Stockton. California March 3, 2003 Page t 2.0 SUMMARY OF SITE ASSESSMENT lCanepa' s Car Wash is located in a heavily urbanized area of Stockton (Figure 1 ). The business consists of an automated car wash, a gasoline/diesel fuel station, and a convenience store. The business area is paved with either concrete or asphalt. - � 2.1 INVESTIGATION HISTORY In early 1993, three underground fuel (gasoline and diesel) storage tanks (USTs), fuel lines, and dispensers were removed and replaced with a doubled walled system. Multiple samples were collected at the site with - maximum total of petroleum hydrocarbons as gasoline (TPH-G) concentrations in soil samples collected from under the dispenser island [(3 ,800 milligrams per kilogram (mg/kg)] . Soil boring B-1 , installed in 1 March 1993, encountered groundwater approximately 56 feet below the ground surface (bgs). In September 1993 , monitoring wells MW- 1 through MW-4 were installed at the site (Figure 2). In March 1994, monitoring wells MW-5 through MW-8 were installed. Quarterly groundwater monitoring was conducted at the site from March 1994 through June 1995, and from August 1996 through the present. i` A 24-hour pump test was conducted at the site in December 1994. The results indicated an optimum pumping rate of 5 gallons per minute (gpm) with an effective radius of 140 feet. Aquifer permeability for a 20-foot screen length was estimated at 126 gallons per day per feet squared (gpd /ft), JAdditional soil borings were installed in 1998 and were described in Report — Soil and Groundwater Investigation, dated June 12, 1998. Additional soil boring installation, cone penetrometer boring installation, hydropunch sampling, and the installation of three additional wells were conducted in December 2001 and r, were described in the Additional Soil and Groundwater Investigation Report dated January 21 , 2002. In August 2001 , a sensitive receptor survey was conducted within a 2,000-foot radius of the site. The i results described in the Quarterly Groundwater Monitoring (Third Quarter 2001) and Sensitive Receptor Survey Report dated August 16, 2001 indicated the presence of several domestic and municipal wells, two schools, three child-care facilities, and three leaking underground storage tank (LUST) sites within the .i study area. No actively pumped drinking water wells were identified within 500 feet of the site. 2.2 REMEDIATION HISTORY At the time of UST removal, approximately 600 cubic yards of contaminated soil was removed. Shortly after - the new USTs were installed in 1993 , nine soil vapor extraction (SVE) wells were installed in the area of the Riel dispenser islands. An internal combustion unit (ICU) was installed for vapor extraction and treatment. I,I I The ICU operated from March 1994 through June 10, 1995 . Average influent organic vapor concentrations, measured with a photo ionization detector (PID), exceeded 2,200 parts per million (ppm). j I An evaluation of the SVE system was conducted and reported in the Soil Vapor Extraction (SVE) System Evaluation, dated September 23, 1996. That report recommended that the ICU operations be suspended because the system did not appear to meet permit conditions (95% destruction efficiency). The configuration of the existing SVE wells appeared to be sufficient to remove a majority of the remaining contaminants in the vadose zone. A larger thermal oxidizing SVE system began operation in March 1999. Initial concentrations of total volatile organics up to 1 ,050 ppm were reduced to approximately 50 ppm by February 2001 . SVE operation was stopped on February 6, 2001 as a result in a drop in the SVE efficiency below 95%. The SVE system was 4 CONDOR i