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IPRELIMINARY ASSESSMENT OF HYDROCARBON CONTAMINATION ARCO MINI MART 4511 PACIFIC AVENUE STOCKTON, CA 1. 0 BACKGROUND ' The site is located in a flat commercial/residential area on a busy street in north Stockton (Figure 1) . According to the site plan provided to Geological Audit Services (GeoAudit) by the owner of the property, Mr. Arthur Wyatt, six underground storage tanks are present on the site, ranging from 8, 000 to 14 , 000 gallons in capacity. It is our understanding from the gasoline distributor that supplies the station, Iowever, that at least five of the tanks are 12 , 000 gallons in capacity. It is our understanding that these tanks were installed in 1981, prior to the sale of the property to Mr. Wyatt. The dimensions and exact locations of the tanks are uncertain, but we believe them to be 8 feet x 32 feet and arranged as shown in Figure 2 . The volume of the diesel tank is uncertain, but due to space limitations it appears unlikely that it could be significantly larger than 8 , 000 gallons, which is the size shown on the architect ' s site plan provided by Mr Wyatt. on 19 February 1991, gasoline began pooling on the northern I dispenser island, and the station immediately ceased operation. Western Meter was called to the site, and opened a narrow trench approximately 20 feet long x 2 feet wide between the north and central dispenser islands, exposing the product lines (Figure 2) . Attempts to locate the leak were unsuccessful, and representatives of Falcon Energy Associates were dispatched to the site on 20 February to investigate further. Falcon proceeded to excavate a T- shaped extension a few feet to the west, and located a leaking coupling in an unleaded fuel line. After repair of the leak, the trench was covered with a steel plate and the station was allowed Ito reopen for business. Two sail samples (a and b, Figure 2) were collected by geologists from WaterWork, Inc. and analyzed for TPH-gasoline and BTE&X. Total I petroleum hydrocarbon (TPH) concentrations of 100 and 13 , 000 ppm and benzene concentrations of 1 and 140 ppm were reported in these samples at depths of 8 and 23 ft below grade (see Appendix A) . On 10 August 1991, at the request of Mr. James Hoblitzell of Falcon Energy Associates, GeoAudit submitted a Site Contamination Workplan to assess the extent of soil contamination resulting from the gasoline leak in February 1991. This workplan was approved by San Joaquin EHD in mid-August. Subsequently, representatives of GeoAudit met with the owner of the property, Mr. Arthur Wyatt, and the operators of the gasoline station, Messrs. Balwindar Brar and D. C. Gill, to discuss the possibility of replacing the underground storage tanks. Based on these discussions, on behalf of the owner Iand operators, GeoAudit submitted a letter on 7 November 1991 to