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x 1� l:\pmj cots\531-001\us%rcp Introduction The subject site is a truck stop, sales, repair, and fueling facility. The site is mostly paved with concrete and asphalt and the topography is flat. There are currently six fuel islands on site dispensing regular and unleaded gasoline and diesel fuel, as shown on Figure 1 - Site Plan with Boring Locations. The underground tank cluster lies east of the fuel islands and consists of five tanks: two 10,000-gallon diesel tanks manifolded together, one 8,000- gallon diesel tank, one 8,000-gallon regular gasoline tank, and one 7,500-gallon.regular gasoline tank. There is also a 2,000-gallon unleaded gasoline tank approximately 30 feet south of the larger fuel island in the center of the site. This site assessment is in response to unauthorized releases of fuel documented by San Joaquin Co.PHS/EHD from a diesel pipeline on May 23, 1988,a regular gasoline pipeline on April 5, 1989, and a full tank system testing failure on June 29, 1989. There were , additional unauthorized releases documented from waste oil tanks, which have been removed from the site. t. The purpose of this investigation is to assess the vertical and lateral extent of hydrocarbons (or other possibly hazardous materials from the waste oil tanks)in the subsurface by drilling and sampling soil borings around the tanks and product lines. The maximum boring depth ti was 50 feet;ground water was not found in any of the borings. Information from a well on site indicates that first ground water is at a depth of approximately 70 feet. A Work Plan and Health and Safety Plan for the site were prepared by ESE and submitted to San Joaquin County PHS/EHD. This agency-also granted boring permits and witnessed the backfilling of the borings. Procedures A total of fourteen borings were drilled on site around the underground tanks, along the product lines and near the former locations of the waste oil tares, as shown on Figure 1, y to assess the extent of hydr ocarboas in-the soil. The borings ranged in depth from 5 to 50 feet. Thirteen of the borings were drilled with a track-mounted hollow-stem auger rig(131- B13),and one boring was drilled with a hand-auger hi an area not accessible to tha drilling t rig (HA-1). The borings were logged lithologically by a geologist and soil samples were obtained every 5 feet and screened by sight and odor for hydrocarbons as well as with an Organic Vapor Analyzer (OVA). The borings were drilled to at least 20 feet near the tanks and 10 feet near the product lines, or until OVA readings were less than 50 parts per million(ppm),an. indication Shat-the soil-at that depth-did-not contain high r levels of hydrocarbons. If there was evidence of hydrocarbons in soil samples obtained LI from a boring, based on OVA readings, a sample.was sent to a State-certified laboratory to be analyzed for Total Petroleum Hydrocarbons(TPH) as gasoline and diesel,using EPA F Method 8015, and for Benzene, Toluene,Ethylbenzene, and total Xylenes (BTEX) using i .