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Ms. Carol Oz August 12, 1999 Project 791700 Page 2 • Removal of approximately 1,000 cubic yards (cy) of stockpiled soil on July 2, 3, and 5, 1999. BACKGROUND UST Complex The former gasoline UST complex consisted of two 10,000-gallon and one 8,000-gallon single-wall fiberglass tanks. The 8,000-gallon UST formerly stored super unleaded gasoline and the two 10,000-gallon USTs formerly stored regular unleaded gasoline. The gasoline UST fill ports were located at the northern ends of the tanks. Fiberglass piping located at the northern ends of the USTs, proceeded along the western edge of the site, connected the USTs to two dispenser islands located north of the station building (see Figure 2). Previous Investigations In August and September 1995, EMCON observed the drilling of six borings (13-1, B-3 through B-5, B-7, and B-8) and two 45 degree angle borings (13-2 and 13-6). Three of the borings (13-1, B-4, and B-5) were converted to groundwater monitoring wells (MW-1 through MW-3), and three of the borings (13-3, B-7, and B-8) were converted to duel completion vapor extraction wells (VW-1 through VW-3). In October 1996, EMCON observed the drilling of boring B-9. The boring was converted to groundwater monitoring well MW-4. Low residual concentrations of total petroleum hydrocarbons as gasoline, benzene, toluene, ethylbenzene, and total xylenes in soil remain at depths of 31 to 56 feet below ground surface. The highest detected dissolved petroleum hydrocarbon concentrations have historically occurred in well MW-1. The groundwater flow direction is generally east-southeast to east-northeast. UST AND PIPING REMOVAL Henderson Construction (Henderson) of Stockton, California, obtained UST re moval permits from the SJCPHS and provided UST and product delivery Pipingremoval and replacement, and excavation backfilling services. Asphalt above the USTs and piping was removed and disposed as construction debris. CP\E:\ARCO\2186\REPORTS\2186 P105.DOC-951sg:1 �ccrKcicQe