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t w i <br /> I <br /> Mr. Kyle Christie Project 20805-146.006 <br /> August 5, 1996 <br /> Page 2 <br /> • Excavation backfilling conducted on February 14 and 15, and June 3 through <br /> June 6, 1996 <br /> BACKGROUND <br /> UST Complex <br /> The UST complex consisted of two 6,000-gallon, single-wall steel tanks: one 8,000-gallon; <br /> single-wallsteel tank; and one 10,000-gallon; single-wall fiberglass tank (see Figure 2). <br /> The-UST fill ports were located at the eastern ends of the tanks. Fiberglass piping located <br /> at the western ends of the USTs connected the USTs to two dispenser islands located to <br /> the south of the station building. A third set of fiberglass product delivery piping connected <br /> to a potential dispenser location to the west of the station building was encountered during <br /> overexcavation activities. <br /> According to the information contained in the San Joaquin County Public Health Services <br /> (SJCPHS), Environmental Health Division, files, the two 6,000-gallon USTs and the <br /> 8,000-gallon UST were installed in the early 1970s. The 6,000-gallon USTs previously; <br /> contained regular leaded gasoline, and the 8,000-gallon UST previously contained premium, <br /> leaded gasoline. Prior to removal, the 6,000-gallon USTs contained mid-grade unleaded <br /> gasoline, and the 8,000-gallon UST contained supreme grade unleaded gasoline. The <br /> 10,000-gallon UST reportedly was installed in 1990'and contained regular unleaded <br /> gasoline throughout its-service period. In addition, an underground waste oil tank was <br /> formerly located in the northeast corner of the site. According to information provided by <br /> ARCO, the waste oil tank was removed on November 18, 1986. <br /> i <br /> I <br /> Previous Investigations <br /> RESNA Industries (RESNA) of Rancho Cordova, California, observed the drilling of four soil <br /> borings (B-1 through B-4) at the site in July 1991 during a preliminary tank replacement ' <br /> assessment investigation. Residual gasoline hydrocarbons were detected in soil samples <br /> collected from the borings. Boring locations are shown on Figure 2. The site was added to the <br /> SJCPHS pilot program on August 5,'1991. <br /> I. In April and May 1992, RESNA observed the drilling of eight additional soil borings (B-5 <br /> through B-12) and the installation of three groundwater monitoring wells (MW-1 through- <br /> MW-3) and three vapor extraction wells (VW-1 through VW-3). Well locations are shown <br /> on Figure 2. Gasoline hydrocarbons were detected in samples collected from the borings. <br /> SA(�IN:WlPMSO"9051460.6 RS-95\cjb:3 <br />