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�! SUPPLEMENTAL SITE ASSESSMENT REPORT <br /> GREYHOUND TERAIINAL <br /> STOCKTON, CALEFORNIA <br /> PROJECT BACKGROUND <br /> Greyhound Lines, Inc. (Greyhound) operates a passenger bus terminal at 121 South <br />' Center Street, Stockton, California (Figure 1). As part of normal operations, <br /> Greyhound formerly utilized and maintained one 12,000-gallon underground diesel fuel <br /> storage tank for the purpose of refueling the motor bus fleet. In May 1991, Greyhound <br />' removed this underground fuel storage tank (UFST) and associated piping. Soil <br /> samples were collected to assess the potential for environmental contamination <br /> associated with the past operation of the UFST. Samples collected at the base of the <br />' tank pit excavation contained total petroleum hydrocarbons as diesel (TPHD) at <br /> concentrations as high as 4,200 mg/Kg (Groundwater Technology, 1991) In addition, <br /> soil samples collected from the piping trench contained levels of TPHD concentrations <br />' up to 11,000 mg/Kg. Based on these analytical results, San Joaquin County Public <br /> Health Services, Environmental Health Division (PHS-EHD) requested an additional <br /> investigation at the site to characterize the extent of soil and/or groundwater <br />' contamination. <br /> In September 1991, a Preliminary Site Investigation (PSI) was initiated by <br /> Engineenng-Science, Inc. (ES) in accordance with the work plan submitted to and <br /> approved by the PHS-EHD A total of five soil borings were advanced (B-1, B-2, <br /> MW-1, MW-2, MW-3 in Figure 2) Soil samples from each boring were collected and <br /> analyzed for TPHD, TPHG, benzene, toluene, ethylbenzene, and total xylenes <br /> (BTEX). Analytical data collected during the PSI indicated the presence of TPHD in <br /> soil samples at concentrations exceeding the maximum allowable levels (100 mg/Kg) as <br /> calculated using the leaching potential analysis and the general risk assessment cntena <br />' outlined in the LUFT Manual (Engineenng-Science, 1991; Appendices D and E). <br /> Based on analytical results, it was determined that groundwater at the site had not been <br /> impacted. Three of the soil bonngs were converted to groundwater monitoring wells to <br />' characterize hydrogeoiogic conditions and groundwater quality. No free product or <br /> hydrocarbon sheens were observed in these wells Groundwater samples were collected <br /> from each well and analyzed for TPHD, TPHG, BTEX and Fecal Coliform None of <br />' the analytes were detected <br /> In June 1992, Greyhound implemented a program of monthly groundwater <br /> monitoring and quarterly groundwater sampling Quarterly sampling was requested by <br /> the PHS-EHD to confirm the groundwater sample results obtained during the PSI. The <br /> monthly monitoring program was proposed by Greyhound to ensure timely discovery of <br />' significant changes in conditions at the site In addition, the PHS-EHD requested that <br /> Greyhound undertake a supplemental site assessment (SSA) to define the vertical and <br /> horizontal extent of soil contamination at the site. In October 1992, Greyhound <br /> submitted the work plan for the SSA to the PHS-EHD for approval. The work plan for <br /> that investigation was approved without revision in December 1992. <br /> PARESSYROI1VOLi WP1725386 08969125386802 DOC <br />' 1 <br />