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1 <br /> SUPPLEMENTAL SITE ASSESSMENT REPORT <br /> GREYHOUND TERMINAL <br /> STOCKTON, CALIFORNIA <br /> ' PROJECT BACKGROUND <br /> Greyhound Lines, Inc (GLI) 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, GLI <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 (GroundwaterTechnology, 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 (SJCPHS/EHD) requested an <br /> additional 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 SJCPHS/EHD A total of five soil bonngs 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 criteria <br /> ' outlined in the LUFT Manual (Appendices D and E, Preliminary Site Assessment, <br /> November 1991) Based on analytical results, it was determined that groundwater at <br /> the site had not been impacted Three of the soil borings were converted to <br /> ' groundwater monitoring wells to characterize hydrogeologic conditions and <br /> groundwater quality. No free product or hydrocarbon sheens were observed in these <br /> wells Groundwater samples were collected from each well and analyzed for TPHD, <br /> ' TPHG, BTEX and Fecal Coliform. None of the analytes were detected <br /> Following the PSI, Greyhound implemented a program of monthly groundwater <br /> monitoring and quarterly groundwater sampling Groundwater samples collected to <br /> date have been non-detect for TPHG, TPHD and BTEX contamination with the <br /> exception of toluene which was detected at a concentration of 0 5 ppb in MW-1 in the <br /> ' December 1992 sampling event. <br /> Based on the soil sample results from the PSA, the SJCPHS/EHD requested that <br /> GLI undertake a supplemental site assessment (SSA) to completely define the vertical <br /> and horizontal extent of soil contamination at the site In October 1992, Greyhound <br /> submitted the work plan for the SSA to the SJCPHS/EHD for approval The workplan <br /> FIS/SY355 0510005 <br /> 1 <br />