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phase If Environmental Site Assessment Heritage Square Page 2 underground storage tank (UST, TK2) located east of the Women's Center of San Joaquin County (Women's Center) building. This structure is adjacent to the Heritage Square building. TK2 is situated ' south of the back entrance stairs to the Women's Center and is located entirely within the parcel owned by the Women's Center. The backhoe was used to expose the top of TK2, which measured three feet wide by ten feet long and is approximately 500 gallons in volume. A shovel handle was lowered inside TK2, and the contents appeared to be a diesel-type of fuel and not a black viscous fluid. Cruz Brothers locating service was used to trace the fuel lines north of the geotechnical borehole to inside the Heritage Square building and back outside to a second UST (TK1) located north of the building. A black viscous fluid was present on the stick used to check the contents of TK1. The dimensions of TK1 were not investigated at this time The fuel lines were also traced to an old natural gas-fired boiler located inside the Heritage Square building. On May 22 and 23, 2002, Condor collected one soil sample from beneath TK2 located on the east side of the building and eight soil samples from beneath the fuel lines outside of the building. The samples were analyzed for total lead, kerosene, diesel, and motor oil, and for the same volatile hydrocarbons as the sample collected at the time of the geotechnical borehole advancement. The sample from beneath the tank was also analyzed for semi-volatile hydrocarbons by EPA Method 8270D. The laboratory analyses of the ' soil sample from beneath the tank detected diesel at a concentration of 3,800 milligrams per kilogram (mg/kg). Volatile hydrocarbons were detected at concentrations similar to those detected in the soil sample collected at the time of the geotechnical borehole advancement. Total lead was detected in each soil sample collected from beneath the piping and TK2 at concentrations below the PRG for residential sites and the TTLC. Based on the results from the laboratory analysis, the viscosity of the product present in the pipe, the proximity of the underground piping to both an existing boiler and two USTs, and the apparent age of the boiler, Condor suspected that the former tanks stored bunker or diesel type hydrocarbon fuel. Visual inspection of the contents of TK1 confirmed that the UST stored World War II- era bunker oil, a motor oil-like heavy hydrocarbon. Additional information regarding the backhoe work, the investigation and removal of the underground piping, and the soil sampling procedures and analytical results for the piping trenches is available in the "Underground Pipe .lnvestigation and Removal Report," dated June 24, 2002, and prepared by Condor. During the course of performing fieldwork at the site, Condor located an abandoned water well on the east side of the Heritage Square building (Figure 3). A sensitive receptor survey performed by Condor for an adjacent site did not identify any existing state or county records for the well, and the construction details of the well are not known. Condor was retained by David and Marianne Warwick in cooperation with SUSD to further investigate the site for potential subsurface hydrocarbon contamination in association with the one on-site UST (TK1) and the one off-site UST (TK2) in close proximity to the site that were previously unidentified. Condor submitted a Work Plan dated June 5, 2002 to the San Joaquin County Environmental Health Department(EHD) outlining our proposed work for the site. Ms. MargaretLagorio of EHD gave a verbal approval of the Work Alan on June 7, 2002 3.0 LOCAL GEOLOGY The local geology underlying the subject site consists primarily of medium to stiff tight clay with lenses of sandy to silty clay. The sandy to silty clays become more prominent with depth, but individual layers are characterized by limited horizontal extent. According to published geologic maps, surface deposits underlying the site consist of eolian sands belonging to the upper member of the Modesto Formation. o CONDOR