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4./ 09 February 2005 AGE-NC Project No. 03-1153 Page 2 of 5 The Modesto, Riverbank, and Turlock Lake Formations and overlying Recent alluvium are the principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Water Basin (Basin 5-22). 2.2. UNDERGROUND STORAGE TANK REMOVAL On 06 and 07 May 2004,AGE was present at the site during UST and piping excavation activities, performed by Thorpe Oil of Stockton,California. One 4,000-gallon heating oil UST and associated piping were removed.Approximately 5 cubic yards of soil were displaced during the excavation and stockpiled on-site on plastic sheeting for soil disposal characterization. Six soil samples were collected for laboratory analysis from the floor of the UST and piping excavations and from the soil stockpiles (Figure 2). The samples were transported to Cal Tech Analytical Laboratories(CTEL),a State of California Department ofHealth Services(DHS)-certified analytical laboratory, and analyzed for: • Total petroleum hydrocarbons quantified as gasoline,diesel,and heating oil(TPH-g,TPH-d, and TPH-ho, respectively)by EPA Method 8015M; and • Benzene, toluene, ethylbenzene, and total xylenes (BTEX) and the fuel oxygenates methyl tertiary-butyl ether(MTBE),tertiary-butyl alcohol(TBA), di-isopropyl ether(DIPS), ethyl tertiary-butyl ether (ETBE), tertiary-amyl methyl ether (TAME), 1,2-dichloroethane (1,2-DCA), and 1,2-dibromoethane (EDB) by EPA Method 8260B, and lead by EPA Method 6010B. The laboratory analysis detected TPH-ho in the soil samples collected from the excavation stockpile (EXE SP) and from the north end of the UST pit (TK1-N) at concentrations of 16,000 mg/kg and 14,000 mg/kg,respectively.No other analytes were detected at or above laboratory reporting limits. Figure 2 depicts the approximate locations of the sample collection points; analytical results are summarized in Table 1. On 16 September 2004, soil stockpiled on-site was sampled and transported to CTEL for analysis for petroleum hydrocarbons by EPA Method 8260B full scan, as well as heavy metals cadmium, chromium, lead, nickel, and zinc by EPA Method 6010B. Chromium, lead, nickel, and zinc were detected at concentrations of 19 mg/kg, 170 mg/kg, 6.3 mg/kg, and 37 mg/kg, respectively. Stockpiled soil was subsequently disposed of at Forward Landfill in Manteca,California.A copy of the non-hazardous waste manifest is provided in Appendix A.