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i Gedogical Tecluucs Inc. Page 4 Site Conce,tual Model Project No. 989.2 December 17,2003 ' soil and groundwater samples collected over the past 9 years. All analyzed fuel oxygenate samples have been tion-detect above laboratory reporting limits with the exception of MtBE. ' Chemicals of concern at the Valley Wholesale Drug Company site in Stockton; California are: BTEX, TPH-G and MtBE. ' 3.1.1 Nature of Soil Contamination The heaviest soil contamination was detected in samples collected from the UST excavation ' pit. This soil was disposed of at a licensed landfill and GTI believes the bulk of the contamination has been removed, leaving only distal remnants of NAPL at the site. The soil contamination appears to be concentrated between 10 and 20 feet bgs (Table 1). ' Sections 3.2 and 4.6 discuss the assumptions used in calculating TPH-G and MtBE p g concentrations, based on the zone of detectable hydrocarbons. Soil boring and monitoring well installation soil samples, collected from 10 to 20-feet bgs, ' have indicated the presence of the following constituents: • TPH-G (ranging from ND<l to 2,600 mg/Kg) • Benzene (ranging from ND<0.003 to 1.8 mg/Kg) • Toluene (ranging from ND<0.003 to 19 mg/Kg) • Ethyl benzene (ranging from ND<0.003 to 5.14 mg/Kg) • Total xylenes (ranging from ND<0.003 to 34 mg/Kg) ' • MtBE (ranging from ND<0.005 to 0.030 mg/Kg) The highest concentrations of BTEX and TPH-G constituents found in soil samples collected at the site are near e former gasoline USTs (Figure 2). TPH-G mass estimate calculations indicate there i 74.9 gallons TPH-G remaining in the soil at the VWDC location (Table 6). See Section 4. for details on contaminant mass estimate calculations. t MtBE in soil samples was not analyzed until September 2000. Concentrations of MtBE in p Y p soil samples, collected on or after September 2000, increase with distance from the former ' tank pit. MW-6, approximately 175 feet downgradient of the tank pit, showed the highest soil concentrations of MtBE in soil. MtBE mass estimate calculations indicate there i 078 gallons of MtBE remaining in the soil at the VWDC location (Table 7). See Section 4.6 for ' details on contaminant mass estimate calculations. ' 3.1.2 Nature of Groundwater Contamination Groundwater samples were collected and analyzed from Soil Boring and GeoProbe ' investigations at VWDC. Additional laboratory tests have been performed on groundwater samples collected from monitoring wells during routine groundwater-monitoring events. Quarterly Groundwater Monitoring Reports have been prepared and submitted to SJC