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Antonia Vorster - 2 - 4 March 2009 Volpi Farm Property, Stockton • Later in July 1998, Volpi excavated five additional trenches. Soil and groundwater contained minor concentrations of petroleum hydrocarbons. • In December 1999, Volpi excavated about 300 cubic yards of contaminated soil to a maximum depth of 11 feet bgs and transported it offsite for disposal. • On 31 May 2000, Volpi installed six monitoring wells (MW-1 through MW-6) screened from five to 15 feet bgs and sampled them sporadically from 2000 to 2005. Average depth to groundwater is five feet bgs, and the plume is centered near MW-3 (see Table 1). • On 5 May 2008, Volpi collected a soil sample from the sidewall of the excavation near a previous sample containing petroleum hydrocarbons. This sample did not contain any petroleum hydrocarbons. Volpi also collected a grab groundwater sample from the water that collected in the excavation, and this sample did not contain petroleum hydrocarbons. • On 5 May 2008, Volpi sampled MW-1 and MW-3, and attempted to sample MW-7, but was unable to locate this well in the field. MW-7 has not been sampled since May 2003. A summary of the last five monitoring events is shown in Table 1. Extent Defined: Yes Residual Concentration: Minor concentrations of petroleum hydrocarbons remain in the soil following the excavation. Maximum soil concentrations remaining following the December 1999 excavation are 450 milligrams per kilogram (mg/kg) of total petroleum hydrocarbons (TPH) as diesel and 220 mg/kg of TPH as gasoline. Threat to Groundwater: In 2006, Volpi's consultant conducted a 100-year fate and transport analysis to determine potential effects on shallow downgradient wells 130 feet from the source area (equivalent to the distance to the upgradient domestic well onsite). The analysis was conducted for benzene, toluene, ethylbenzene, xylenes (collectively BTEX) and MTBE in soil and for MTBE in groundwater. The model predicted that BTEX and MTBE source concentrations will be below detection limits within one to two years, and that MTBE would not be detected in groundwater 130 feet downgradient. Site remedial activities have reduced the threat to groundwater quality. MTBE concentrations remaining in groundwater are expected to continue to decline to water quality objectives. In addition, the one domestic well onsite is upgradient of the AGTs and does not contain petroleum hydrocarbons. Any future domestic wells at the Site will be installed according to current State regulations and will include a sanitary seal that will prevent the migration of the remaining MTBE in groundwater to the well. Threat to Human Health: ;arming Vapor Intrusion Hazard: There is no vapor intrusion hazard at the Site. Current land use is and no buildings are located near the source area. • Dermal Contact Hazard: There is no dermal contact hazard at the Site. Summary: Based on these evaluations, the remaining petroleum hydrocarbons in soil and the MTBE in groundwater do not present either a threat to water quality or to human health.