SITE INFORMATION AND CORRESPONDENCE

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Y Chevron - Michael Oliphant -4- 19 January 2012 NFAR - Mountain House Deve}opment Site#6 radius of the area of affected groundwater. Considering the distances noted it is not likely the wells would be affected by TPH compounds in groundwater. Threat to Human Health: The oral and direct contact exposure to onsite soils and cancer risks were estimated and the risk for individual COPCs and summation of risks of all COPCs for these exposure routes were determined. Potential future indirect inhalation exposures to onsite soils and cancer risk were also estimated. The combined total potential cancer risk to a hypothetical future resident from for oral, dermal, and indirect inhalation exposures was estimated to be 5E-06 which is above the lifetime cancer risk of 1 E-06, but within the acceptable risk range of 1 E-06 to 1 E-04 for exposure to onsite soils. The Site land use is part of and within/along and/or adjacent to the highway, pipelines, railroad tracks easements. bow concentrations of volatile organic compounds in groundwater indicate potential risks associated with this pathway are low. The HHSE utilized analytical results for samples from depths of 0 to 10 feet bgs and developed using risk and hazard algorithms developed by the DTSC and provided in the PEA Guidance Manual. The level of risk and hazard to a hypothetical future resident was determined to be below de minimus levels. The Site is located within the highway and utility corridor and part of an alfalfa field and usage is not expected to change, thus reducing/minimizing potential human contact with residual TPH compounds. Summary: • The TPH detected in soil and groundwater is degraded, highly immobile and limited in extent, defined in close proximity to the former pipelines, and will continue to attenuate naturally. There are no monitoring wells to be destroyed. Based on results of the Site investigations/characterizations coupled with the findings outlined in the 2011 HHSE, it is not anticipated that the residual crude oil remaining at the Site will present a threat to human health for hypothetical future residents or construction workers. • Consistent with SWRCB Resolution No. 92-49, an evaluation of alternative cleanup technologies indicates that methods other than natural attenuation would be infeasible and cost prohibitive since the affected area is beneath and within the public roadway ROW, a utility corridor and part of vacant agricultural fields. • The SGMP acts as a management reference designating Chevron as the responsible party if any affected soil or groundwater, attributable to the historical crude oil pipelines, is encountered during future utility corridor maintenance work. • The Mountain House Community Services District (MHCSD) has jurisdiction and responsibility for administration of activities within the ROW. A copy of the SGMP was provided to the MHCSD. • No comments were received during the 30-day public notice period from adjacent property owners or owner(s) of property determined to have been affected by leaks from the historical pipelines.