SITE INFORMATION AND CORRESPONDENCE

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No Further Action Required f ermination - 3 - 30 September 2008 Mountain House DevelopmeSite #2 • On I August 2008, Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff submitted notification to property owners and adjacent property owners that the Central Valley Water Board was considering a no further action determination for Mountain House Development Site #2 and that any comments to this action should be submitted within 30 days. No comments were received. Extent defined: Yes. Estimated Residual Petroleum Mass: Unknown. Petroleum occurs primarily as degraded TPHc (immobile petroleum hydrocarbon fractions) at depths of approximately 2 to 27 feet bgs. The highest TPHc concentration was detected at a depth of 20 feet bgs. Threat to Groundwater: The historical pipelines, the source of the crude oil leaks, were removed from service approximately 35 or more years ago. The lateral and vertical extent of affected groundwater is limited having the same approximate dimensions as the area of affected soil. Affected groundwater has been defined beneath the highway within the highway ROW easement. Three existing water wells were identified downgradient within '/z mile of the area of affected groundwater. Review of the Department of Water Resources records indicate that the surface seals of these wells extend below the depth of affected groundwater. It is not anticipated these wells will be affected by the crude oil. Considering the site is located within the highway ROW easement, the installation of new water wells is not anticipated. Threat to Human Health: • Vapor intrusion hazard: there is no vapor intrusion pathway. • Dermal contact hazard: future maintenance excavation within the ROW is possible. Consequently, the applicable ESLs are for a construction/trench worker scenario. The concentrations of residual crude oil are below health protection ESLs for construction/trench workers. The site is located within the Byron Road ROW easement and usage of this feature is not expected to change, thus reducing/minimizing potential human contact with TPH compounds remaining at the site. Summary: The TPH detected in soil and groundwater is highly immobile and limited in extent, defined in close proximity to the former pipelines, and will continue to attenuate naturally with time. There are no monitoring wells to be destroyed. Based on results of the site investigations/characterizations coupled with the findings outlined in the 2007 ERE, it is not anticipated that the residual crude oil remaining at the site will present a threat to human health for the construction/trench worker scenario. Consistent with SWRCB Resolution No. 92-49, alternative cleanup technologies other than natural attenuation would be infeasible and cost prohibitive since the affected area is beneath and within the public roadway ROW.