SITE INFORMATION AND CORRESPONDENCE

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" Lee Higgins -3- 6 May 2011 No Further Action Required Determ*n • Mountain House Development Site#3 Recommendations for Preliminary Investigation and Evaluation of Underground Storage Tank Sites, Section 6.5 NFAR for Cases Exceeding Water Quality Objectives. • A site-specific Soil and Groundwater Management Plan (SGMP) submitted in January 2011 , describes procedures to follow and contains the contact names and prone numbers for representatives of Chevron and the San Joaquin County Environmental Health Department if future activities encounter crude oil-affected soil. The SGMP serves as a guideline for Chevron to implement for the handling, reuse, and disposal of any crude oil-affected soil and/or groundwater that may be encountered or excavated at the site in the future, The SGMP provides procedures for site property owners, developers, and/or maintenance firms to follow that addresses such topics as trench excavations, dewatering, and health and safety guidelines. On 30 March 2011 , Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff provided 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 #3. No responses were received during the 30 day comment period. Extent defined: Yes. Estimated Residual Petroleum Mass: Unknown; petroleum occurs primarily as degraded TPHc (immobile petroleum hydrocarbon fractions) at approximate depths of 2 to 33 feet bgs. A smali volume of separate phase crude oil was noted at approximately 35 feet bgs. The highest TPHc concentration was detected in soil at a depth of six feet bgs, Threat to Groundwater: The historical pipeline leaks, the source of the crude oil, were removed from service approximately 35 or more years ago. The lateral and vertical extent of affected groundwater is limited having slightly larger dimensions than the area of affected soil. Affected groundwater beneath the highway and existing active pipelines has been defined to be within the highway ROW, the active pipeline easement, a small part of the UPRR easement, and the adjacent alfalfa field. Concentrations of total dissolved solids in groundwater surrounding and underlying the site exceed numerous California and Federal drinking water and agricultu4 standards. Since the site is described within a highway/pipeline/UPRR ROW easement and beneath an agricultural field, it is unlikely that the installation of drinking water wells would be considered. Review of Department of Water Resources records, indicated five existing water wells within a 2,000 feet radius of the area of affected groundwater. The well uses were not designated. Threat to Human Health: • Vapor intrusion hazard: the site is undeveloped and land use is not anticipated to change. Low concentrations of volatile organic compounds in groundwater indicate potential risks associated with this pathway are low. • Dermal contact hazard. the HHSE utilized analytical results for sample from depths of 0 to 10 feet bgs. SAIC developed the HHSE using risk and hazard algorithms developed by the DTSC and provided in the Preliminary Endangerment Assessment Guidance Manual. The level of risk and hazard to a hypothetical future resident was determined to be beiow de minimus levels The site is located within the highway and