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M. Scott Mansholt -3 - 18. March 2009 <br /> Mountain-House Development Si* <br /> water supply wells is unlikely since the Site is within the Byron Road easement ROW, the <br /> groundwater is of poor quality, and in fine-grained soil that typically yield low flow wells. <br /> Summary and Conclusions <br /> Future Site use and access will likely be limited to construction/maintenance activities <br /> associated with the highway and/or possibly utilities. Consequently, SAIC conducted an <br /> environmental risk evaluation (ERE) based on the potential exposure by a construction/trench <br /> maintenance worker associated with features within the highway ROW easement. <br /> According to the August 2008 ERE report, SAIC concluded that the residual crude oil <br /> compounds remaining at the site do not pose a threat to human health. They do not exceed <br /> applicable TPH screening values described in - Screening for Environmental Concerns at <br /> Sites with Contaminated Soil and Groundwater, Interim Final May 2008 (ESLs), San Francisco <br /> Bay Regional Water Quality Control Board, for a construction/trench worker exposure <br /> scenario. Central Valley Water Board staff concur that based on the findings and the ERE <br /> report, the presence of residual petroleum hydrocarbons in soil and groundwater do not pose <br /> an unacceptable risk to future utility workers under the conditions evaluated. <br /> Consistent with other OVP/TAOC sites, Chevron submitted a site-specific Soil and <br /> Groundwater Management Plan (SGMP), dated 25 November 2008 to UPRR and Mountain <br /> House Community Services District representatives. The SGMP designates Chevron as the <br /> responsible party and serves as a guideline for Chevron to implement for the handling, reuse, <br /> and disposal of any soil and/or groundwater affected by the degraded crude oil that may be <br /> encountered or excavated during future Site activities. The SGMP outlines detailed <br /> procedures for future property owners, developers, and/or maintenance firms to follow <br /> addressing such topics as dewatering from excavations, and health and safety guidelines. <br /> Contact telephone numbers for Chevron and San Joaquin County Environmental Health <br /> Department are included. <br /> In a 27 September 2007 letter to Chevron, Central Valley Water Board staff concurred that the <br /> crude oil in soil and groundwater had been adequately delineated, additional characterization <br /> was not needed, and a request for an NFAR determination could be submitted. SAIC's recent <br /> report provided documentation to support Site closure in accordance with California Regional <br /> Water Quality Control Board, Central Valley Region's 16 April 2004 update to Appendix A of <br /> the Tri-Regional Board Staff Recommendations for Preliminary Investigation and Evaluation of <br /> Underground Tank Sites - No Further Action Requests. <br /> Previously, SAIC assessed available cleanup technologies and various remedial alternatives <br /> for residual crude oil in soil and groundwater at OVP/TAOC projects. The assessment <br /> summarized that the residual weathered crude oil is highly viscous, relatively immobile, and <br /> primarily occurs within low permeability soil found at the Site. Thus, the existing Site <br /> conditions limit most forms of remediation such as passive in-well recovery, pumping and <br /> extraction, and/or excavation. SAIC determined the low permeability soil generally limits the <br /> migration of the degraded crude oil in the subsurface. SAIC concluded that affected <br /> soil/groundwater has been delineated within/beneath the highway ROW and in-place <br /> management of residual crude oil by natural attenuation is cost effective, feasible, and easily <br /> implemented. Concentrations of petroleum hydrocarbons will reduce with time. Based on the <br />