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Chevron January 20, 1997 Chevron b Mr. Joel Weiss Chevron Pipe Line Company Regional Water Quality Control Board, Central Valley Region 4000 Executive Parkway,Suite 400 3443 Routier Road, Suite A San Ramon,CA 94583 Sacramento, CA 95827-3098 P0.Box 5059 San Ramon,CA 94583-0959 Subject: Response to May 1, 1996 Letter: Mountain View Town Homes Project Tracy, California Dear Joel: Per your conversations with Mr. Dan Lapporte of my staff, Chevron Pipe Line Company (CPL) is prepared to move forward with site closure activities for the subject property. The November 18, 1996, Technical Approach to Site Evaluation and Decision-Making Old Valley Pipeline Sites (Approach) prepared by Geomatrix Consultants, Inc. on behalf of CPL, summarize CPL's plans for Old Valley Pipeline (OVP) sites. Specifically, the document proposes a rational approach to existing and probable future OVP sites that likely pose low- to no-risk to the groundwater resource or human health and the environment. Your January 3, 1997, comment letter on the Approach will be discussed in the near future. Based on the Approach and your May 1, 1996, letter, CPL is prepared to initiate four consecutive quarters of groundwater monitoring at the site. Your letter requested an additional groundwater monitoring well to "...determine the threat contaminated soils pose to groundwater and whether the groundwater has already been impacted. " CPL believes installation of a fourth well may not be necessary unless the existing wells are proven ineffective at intercepting the changing groundwater flow direction. Therefore, CPL proposes conducting additional groundwater sampling and collection of groundwater elevation data prior to installation of any new wells at the site. Quarterly groundwater monitoring reports will be submitted following each event, and the necessity for installation of an additional well will be addressed. CPL'S August 2, 1996, letter summarizes activities at the site including removal of the historic OVP and excavation of impacted soil up 24 feet below ground surface. CPL believes a small mass of contaminants remains in the subsurface and fluctuations in the hydraulic cycle over four consecutive quarterly sampling events will sufficiently intercept groundwater traveling through impacted soils. Therefore, CPL believes the final recommendation in your May 1, 1996, letter regarding leachability tests to determine the feasibility of leaving contaminated soils in place is inappropriate. We believe steady state leaching has been occurring in the subsurface since the release and, based on downgradiant groundwater samples previously collected and proposed quarterly sampling, chemicals of concern are not impacting groundwater. As described in the Approach, non-detectable or decreasing downgradiant concentrations of the soluble fraction of weathered crude oil (polynuclear aromatic hydrocarbons and/or BTEX) indicate no leaching from the remaining contaminant mass which CPL proposes leaving in place.