SITE INFORMATION AND CORRESPONDENCE

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I ! F EO-uKG r?- BnOVIN JA. _ � � i✓i''`y� npvAXon RODRIOusz serasrnur CDR pnvwnur.curAl nnnrsrnn� Water Boards i Central Valley Regional Water Quality Control Board TO: Shelton R. Gray �� Senior Engineering Geologtst FROM: C. Dean Hubbard f Engineering Geologist DATE: 18 October 2012 SUBJECT: . CONSIDERATION OF REQUEST FOR NO FURTHER ACTION REQUIRED DETERMINATION, FORMER VERNALIS PUMP STATION, VERNALIS, SAN JOAQUIN AND STANISLAUS COUNTIES Rationale: Crude oil affected soil and groundwater, as the result of leaks from the former Vernalis Pump Station and associated crude oil pipelines project (Site), has been delineated. It is of limited extent where total petroleum hydrocarbons as crude oil (TPHc) were detected. It has been defined onsite, beneath/within the historical Old Valley Pipeline (OVP) pipeline right-of-way easements, the Union Pacific Railroad (UPRR) tracks, California State Highway 33 easements on the east side, and some nearby agriculture land downgradient to the east. There are two active refined petroleum product pipelines present within the easements. The downgradient offsite groundwater conditions were I investigated separately by Chevron Environmental Management Company (Chevron), as the Vernalis Offsite project with regulatory oversight by Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff. In June 2010, a no further action required (NFAR) determination was issued to Chevron for Vernalis Offsite. Chevron is an OVP predecessor company. Chevron's consultant, Science Applications International.Corporation Energy, Environmental & Infrastructure, LLC.SAIC), indicated the vertical extent of crude oil affected soil was defined, and that crude oil affected soil is limited to the immediate vicinity nearlbeneath the historical crude oil pipelines and pump station facility. Laterally, affected soil is defined in the southeast corner of the Site, with dimensions of about 300 by 750 feet, in close proximity to the former pump/boiler-heaterr-house structures, and offsite as described above. Within the affected area, a smaller circular area of separate phase crude oil in soil and groundwater, defined as about 75 feet across, occurs near/between the former pump/boiler houses. Fuel fingerprint evaluation confirmed the petroleum hydrocarbons present were consistent with degraded San Joaquin Valley (SJV) crude oil. Residual concentrations of crude oil remaining at the Site will naturally degrade with time, likely over a period of several years, and are not anticipated to pose an unacceptable health risk. The extent of impacted groundwater includes the area of affected soil, and has approximate dimensions of about 1,000 by 1,200 feet, projected downgradient to vacant and agricultural land east of the Site. Depth to upper groundwater occurs at about 30 to 37 feet below ground surface (bgs). Groundwater samples collected from the step-out borings were submitted for total petroleum hydrocarbon analysis. The analytical results for TPH as diesel (TPHd) reported concentrations from non-detect (ND) to 71 to 79 micrograms per liter (pg/Q. Other crude oil analytes were ND and/or did not exceed environmental screening levels. The results defined the lateral extent of crude oil affected groundwater. The findings of SAIC's September 2010 human health screening evaluation considered a hypothetical i e soil. The risk residential land use scenario for exposure to TPH chemicals of potent ial concern in onsite evaluation was conducted using a methodology and approach described in the California KARL. E. LONGLEY Scp, P.E.,CHAIR I PAMELA C. CP,EEooN P.E. BCEE. EXECUTIVE OFFICER 1665 E Street,Fresno,CA 93706 j wwa.waterboarp s.ca-gpv/cenvaWallgy �� ncov¢GGo rnrcn