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4f EUMUNU G.BROWN JH. ; .. GOVERNOR a 'MATTHEW ODRIOUEZ G A L I P I A SECRETARY POO O R N ENVIRONM6NTAl PROTECTION Water Boards Central Valley Regional Water Quality Control Board RSCSIVSD 18 December 2013 EC 2 3 2013 ENV"ONMEN"AL N pERJ lir' RVIC S lT� Michael N. Oliphant Chevron Environmental Management Company 6001 Bollinger Canyon Road San Ramon, CA 94583 REVIEW— SOIL VAPOR INVESTIGATION WORKPLAN, 990 BEECHNUT AVENUE, TRACY, SAN JOAQUIN COUNTY Chevron Environmental Management Company (Chevron) submitted the Soil Vapor Investigation Workplan (Workplan) for the 990 Beechnut Avenue project dated 18 November 2013. The Workplan was prepared for Chevron by AMEC Environment & Infrastructure, Inc. (AMEC) and submitted to Central Valley Regional Water Quality Control Board staff (Staff) for review and comment. The Workplan proposes three offset soil borings to collect vapor samples. Previous site investigative findings detected low concentrations of naphthalene (0.066 and 0.096 milligrams per kilogram [mg/kg]) in two soil samples collected from two borings drilled along the southwest perimeter of the project. In addition, ethylbenzene was detected at a concentration of 0.014 mg/kg in one sample obtained at a depth of nine feet below ground surface (bgs) near the northeast corner of the project. A third location will also be investigated where total petroleum hydrocarbons as crude oil (TPHc) at a concentration of 76,000 mg/kg was reported in a sample from just less than ten feet bgs in a boring drilled in the northwest corner of the project. The purpose of the Workplan is to evaluate the extent of the naphthalene and ethylbenzene previously identified at two boring locations. In addition, an evaluation for the extent of soil vapor possibly associated with the TPHc found at that respective location would be completed. The soil vapor results would be used to revise a previous Screening Level Risk Assessment (SLRA) in support of a future unrestricted use, (i.e., suitable for either future commercial/industrial or residential use scenario). Shallow borings and appropriate soil vapor sampling and collection equipment will be utilized. The soil vapor samples will be analyzed by an onsite State-certified mobile laboratory. For each day of borings and soil vapor sampling, one background ambient air sample will be collected and submitted to a State-certified laboratory for determination of benzene, toluene, ethylbenzene and xylenes, and naphthalene. Soil samples will also be collected and submitted for soil properties determination in support of evaluating the vapor pathways. KARL E. LONOLEY SCD, P.E.,CHAIR I PAMELA C, CREEDON P.E., BCEE,EXECUTING Omom 7685 E Street,Fresno,CA 93706 1 www.waterboards.ca.gov/ceatralvalley .R,RECYCLED PAPER