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San Joaquin County DIRECTOR <br /> Donna Heran, REHS <br /> Environmental Health Department ASSISTANT DIRECTOR <br /> 600 East Main Street Laurie Cotulla,REHS <br /> Stockton,. California 95202-3029 PROGRAM COORDINATORS <br /> latv.h_ .' :.• Carl Borgman, REHS <br /> • d -�. P OV.O/ Mike Huggins,REHS, RDI <br /> Website: www.sjgov.org/�hd 6'g�� /8 H/ehd Margaret Lagorio,REHS <br /> Phone: (209) 468-3420 Robert McClellon,REHS <br /> Fax: (209)464-0138 Jeff Carruesm, REHS,RDI <br /> Kasey Foley,REHS <br /> GERALD L. THIEMANN JAN 1 1 2008 <br /> 327 BLOSSOM DRIVE <br /> RIPON CA 95366 <br /> RE: Former Thiemann's Service Station SITE CODE: 1479 <br /> 106 West Second Street <br /> Ripon, California 95366 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed Work Plan for <br /> Soil Vapor Study at Former Thiemann's Service Station, 106 West Second Street, Ripon, <br /> California, Site 1479 submitted by ATC Associates Inc. (ATC) on your behalf. The work <br /> plan was submitted in response to the EHD letter dated October 11, 2007, directing you to <br /> evaluate site data against the Environmental Screening Levels (ESLs) issued by the San <br /> Francisco Bay Regional Water Quality Control Board, and against the California Human <br /> Health Screening Levels (CHHSLs) developed by the Office of Environmental Health <br /> Hazard Assessment, and to evaluate the potential threat for vapor intrusion inside the <br /> buildings located onsite. <br /> In this work plan, ATC proposes to advance six soil borings to install six temporary soil <br /> vapor probes to collect soil gas samples. The soil borings will be advanced to five feet <br /> below surface grade (bsg) at locations illustrated on Figure 2 of the work plan using direct <br /> push technology. A leak test using 1,1-difluoroethane will be performed at all potential <br /> ambient air intrusion locations. Although ATC proposes to collect soil gas samples using <br /> syringes, there is no mention that these syringes must be leak-checked before each use to <br /> confirm that the syringes are gas-tight. ATC states that soil gas samples will be collected <br /> in accordance with the Department of Toxic Substances Control (DTSC) guidelines <br /> entitled Advisory-Active Soil Gas Investigations dated January 28, 2003, and Interim Final <br /> — Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air <br /> dated December 15, 2004, revised February 7, 2005. The second DTSC guidance <br /> document states that "When collecting soil gas samples with glass bulbs or glass syringes <br /> and analyzing the gas samples for volatile organic compounds (VOCs) by Method 8260B <br /> (USEPA, 1996) modified for air analysis with a mobile laboratory, the results of the field <br /> work should be independently confirmed through the collection of duplicate soil gas <br /> samples in SummaTM canisters. The collection of duplicates will confirm the mobile <br /> laboratory detection limits and identify other potential chemicals-of-concern (COC) at the <br /> site. DTSC recommends that ten percent of the soil gas samples collected in the field be <br />