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California Regional Water Quality Cool Board <br /> Central Valley Region = i <br /> Katherine Hart, Chair a <br /> Linda S.Adams 11020 Sun Center Drive#200,Rancho Cordova,California 95670-6114 Arnold <br /> Secretary/or Phone(916)464-3291 •FAX(916)464-4645 Schwarzenegger <br /> Environmental http:/An .waterboards.ca.gov/rentralvalley Governor <br /> Protection <br /> 19 April 2010 <br /> Ms. Stephanie McKenna Mr. Jay Allen <br /> Chevron Environmental Management Company Stone Brothers Management Company <br /> 6001 Bollinger Canyon Road 1024 W. Robinhood Dr. <br /> San Ramon, CA 94583 Stockton, CA 95207 <br /> DOCUMENT REVIEW, MONTGOMERY WARDS AND UNOCAL STATION#5098, 5400-5606 <br /> PACIFIC AVENUE, STOCKTON, SAN JOAQUIN COUNTY, CASE NOS. 390258 AND <br /> 390014 <br /> On 1 April 2010, Sergio Borgiotti for Chevron Environmental Management Company (Chevron) <br /> and Nichole Gleason of Downey Brand, representing Stone Brothers Management Company <br /> called me concerning a 30 March 2010 request from consultant Geocon Inc. (Geocon) for a <br /> 60-day extension of submittal of the work plan for the additional soil and groundwater <br /> investigation under Robinhood Drive. After I was informed that the extension request was <br /> made to ensure time to transfer funding from Chevron to Geocon, since the UST Cleanup <br /> Funds under the Commingled Plume Account have been exhausted, I approved the extension. <br /> Chevron then submitted the Work Plan for Soil Vapor Investigation (Workplan) on 5 April <br /> 2010, written by their consultant AECON Environment. The Workplan proposes installation of <br /> three 6-inch screened soil vapor wells (SV-1 through SV-3) by hand auger to a total depth of 5' <br /> to 6' below ground surface, wait at least 48 hours for the wells to equilibrate per Los Angeles <br /> Region 2 and API guidances, and sample soil vapor one week after installation per the DTSC <br /> and New York State Department of Health guidances (excerpts included in the Workplan), <br /> collecting vapor samples in a SummaTm canister for analyses of total petroleum hydrocarbons <br /> as gasoline (TPHg), naphthalene, benzene, toluene, ethylbenzene, and xylenes (BTEX) by <br /> USEPA Method 82606; with oxygen (02), carbon dioxide (CO2), Helium (He, a line tracer gas), <br /> and methane (CH4) by ASTM Method D-1946. Soil samples from the vapor wells screened <br /> interval will be sampled for TPHg by USEPA Method 8015M and BTEX by USEPA Method <br /> 8060B. BTEX results will be compared to the California Human Health Screening Levels <br /> (CHHSLs). If the CHHSLs screening levels are exceeded, then a Johnson and Ettinger model <br /> will be used to conduct a Tier 2 risk assessment. If the Tier 2 shows levels exceed 10-6 for <br /> cancer risk and the 1.0 health risk factor for non-cancer risk, Chevron will work with the <br /> Regional Board to provide an additional vapor intrusion investigation for the adjacent buildings. <br /> A report of soil vapor investigation will be submitted within two months of completion of the <br /> field work. <br /> The Workplan is appropriate and necessary, and is approved with the addition of a direct <br /> comparison of the soil vapor results to the San Francisco Bay Regional Board Environmental <br /> Screening Levels (ESLs) for residential and commercial scenarios without utilizing the <br /> Workplan Table 2 attenuation factors. The ESLs also include soil vapor (gas) screening levels <br /> for TPHg and naphthalene. Please acquire the necessary well permits and give the <br /> California Environmental Protection Agency <br /> �a Recycled Paper <br />