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San Joaquin County <br /> Environmental Health Department DIRECTOR <br /> �,. _,��••,p � Donna Heran, RENS <br /> 600 East Main Street <br /> Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> Robert McClellon, REHS <br /> Jeff Carruesco,REHS,RDI <br /> cq•.. �;..�;��' Website: wwwKasey Foley,REHSsjgov.org/ehd Linda Turkatte,RENS <br /> F a Phone: (209) 468-3420 <br /> Fax: (209)464-0138 <br /> February 18, 2011 <br /> Mr. Ken Hilliard <br /> 7-Eleven, Incorporated FEB 2 2 2011 <br /> Post Office Box 711 <br /> Dallas, Texas 75221-0711 <br /> Subject: 7-Eleven Store No. 19976 <br /> 1399 North Main Street <br /> Manteca, California 95336 <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed Vapor Risk <br /> Assessment Report and Work Plan for Additional Soil Gas Assessment (work plan), dated 08 <br /> December 2010, prepared and submitted by Stantec Consulting Corporation (Stantec) on your <br /> behalf for the above-referenced subject site. In the work plan, Stantec describes how soil gas <br /> samples were collected at three feet below ground surface (bsg) on 18 September 2000. <br /> Stantec compared the maximum concentrations of contaminants of concern detected in the <br /> 2000 investigation to Environmental Screening Levels (ESLs) established by the San <br /> Francisco Bay Regional Water Quality Control Board, and California Human Health Screening <br /> Levels (CHHSLs) published by the Office of Environmental Health Hazard Assessment, <br /> California Environmental Protection Agency. Stantec concluded that the screening level <br /> human health risk assessment (HHRA) indicated that the cumulative cancer risk was greater <br /> than one in a million (1.0E-06) and the hazard index (HI) was greater than 1.0. In view of the <br /> HHRA results from 2000, Stantec proposes to perform another soil gas investigation and has <br /> submitted the work plan to assess the current human heath risk. <br /> In the work plan, Stantec proposes to advance five soil gas probe borings (SG-12 through <br /> SG-16) to total depths of approximately five feet below surface grade (bsg) using a hand <br /> auger at locations illustrated on Figure 2. Soil will be collected for lithological evaluation and <br /> screened in the field for the presence of volatile organic compounds using a photo-ionization <br /> detector. Stantec proposes to collect one soil sample per borehole to be analyzed by a <br /> California State certified laboratory for total petroleum hydrocarbons as gasoline (TPHg); <br /> benzene, toluene, ethylbenzene, and total xylenes (BTEX); methyl tertiary-butyl ether (MTBE), <br /> ethyl tertiary-butyl ether (ETBE), di-isopropyl ether (DIPE), tertiary-amyl methyl ether (TAME), <br /> and tertiary butyl alcohol (TBA). If groundwater is encountered, Stantec proposes to advance <br /> a borehole nearby and collect a soil sample several inches above the anticipated <br /> groundwater. Stantec proposes to construct the soil gas probes using 1/8-inch diameter <br /> Nylaflow®tubing and a vapor point. <br /> Stantec proposes to collect soil gas samples in mini Summa® canisters to be analyzed for <br /> TPHg, BTEX, MTBE, ETBE, TAME, TSA, naphthalene, and 1,1-difluoroethane (1,1-DFA), or <br />