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San Joaquin County DIRECTOR ,Oa • "'" Environmental health Department Ronna Heran,RENS ..p � ASSISTANT DIRECTOR 600 East Main Street Laurie Cotulla,REHS H. :< Stockton, California 95202-3029 PROGRAM COORDINATORS • Carl Borgman,REHS Mike Huggins,REHS,RDI Website:www.sjgov.org/ehd Margaret Lagorio,REHS Phone: (209)468-3420 Robert McClellan,REHS Fax: (209)464»0138 Jeff Carruesco,REHS,RDI Kasey Foley,REHS SERGIO MORESCALCHI AUGZO07 ATLANTIC RICHFIELD COMPANY P O BOX 1257 SAN RAMON CA 94583 RE: ARCO Service Station No. 2186 3212 North California Street Stockton, California 94570 San Joaquin County Environmental Health Department (EHD) has reviewed Work Plan for Soil Vapor Survey dated August 9, 2007, prepared by SECOR International Incorporated (SECOR) on your behalf. The work plan was submitted in response to the END letter dated June 7, 2007, directing you to evaluate the potential for vapor intrusion into existing onsite and offsite buildings. In the work plan SECOR proposes to install three permanent soil vapor probes at the site by advancing three borings to total depth of approximately six feet below ground surface (bgs) and installing soil vapor probes screened between approximately 5'/4 to 53/4 feet bgs. To evaluate the potential threat of soil vapor petroleum hydrocarbon concentrations, SECOR proposes to collect soil. gas samples in Summa canisters from each soil vapor probe and analyze the soil gas samples for total petroleum hydrocarbons quantified as gasoline (TPI -g) between carbon ranges C4 and C20; benzene, toluene, ethyl benzene, and total xylenes (BTEX); methyl tertiary-butyl ether (MTBE), ethyl tertiary-butyl ether (ETBE), tertiary butyl alcohol (TBA), di-isopropyl ether (DIPE), tertiary-amyl methyl ether (TAME), naphthalene, 1,2-dibromoethane (EDB), isopropyl alcohol, and 1,2- dichloroethane(1,2-DCA). SECOR proposes to install one soil vapor probe (VP-1) along the east property line approximately 25 feet north/northeast of monitoring well MW-2; one probe (VP-2) adjacent to the sidewalk directly north of the station building approximately 65 feet southeast of MW-3; and one probe (VP-3) adjacent to the north side of the canopy approximately 30 feet south of MW-1. EHD approves the location for soil vapor probes VP-2 and VP-3; however, EHD believe VP-I should be relocated along the east property line between MW-I and the residential home adjacent to the east side of this site at 522 East Alpine Avenue. Because groundwater samples collected from MW-1 have the highest. concentrations for TPH-g, BTEX, MTBE, and TBA, and groundwater flow direction tends to be toward the east-northeast, EHD believes a soil vapor probe located between MW-1 and the adjacent hone will provide the; most relevant information concerning the potential for soil vapor intrusion into the closest residential structure.---�--� EHD conditionally approves the work plan with this revision; otherwise, 1 I� ftl�t 4