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San Joaquin County DIRECTOR <br /> Donna Heran, REHS <br /> Environmental Health Department p,. _ .. �. p ASSISTANT DIRECTOR <br /> 600 East Main Street Laurie Cotulla,REHS <br /> 2: .z <br /> Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> �• ` Carl Borgman,REHS <br /> -�. Mike Huggins, REHS,RDI <br /> 0. Website: www.sjgov.org/ehd Margaret Lagorio,REHS <br /> 9�iFOR°' Phone: (209)468-3420 Robert McCiellon, REHS <br /> Fax: (209)464-0138 ,teff Carruesco, REHS,RDI <br /> Kasey Foley, REHS <br /> August 22, 2008 <br /> Mr. Sergio Morescalchi <br /> Atlantic Richfield Company <br /> Post Office Box 1257 <br /> San Ramon, California 94583 <br /> Subject: ARCO Service Station No. 2186 <br /> 3212 North California Street <br /> Stockton, California 94570 <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed Results <br /> of Additional Assessment dated April 9, 2008, prepared by SECOR International <br /> Incorporated (SECOR) on your behalf. The report documents the installation of three on- <br /> site soil vapor probes at soil borings VP-1, VP-2, and VP-3, and the analytical results <br /> from soil gas samples collected from the three probes for evaluation of the potential for <br /> vapor intrusion into existing on- and off-site buildings. <br /> Gasoline range organics (GRO) were detected in soil gas samples collected from VP-1, <br /> VP-2, and VP-3 at 8,300 micrograms per cubic meter (pg/m3), 8,500 gg/m3, and 3,100 <br /> gg/m3, respectively. These concentrations are less than the Environmental Screening <br /> Level (ESL) concentration of 10,000 gg/m3; therefore, the EHD will not require a human <br /> health risk assessment. However, do provide an explanation for the relationship between <br /> the soil gas results and the contaminants' distribution in soil and groundwater at this site. <br /> The EHD concurs with SECOR's recommendation to abandon VP-1 through VP-3. <br /> Please submit a work plan to the EHD by October 17, 2008, for the destruction of the soil <br /> vapor probes. <br /> In Site Conceptual Model dated September 13, 2007, SECOR proposed destroying MW-1 <br /> and MW-3 because the screen intervals for these two wells appear to cross two <br /> groundwater bearing zones. The EHD first expressed concern that MW-1 may be acting <br /> as a vertical conduit by letter dated June 7, 2007. Based on field logs, it appears that <br /> MW-1, screened between approximately 45.5 and 74.5 feet below surface grade (bsg), <br /> has a potential aquitard at approximately 58 to 67 feet bsg; and MW-3, screened between <br /> approximately 55.5 and 74.5 feet bsg, has a potential aquitard at approximately 63 to 72 <br /> feet bsg. <br />