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San Joaquin County DIRECTOR <br /> a�+N Donna Heran,REHS <br /> 1.0o Environmental Health Department ASSISTANT DIRECTOR <br /> Laurie Cotulla,REHS <br /> 600 East Main Street <br /> PROGRAM COORDINATORS <br /> Stockton, California 95202-3029 PCarl Borgman,REHS <br /> . 4.. Mike Huggins,REHS,RD1 <br /> Website: www.sjgov.orglehd Margaret Lagorio,REHS <br /> Phone: (209)468-3420 Robert McClelion,REHS <br /> Fax: (209)464-0138 Jeff Carruesco,REHS, RDI <br /> Kasey Foley,REHS <br /> DON PRATT [JUN 0 7 207 <br /> ATLANTIC RICHFIELD COMPANY <br /> P O BOX 1257 <br /> SAN RAMON CA 94583 <br /> RE: ARCO Service Station No. 2186 <br /> 3212 North California Street <br /> Stockton, California 94570 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed analytical <br /> results for groundwater and vapor samples collected since August 30, 2004, when the soil <br /> vapor extraction (SVE) system was first operational as an interim remediation method at <br /> the above-referenced site. Concentrations for chemicals of concern (COC), including <br /> gasoline-range organics (GRO); benzene, toluene, ethylbenzene, and total xylenes <br /> (BTEX); 1,2-dichloroethane (1,2-DCA); and methyl-tertiary butyl ether (M'1BE); have <br /> decreased significantly in groundwater samples collected from the two most-impacted <br /> monitoring wells MW-1 and MW-4. Also, vapor samples collected each month from the <br /> influent, intermediate vapor stream, and effluent of the SVE systern and analyzed for <br /> ORO, BTEC, and MTBE have demonstrated non-detect concentrations for BTEX and <br /> MTBE since December 13, 2006; and low to non-detect concentrations for GRO in air <br /> samples collected from the influent. Based on these results, SECOR International <br /> Incorporated (SECOR) recommends suspending the SVE system operation for three <br /> months followed by the performance of a rebound test. EHD concurs with SECOR's <br /> recommendation to terminate the SVE operations for three months after which SECOR <br /> will perform a rebound test. <br /> Both the fourth quarter 2006 and first quarter 2007 groundwater monitoring reports <br /> indicate that the total well depth measured for MW-8 (the only deep-screened well) was <br /> approximately 131 feet below ground surface (bgs). This monitoring well has a screened i <br /> 1 <br /> interval from 129 to 134 feet bgs. EHD is concerned the results for groundwater samples <br /> collected from this well may be compromised because the more permeable silty sand in <br /> the screen interval is filled and only the less permeable clayey silt with sand is open to <br /> the screen. EHD directs you to redevelop MW-8 prior to the next saunpling event. <br /> The Central Valley Regional Water Quality Control Board (CVRWQCB) has identified <br /> vapor l.ntnision of structures from underground storage tank sites as a potential health <br /> hazard; therefore, EHD directs you to evaluate the threat of vapor intrusion inside the <br /> building onsite and adjacent offsite structures. Please submit a work plan to EHD by <br /> August 10, 2007, to assess the potential for vapor intrusion into the existin I onsite and <br /> offsite buildings. LOU) 1�1 11 T T <br /> I <br /> JUN D 8 2001 <br /> F3y._ -.. _ <br />