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San Joaquin County DIRECTOR <br /> PQ U'N Donna Heran,REHS <br /> gyp.. �.cp Environmental Health Department ASSISTANT DIRECTOR <br /> 2 ,K-� 600 East Main Street Laurie Cotulla,REHS <br /> Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> Carl Borgman,REHS <br /> p". �P • <br /> Mike Huggins, REHS,RDI <br /> Website: www.s Ov.or 1ehd <br /> gCiFO Rc� 19 9 Margaret Lagorio,REHS <br /> Phone: (209)468-3420 Robert McClellon,REHS <br /> Fax: (209)464-0138 Jeff Carruesco,REHS,RDI <br /> Kasey Foley,REHS <br /> 1'(�,T 7129 <br /> 23 July 2008 <br /> Mr. Denis L. Brown Mr. Michael A. Dominquez <br /> Shell Oil Products US 2494 E. Fremont Street <br /> 20945 S. Wilmington Stockton, CA 95205 <br /> Carson, CA 90810-1039 <br /> Subject: Fremont Shell Station Site Code: RO#251 <br /> 2494 E. Fremont Street Global ID#: T0607700736 <br /> Stockton CA 95205 <br /> The San Joaquin County Environmental Health Department (EHD) has received and reviewed <br /> Corrective Action Plan/Response to Request for Interim Remedial Action (CAP), dated 10 July <br /> 2008, prepared Conestoga-Rovers & Associates (CRA). The CAP was prepared in response to <br /> the EHD letter dated 04 June 2008 directing a proposal to conduct interim remediation at the <br /> site. The EHD comments as follows: <br /> In the CAP, CRA concludes that the vertical extent of contaminant-impacted soil is primarily <br /> located at depths between 40 and 70 feet below surface grade (bsg). The EHD accepts that <br /> conclusion, but notes that the data for unimpacted soil at 70 feet bsg is from boring SB-4 at 70 <br /> feet bsg; however, soil sample SB4-65' contained only 2.6 milligrams per kilogram (mg/km) total <br /> petroleum hydrocarbons quantified as gasoline (TPH-g), while the more intensely impacted S1 <br /> at 65 feet bsg contained 1600 mg/kg TPHg. Although the two borings are fairly close to each <br /> other, it's possible that boring SB-4 may be just outside the main plume. <br /> CRA also concluded, based on soil samples collected at depths ranging from 4.5 to 6 feet bsg <br /> that natural attenuation is occurring on site. Intuitively, the site is most likely undergoing natural <br /> attenuation, but the data presented to demonstrate the activity is from a very thin, very shallow <br /> interval of soil that may not have been impacted in the first place — no direct comparison with <br /> previously acquired appropriate sample data was offered. <br /> CRA asserts that the 1,2-dichloroethane (1,2-DCA) concentrated in the dispenser area is from <br /> the former ARCO site north of your site across Fremont Street. The EHD does not consider this <br /> conclusion convincingly demonstrated, at least not in the CAP. The data from the two sites can <br /> be interpreted to indicate one 1,2-DCA source on the former ARCO site, but the data is not <br /> inconsistent with an interpretation of two sources of 1,2-DCA, one on the former ARCO site, one <br /> near your northern dispenser area. If there are two distinct 1,2-DCA sources, there could <br /> certainly be some commingling of the plumes, but until you can demonstrate significant <br /> inconsistencies with the two-source model, the EHD will consider the bulk of the 1,2-DCA on <br /> your site to have originated on your site and is your responsibility. <br /> CAP and WP Comment Letter 0708 FILE COP Y <br />