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San Joaquin County DIRECTOR <br /> Donna Heran,REHS <br /> 'oP "..�o Environmental Health Department ASSISTANT DIRECTOR <br /> G <br /> 6Laurie Cotulla,REHS <br /> 00 East Main Street <br /> Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> Mike Huggins,REHS,RDI <br /> Margaret Lagorio,REHS <br /> • C<...• �P • Website: www.sjgov.org/ehd Robert McClellon,REHS <br /> i Foad Phone: (209) 468-3420 Jeff Carruesco,REHS,RDI <br /> Fax: (209) 464.0138 Kasey Foley,REHS <br /> June 8, 2009 <br /> Denis L. Brown <br /> Shell Oil Products <br /> 20945 S. Wilmington Blvd. <br /> Carson, CA 90810-1039 <br /> Subject: Shell-Branded Service Station Site Code: 1223 <br /> 6131 Pacific Avenue <br /> Stockton, CA 95207 <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed <br /> Remediation System Shutdown Request (Request) dated April 27, 2009, prepared on your <br /> behalf by Conestoga-Rovers &Associates (CRA) and has the following comments. <br /> In the Request CRA reports that the Dual Phase Extraction (DPE) remediation system that <br /> began operation at this site in April 2007 was shut down on February 2, 2009. CRA justified <br /> the shutdown of site remediation on de minimus vapor recovery rates. Prior to operation of <br /> the DPE system, a soil vapor extraction (SVE) system was operated for approximately four <br /> months. CRA estimates total contaminant mass recovered from the remediation systems to <br /> be 3,219 pounds (Ibs) total petroleum hydrocarbons as gasoline (TPHg) and 39.38 lbs <br /> benzene from the soil, and 10.4 lbs TPHg and 0.29 lbs benzene from the groundwater. In <br /> "Remedial Action Plan" dated November 18, 2005, Cambria Environmental Technology, Inc. <br /> (currently doing business as CRA) estimated that prior to active remediation, 8,129 lbs of <br /> TPHg and 86 lbs benzene remained in the soil, and 83 lbs TPHg and 3 lbs of benzene <br /> remain in the groundwater at this site. Therefore, less than half the estimated contaminant <br /> mass in the soil and less than one eighth of the estimated mass in the groundwater at this <br /> site was removed by the SVE/DPE remediation systems. <br /> In 'Corrective Action Plan and Risk-Based Corrective Action Analysis' (CAP) dated <br /> September 9, 2005, CRA stated the specific CAP objectives were to: <br /> - "Remove the most heavily impacted hydrocarbons in the identified source areas; <br /> - Mitigate further hydrocarbon migration in soil and groundwater; <br /> - Continue the groundwater monitoring program to monitor water quality; and <br /> - Establish a contingency plan to expedite or enhance remediation, if necessary." <br /> To meet these objectives CRA recommended implementing the full-scale DPE remediation, <br /> anticipating the system to operate from 2-4 years. In Remedial Action Plan (RAP) dated <br /> November 18, 2005 CRA proposed installation of DPE wells and discussed details of the <br /> proposed DPE system operation and maintenance. In discussion of turning the DPE system <br /> off due to loss of effectiveness, CRA stated that if the system became ineffective <br /> (asymptotic) before soil and groundwater clean-up goals are met, an alternate approach <br /> would be implemented, but they did not include a "specific contingency plan to expedite or <br /> enhance remediation" in the RAP. <br />