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SanJoaquin <br /> Department <br /> County <br /> ronme <br /> Envintal Health Detment DIRECTOR <br /> o?' C p Donna Heran,REHS <br /> 600 East Main Street <br /> PROGRAM COORDINATORS <br /> T Stockton, California 95202-3029 Robert McClellon,REHS <br /> Jeff Carruesco,RENS,RDI <br /> Kasey Foley, REHS <br /> Website: www.Sjgov.org/ehd <br /> Phone: (209) 468-3420 <br /> Fax: (209)464-0138 <br /> September 7, 2010 <br /> Stephanie Furgal <br /> Chevron Environmental Management Company <br /> 6111 Bollinger Canyon Road Room 3652 <br /> San Ramon, CA 94583 <br /> Subject: Former Unocal #2859 <br /> 9665 Pacific Avenue <br /> Stockton, CA <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed Site <br /> Assessment and First Quarter 2009 Groundwater Monitoring Report, dated July 31, 2009, and <br /> Soil Vapor Investigation Report and Vapor Intrusion Pathway Evaluation (SVI Report), dated <br /> November 20, 2009, both prepared by ARCADIS for the above subject site. The site conceptual <br /> model (SCM) submitted in 2006, prepared by ENSR and other site data were also reviewed. <br /> The review was conducted to determine whether further site investigation or corrective action <br /> was required, or if the site is a candidate for a low-risk closure consideration. <br /> As a result of the review, the EHD finds: <br /> • The extent of impacted soil has been adequately delineated vertically and laterally. <br /> • A KVA C-Sparge ozone injection system was utilized from August 2002 to April 2005 <br /> with modest benefit, if any, on impacted groundwater. <br /> • The vertical and lateral extent of impacted groundwater has been adequately delineated. <br /> Groundwater persistently impacted by the various chemicals of concern (CDCs) is <br /> monitored by monitoring wells MW-10 and MW-2; groundwater monitored by deeper <br /> monitoring wells or laterally equivalent wells have either low concentrations or less than <br /> detectable concentrations of the various CDCs. <br /> • Most shallow soil gas samples (collected at approximately 6 feet below surface grade) <br /> passed the environmental screening levels (ESLs) established by the San Francisco Bay <br /> Regional Water Quality Control Board for vapor intrusion evaluation except for two that <br /> exceeded the ESL for total petroleum hydrocarbons quantified as gasoline (TPHg). <br /> Arcadis' analysis of the data lead them to the interpretation that the TPHg concentrations <br /> in the soil gas samples did not result in a significant health risk as volatile organic <br /> compounds did not comprise a significant fraction of the TPHg. Deeper soil gas samples <br /> (collected at approximately 20 feet below surface grade) greatly exceeded ESLs for <br /> vapor intrusion, but Arcadis discounted the potential for vapor intrusion by attributing the <br /> vertical decline of contaminant concentrations from the deep sampling points <br /> NFAR Directive Letter 0910 <br />