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In 2007, a work plan for upgrading the remediation system was approved by the RWQCB. <br /> The SVE system was modified to include air sparging (AS), to target petroleum hydrocarbons <br /> located deep beneath the Site. The upgraded system operated from July 2008 until <br /> September 2009. In a letter dated September 8, 2009, the RWQCB authorized turning off the <br /> AS/SVE system to test its effectiveness through "rebound testing" of contaminant levels in the <br /> groundwater. <br /> Groundwater rebound sampling began in February 2010, to evaluate if petroleum <br /> hydrocarbon concentrations rebounded following remediation system shutdown. <br /> Groundwater analytical data were collected during February and August 2010, and compared <br /> to baseline groundwater concentrations from April 2008. The most recent groundwater <br /> analytical data shows that petroleum hydrocarbon concentrations have decreased by up to <br /> three orders of magnitude since April 2008. This result indicates that no significant rebound in <br /> groundwater concentrations has occurred since the remediation system was turned off, and <br /> that the Site has been deemed a candidate for low-risk closure. <br /> In December 2010, a soil vapor intrusion study was conducted to evaluate potential health <br /> risk at the Site from the presence of hydrocarbons in soil vapor beneath the Site that could <br /> potentially migrate to indoor air. Following U.S. Environmental Protection Agency (EPA) and <br /> California Environmental Protection Agency (Cal EPA) guidelines, risk assessments were <br /> done for estimated current and potential future on-site exposures in both residential and <br /> commercial/industrial exposure scenarios. The responsible parties submitted the soil vapor <br /> intrusion study report to the RWQCB for review. The RWQCB concurred with the study's <br /> conclusion that vapor intrusion is not a health risk at the Site since the calculated, estimated <br /> health risks are below applicable EPA and Cal EPA established levels of acceptable risk. <br /> The responsible parties contend that petroleum hydrocarbons in soil and groundwater <br /> beneath the Site have been adequately delineated, evaluated, and cleaned up and have, <br /> therefore, requested that the RWQCB review the Site for case closure. Anyone interested in <br /> obtaining additional information regarding this Site, or to make comments by 08 June 2011 <br /> regarding the case closure review, should contact: <br /> Mr. James L. L. Barton, P.G. <br /> Regional Water Quality Control Board — Central Valley Region <br /> 11020 Sun Center Drive, Suite No. 200 <br /> Rancho Cordova, California 95670-6114 <br /> Tel. (916) 464-4615 <br /> email: jbarton@waterboards.ca.gov <br />