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<br /> tSeveral phases of subsurface investigations have been performed at the Site since 1993 resulting in the
<br /> installation of groundwater monitoring wells MW-4 through MW-13, soil vapor extraction(SVE)wells
<br /> ' SVE-1 through SVE-12 and VX-1, air sparge (AS)wells AS-1 through AS-5,removal of free-product,
<br /> and installation and operation of a SVE and AS system. Approximately 32 gallons of free-product was
<br /> reported to have been removed during free-product recovery, and free-product has not been reported at
<br /> ' the Site since 1994 (MW-2). The onsite SVE/AS system operated from August 3, 2001, through
<br /> October 13,2005. Shaw Environmental, Inc. estimated that approximately 333 pounds of gasoline and 3
<br /> pounds of benzene were removed by the onsite SVE system. The site investigations have defined the
<br /> ' lateral and vertical extent of the gasoline impacts, with the greatest dissolved total petroleum
<br /> hydrocarbons as gasoline (TPHg) groundwater impacts (>1,000 micrograms per liter [µg/1]) in the
<br /> vicinity of the former USTs(wells MW-1,MW-3 and GWX-1).
<br /> ' On July 2, 2008, we submitted a Revised Human Health Risk Evaluation (HBRE) per
<br /> December 21, 2007, and February 5, 2008, directives from the CVRWQCB. The results of the revised
<br /> HHRE show that there is not an excess carcinogenic or non-carcinogenic risk to human health under
<br /> either a residential or cormnercial land use scenario due to the presence of potential contaminants of
<br /> concern (PCOCs) in soil and groundwater beneath the Site. Based on the revised HHRE results, we
<br /> concluded that no additional site investigation activities appear warranted for the Site.
<br /> ' In a directive dated February 24, 2009, the CVRWQCB agreed to decrease the sampling interval for
<br /> wells MW4 through MW-13. The updated groundwater sampling program calls for analysis of TPHg,
<br /> ' benzene, toluene, ethylbenzene, total xylenes (BTEX), fuel oxygenated compounds (FOCs) including
<br /> methyl tert-butyl ether (MTBE), tert-butanol (TBA), di-isopropyl ether (DIPE), ethyl tert-butyl ether
<br /> (ETBE) and tert-amyl methyl ether (TAME), 1,2 dichloroethane(1,2-DCA), naphthalene and ethanol in
<br /> ' accordance with the following table:
<br /> WellID Quarterly' Semi-Annual Annual 2"a and 4th Quarters only) 4th Quarter only)
<br /> MW-1, GWX-1 MW-3 X
<br /> MW-2 X
<br /> ' MW-4 through MW-13,VX-1 X
<br /> ' On April 28, 2009, we submitted our Soil Vapor Extraction Pilot Test and First Quarter — 2009
<br /> Groundwater Monitoring and Progress Report in which we concluded that a full-scale SVE system is
<br /> not warranted and that no additional soil vapor,investigation activities are needed for the Site.
<br /> Additionally, we recommended that each of the existing SVE wells with the exception of VX-1 be
<br /> appropriately destroyed.
<br /> On July 2, 2009, we submitted our Air Sparge and Ozone Sparge Pilot Test Report concluding that
<br /> ' ozone sparging is an effective remedial technology for reducing the dissolved petroleum hydrocarbon
<br /> concentrations in the groundwater beneath the Site without creating adverse intermediate by-products.
<br /> We recommended installation of a full-scale ozone injection system for the Site, destruction of the
<br /> ' existing SVE wells (except VX-1) and destruction of the existing sparge wells.
<br /> In a letter dated September 21, 2009, the CVRWQCB concurred with our recommendations and
<br /> directed the submission of a well destruction workplan to be followed by a CAP detailing the
<br /> installation of an ozone-injection system. We submitted our Well Destruction Workplan to the
<br /> CVRWQCB on October 5, 2009, and the wells were destroyed during the week of November 9, 2009.
<br /> ' Project No.59183-06-02 -2- November 11,2009
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