ARCHIVED REPORTS_GROUNDWATER MONITORING AND PROGRESS REPORT 4TH QUARTER 2011

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' October 13, 2005. Shaw Environmental, Inc. estimated that approximately 333 pounds of gasoline and 3 pounds of benzene were removed by the SVE system. The site investigations have resulted in ' definition of the lateral and vertical extent of the gasoline impacts, with the greatest dissolved total petroleum hydrocarbons as gasoline (TPHg) groundwater impacts (>1,000 micrograms per liter [µg/11) in the vicinity of the former USTs (wells MW-1, MW-3 and GWX-1). Historical groundwater ' elevation and analytical data are presented in Tables 1 through 3. The site-related groundwater monitoring wells are completed in at least two separate saturated sand ' lenses referred to as the shallow zone (MW-1 through MW-7, GWX-1 and VX-1), the intermediate zone (MW-8, MW-10 and MW-12) and the deep zone (MW-9, MW-11 and MW-13). Based on our review of the site hydrogeology, the intermediate zone is the same saturated sand lens as the shallow zone but with the wells screened at the base of the sand lens rather than across the top of the lens. The ' well construction details for the above listed wells are presented in Table 4. On July 2, 2008, we submitted to the Central Valley Regional Water Quality Control Board (CVRWQCB) ' a Revised Human Health Risk Evaluation (HHRE) demonstrating that there is not an excess carcinogenic or non-carcinogenic risk to human health under either a residential or commercial land use scenario due to the presence of potential contaminants of concern in soil and groundwater beneath the Site. ' Based on the revised HHRE results, we concluded that no additional site investigation activities appear warranted for the Site. On October 13, 2008, we recommended decreasing the sampling interval for wells MW-4 through MW-13. The CVRWQCB agreed with our recommendation in a directive dated February 24, 2009. The groundwater sampling program calls for analysis of TPHg, benzene, toluene, ethylbenzene, total ' xylenes (BTEX), fuel oxygenated compounds (FOCs) including methyl tert-butyl ether (MTBE), tert-butanol (TBA), di-isopropyl ether (DIPE), ethyl tert-butyl ether (ETBE) and tert-amyl methyl ether (TAME), 1,2 dichloroethane(1,2-DCA), naphthalene and ethanol in accordance with the following table: ' Well ID QuarterlySemi-Annual Annual 2nd and 4t" Quarters only) 4'" Quarter only) MW-1, GWX-1 MW-3 X MW-2 X MW-4 through MW-13,VX-1 X ' On April 28, 2009, we submitted our Soil Vapor Extraction Pilot Test and First Quarter — 2009 Groundwater Monitoring and Progress Report in which we concluded that a full-scale SVE system is ' not warranted and that no additional soil vapor investigation activities are needed for the Site. Additionally, we recommended that each of the existing SVE wells with the exception of VX-1 be appropriately destroyed. 1 On July 2, 2009, we submitted our Air Sparge and Ozone Sparge Pilot Test Report concluding that ozone sparging is an effective remedial technology for reducing the dissolved petroleum hydrocarbon ' concentrations in the groundwater beneath the Site without creating adverse intermediate by-products. We recommended installation of a full-scale ozone injection system for the Site and again recommended the destruction of the existing SVE wells(except VX-1)and also destruction of the existing sparge wells. ' Project No.59183-06-03 -2- January 30,2012