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Addendum to Interim Corrective Action Plan <br /> Frontier Transportation, Inc. <br /> April 14, 2006 <br /> Page 1 <br /> i <br /> ll 1.0) INTRODUCTION <br /> On March 2, 2006 Biophysics Environmental Assessments, Inc. (BEA) was <br /> - - instructed by the San Joaquin Environmental Health Department to amend the Interim <br /> Corrective Action Plan dated December 20, 2006. This addendum addresses the <br /> technical achievability and details of the following: <br /> A. Soil Vapor Extraction <br /> B . Neutron Thermalization Logging <br /> C. Excavation of the source area contaminant mass <br /> D. Aquifer Testing and Groundwater Extraction <br /> Based upon the identification of free phase gasoline product in two monitoring wells <br /> duringfirst quarter 2006 <br /> q groundwater monitoring at the site, BEA has also addressed the <br /> 1 immediate need for containment by removal of the apparent source, free phase gasoline, <br /> identified at 15 ' to 18 ' below grade surface (bgs), and identified in two down-gradient <br /> monitoring wells 15 years after underground storage tank removal. <br /> –I Free phase gasoline range petroleum hydrocarbons were identified in March 2006 <br /> immediately northwest, hydraulically down gradient of the source area. Dissolved TPH- p <br /> gas in the groundwater for each well, MW-2 and MW-21 , was found to be at 6, 100 ug/L ZV4J+ ; rta ? , rrni <br /> and 231 ,000 ug/L, respectively. Both monitoring wells are screened from 1-0 '-to-20' (^Jo �X <br /> below grade surface and measure contamination in the shallow water bearing soil n p 1 �� <br /> underlying the site. J7/WL - S - 2S ' rho " ` <br /> $ x• 20 <br /> hi addition, the least retarded gasoline constituent, the oxygenate MTBE, continues to <br /> j impact the down gradient, western sentinel well, MW 9, in dissolved phase on-site. This <br /> supports that the MTBE represents the leading edge of the dissolved gasoline plume with <br /> free product near the source approximately 200 ' hydraulically up gradient of the removed <br /> UST area — – – – – <br /> 2.0) SITE LOCATION AND HISTORY <br /> The site is located in Tracy, California at 425 Larch Road in the northwest <br /> lquarter of section 16, Township 2 South, Range 5 East, Mount Diablo Baseline at <br /> Meridian. The site consists of a trucking facility with one metal frame building and <br /> all parking and work areas capped by cement and/or asphalt. The site is located in <br /> j an industrial park. <br />� j <br /> I <br /> 1 <br />