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' tank location Two additional monitoring wells (MW-3 and MW-4) were <br /> installed on 10 November 1998 The results of samples collected from <br /> these two wells indicated that petroleum hydrocarbon concentrations <br /> were present in ground water immediately downgradient of the former <br /> tank location, but upgradient concentrations were non-detectable <br />' Based on all the EHD results,sample PHS requested that additional soil <br /> p / <br /> borings be advanced to delineate the total depth of soil and ground water <br />' impacts at the former tank location, such that the extent of all <br /> hydrocarbon impacts at the former tank site would be defined Therefore, <br /> t ERM installed three additional soil borings and one ground water <br /> HydroPunch at the former tank site on 11 February 1999 The results of <br /> this sampling event were presented in Investigation Results Report (ERM, 13 <br />' April 1999) Following this investigation, PHS/EHD concurred that the <br /> lateral and vertical extent of soil and ground water impacts at the former <br /> tank site had been defined <br />' 2.4 GROUND WATER REMEDIATION <br /> Following completion of the investigation activities,PHS/EHD asked <br /> Heinz to evaluate potential strategies for reducing the concentration of <br /> petroleum hydrocarbons in ground water An evaluation of potential <br /> remediation technologies for ground water was completed and presented <br />' in the Investigation Results Report As presented in that report, injection of <br /> ORC was selected as the best available technology for reducing ground <br /> water concentrations at the former tank site (Section 4 of this report <br />' presents the rationale for detern- ring the best available technology for <br /> ground water remediation) <br />' ORC injection was performed at the former tank site during the week of 7 <br /> June 1999 ORC injection was performed at 30 locations downgradient of <br />' the former tank location Routine ground water monitoring(discussed <br /> below) was conducted every 2 months following ORC injection to track <br /> the reduction in petroleum hydrocarbon concentrations in ground water <br /> 1 <br />' 2.5 GROUND WATER MONITORING <br /> Ground water monitoring has been performed at MW-1 since 1 May 1998 <br />' and at MW-3 and MW-4 since 16 November 1998 <br /> Overall, the concentrations of compounds in ground water at MW-1 have <br /> reduced since monitoring began In addition, chemical concentrations <br /> ERM 8 HEINZ USA 3374 60.3/27/00 <br />