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March 18, 1993- <br /> Page 9 <br /> C Considering the data presented and other pertinent information, PACIFIC <br /> recommends application of Alternative 1. The recommended alternative is <br /> detailed below. <br /> a i <br /> The Recommended Alternative <br /> Ile:Irecommended alternative (Alternative 1) consists of three major components: <br /> soil yapor extraction and treatment, completion of residual plume delineation, and <br /> groundwater monitoring. Soil vapor extraction and treatment and residual plume <br /> delineation are discussed in the sections below. Groundwater monitoring is not <br /> discussed because a program has previously been established. <br /> Soil Vapor Extrac.tion.and Treatment <br /> Removal of petroleum hydrocarbons will be accomplished by circulating ambient <br /> air through the subsurface environment. Air_flow_willpromote volatilization of� <br /> $squid=phase,-dssolved;.and adsorbed petroleum hydrocarbons: Vapor-phase <br /> hydrocarbons will be removed with the air stream. Extracted petroleum hydrocar <br /> bons'will be reduced or recovered as.part of soil vapor treatment before atmo- <br /> spheric discharge. <br /> Extracted soil vapor will be treated using either an internal-combustion engine, <br /> `catalytic therinai-oxidation;of vapor-phase-carbon adsorption. Treatment method <br /> -' specification will be based upon initial concentration and modeled concentration <br /> decay. If soil.vapor concentrations are relatively high,use of an internal <br /> combustion engine will probably be recommended. If vapor concentrations are <br /> moderate,use of catalytic thermal oxidation will be suggested. Vapor-phase <br /> carbon adsorption would be recommended for low concentrations. In some <br /> instances,it may be economically prudent to begin with an internal combustion <br /> engine or with catalytic thermal oxidation and finish with vapor-phase carbon <br /> Ldso�pton___6inAuthority toConstruct andPer-mit.to-Operate from thegoverning <br /> Po1 ution Control l) strict will be-necessary for use of_either treatment, <br /> technology.Termination of soil vapor extraction will be considered after soil vapor hydrocar- <br /> bon concentration drops to,10 percent of the-maximum concentration-exhibited-----n, <br /> aftersparginghas been initiated. This-guideline is specified because it is the,pomt <br /> where-further-operation is not-incrdmentally.aieneficial,. <br /> - <br /> �: 3100104/IRAP <br />