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s xg. <br /> - Z M - <br /> J. H. KLEINFELDER &ASSOCIATES <br /> File: PW86-1041/14:381 <br /> July 29, 1986 <br /> Page 4 <br /> Volatile organic compounds VO'' <br /> gasolinewhich include <br /> compounds) in unsaturated soil tend toward chemical <br /> equilibrium between solid, liquid, and gaseous phases. <br /> Chemical equilibrium is more closely approached the longer <br /> the VOCs are ret;,Ined in the soil. <br /> equilibrium If VOCs approach local <br /> between solid, liquid, and gaseous phases, then <br /> VOC losses from the gaseous phase produce a negative <br /> chemical gradient between the gaseous phase and the liquid <br /> and solid phases. As a result <br /> (volatized) from the liquid and sclidVOCs <br /> are ireleasnto e <br /> gaseous te <br /> phase as the system attempts to reestablish <br /> equilibrium. <br /> Vapor phase extraction techniques remove VOCs from <br /> soil <br /> by continuously exhausting VOCs from the gaseous phase <br /> thereby maintaining a large negative chemical gradient <br /> between the gaseous phase and the liquid and solid phases. <br /> This large negative gradient accelerates the transfer of <br /> VOCs from liquid and solid phases into the gaseous phase. <br /> The continuous replacement of VOC-contaminated <br /> � ._.: clean air results gases with <br /> in a net reduction of VOC cone <br /> entr <br /> in the soil matrix. The following discussion addressestions soil <br /> characteristics, general site features, and design <br /> parameters which must he considered for effective operation <br /> Of a vapor phase extraction system. <br /> Optimal Soil Characteristics <br /> # Optimal soil characteristics for vapor phase extraction <br /> f of volatile organic compounds are a uniform coarse soil <br /> texture with low moisture content <br /> i be <br /> Present on this site. Uniformity Provides appears to for a minimal <br /> al <br /> to delineate <br /> sampling densitysoil lithology and chemical <br /> distribution in the soil before and after vapor extraction. <br /> Coarse--textured soils with low moisture content provide for <br /> more efficient release of volatile organics into the gaseous <br /> Phase and high air permeability through the soil. <br /> _ Proposed Study <br /> The- proposed-vapor-phase-extraction----- roject includes <br /> �µ data review, preliminary design engineering <br /> design of the vapor extraction system. (Table 1) and final <br /> s <br /> f <br /> i <br />