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4 <br /> (�fF <br /> f <br /> k <br /> S � 2.O sarL AAs ;uRVEr <br /> t' <br /> 2.1 TECHNICAL APPROACH <br /> A two- to t-;gree-day soil gas survey will be conducted to obt <br /> detailed information on the possible lateral distribution cif so?v cin round <br /> hydrocarbons in the subsurface. Lrsin scil errs and <br /> obtained rt a relatively large number Of sample pointscwithinsa short can be <br /> period <br /> � of time. In addition, analytical results -ire available in Lhe f <br /> that planned probe locations can be modified on the spat to optimize data <br /> field so <br /> obtained <br /> tolguide the Information <br /> f boreholes and emonitosoil $in as survey can then be used <br /> Site Investigation. g 1s in the Phase IT <br /> j4 2.2 METHODOLOGY <br /> _ 1-• The presence of <br /> volbtile organic: compounds (VOCs) in soil gas <br /> indicates that .:he observed compounds may either be present in the vadose <br /> zone near the sem lir_ <br /> p g point (probe) or in the ground water below the probe. <br /> is Soil gas tecanology <br /> halogenated is most effeacive in ma in low molecular weight <br /> solvent chemirals and petroleum hydrocarbons possLssing high <br /> r vapor pressures and low <-4uenus solubilieies, 'These comrounds readily <br /> �,. volatilize from the ground water and become part of the soil gas as a result <br /> c£ Lhein high g gas/liquid partitioning coefficients. Once in the soil gas, <br /> VOCE diffuse vertically and horizontally through the soil to the ground <br /> r 'surface where they dissipate into the atmosphere, Therefore <br /> contaminated none acts as a s once and the p,. . , the— <br /> } �' atmosphere acts as a sink or <br /> receptor,, typically creating a concentration gradient between the two zones. <br /> The contentxa;:lon graclient in coil gas lae�ween the source and ground <br /> surface may bF locally distr;rred by hylvolopic and geologic factors such as <br /> t impermeable ,lays or perched water. <br /> concentrations is generally However, -n.,pping sail gas . <br /> chemicals is often broader ineareal iext extent than,ecause thetloc t4On of the target <br /> ` and is best defined ..u5ing a laige data base, The geologic barriers <br /> obstructions on, a sr„a'iI scale terds to create anomalie; in the soil as- <br /> presence of geologic <br /> ground water correlation, but generally does not obscure the broader areal <br /> pictures o£ the chemical cnzzstituent distribution. Other variables that <br /> influents the movement of VliCs the soil in, ode <br /> properties of the organic chemicals phy:nical and chemical <br /> h}'drogeolagical properties of the site; vapor epr ssuree waterurated solubility, <br /> and concentration of the chemical; porosity, moisture <br /> hi water.content of tj,e site soils; content, and organic <br /> t.a and the flow direction and velocicy of the ground <br /> _ <br /> 2.3 SAMPLING AND ANALYTICAL PROCEDURES <br /> Dames & tioore will conduct: the soil gas survey at the site utilizing a <br /> field van equipped with a Photovac Cas Chromatograph (IOS50). Sa0pling <br /> equipment used to sample soil vapor include stainless steel drive-tips, a <br /> LDC?.,022 <br /> e.. 3 <br /> t3rW2RM9L-,I111111111 MORONISM <br /> i <br /> ;i <br />