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RICSw <br /> Working To Restore Nature <br /> ' {=> were found on only three occasions and these consisted only of trace amounts of toluene, <br /> f ethylbenzene and xylenes. <br /> If If No detectable concentrations of any petroleum hydrocarbon analytes have been found during the <br /> four rounds of groundwater sampling since excavation occurred. This lack of impact may best <br /> be explained-by the partitioning of diesel hydrocarbons between soil and water at the site. <br /> The concentration of a substance in groundwater (Cw) can be predicted by the concentration in <br /> -:� soil (Cs) with which it is in contact. This is accomplished by use of the soil distribution <br /> coefficient (Kd) (Hounslow, 1990). Distribution coefficients are substance specific, unitless <br /> �. relationships defined as: <br /> F:`=1 Kd = Cs/Cw <br /> The larger the value of Kd the greater the tendency of a substance to remain within the soil. <br /> Kd values are expected to increase with increasing organic carbon and clay content in the soil. <br /> One study (EPA, 1978) directly determined soil distribution coefficients for eleven organic <br /> f compounds in sediment from Coyote Creek in Santa Clara County, California. .The organic <br /> L carbon content of the sediment was 1.4%, similar to that in the Capay Clay at the Western Stone <br /> r-= site. Utilizingthe experimental data a relationship between the soil distribution coefficients for <br /> t{::I A P <br /> organic substances and their respective solubilities was derived: <br /> log Kd = 5.35 - .66 log sol (ppb) <br /> i12 <br /> �r <br /> This equation indicates that the distribution coefficient decreases with increasing solubility. <br /> f <br /> Assuming a solubility for diesel of 4000 b Guard N &Lau hlin 1983 measured 1300 b <br /> g ty PA ( g g ppb) <br /> the soil distribution coefficient for diesel would be approximately 940. <br /> j <br /> 'f <br /> 0W01951REP0RT51CL012594.FNL 10 <br /> iI <br /> �J <br />