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Human Health Risk Assessment <br /> Former Mobil Oil Bulk Plant 04-343 <br /> 500 East Grant Line Road <br /> Tracy, California <br />�a PERTIES EFFECT <br /> rganie Content of Soil High organic content in soil will increase the sorptive characteristics and, therefore, reduce the <br /> emission rate of a chemical. In addition, higher organic content may increase microbial action. The <br /> model used in this analysis does not account for the adsorptive capacity of organic carbon in soil. <br /> "Microbial Activity Microbial activity may reduce the emission rate of a chemical by reducing the quantity of a chemical <br /> present in soil. Conversely, gas formation as a by-product of microbial activity may tarn, volatile <br /> chemicals to the soil surface. <br /> epth to Contamination Emission rates decrease with increasing depth to contamination. For the adsorbed-phase,the average <br /> depth to the contamination is assumed to be the mid-point of the vadose zone. For the dissolved <br /> phase, the depth to contamination is taken as the average depth to ground water. <br /> Wind Wind removes volatilized compounds from the bounds _ <br /> p boundary layer over a particular site, v <br /> $ removing <br /> compounds from the boundary layer, the driving force for volatilization is maintained. <br /> :Jiffusivit <br /> y Diffusivity describes the movement of a molecule is a liquid or gas medium as a result of differences <br /> in concentration. It is used to calculate the dispersive component of chemical transport. The higher <br /> the diffusivity, the more likely a chemical is to move in response to concentration gradients. <br /> i <br /> P- <br /> 30-0136-11 <br /> i <br />