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r <br /> 4 FATE AND TRANSPORT MODELING <br /> Based on the groundwater sample analytical results from the October 2004 sampling <br /> event and iso-concentration contour interpretations, fate and transport models for <br /> benzene and TPH-G have been prepared as requested in SJCEHD correspondence <br /> dated September 24, 2004 The models have been presented in Appendices C and D, <br /> 4 respectively <br /> 4.t Model Calculations <br /> PSC evaluated groundwater models for TPH-G and benzene as contaminants <br /> of concern using an ASTM Risk Based Corrective Action (RBCA) approach <br /> (ASTM E-1739-95) This model provides an indication of the risk for TPH-G <br /> and benzene to jeopardize potential receptors, particularly through the <br /> groundwater ingestion exposure route <br /> The RBCA groundwater model calculation predicts a contaminant <br /> concentration at a distance X along the centerline of a groundwater plume <br /> emanating from a vertical planar source in the aquifer This model accounts <br /> for three-dimensional dispersion and biodegradation The model allows for <br /> typical default values and for site-specific data, such as source concentration, <br /> source width, source thickness, hydraulic conductivity, and groundwater <br /> gradient Parameters in the equation include <br /> X = Distance from the planar source to the location of concern, along the <br /> centerline of the groundwater plume (in a down gradient direction) <br /> C, = The concentration of the contaminant at a distance X from the <br /> source <br /> Cs = The concentration of the contaminant at the source <br /> a,t,y,Z= Dispersivity in the x, y, and z directions <br /> U = Specific discharge (flow velocity) using hydraulic conductivity (K), <br /> — total soil porosity (9T) and hydraulic gradient (I) <br /> X — First order degradation constant of the contaminant <br /> SW= Width of groundwater source in the y direction <br /> So = Depth of groundwater source in the z direction <br /> ' 12 <br /> Quarterly Groundwater Monitoring Report <br /> October 2004 <br /> The Earthgrams Company Facility <br /> 2651 South Airport Way-Stockton,California <br /> Prepared for SARA LEE BAKERY GROUP Prepared by Philip Services Corp <br /> 1-i 1ENVk624001321521382EG\Stockton Airport WayVnvesugauon and Quarterly Aeports\Quarterly Report 10_2004 doc December 09,2004 <br />