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1 <br /> 1 Model input Parameters <br /> Source Concentration (Co). Co is the concentration of each chemical dissolved in <br /> the soil solution (µg/1) at the source, and is calculated according to the relationship <br /> Co = Cs <br /> [Kdl X [n] <br /> where Cs = total soil concentration (micrograms per kilogram [pg/kg]) <br /> Kd= soil-to-water partition coefficient (liters per kilogram [1/kg]) <br /> p=bulk soil density (grams per cubic centimeter [g/cm3]) <br /> In = soil porosity (unitless) <br /> Kd was calculated as follows <br /> Kd = Koc x foc (Freeze & Cherry, 1979) <br /> where Koc =organic carbon-to-water partition coefficient (l/kg) <br /> ' foc = soil organic carbon content (unitless) <br /> Values for Koc are from Attachment A, Region IX preliminary remediation goals (PRGs) <br /> first half 1995 (USEPA, Region IX, February 1995) Values for foc were assumed to be <br /> I percent (0 01) <br /> The concentrations in the source area are presented in Tables A-1 through A-4 <br /> Distance (L). This distance (9 5 meters) was taken to be the distance from the bottom <br /> of the interval below where chemicals were detected in the soils from boring B-1 (i e , <br /> I 1 5 feet BGS) to the depth to groundwater (i e , 45 feet BGS) Although the depth to <br /> groundwater was measured at 72 feet BGS in November 1994, the SJCPHS <br /> recommended we use a depth of 45 feet BGS to represent times when the water table is <br /> elevated <br /> Depth (Z) and Width (X) of Plume in the Saturated Zone. The chemical results <br /> from boring MW-1 show that chemicals were detected in soil collected from 11 to <br />' <br /> 115 feet below ground surface (BGS), and no compounds were detected in the interval <br /> 15 5 to 16 feet BGS The value for Z was therefore assumed to be about 3 feet (i e , <br /> about 1 meter) The width of the impacted area was assumed to be half the distance to the <br /> nearest boring in which no impact was detected (i e , boring B-1) on either site of Well <br /> MW-1 This distance was estimated to be about 20 feet (i e , about 6 meters) <br /> Dispersion Coefficient (Dt). Hydrodynamic dispersion (i e , the spreading of a plume <br /> out from the source) is the combined result of two dispersive processes mechanical <br /> dispersion and molecular diffusion In most aquifers, the rate of molecular diffusion is <br /> considered negligible compared with that of mechanical dispersion This is especially true <br /> J 1SEC*RPJ2120740010 ISR-95VJt 2 D-2 <br />