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alculations <br /> C - Analy„_tical- Model_ <br /> 1) Calculation of velocity of groundwater. <br /> (a) Velocity,,u,= Groundwater Velocity = ki/n, <br /> where: k = hydraulic conductivity = 5x104 <br /> cm/sec. (estimate based on lzthology) <br /> i = Groundwater gradient = 0. 003 , based on July <br /> 23 , 1993 ,groundwater elevation data) . <br /> n,; = effective porosity = 0. 15 (estim. ) . <br /> Owaur = 1x10-5 cm/sec - 0. 028 ft/day <br /> (b) Distribution Coefficient = Kd = Koc x TOC <br /> where: Koc = organic carbon adsorption coefficient = 83 <br /> ml/g. <br /> TOC = total organic carbon in saturated zone <br /> (estim. ) . sediment = 0. 0005 g/g (0. 05%) <br /> Kd = 0. 0415 ml/g <br /> (c) Retardation Factor = Rd = 1 + (P/n,,) Kd <br /> where: P = dry bulk density = 1. 5 g/cm3 (published value <br /> for silts) . <br /> n. = effective porosity = 0. 15 (estim. ) . <br /> Kd = distribution coefficient = 0. 0415 ml/g. <br /> Rd = 1.415 , <br /> fi <br /> (d) Vbm =, = Velocity of Dissolved Benzene = Vw,t,,/Rd <br /> Vbenme = 0. 02 ft/day <br /> 2) Degradation rate for dissolved benzene - Lateral Relationship <br /> The lateral relationship method of estimating degradation rate <br /> involves the observed decline in dissolved benzene concentrations <br /> as the groundwater mass migrates downgradient. The apparent <br /> degradation/attenuation rate is calculated utilizing the maximum <br /> observed benzene concentrations in MW--4 and MW-5. <br /> I <br /> i It should be noted that the calculated degradation/attenuation rate <br /> 3 <br />