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' Phase II Field <br /> ARCADIS Investigation and LNAPL <br /> Mobility Evaluation Report <br /> Union Pacific Railroad Company <br /> Former Maintenance Facility <br /> Tracy,California <br /> then used to calculate velocity. Soil capillary pressure characteristics in this <br /> ' spreadsheet follow the van Genuchten model for relating fluid saturation to capillary <br /> pressure,which is the appropriate model for representing mobility in soils already <br /> impacted with LNAPL. The calculation spreadsheet's inputs and key algorithms follow. <br /> ' Input parameters for the spreadsheet were obtained from laboratory analysis of <br /> undisturbed soil cores and the LNAPL sample, as described above(Section 4.1.4)and <br /> include the following: <br /> Site Characteristics: hydraulic gradient, hydraulic conductivity <br /> • Fluid Characteristics: LNAPL and water density,air-water-LNAPL interfacial <br /> ' tensions <br /> • Aquifer Characteristics: porosity, soil capillarity parameters(van Genuchten N and <br /> ' alpha), irreducible water saturation, residual LNAPL saturation <br /> Three saturation relationships are necessary to arrive at effective saturations required <br /> as inputs to the relative permeability calculation and LNAPL saturation required as an <br /> input to the velocity calculation. Effective water saturation,total liquid effective <br /> saturation,and t,NAPL saturation relationships are presented in Equations 2, 3,and 4, <br /> respectively. Effective water saturation accounts for the presence of the non-wetting <br /> fluids(LNAPL and air).Total liquid effective saturation essentially combines the <br /> presence of LNAPL and water as a single fluid for saturation considerations. LNAPL <br /> 1 saturation under saturated conditions is simply one minus the saturation of water. <br /> S _ Sw —S" (Equation 2) <br /> Se[w] 1—Swr —`$nr <br /> Se1r1 _ SW +Sn —Swr —`Snr (Equation 3) <br /> 1—Swr —Snr <br /> ' Sn ——1—Sw (Equation 4) <br /> Where, <br /> Selwl= effective water saturation, dimensionless <br /> Sw = water saturation, dimensionless <br /> ' Swr = residual(irreducible)water saturation, dimensionless <br /> Sn = LNAPL saturation, dimensionless <br /> 20 <br /> M-w�+xreuo�.mW l 14c2010).arc <br />