Equations for Calculating Site-Specific Soil Cleanup Objectives

Section 259 Section 259.350  Equations for Calculating Site-Specific Soil Cleanup Objectives a)         Site-specific soil cleanup objectives for pesticides are determined by the following equation: Where: SCO = soil cleanup objective (mg/kg) C w = target soil leachate concentration (mg/L) K oc = organic carbon partition coefficient (L/kg) f oc = organic carbon content of soil (kg/kg) Θ w = water-filled soil porosity (L water /L soil ) Θ a = air-filled soil porosity (L air /L soil ) H' = Henry's law constant (dimensionless) Ρ b = dry soil bulk density (kg/L) References: "Soil Screening Guidance:  User's Guide", p. 29, eq. 10. "Soil Screening Guidance:  Technical Background Document", p. 37, eq. 24. 1)         The target soil leachate concentration can be determined by the following equation: Where: C w = target soil leachate concentration (mg/L) DF = groundwater dilution factor (dimensionless) GW obj = groundwater cleanup objective (mg/L) 2)         The dilution factor can be determined by the following equation: Where: DF = groundwater dilution factor (unitless) K = aquifer hydraulic conductivity (m/yr) i = hydraulic gradient (m/m) d = mixing zone depth (m) R = groundwater recharge rate (m/yr) L = length of contaminated soil parallel to groundwater flow (m) W = width of contaminated soil perpendicular to groundwater flow (m) b)         Site-specific soil cleanup objectives for nitrate as nitrogen can be determined by the following equation: Where: L = Liter C w = Target soil leachate concentration (mg/L) c)         Site-specific soil cleanup objectives for ammonium can be determined by the following empirical equation: Where: CEC = cation exchange capacity (meq/100g) Reference: Potential Soil Cleanup Objectives for Nitrogen-Containing Fertilizers at Agrichemical Facilities, Soil and Sediment Contamination. d)         The default values for the equations in subsections (a) and (b) of this Section are: Parameter Description Default Value DF Groundwater dilution factor 30 (dimensionless) f oc Organic carbon content of soil 0.008 kg/kg (0.8%) surface or 0.002 kg/kg (0.2%) subsurface Θ a Air-filled soil porosity 0.2 (20%) L air /L soil Θ w Water-filled soil porosity 0.2 (20%) L water /L soil Ρ b Dry soil bulk density 1.6 kg/L H' Henry's law constant see Appendix E K oc Organic carbon partition coefficient see Appendix E GW obj Groundwater cleanup objective see Appendix D CEC Cation exchange capacity see Appendix F