Notes on Chemical-Specific Parameters Ė Physical 
and Chemical Properties

Quick Links: ● Soil Organic Carbon-Water Partitioning Coefficient (Koc)Distribution Coefficient (Kd)Henry's Law Constant (Hcc)Aqueous Solubility Soil Organic Carbon-Water Partitioning Coefficient (Koc) The soil organic carbon-water partitioning coefficient is the ratio of the mass of a chemical that is adsorbed in the soil per unit mass of organic carbon in the soil per the equilibrium chemical concentration in solution. It is the "distribution coefficient" (Kd) normalized to total organic carbon content. KOC values are useful in predicting the mobility of organic soil contaminants; higher KOC values correlate to less mobile organic chemicals while lower KOC values correlate to more mobile organic chemicals. This parameter is used to calculate a soil concentration that is protective of ground water using the 3-phase and 4-phase equilibrium partitioning models. The parameter is chemical- specific. Only values for organics are published in the CLARC Information System. Koc is used to derive a Kd value for organics using Equation 747-2. See WAC 173-340- 747(4)(c). References: The default Koc values published in CLARC are based on a pH of 6.8 and were obtained from the following hierarchy of sources:
    Source
    U.S. EPA, Soil Screening Guidance: Technical Background Document ,
    EPA/540/R-95/128, May 1996, Table 38.
    U.S. EPA, Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites, Peer Review Draft, OSWER 9355.4-24, March 2001, Table C-1.
    U.S. EPA, Soil Screening Guidance: Userís Guide, EPA/540/R-96/018, April 1996,
    Table C-1.
    U.S. EPA, Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites, Peer Review Draft, OSWER 9355.4-24, March 2001, Table C-2.
    U.S. EPA, Technical Background Document for Draft Soil Screening Level Guidance, EPA/540/R-94/018, March 1994.
    ATSDR Toxicological Profile for 1,2 -Dibromoethane (TP 91/13)
    Gustafson, J.B. et al., Selection of Representative TPH Fractions Based on Fate and Transport Considerations, Total Petroleum Hydrocarbon Criteria Working Group Series, Volume 3 (1997).
    U.S. Geological Survey, Final Report on Fuel Oxygenates, March 1996.
Distribution Coefficient (Kd) The "distribution coefficient" (Kd) is the "soil-water" partitioning coefficient. Kd(L/kg) is the ratio of a chemical's sorbed concentration (mg/kg) to the dissolved concentration (mg/L) at equilibrium, as illustrated below: Kd(L/kg) = Sorbed Concentration (mg/kg) / Dissolved Concentration (mg/L). For organics, Kd may be calculated by multiplying Koc (the soil organic carbon-water parti- tioning coefficient) by foc (the mass fraction of soil organic carbon content), as illustrated below: Kd = Koc x foc [Equation 747-2]. This parameter is used to calculate a soil concentration that is protective of ground water using the 3-phase and 4-phase equilibrium partitioning models. The parameter is site- specific and chemical-specific. Only values for metals are in the CLARC Information System. See WAC 173-340-747(4)(c). References: The default Kd values in the CLARC Information System are based on a pH of 6.8 and were obtained from the following sources:
    Source
    U.S. EPA, Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites, Peer Review Draft, OSWER 9355.4-24, March 2001, Table C-4.
    Baes, C.F. (III), and R.D. Sharp, A Proposal for Estimation of Soil Leaching and Leaching Constants for use in Assessment Tools, J. Environ. Quality, Vol. 12, No. 1, pp. 17-28, 1983.
    Radian Corporation, Evaluation of Soil Remedial Levels for Frontier Hard Chrome, Vancouver, Washington, Draft Technical Memorandum, October 1990.
    U.S. EPA, Composite Model for Leachate Migration with Transformation Products (EPACMTP), April 1994.
Henry's Law Constant (Hcc) Henry's law constant (Hcc) is the ratio of a chemical's concentration in the air to its concen- tration in water at equilibrium. This parameter can vary significantly with temperature for some chemicals. For the purposes of the regulation, the dimensionless form of this parame- ter is used. This parameter is used to calculate a soil concentration that is protective of ground water using the 3-phase and 4-phase equilibrium partitioning models. The parameter is chemical- specific. See WAC 173-340-747(4)(d). References: The default values in the CLARC Information System were obtained from the following sources:
    Source
    U.S. EPA, Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites, Peer Review Draft, OSWER 9355.4-24, March 2001, Table C-1.
    U.S. EPA, Soil Screening Guidance: Userís Guide, EPA/540/R-96/018, April 1996,
    Table C-1.
    Gustafson, J.B. et al., Selection of Representative TPH Fractions Based on Fate and Transport Considerations, Total Petroleum Hydrocarbon Criteria Working Group Series, Volume 3 (1997).
    U.S. Geological Survey, Final Report on Fuel Oxygenates, March, 1996
    MTCA Cleanup Regulation, WAC 173-340-747(4)(d).
Aqueous Solubility (S) This parameter is used to calculate a soil concentration for petroleum and other mixtures that is protective of ground water using the 4-phase equilibrium partitioning model. This parameter is also used to calculate the soil saturation limit for single hazardous substances. The parameter is chemical-specific. References: The default values in the CLARC Information System were obtained from the following sources: