Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:5:p7
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 5 (pt 7/10)
Character Range: 1458281–1461178

threshold EGVs from other national regulators.

Although EGVs are provided, the New Zealand framework stresses that the original reference document for an EGV must be referred to in order to assess if the EGV is relevant for the contaminated soil being investigated. Therefore, the EGVs and the framework are guidelines to obtain the most relevant EGV for a contaminated site.

5.2              Appendix B: method for deriving EILs that protect aquatic ecosystems

5.2.1         Determining the leaching potential of inorganic contaminants
The key physicochemical property of inorganic contaminants that controls their potential movement to ground and/or surface waters is the soilwater partition coefficient (Kd). This is the ratio of the concentration of a contaminant bound to the soil to that dissolved in soil pore water at equilibrium and therefore is related to the aqueous solubility of that contaminant. The lower the Kd, the more of a contaminant that will be present in the soil pore water. This may increase the potential for plants and soil invertebrates to be exposed via the pore water and increase the potential for leaching to groundwater and for groundwater organisms to be exposed. Although Kd is soil- and contaminant-dependent, a conservative cut-off point for inorganics at a log Kd of 3 is used in the methodology. The log Kd thresholds are presented in Table B1.

Table B1. Classification system used for the mobility of inorganic contaminants in soil, based on the logarithm of the soilwater partition coefficient (log Kd).
Log Kd value  Leachability
<3            High potential to leach (H)
≥3            Low potential to leach (L)

For inorganics with a log Kd <3, leaching of the contaminant should be addressed if there is a water source in the immediate vicinity.

5.2.2         Determining the leaching potential of organic contaminants
There are two partition coefficients related to the leaching potential of organic contaminants. The first is the octanolwater partition coefficient (Kow), that is, the ratio of the concentration of a contaminant that is dissolved in n-octanol to that dissolved in water at equilibrium and at a specified temperature. It is used as a surrogate to estimate the potential for contaminants to accumulate in tissue—both plant and animal (Connell 1989, Posthumus & Slooff 2001). The second is the organic carbonwater partition coefficient (Koc). Both Kow and Koc are chemical-specific values and collations of values for contaminants are widely available e.g. at http://www.epa.gov/region9/superfund/prg/.
Contaminants with a high log Koc preferentially partition to soil organic matter rather than water and thus have a low potential to leach. Conversely, contaminants with a low log Kow tend to have a high potential to leach. Log Kow and log Koc have a linear relationship (Briggs 1981, Connell 1989).
log Koc = 0.9 x log Kow +