Determining the partitioning of contaminants between soil and water at a site is an important part of any assessment. The following calculator uses the EPA soil/water partition equation for organic contaminants (Soil Screening Guidance Technical Support Document, EPA, 1996). This equation is used to relate the contaminant concentrations in soil moisture to the total concentration detected in a soil sample.
Where: Ct = soil concentration (mg/kg)
Cw = aqueous concentration (mg/L)
koc = soil organic carbon/water partition coeffiecient (L/kg)
foc = fraction organic carbon (kg/kg)
Pw = water-filled soil porosity
Pa = air filled soil porosity
Pb = dry soil bulk density (kg/L)
Hd = dimensionless Henry’s Law
This equation can be used for several regulatory purposes, including RBCA in several states. The newly released RBCA Tool Kit for Chemical Releases v2.0 makes calculations and report writing for RBCA regulations significantly easier.
There is a known Benzene source, with a concentration of 6.04 x 10-2 mg/L in a sand aquifer (properties of sand: foc=0.06, Pw=0.079, Pa=0.321, Pb=1.5 kg/L). The koc and Hd of Benzene are found to be 6.17 x 101 L/kg and 2.28 x 10-1 respectively. What is the expected concentration of Benzene in the sand?
The solution is 2.85 x 10-2 mg/kg.
EPA, 1996. Soil Screening Guidance Technical Support Document.