Human Health Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 218

representative
SOIL CONTENT

distribution
over
soil fractions

SOIL-AIR
concentration

PORE WATER
concentration

transport to
SURFACE SOIL

transport to
GROUNDWATER

uptake by /
deposition on
VEGETATION

transfer-
processes

dilution in
INDOOR and
OUTDOOR AIR

transport to
DRINKING WATER

permeation into
DRINKING WATER

inhalation,
dermal uptake
AIR

ingestion, inhalation,
dermal uptake
SOIL

direct
exposure

consumption of
VEGETATION

intake DRINKING WATER,
dermal contact, inhalation
SHOWERING

indirect
exposure

Fig. 5.2 Layout of the CSOIL model, as an example of the layout of exposure models

5.3.3.2 Contaminant Distribution

The distribution of contaminants over the soil phases (solid phase, pore water and
soil gas) can be calculated on the basis of partition equations. Partition or distribu-
tion coefficients describe the (equilibrium) relationship between the concentrations
in the solid soil phase and the pore water, and between the pore water and the soil
air, as follows:

ρ b ∗ C To t = θ pw ∗ C pw + ρ b ∗ C s + θ a ∗ C a (5.1)

where
C Tot is the total soil concentration (M/kg dw ), C pw (M/L pw ), C s (M/kg dw ) and C a
(M/L air ) are the concentrations in pore water, solid soil phase and soil air, respec-
tively, ρ b is the bulk density of the soil (M/L) and θ w and θ a represent volumetric

water and air content of the soil (-), respectively.
The concentrations in the mobile phases of the soil can be calculated as follows:

C pw = C To t / K d (5.2)