Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 354

Figure 10.10 Inverse application of the site-specific risk assessment to determine acceptable concen-
tration in the source.

The inverse application of risk assessment and transport modeling to calculate the
site-specific environmental target concentration from the requirement of the receptors
(users of the land) is explained in Figure 10.10 below.
The site-specific target concentration of the contaminant in the case of certain land
use is determined by the sensitivity of the users; this value is the PNEC in the case of
ecosystem and ADI for humans. Applying a transport model fitted to the local environ-
ment (using the site-specific transport and exposure parameters), we can determine the
maximum permissible emission of the contaminants from the source (source criteria).
From this maximal emitted amount we can calculate the concentration of a discharge
if the flux or the maximum concentration in a delineated area, the size of the surface,
etc. are known.
To be able to calculate the maximum permissible quantity released from the source,
we have to establish a direct relationship between the receptors (the environment used
by them) and the source of the contaminants. This can be done by the transport and
fate models which consider the following:

- The behavior of the contaminants released from point or nonpoint sources;

- Their transport/migration through the soil to the downstream aquifer or surface

water as well as to the atmosphere; and

- The resulting impact on the groundwater or surface water quality and ecosystem

at the specified target or inflow points at local or watershed scale.

Case study 4

Example of chloroform-contaminated groundwater in an industrial facility in the vicin-
ity of a residential area. It demonstrates the inverse calculation of the maximum