Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 328

- Assessment of the risk of the point source at a certain point and time, assuming

the most sensitive land use;

- Determination of the target concentration in the vicinity of the receptor, based on

the screening risk level of RCR

1. The smaller than one criterion means that
the predicted (calculated) site-specific concentration is lower than the “no effect''
or acceptable concentration. RCR = PEC/PNEC for the ecosystem: the ratio of
the predicted environmental concentration to predicted no effect concentration
for the ecosystem in question. For humans, the daily intake calculated from PEC
is compared to the acceptable intake;

≤

- Defining the scale of necessary risk reduction by inverse application of the trans-

port model starting from the target concentration in the compliance point back to
the source and to its emission ( E ) or concentration ( C );

- Selection of risk reduction alternatives: source removal, emission reduction, hin-

dering transport, remediation of the already contaminated soil, groundwater,
surface water or sediment;

- Finding and applying the risk reduction measure which can reduce emission or/and

transport from the point source, fulfilling the “no effect'' target concentration in
the target point;

- Confirming the effect of risk reduction by long-term environmental monitoring.

3.2 Management of diffuse pollution
Diffuse sources are multiple and heterogeneously distributed nonpoint sources. The
pollutant emission events are seasonal and episodic (slurry application, nutrient and
pesticide application on soil, etc.) but the transport of the emitted contaminants is
associated with dynamic weather conditions (rainfall, moisture content of soil, storm
events, etc.) and is dependent on topography, geochemistry and hydrogeology of the
respective area.
In the risk management of diffuse source pollution, the following aspects are taken
into account:

- Time and space dependence of contaminant transport from the source to the

receptor;

- The distance between the diffuse sources and the final receptor (e.g., surface water)

may be rather large within a watershed;

- The environment at risk, i.e., surface water, ambient air or drinking water, is

monitored;

- Risk reduction usually targets the very beginning of the transport route, the

discharge points or areas;

- The effectiveness of the implemented risk reduction measure or remediation can

be confirmed only over the long term, at a great distance from the source, and
with high uncertainty;

- Prevention and restriction have priority because remediation of extensive areas is

often not feasible;

- Only management of identified source technologies and emissions is possible;