Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 331

◦ Immobilization of contaminants is an emerging tool for the management of

diffuse pollution. It means the reduction of the physical and chemical mobility
of “diffuse'' pollutants by:
◦

Erosion control;

◦ Runoff control;

◦ Construction of a buffer zone/protective strip between agricultural land

and surface waters;

◦ Enhancing biodegradation of diffusely polluting biodegradable contaminants

by treating contaminated runoff in buffer ponds, artificial wetlands before
entering surface waters;

◦ Improving self-purification potential of surface waters, first of all in the

discharge zone;

◦

Isolated containment of agrochemicals;

◦ Changing the chemical form of contaminants that cause diffuse pollution;

◦ Preventing acidification at metal-contaminated sites;

◦ Preventing redox potential increase in metal-contaminated wetlands and

swamps;

- Confirmation of the effectiveness of risk reduction by long-term environmen-

tal monitoring. Compliance monitoring of diffusely polluted areas is mainly
done in the final target compartment and is extremely useful in preparing the
monitoring plan.

4 TRANSPORT MODELING FOR POINT AND
DIFFUSE SOURCES

K. Gruiz & E.Vaszita
The conventional assessment practice whether a source poses risk to soil and ground-
water, has been focused on the measurement or prediction of contaminant concentra-
tion or load at the local scale. The management of surface waters should focus on the
risk posed at watershed scale, while in the case of air at local, regional and global scales.
The estimation of the concentration in groundwater, soil, surface water and air is typ-
ically based on contaminant fate and transport modeling. Figure 10.4 demonstrates
three cases of contaminant attenuation between the source and receptors. 1. No source
control, no retention, no degradation in the soil, just dispersion. 2. No source con-
trol, retention and degradation of the contaminant occur. Red curves do not reach the
acceptable concentration level (green line), meaning that natural interactions are not
sufficient to reduce the contaminant concentration to a “no-risk'' level. 3. Source con-
trol, restrictions, remediation or other risk reduction measures are applied to further
reduce the concentration (green line). In practice natural attenuation may fulfill target
quality criteria, but if not, additional intervention is necessary to reach the threshold.
Through fate and transport modeling the aim is to improve our understanding of
how contaminants are affected by the physical, biological and chemical processes that
occur within the vicinity of a contaminated site/source. The environmental phases,
the interactions of the contaminants with the phases of the environmental medium