Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 330

- Establishment of the risk reduction scale in the remotely situated source area of

a watershed by the inverse application of the GIS-based transport model (Fig-
ure 10.8). The target concentration imposed on the surface water at the compliance
point can be “back-calculated'' to corresponding site-specific limit values in the
source area taking into account the risk reduction and retention ( RRR ) capacity of
the site at watershed scale (characterized by RRR watershed ). This provides the target
values for risk reduction measures/remediation of the source area. For example,
pesticide-contaminated agricultural land may be the diffuse source of surface water
pollution. Air pollution is the source of diffuse contaminant deposition onto soil
or water surfaces. Quality criteria shall be imposed on the receptor environment
of diffuse pollution including the ambient air, or the water of the watershed or
large land areas;

- If the target and the scale of the required risk reduction and the equivalent

concentration are known, the risk reduction measures can be selected and imple-
mented. The measure should be capable of reducing emission and/or transport
from diffuse sources into the surface water at watershed scale, aiming to decrease
contaminant concentration in the surface water to the targeted “no effect''
level;

- Abatement of diffuse load is focused on land and runoff legislation and man-

agement practices, unlike for point sources where treatment is the most effective
method of risk reduction. Risk reduction alternatives of diffuse pollution include
legal tools, technological modifications and remedial activities:
◦

Legal tools for activity regulation include restrictions on production, usage
and emission of chemical substances such as the CO 2 quota, or reduced use
of fertilizers, restriction or ban on certain agrochemicals, for example, too
mobile N-fertilizers and persistent pesticides;

◦ Emission from remote sources can be reduced by changing/replacing the

emitting technology and contaminating chemicals either by “in-pipe'' or
“end-of-pipe'' measures in the case of industries;

◦ Emission load from the source area can be reduced by changing agrotech-

nologies, rotating agrochemicals, reducing the amount and frequency of the
application of agrochemicals, etc.;

◦ Environmental technological measures at watershed scale may focus on the

source, on the transport route or on the environmental compartments at risk;

◦

Partial removal of primary and secondary sources, capping identified sources.
This is generally the most expensive and less feasible solution, but it is still
applicable in some cases;

◦ Stopping/reducing transport by changing and controlling transport routes

(controlling runoff with ditches; subsurface infiltrates with drainage), improv-
ing self-purification and contaminant retention ability of the soils, wetlands
and shallow waters within the watershed maintaining them natural or estab-
lishing artificial wetlands, runoff-treating ponds, protective soil zones, forest
belt, etc.;

◦ Reduction of the sewage amount, enhancing wastewater treatment, separation

of runoff from sewage. Developing natural or seminatural treatment meth-
ods/technologies could be an efficient tool for preventing surface waters from
diffuse pollution;