Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 326

- The most important pollutants from diffuse sources subject to management and

control are suspended solids, nutrients, organisms of fecal origin and toxic
chemical substances;

- Diffuse pollutant emission into atmosphere occurs as gas and PM from a variety

of point sources.

3 DIFFERENT RISK MANAGEMENT APPROACHES
FOR POINT AND DIFFUSE POLLUTION

K. Gruiz & E.Vaszita
Point sources are separate, identifiable, delineable pollution sources originating from
known activities, whereas sources of diffuse pollution are difficult to identify as they are
unknown, heterogeneously distributed and are made up of many small point sources
within a large area.
Contaminants from point sources in surface water and groundwater can usually
be found in a plume that has generally decreasing concentrations from the source (such
as the end-of-pipe or an underground injection system) moving away on the transport
route (Ferrier et al., 2004). Greater discharges from major point sources may result
in lower concentrations (but not necessarily lower loads) in high flow rate rivers or
subsurface waters due to dilution.
For diffuse pollution, the proportion of the land use from which the pollution is
derived is of importance. Where the pollutants of concern are diffusely distributed (for
example, suspended solids in a mining-affected watershed or phosphorus in a livestock
farming watershed), higher flows often mobilize greater amounts of pollutant enter-
ing the watercourses and in higher concentrations (and vastly greater loads) (Ferrier
et al., 2004).
Diffuse contamination (event) and the transport of the contaminant are separable
in time. For example, diffuse contamination of soil is related to seasonal or ad hoc
agricultural activities, while the resulting contaminant load in surface waters is mostly
based on weather conditions, i.e., surface runoff after a rainfall event. This results in
large spatial and time-related variability and uncertainties in mapping the contaminant
and modeling its transport. The resulting air and water contamination in the receptor
environment is measurable but the contaminant-transport pathway system remains
often a black box. To explore this black box historically, the diffuse source types and
contaminants have to be identified. Modeling their transport became possible using
GIS-based calculations for the water and material fluxes as a function of topography,
land cover and pollution level.
Because of the differences in the characteristics of point and diffuse sources and the
mechanisms of pollutant movement through the environment, the risk management
approach also differs for point and diffuse source pollution.

3.1 Management of point source pollution
Point source pollution is easier to manage than diffuse source pollution because it can
usually be traced to a single source. Traditional, local-scale risk management approach