Site-specific risk assessment and management of point and diffuse sources - Environmental Deterioration and Contamination: Problems and their Management - page 319

from wastewater treatment works, landfill sites and oil spillage via a pipeline from
industrial sites. Typical subsurface contaminants result from substances stored in
underground tanks and transported by pipelines. Low-density non-aqueous liquid
phase and high-density non-aqueous liquid phase contaminants released/seeped from
pipelines into soil may float on the surface of the groundwater or sink to its bot-
tom. Some of the most persistent point source pollutants in groundwater are volatile
organic compounds, which include manufactured and refined toxic substances such as
solvents, oils, paints and fuel products.
Traditional point source pollutants include dissolved inorganic and organic chemi-
cals, suspended solids and their organic content, nutrients (nitrogen and phosphorous)
and pathogenic microorganisms. The biodegradable organics reduce dissolved oxygen
levels in the receiving water bodies and this is why their concentration is often given
as biochemical oxygen demand, i.e. the amount of oxygen necessary for their aer-
obic biodegradation. Organic contaminants may cause the accumulation of organic
sludge, increase sediment oxygen demand and promote the nuisance of algal growth
(Campbell et al., 2004).
The various types of point source pollutants found in waters are as varied as the
types of business, industrial, agricultural and urban sources that produce them (Water
Encyclopedia, 2013). Point sources of water pollution include municipal sewage treat-
ment plant discharges and industrial plant discharges. Municipal sewage treatment
plants—typical point sources—may contribute to the pollution in the form of oxygen
depleting nutrients and in the form of pathogens that cause serious health hazards
in drinking water and swimming areas. Industrial point sources can contribute to
pollution in the form of toxic chemicals and heavy metals.
Point source pollution is generally controllable as it is possible to identify where it
is coming from, how much and what kind of harmful agents and materials it contains.
This way those responsible for causing the pollution can take preventive measures
through various risk reduction actions such as

Immediate reduction of the produced or used amount of chemical substance, its
substitution with less hazardous materials;
Long-term investment in treatment and control facilities, i.e., modifying or replacing
the production or usage technology with a cleaner one, application of “in-pipe''
technologies for the reduction of the formation of environmental contaminants.
Waste treatment and utilizing technologies are included in this category;

- Use of “end-of-pipe'' protective technologies or accessories for the removal of

contaminants already formed;

- Remediation of the contaminated environment.

2.2.2 Diffuse pollution from point and diffuse sources

The definition of Campbell says: “Diffuse pollution comprises nonpoint source con-
tamination such as sheet run-off from fields and seepage from soil into groundwater,
as well as pollution arising from a multiplicity of dispersed, often individually minor
point sources such as surface water drains in urban areas, field drains and ferruginous
springs associated with abandoned mine workings'' (Campbell et al., 2004).