Environmental Engineering Reference
In-Depth Information
There are different definitions of water pollution, depending on the approach and field of
specialization of the author, but we apply this term in all cases when natural water quality
has been altered in such a way that subsequent uses have become less acceptable. Ellis
(1989) formulates surface water pollution as “…the alteration in composition or
condition of surface water, either directly or indirectly, as the result of the activities of
men, which initiates modification of ecological systems, hazards to human health and
renders the stream less acceptable to downstream users.” There are three points in this
formulation, which clarify the term:
• Pollution is defined as a consequence of human activities.
• We consider that natural water is polluted not only in the cases of public health hazard,
but when the natural environment is modified.
• Pollution is an act leading to the impairment of subsequent water use for a stated
purpose.
Although this definition is formulated for surface water only it can be applied to ground
water resources as well, and it could be stated that:
Water pollution
is the alteration in the composition or condition of natural water, either
directly or indirectly, as the result of human activities, which initiates modification of
ecological systems, hazards to human health and impairs the subsequent water use.
The process of evaluation of the pollution status of a water resource system requires
information regarding its natural (background) quality, in order to evaluate how much it
has been affected by human activities.
Background pollution
represents the physical, chemical and biological composition
of surface or groun dwater, which could result from natural causes and factors. It
varies with climatic, geographic and soil conditions and it is an indicator of the
level of contamination of water in its pristine status, uninfluenced by human
activities. Surface natural water quality is more prone to variation compared to
ground water, the natural composition of which is dependent mostly on the
geological formation of the aquifer.
Pollution contributed to water resources could be expressed in terms of pollution loads
received by the corresponding natural water body from a specific source.
Pollution loads
represent the mass quantity of pollution discharged per unit time
into water bodies and are equal to the product of pollution concentrations and the
flow rates during a stipulated period of time. We use the term
“pollution load”
in
cases where an external source (a wastewater discharge, a tributary of a river, or a
river itself) contributes pollution to a given water body (natural stream, river, lake
or aquifer). Pollution loads contributed by different media within a water body
could be regarded as pollution flux. Therefore, during the process of assessment
and evaluation of pollution, both quantitative and qualitative measurements and
data are needed in order to assess and evaluate impacts and effects.
