Surface Water Contamination
What kind of contamination is it?
Surface water is usually rain water that collects in
surface water bodies, like oceans, lakes, or streams.
Another source of surface water is groundwater that
discharges to the surface from springs. Surface water
pollution occurs when hazardous substances come into
contact and either dissolve or physically mix with the
water. Because of the close relationship between
sediments and surface water, contaminated sediments
are often considered part of surface water
contamination. Sediments include the sand and soils
on the bottom of an ocean, lake, or stream.
How did it get there?
Surface water can become contaminated in many
ways. Surface water can be contaminated when
hazardous substances are discharged directly from an
outfall pipe or channel or when they receive
contaminated storm water runoff. Direct discharges
can come from industrial sources or from certain older
sewer systems that overflow during wet weather.
Storm water runoff becomes contaminated when rain
water comes into contact with contaminated soil and
either dissolves the contamination or carries
contaminated soil particles. Surface water can also be
contaminated when contaminated groundwater
reaches the surface through a spring, or when
contaminants in the air are deposited on the surface
water. Contaminated soil particles carried by storm
water runoff or contaminants from the air can sink to
the bottom of a surface water body, mix with the
sediment, and remain.
How does it hurt animals, plants and humans?
A change in the water chemistry due to surface water
contamination can negatively affect all levels of an
ecosystem. It can impact the health of lower food
chain organisms and, consequently, the availability of
the food supply up through the food chain. It can also
impact the health of wetlands and impair their ability
to support healthy ecosystems, control flooding, and
filter pollutants from storm water runoff. Contaminated
surface water can also affect the health of animals and
humans when they drink or bathe in contaminated
water or, for aquatic organisms, when they ingest
contaminated sediments. One of the major concerns
associated with contaminated surface water is the
ability of aquatic organisms, like fish, to accumulate
and concentrate contaminants in their bodies. When
other animals or humans ingest these organisms, they
receive a much higher dose of contamination than
they would have if they had been directly exposed to
the original source of the contamination.
How can we clean it up?
The most effective approach for cleaning up
contaminated surface water is to prevent further
discharges from contaminated sources and enable
natural biological, chemical, and physical processes to
break down the existing contamination. In some
surface water bodies where natural processes are not
enough to break down the contaminants, other
cleanup approaches such as mixing and aeration may
be required to further promote natural cleanup. A
significant source of surface water contamination may
be contaminated sediments. Contaminated sediments
generally contain persistent contaminants and are
difficult to clean up. Three main approaches to
cleaning up contaminated sediments are: 1) remove
them by dredging; 2) place a cover over them to
prevent contact with the surface water; or 3) allow
natural processes to cover them or break them down
over time. For contamination that does not mix with
surface water and floats on the surface, such as that
encountered during an oil spill, contamination can be
removed by skimming it from the surface using a
"boom."