There is evidence of widespread contamination of water
resources in many areas of our country. The Environmental
Protection Agency's National
Water Quality Inventory of 1994 has identified agriculture,
urban runoff/storm water, and municipal point sources as the
largest pollutant sources for rivers, lakes, and
estuaries(5). Contaminants from these sources include
pesticides, metals, nitrates, solvents, and other wastes. More
than 200 chemical constituents have been documented in
groundwater alone (2). The health effects of long term exposure
to many of the contaminants entering our water supply are
unknown. But it should be noted that not all contamination events
pose a threat to our health. The
National Water Quality Inventory 1994 Report to Congress
states that 40% of flowing river and stream miles can be used for
drinking water after conventional water treatment, and 37% of
lake and reservoir acres meet the designated use criteria for
drinking water.
Pollutant concentrations become diluted when they enter water
sources and are further reduced by biological degradation,
filtration, and adsorption to soil. Some chemicals, such as the
man-made chlorinated hydrocarbons, are very stable in the
environment. Some of these compounds accumulate in living
organisms and are not readily metabolized and excreted.
The impacts of contamination events to lakes and reservoirs
are more severe and persistent than streams and rivers because
there is not a natural flushing process as is characterized by
the flow in streams and rivers.Contamination is even more
persistent in groundwater due to lack of biological degradation.
The most biologically active bacteria live within the soil above
groundwater supplies.
In contrast to surface water there is not a lot of mixing when
a contaminant enters groundwater. When a contaminant first enters
the soil it will travel down vertically with gravity until
contact with groundwater. At this point it will begin to flow
primarily in a horizontal direction (3). The contaminant will
then spread out three-dimensionally like smoke from a chimney and
is called a plume. Groundwater does not exhibit turbulent flows
as found in surface water. The flow is defined by gravity,
pressure and friction. It is much more constant than surface
water. An aquifer can flow at a fraction of an inch per day up to
a few feet per day (2).
The most effective way of reducing contaminants in drinking
water is by controlling it at the source. Preventative measures
such as modification of tilling methods and run-off control in
agriculture, the use of lined catchment ponds for treatment of
wastes, and double lined underground storage tanks can greatly
reduce contamination of drinking water sources. As consumers we
can educate ourselves about the source of our tap water,
contamination, and the options for treatment.
References
1. A Citizen's Handbook on Groundwater
Protection. 1984. Wendy Gordon, Natural Resources Defense
Council, Inc. New York, NY. pp.1
2. EPA Handbook. Ground Water Volume 1: Ground
Water and Contamination. September 1990. USEPA, Office of
Research and Development, Washington DC.
3. EPA. Index of Watershed Indicators. Rev.
September 8, 1997. URL:
http://www.epa.gov/surf/iwi
No comments:
Post a Comment