Wednesday, April 20, 2011

Ground water pollution

An exhaustive study of urban water supply system in developing countries revealed that at least 60% of the pollution is still dependent on underground sources of drinking water, especially in outer city areas and distant villages. This very important source of water is now polluted from seepage pits; refuse dumps, septic tanks, and barnyard manures. Otherwise important sources of ground water pollution include sewage and soluble salts. In attributes in the rise of cholera, hepatitis, dysentery and other water-borne diseases, to the pollution of ground water especially in the zones where the water table is high. Control of ground water pollution needs accurate information on the distance between aquifer and he ground, the volume of the ground water body and the structure of the underlying stratum, and also the physio-chemical and biological characteristics of the pollutants.
Contamination: In areas utilizing ground water, the water is located in aquifers at various depths. Some aquifers have been shallow and the first to be used. Others are deeper and trapped only when the shallower aquifers become contaminated or depleted. Water drawn up from and aquifer has been used and discarded as either household or industrial waste water. If the waste water is released into lagoons or cesspools, it will slowly percolate back into the aquifer under influence of gravity. In addition, pesticides, fertilizers, and de-icing compounds also tend to enter the water table through percolation. Most of the bacteria as well as the suspended organics and most of the pesticides get filtered out or absorbed by the sediment within approximately 30 feet of the source of input. Soluble substances like dissolved metals and nutrients pass unchanged into the water table. The nutrients are converted from their organic to their inorganic form by bacterial action. Excessive phosphorus, in any form, is not having any apparent deleterious physiological effects. A potential source of contamination has been in the disposal of waste materials by injection wells. This system of liquid waste disposal may cause unforeseen environmental hazards.
Depletion: As an area develops and population increases, the volume of waste water increases, resulting in an increase in the deleterious substances leaching into local aquifers. Then, the water will get contaminated and reach a state where it will be either unsafe or unaesthetic for use. In addition to contaminating the deeper aquifer, this increase in vertical flow will tend to deplete the upper aquifer. This is undesirable because it has been this aquifer which supplies the majority of water to streams, lakes, and rivers. Another consequence of excessive ground water depletion may be subsidence of the land surface to fill the void created by removal of the ground water.


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