ues and combustion products from automobiles along roadways. All of these are considered harmful if ingested in sufficiently high amounts of drinking water, and in some instance may be carried into surface water bodies by ground water.Each human activity has a particular impact on ground water. Some agricultural activities add nitrate, nitrogen and pesticides to the ground water. Residential areas add nitrate, nitrogen, and pesticides from landscaping activities. Those with septic systems usually add nitrate, nitrogen, bacteria, viruses, and synthetic organics used in household cleaning products and septic tank cleaners. Industrial activities tend to add organic chemicals and metals, through in widely varying amounts. Gasoline storage area (including service stations) may have leaks and spills of petroleum products. Roadways contribute petroleum pollutants leaked from vehicles and metals from exhaust fumes. The most concentrated impact comes from older sanitary landfills, whose leach ate may contain many different chemicals at relatively high concentrations. Since ground water moves slowly, many years may pass before a pollutant released on the land surface above the aquifer is detected in water taken from the aquifer some distance away. Unfortunately, this means that contamination is often widespread before being detected. Even if release of the contaminant is stopped, it may take many years for an aquifer to purify itself naturally. Although water can be treated to remove contaminants, this can be very costly. The best protection against water pollution is prevention.Ground water becomes depleted in areas where more water is being drawn out of an aquifer and consumptively used than is entering or recharging the aquifer. This usually causes a lowering of the water table, making the ground water more difficult and expensive to obtain. “Deserts have been expanding rapidly in China because of drought and sinking under...
