f the precipitation return to the atmosphere by evapotranspiration (evaporation plus transpiration by plants), but much of it either flows overland into streams as direct runoff or enters streams as base flow (discharge from one or more aquifers).” (Ground Water Atlas of the United States) The remaining water, called recharge water, drains down through the soil to the saturated zone, where water fills all the spaces between soil particles and rocks. “Upon percolating downward below the water table, soil waters become ground waters.” (Berner, Berner, 1987) The top of the saturated zone is the water table, which is usually the level where water stands in a well, if the local geology is not complicated. Water continues to move within the saturated zone from areas where the water table is higher toward areas where the water table is lower. When ground water comes to a lake, stream or ocean it discharges from the ground and becomes surface water. This water then evaporates into the atmosphere, condenses, and becomes precipitation, thus completing the water cycle.Ground water is often taken for granted. In many locations pollution is beginning to change the quality of the water. Contaminants which threaten people’s health have been found in several important ground water reservoirs. Some of the contaminants may be so expensive to remove that they make the water virtually unusable for years. “Dissolved solids in ground water primarily result from chemical interaction between the water and the rocks or unconsolidated deposits through which the water moves.” (Ground Water Atlas of the United States)Ground water becomes polluted when undesirable substances become dissolved in water at the lands surface and are carried down, or leached, to the aquifer with the percolating water. To determine whether a particular substance will pollute a particular aquifer, the properties of the unwanted substance and...
