tems can be grouped into three categories, depending on the degree of consolidation of the rocks and deposits that compose the aquifers. Rocks of Precambrian, Paleozoic, and early Mesozoic ages generally are consolidated; rocks of Cretaceous and Tertiary ages generally are semi consolidated; and deposits of Quaternary age generally are unconsolidated. (Ground Water Atlas of the United States)Most people are more familiar with surface water than ground water. Surface water bodies such as lakes, streams and oceans can be seen all around, but not ground water bodies. One important difference between ground water and surface water bodies is that ground water moves much slower than surface water. Water in a stream may move several feet per minute, but water in an aquifer may move only several feet per month. This is because ground water must overcome more friction, or resistance, to move through small spaces between rocks and soil underground. The exchange of water between surface water bodies and aquifers is important. Rivers usually start as small streams and get larger as they flow downstream. The water they gain is often ground water. Such a stream is called a gaining stream. It is also possible for streams to lose water to the ground at some points. In these cases, aquifers are replenished or recharged by water from the losing stream. A stream that flows near the surface of an aquifer will lose water to the aquifer if the water surface in the stream is higher than the water table of the aquifer. A stream will gain water if the water surface of the stream is lower than the water table in the adjacent land. “The water in transit through ground water systems may also be viewed as water in storage.” (Speidel, Ruedisili, 1988)Ground water is an integral part of the water cycle. The cycle starts with precipitation falling on the surface. Runoff from precipitation goes directly into lakes and streams. “Some o...
