Unconsolidated formations are composed of sand and gravel, cobblestones or loose earth or soil material. The amount of groundwater in an unconsolidated formation varies depending on how closely packed the solid materials are and how finely grained they are. Sand, gravel and cobblestone formations are generally high yield aquifers, whereas finer grained earth materials may have low yields. Groundwater may come to the surface naturally as a spring or be drawn to the surface from a well. A spring occurs where the water table meets the land surface as illustrated in Figure 2.
Most people are more familiar with surface water than groundwater.
Surface water bodies such as lakes, streams and oceans can be seen all around but not groundwater bodies. Some important differences between groundwater and surface water bodies are worth noting. Groundwater usually 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 groundwater must overcome more friction or resistance to move through small spaces between rocks and soil underground.