|Exploration for Groundwater|
Groundwater is precipitation that has drained through the soil into the gravels and bedrock fractures and faults below. It is found nearly everywhere, but useable, reliable quantities can only be tapped in sand, gravel, and rock formations that have sufficient void space to hold and conduct water. These formations are known as aquifers. Most groundwater used for domestic supply comes from relatively shallow wells (less than 150 feet in depth) in fractured bedrock or unconsolidated materials. The bedrock may be shale, sandstone, siltstone, limestone, or coal. Water can be stored in all these rocks, but rapid movement of water is primarily controlled by secondary fractures--joints or faults that penetrate the rock near the land surface (Wyrick and Borchers, 1981; Kipp and Dinger, 1991).
Joints and faults in the earth's crust may extend for tens of feet up to several miles in length. The more lengthy of these features, called linear terrain features, fracture traces, or lineaments, can be seen on different types of aerial photographs and satellite imagery. These features may collect, store, and transport large amountts of groundwater that can provide sufficient water to communities and industry.
Little effort has been made in the past to determine the groundwater resource potential as it relates to high-yield wells. Recent efforts in the upper Kentucky River Basin, in which satellite imagery was used to locate wells, led to three out of four resulting wells producing more water than 90 percent of all the recorded wells in the area, and having enough water to supply from 50 to 250 homes per well.
Exploiting geologic features such as fracture traces and lineaments is a common technique used for the exploration of subsurface fluids, including groundwater (Siddiqui and Parizek, 1971; Mabee and others, 1994) and petroleum (Driscoll, 1986). Fracture traces are linear expressions on the earth's surface that are less than 1 mile in length; those greater than a mile are termed lineaments. Linear features that are not readily apparent on the ground can often be distinguished at high altitudes. Currently, private vendors as well as foreign agencies have made high-resolution satellite photos and radar images available. These data can be used in detailed surficial analysis for linear features that can be related to high-production groundwater zones.