Groundwater Availability
 

Ashlock Formation and Calloway Creek Limestone (Oaf)
Topography
These formations form gently to moderately rolling uplands away from major streams--more highly-dissected where shale content increases, and small sinkholes, minor underground drainage, and broad, flat valleys where limestone predominates.

Hydrology
These formations yield 100 to 500 gal/day to drilled wells in broad valleys and along streams in uplands, but almost no water to drilled wells on hillsides or ridgetops. They do yield water to small springs. Water is hard and in valley bottoms may contain salt or hydrogen sulfide. Where thick limestone beds with little shale occur below stream level in valley bottoms or on uplands, they may have undergone solutional enlargement of fractures and bedding-plane openings. Wells drilled into these limestone beds may produce more than 500 gal/day. These thick beds also yield water to some large springs.

Garrard Siltstone (Okc)
Topography
The Garrard forms prominent ledges along hillsides.

Hydrology
The well-cemented siltstone and fine-grained sandstone and siltstone do not provide many openings for water and yields almost no water to wells. Water is hard.

Clays Ferry Formation and Kope Formation (Okc)
Topography
These rocks form rugged topography of narrow, steep-sided ridges with narrow V-shaped valleys
of dendritic drainage. Steep slopes erode easily and are covered with thin limestone slabs in many places. In the lower part of the formation topography becomes more gently to moderately rolling uplands, with small sinkholes and some underground drainage where limestone predominates.

Hydrology
These rocks yield 100 gal/day to drilled wells in valley bottoms, and up to 500 gal/day in lower, limestone-rich section along streams. The rocks yield almost no water to drilled wells on hillsides or ridgetops. They do yield water to small springs Water is hard in valley bottoms and may contain salt or hydrogen sulfide. Shale has small, poorly connected openings, and groundwater circulation is slow; as a result, little water is available to wells and springs. On ridgetops the shale prevents downward percolation of water, and creates small semiperched water bodies in lower part of soil and upper part of weathered bedrock.

Upper Part of Lexington Limestone (Tanglewood Limestone, Millersburg, Strodes Creek,
Devils Hollow, Sulfur Well, Brannon and Perryville Members) (Ol)

Topography
The Upper Lexington forms broad flat valleys in uplands. Where dominantly limestone, it has well-developed subsurface drainage and many sinkholes, with gently sloping hillsides adjacent to small streams in uplands. The resistant shale and soft bentonite-rich beds form a subdued benchlike topography along hillsides and streams.

Hydrology
The Upper Lexington yields more than 500 gal/day to wells in valley bottoms and along streams in uplands. It yields 100 to 500 gal/day to many perennial springs and more than 100 gal/min to a few large springs. The amount of water available in rocks of the Lexington Limestone is dependent on the amount of shale. Generally, throughout the whole Lexington Limestone section , the more shale found within the zone of interest, the less water will be found. The Upper Lexington yields water to springs from resistant Brannon Member. Water is hard and may contain salt or hydrogen sulfide in some places. Water from wells near fault zones may contain objectionable amounts of salt.

Lower Part of Lexington Limestone (Ol) (Grier, Logana, Curdsville Members)
Topography
The Lower Lexington forms rolling to dissected uplands. Sinkholes are very common, large ones occurring in the Grier Limestone. Natural outcrops are rare in the rolling upland, but the limestone beneath hill slopes is evident from the benchlike or terrace-like appearance of the slopes. Limestone crops out in discontinuous bands in the valley sides in the dissected part near the Kentucky River.

Hydrology
The Lower Lexington yields 100 to 500 gal/day to wells in most valley bottoms and along streams in uplands, and up to 150 gal/min from thick limestone beds in the Curdsville along large streams. The Lower Lexington also yields water to many small springs. Water is hard and may contain salt in valley bottoms.

High Bridge Group ( Tyrone Limestone, Oregon Formation, Camp Nelson Limestone) (Ohb)
Topography
The High Bridge forms steep slopes and high cliffs along the Kentucky River and lower parts of tributaries. The Camp Nelson forms flat terraces with occasional sinkholes in the bottom of the Kentucky River gorge and steep cliffs along the lower sides. It also extends up the large tributaries, forming flat bottoms and steep walls. The Oregon crops out in a band in the walls of the gorge and up a few large tributaries. The Tyrone crops out in the upper walls of the Kentucky River gorge and extends up the large tributaries nearly to the upland, forming broad, flat valleys with sinkholes and underground drainage.

Hydrology
The High Bridge yields 100 to more than 500 gal/day to drilled wells in valleys of the Kentucky River and large tributaries. Yields have been reported as much as 225 gal/min to wells drilled into the Camp Nelson Limestone adjacent to the Kentucky River, from solution channels and fractures connected with the river. The High Bridge yields water to springs on hillsides and in steep walls along large streams. Water is hard and may contain hydrogen sulfide but generally of good quality. Wells drilled into the High Bridge through overlying rocks produce almost no water because bentonite beds in the Tyrone prevent recharge to underlying rocks, except where the bentonite has been breached or removed by erosion.

Knox Group (Okx)
Topography
The Knox has no surface exposure in Kentucky, but underlies the entire state at varying depths.

Hydrology
In the Inner Bluegrass Region of Kentucky, fresh water has been found in the upper 100 to 250 feet of this largely untested dolomite rich aquifer. Wells often exceed 750 feet in total depth with high concentrations of dissolved solids found in many areas. Average reported yields range in the 10 to 20 gal/min range but as high as 75 gal/min.

You can find out more about the Knox aquifer.

The U.S. Geological Survey's Hydrologic Atlas Series, published cooperatively with the Kentucky Geological Survey, provides hydrologic information for the entire state.

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