Groundwater Availability
 

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

Hydrology
The Garrard yields 100 to 500 gallons per day to drilled wells in valley bottoms, but almost no water to wells on hillsides or ridgetops. It yields little water to springs. 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 (Okc)
Topography
The Clays Ferry forms rugged topography of narrow, steep-sided ridges with narrow, V-shaped valleys of dendritic drainage. Shales on 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
The Clays Ferry yields 100 to 500 gallons per day to drilled wells in large valley bottoms along streams, but almost no water to drilled wells on hillsides or ridge tops. It yields water to small springs and seeps. 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 the lower part of the soil and the upper part of weathered bedrock.

Upper Part of Lexington Limestone (Ol) (Strodes Creek, Millersburg, Tanglewood Limestone, Devils Hollow, Stamping Ground, Sulfur Well, Brannon Members)
Topography
The upper Lexington forms broad flat valleys in uplands, with well-developed subsurface drainage and many sinkholes. It forms gently sloping hillsides adjacent to small streams in uplands. The resistant shale and soft bentonite-rich beds form a subdued bench-like topography along hillsides and streams.

Hydrology
The upper Lexington yields 100 to 500 gallons per day or more to wells in valley bottoms and along streams in uplands, and as much as 300 gallons per minute in some places where thick limestone beds occur at or below stream level along large streams. Springs occur in the Tanglewood Limestone and Brannon Member. Yields to many perennial springs are 100 to 500 gallons per day and more than 100 gallons per minute to a few large springs. The amount of water available in rocks of the Lexington Limestone is dependent on the amount of shale. Generally, the upper part of the Lexington Limestone contains more shale and yields less water in contrast to the lower part, which is mostly limestone in many places. 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, the large ones occurring in the Grier Limestone. Underground drainage is well developed. Natural outcrops are rare in the rolling upland, but the resistant limestone beneath hillslopes is evident from the subdued bench-like 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 more than 500 gallons per day to wells in valley bottoms and along streams in uplands. It yields up to 150 gallons per minute from thick limestone beds in the Curdsville along large streams, and yields water to many small and large springs. The amount of water available in rocks of the Lexington Limestone is dependent on the amount of shale. Generally, the upper part of the Lexington Limestone contains more shale and yields less water in contrast to the lower part, which is mostly limestone in many places. 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.

High Bridge Group (Tyrone Limestone, Oregon Formation, Camp Nelson Limestone) (Ohb)
Topography
The High Bridge forms steep slopes and high cliffs along the Kentucky and Dix Rivers 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 Group yields 100 to more than 500 gallons per day to drilled wells in valleys of the Dix and Kentucky Rivers and large tributaries, and yields as much as 30 gallons per minute to drilled wells along the shores of Herrington Lake. Yields have been reported as much as 225 gallons per minute to wells drilled into the Camp Nelson Limestone adjacent to the Kentucky River, from solution channels and fractures connected with the river. The limestones yield water to springs on hillsides and in steep walls along large streams. Water is hard and may contain hydrogen sulfide, but is 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 and have high concentrations of dissolved solids in many areas. Average reported yields range from 10 to 20 gallons per minute, but are as high as 75 gallons per minute.

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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