Groundwater Availability
 

Alluvium (Qa)
Topography
The alluvium forms narrow floodplains and small terraces along the Kentucky River, Elkhorn Creek, and larger tributaries.

Hydrology
The alluvium yields small to large quantities of water to drilled wells, according to texture and thickness of material. It yields more than 20 gallons per minute from 60 feet of fine-grained material in the Kentucky River Valley, and as much as 20 gallons per minute from 44 feet of similar material in the valley of Elkhorn Creek. It is too thin and fine grained elsewhere to yield large amounts of water. Water is hard.

High-level fluvial deposits (QTf)
Topography
These deposits blanket localized areas of uplands and hilltops having no distinct surface expression.

Hydrology
These deposits yield 100 to 500 gallons per day to wells in thick deposits, but are too thin and scattered to be important as an aquifer otherwise. The formation also yields water to small springs and dug wells. Water is soft.

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 yield almost no water to wells. Water is hard.

Clays Ferry and Kope Formation (Okc)
Topography
This formation creates 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
This formation yields 100 gallons per day to drilled wells in valley bottoms, but almost no water to drilled wells on hillsides or ridgetops. It does yield water to small springs. In the lower, limestone-rich section, drilled wells can yield 100 to 500 gallons per day in valley bottoms along streams. 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 Grounds, Sulfur Well, Brannon Members)
Topography
The upper Lexington underlies broad flat valleys in uplands. Where dominantly limestone, it has a 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 more than 500 gallons per day to wells in valley bottoms and along streams in uplands. It yields 100 to 500 gallons per day to many perennial springs 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, throughout the whole Lexington Limestone section, the more shale found within the zone of interest, the less water will be found. The Lexington yields water to springs from the 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 underlies rolling to dissected uplands. Sinkholes are very common; the larger ones occur in the Grier Limestone. Natural outcrops are rare in the rolling uplands, but the limestone beneath hillslopes is evident from the 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 100 to 500 gallons per day to wells in most 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. It 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 Group lies in 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 yields 100 to more than 500 gallons per day to drilled wells in valley of the Kentucky River and large tributaries. Yields as much as 225 gallons per minute have been reported 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 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 in the 10 to 20 gallons per minute range but can be 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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