Ashlock Formation and Calloway Creek Limestone (Oaf)
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.
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)
The Garrard forms prominent ledges along hillsides.
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)
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.
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,
Devils Hollow, Sulfur Well, Brannon and Perryville Members) (Ol)
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.
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
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.
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
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.
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)
The Knox has no surface exposure in Kentucky, but underlies the entire
state at varying depths.
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
The U.S. Geological Survey's Hydrologic
Atlas Series, published cooperatively with the Kentucky Geological
Survey, provides hydrologic information for the entire state.
to "Groundwater Resources in Kentucky"