The alluvium forms valley flats, floodplains, and, in the Kentucky River
and Elkhorn Creek Valleys, terraces. Flats are dissected by short, steep-sided
gullies near tributaries.
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.
Ashlock Formation/Calloway Creek Limestone (Oaf)
These rocks form gently to moderately rolling uplands away from major
streams, becoming more highly dissected where shale content increases.
Small sinkholes, minor underground drainage, and broad, flat valleys
occur where limestone predominates.
These rocks yield 100 to 500 gallons per 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 gallons per day. These
thick beds also yield water to some large springs.
Garrard Siltstone (Okc)
The Garrard forms prominent ledges along hillsides.
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) and Kope Formation (Okc)
These rocks form 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.
These rocks yield 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 ridgetops. They do yield 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 the weathered bedrock.
Upper Part of Lexington Limestone (Ol) (Strodes Creek, Millersburg,
Tanglewood Limestone, Devils Hollow, Stamping Ground, Sulfur Well, Brannon
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.
The upper Lexington yields 100 to 500 gallons per day to wells in valley
bottoms and along streams in uplands. It yields as much as 300 gallons
per minute in some places where thick limestone beds occur at or below
stream level along large streams. It yields water to springs in the
Tanglewood Limestone and Brannon Member. 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
Lower part of Lexington Limestone (Ol) (Grier, Logana, Curdsville
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
uplands, but the resistant limestone beneath hillslopes is evident from
the subdued bench-like or terrace-like appearance of the slopes.
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
The High Bridge forms cliffs and steep slopes along the Kentucky River
and lower parts of tributaries. The Oregon and Camp Nelson crop out
only in the cliffs of the Kentucky River. 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
The High Bridge yields more than 500 gallons per day to drilled wells
in the Kentucky River Valley, more than 500 gallons per day to some
wells in tributary valley bottoms, and yields water to springs along
the walls of the Kentucky River Gorge and tributaries. Wells drilled
through the Tyrone into the Oregon and Camp Nelson limestones produce
very little water, because impermeable bentonite beds in and at the
top of the Tyrone impede recharge of underlying rocks. Water is hard.
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, and high concentrations
of dissolved solids are found in many areas. Average reported yields
range from 10 to 20 gallons per minute, but are as high as 75 gallons
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"