Alluvium forms valley flats and floodplains. Flats are dissected
by short, steep-sided gullies near tributaries.
The alluvium is too thin and fine-grained 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, and are more highly dissected where shale content increases.
Small sinkholes, minor underground drainage, and broad, flat valleys
occur where limestone predominates.
These formations yield 100 to 500 gallons per day to drilled wells
in broad valleys and along streams in uplands, almost no water to drilled
wells on hillsides or ridgetops, and some 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 has prominent ledges in steep slopes and bluffs along
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
and almost no water to springs. The well-cemented siltstone and fine-grained
sandstone do not provide many openings for water. Water is hard.
Clays Ferry Formation (Okc) and Kope Formation (Okope)
These formations form a 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 drrainage 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 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, Sulphur Well,
The upper Lexington forms broad flat valleys in uplands; well-developed
subsurface drainage and many sinkholes; and 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 100 to 500 gallons per day to wells in
valley bottoms and along streams in uplands, and 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 of salt.
Lower Part of Lexington Limestone (Ol) (Grier, Logana, Curdsville
The lower Lexington is characterized by rolling to dissected uplands.
Sinkholes are very common; the large ones occur in the Grier Limestone.
Underground drainage is well devloped. Natural outcrops are rare in
the rolling upland, but the resistant limestone beneath hillslopes is
evident from the subdued benchlike or terrace-like appearance of the
The limestones yield more than 500 gallons per day to wells in valley
bottoms and along streams in uplands, and up to 150 gallons per minute
from thick limestone beds in the Curdsville along large streams. They
yield water to many small and large springs. The amount of water available
in rocks of the Lexington Limestone depends 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.
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"