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Clays Ferry Formation and Kope Formation (Okc)
Topography
Rugged topography consists 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
Yields are 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; dug wells on ridgetops may yield some water. The formations
yield water to small springs and seeps. Water is hard, and in valley
bottoms may contain salt or hydrogen sulfide. Shale has small, poorly
connected openings, and groundwater circulation is slow. On ridgetops
the shale impedes downward percolation of water. Dug wells, having large
wall areas, are the best option for obtaining this water. On broad ridges
capped by the Grant Lake or Calloway Creek formations, the underlying
Clays Ferry creates a semiperched water body, and dug wells into it
produce some water; however, wells often go dry in late summer and fall.
Garrard Siltstone (Okc)
Topography
The Garrard Siltstone consists of prominent ledges along hillsides.
Hydrology
Yields are 100 to 500 gallons per day to drilled wells in valley bottoms,
but almost no water to wells on hillsides or ridgetops; little water
is yielded to springs. 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.
Upper Part of the Lexington Limestone (Tanglewood Limestone, Millersburg,
Strodes Creek, Devils Hollow, Sulfur Well, Brannon, and Perryville Members)
(Ol)
Topography
Topography is broad flat valleys in uplands. Where the Lexington is
dominantly limestone, there is well-developed subsurface drainage and
many sinkholes; gently sloping hillsides are adjacent to small streams
in the upland areas. The resistant shale and soft bentonite-rich beds
form a subdued bench-like topography along hillsides and streams.
Hydrology
Yields are 100 to 500 gallons per day to wells in valley bottoms and
along streams in uplandds; yields are as much as 300 gallons per minute
in some places where thick limestone beds occur at or below stream level
along large streams. Yields are 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, 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 the Lexington Limestone (Grier, Logana, and Curdsville
Members) (Ol)
Topography
In this rolling to dissected upland, sinkholes are very common; the
large ones occur in the Grier Limestone. Underground drainage is well
developed. Natural outcrops are rare in the rolling upland, 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
Yields are 100 to 500 gallons per day or more to wells in most valley
bottoms and along streams in uplands; yields are up to 150 gallons per
minute from thick limestone beds in the Curdsville along large streams.
Water is yielded to many small and large springs. 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 occurs as cliffs and steep slopes along the Kentucky
River and lower parts of its 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 underground drainage.
Hydrology
Yields are more than 500 gallons per day to drilled wells in the Kentucky
River Valley; some wells in tributary valley bottoms yield more than
500 gallons per day. The High Bridge 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, except where the bentonite has
been breached or removed by erosion. Water is hard.
Knox Group (Okx)
Topography
There is no surface exposure of the Knox in Kentucky, but it underlies
the entire state at varying depths.
Hydrology
In the Inner Bluegrass Region, 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 in many areas. Average reported yields are in the 10 to 20 gallons
per minute range, but 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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