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Alluvium (Qa)
Topography
Alluvium forms narrow floodplains and small terraces along the Kentucky
River and larger tributaries.
Hydrology
The alluvium yields 100 to 500 gallons per day to wells in thick deposits
along the Kentucky River; elsewhere, it is too thin and too fine grained
to yield much water. Water is hard.
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 Formation and Kope Formation (Okc)
Topography
The Clays Ferry and Kope 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.
Hydrology
The Clays Ferry and Kope yield 100 gallons per day to drilled wells
in valley bottoms, but almost no water to drilled wells on hillsides
or ridgetops. They do 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 (Tanglewood Limestone, Millersburg,
Strodes Creek, Devils Hollow, Sulfur Well, Brannon, and Perryville Members)
(Ol)
Topography
The upper Lexington forms broad, flat valleys in uplands. Where dominantly
limestone, it has 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 upper 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 (Grier, Logana, and Curdsville
Members) (Ol)
Topography
The lower Lexington forms rolling to dissected uplands. Sinkholes are
very common, the large ones occurring 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, and it 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 forms 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 valleys of the Dix and Kentucky Rivers and large tributaries.
It yields as much as 30 gallons per minute to drilled wells along the
shores of Harrington Lake. Yields of 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, with high concentrations
of dissolved solids found in many areas. Average reported yields range
from 10 to 20 gallons per minute, but have been 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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