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Borden Formation (MDbb), (Mbf)
Topography
The Borden forms the main part of the Mississippian escarpment, ridges,
and knobs. Shale forms dissected slopes, massive siltstone forms cliffs,
and limestone forms ledges on shale slopes.
Hydrology
The Borden yields 100 to 500 gallons per day to wells in valley bottoms.
It may yield more than 500 gallons per day to drilled wells in broad
valley bottoms from fractured sandy rocks near streams, but almost no
water to wells on hills. Water from wells drilled below stream level
may contain salt, sulfate, or iron less than 100 feet below the level
of the principal valley bottoms. Water from dug wells and small springs
is soft and has a low dissolved solids content. Water from shale is
soft; from the siltstone, hard; and from the limestone, very hard. Because
much of this formation is soft and silty, it has been well suited to
the construction of dug wells in the past.
New Albany Shale (MDnb)
Topography
The New Albany forms broad, flat valleys and flat upland surfaces, and
steep, dissected hillsides and bluffs along streams.
Hydrology
The New Albany yields 100 to 500 gallons per day to drilled wells in
valley bottoms and on uplands, usually at depths of less than 50 feet;
water from greater depths is highly mineralized. It yields water to
small springs. Water may be soft or highly mineralized. Salt, hydrogen
sulfide, and iron are the usual objectionable constituents.
Crab Orchard Formation and Brassfield Dolomite (Scb)
Topography
Shale forms steep, dissected hillsides and broad, flat valley bottoms;
it erodes readily below more-resistant overlying limestone, forming
notches and recesses. Dolomite beds form discontinuous ledges along
hillsides.
Hydrology
Shale yields almost no water to wells or springs, but may yield small
amounts of water to wells in valley bottoms. Water is highly mineralized.
Dolomite beds yield hard water to small springs.
Drakes Formation (Od)
Topography
The Drakes forms dissected upland areas; slopes are moderately steep
where underlain by shale, and moderately undulating to gently rolling
where underlain by limestone. Steep and cliffy slopes occur along large
streams, littered with limestone slabs left as shale beds weather and
wash away.
Hydrology
The Drakes yields 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. It does yield water to small springs.
Water is hard and in valley bottoms may contain salt or hydrogen sulfide.
Shale limits the amount of water that has access to thick limestone
beds, and therefore restricts the number of openings in these beds enlarged
by solution. As a result, the limestone beds yield little water.
Ashlock Formation and Calloway Creek Limestone (Oaf)
Topography
These rocks form gently to moderately rolling uplands away from major
streams. They are more highly dissected where shale content increases,
and have small sinkholes, minor underground drainage, and broad, flat
valleys where limestone predominates.
Hydrology
These formations 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)
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 (Okc)
Topography
The Clays Ferry forms 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 yields 100 gallons per day to drilled wells in valley
bottoms, but almost no water to drilled wells on hillsides or ridgetops.
It does 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 the weathered bedrock.
Upper Part of the Lexington Limestone (Ol) (Strodes Creek, Millersburg,
Tanglewood Limestone, Devils Hollow, Stamping Ground, Sulfur Well, Brannon
Members)
Topography
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 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. These rocks
yield 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 the Lexington Limestone (Ol) (Grier, Logana, Curdsville
Members)
Topography
The lower Lexington forms rolling to dissected uplands. Sinkholes are
very common; the large ones occur 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. It 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
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,
and yields as much as 30 gallons per minute to drilled wells along the
shores of Harrington Lake. Yields of as muc 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 generally is 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, 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
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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