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Alluvium (Qa)
Topography
The 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, the alluvium is too thin and fine-grained
to yield much water. Water is hard.
High-Level Fluvial Deposits (QTf)
Topography
These deposits blanket localized areas of uplands and hilltops having
no distinct surface expression.
Hydrology
These deposits yield 100 to 500 gallons per day to wells in thick deposits;
otherwise, they are too thin and scattered to be important as an aquifer.
They do yield water to small springs and dug wells. Water is soft.
Breathitt Group (Pikeville Formation) (Pbl)
Topography
The Breathitt Group underlies the valleys and forms the hills of the
southeastern corner of the county. Tops of hills and ridges commonly
are capped by sandstone. Shales form wide valleys and moderate or gentle
slopes on hills.
Hydrology
The Breathitt yields more than 500 gallons per day to almost half of
the wells drilled in valley bottoms and more than 100 gallons per day
to about half the wells drilled on hillsides and on ridges. Sandstones
yield water to most wells. Shales also yield water to many wells, and
coal yields water to a few. Near-vertical joints and openings along
bedding planes yield most of the water to wells. Waters are highly variable
in chemical character
Corbin Sandstone Member, Grundy, and Bee Rock Formations (contains
Lee type sandstone of the former Lee Formation) (Plc)
Topography
These rocks form the tops of steep-sided ridges and knobs, steep bluffs,
and cliffs. Some sandstone paleochannels have been cut through shales
of the Paragon Formation into limestone units of Late Mississippian
age.
Hydrology
These rocks yield 100 to 500 gallons per day to drilled wells on broad
ridges, but almost no water to wells on narrow ridges or hilltops. They
do yield water to small springs. Water is soft.
Paragon Formation (Mpk)
Topography
The Paragon is too thin and limited in extent to have distinct surface
expression.
Hydrology
The Paragon yields almost no water. Impermeable shale may hold water
in overlying sandstone and conglomerate.
Slade Formation (in southeastern corner) (Mpn, Mn)
Topography
In the southeastern corner of the county, these limestone beds form
steep hillsides and prominent bluffs in sides of ridges and knobs that
are capped by Pennsylvanian rocks.
Hydrology
The Slade yields 100 to 500 gallons per day to drilled wells in the
few places where it occurs below stream level. It yields almost no water
to wells on narrow ridgetops or hillsides, but does yield water to small
springs on hillsides, particularly at the heads of streams. Springs
have large winter and small summer flows. Water is hard to very hard.
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. It yields 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 uplands. It forms
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. The shale yields water
to small springs. Water may be soft or highly mineralized. Salt, hydrogen
sulfide, and iron are the usual objectionable constituents.
Boyle Dolomite (MDnb)
Topography
The Boyle forms resistant ledges on valley sides between shale slopes
above and below.
Hydrology
The Boyle yields almost no water to drilled wells. It does yield water
to many small perennial springs. Water is hard, but otherwise of good
quality.
Crab Orchard Formation and Brassfield Dolomite (Scb)
Topography
The shale forms steep, dissected hillsides and broad, flat valley bottoms.
The shale erodes readily below more-resistant overlying limestone, forming
notches and recesses. Dolomite beds form discontinuous ledges along
hillsides.
Hydrology
The 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, with slopes that are moderately
steep where underlain by shale, and moderately undulating to gently
rolling where underlain by limestone. The Drakes forms steep and cliffy
slopes 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 upland, 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. The formation is highly dissected where shale content increases,
with 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 and Kope Formation (Okc)
Topography
These formations create the 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
These formations 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,
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. 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 (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.
The lower Lexington 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 uplands,
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.
Yields of as much as 225 gallons per minute have been reported in 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 Group 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 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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