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Alluvium (Qa) / Glacial Deposits (Qg)
Topography
These deposits form valley flats, terraces, and floodplains in the rather
narrow Ohio River Valley, where terraces are long, narrow, and discontinuous.
The deposits are thin in tributary streams but may form floodplains
and small terraces along broad valleys.
Hydrology
These deposits yield moderate to large quantities of water to drilled
wells in the Ohio River Valley according to thickness and texture. Ohio
River alluvium commonly yields 200 gallons per minute, and as much as
800 gallons per minute from gravel-packed wells. The alluvium is too
thin and fine-grained in tributary valleys to yield large quantities
of water. Water is hard and may contain salt or hydrogen sulfide.
Breathitt Group (Pikeville Formation) (Pbl)
Topography
The Breathitt forms ridgetops in the far eastern parts of the county.
The topography is rugged, sandstones form cliffs or steep slopes on
hillsides, and shales form moderate or gentle slopes on hills. Tops
of hills and ridges commonly are capped by sandstone.
Hydrology
The Breathitt yields very little to wells on hillsides and hilltops.
Near-vertical joints and openings along bedding planes yield most of
the water to wells. Waters are highly variable in chemical character.
Slade Formation (Mn)
Topography
Limestone beds in the Slade form steep hillsides and prominent bluffs
in sides of ridges and knobs that are capped by Pennsylvanian rocks.
Massive limestones form cliffs and solution features such as sinkholes,
caves, and hanging valleys.
Hydrology
The Slade yields more than 500 gallons per day to over half of the wells drilled
in valley bottoms, and to many wells drilled on hills. It yields little
water where overlain by Pennsylvanian rocks. It may yield more than
50 gallons per minute to a few wells penetrating large solution cavities in limestone,
the most common aquifer. Sandstone and shale yield water from fractures
to a few wells. Springs are common, particularly at the head of streams,
with some from solution cavities near stream level flow as much as 100
gallons per minute. Springs have large winter and small summer flows. Water is
hard.
Borden Formation (MDbb)
Topography
Shale in the Borden forms dissected slopes, massive siltstone forms
cliffs.
Hydrology
The Borden yields 100 to 500 gallons per day to wells in valley bottoms, and
may yield more than 500 gallons per day to drilled wells in broad valley bottoms
from fractured sandy beds near streams. It yields almost no water to
wells on hills, but small amounts of water to springs and seeps. Water
from wells drilled below stream level may contain objectionable amounts
of salt and sulfate. Water from dug wells and small springs is generally
soft and has a low dissolved-solids content. These rather soft and sandy
rocks are well suited to dug wells, many of which yield more than 500
gallons per day. In valley bottoms the water table is at a shallow depth, and
most drilled wells are less than 50 feet deep. Water of poor quality
is found at shallow depth in many places. Most wells that penetrate
the underlying Ohio shale yield water of poor quality.
Sunbury Shale (MDbb)
Topography
The shale forms steep walls and bluffs of the Ohio River and tributary
valleys.
Hydrology
The shale yields 100 to 500 gallons per day to drilled wells in valley bottoms
or on low hillsides. It yields some water to almost any dug well, and
small amounts of water to springs and seeps. Water quality ranges from
good to poor; salt, sulfate, hydrogen sulfide, and iron are the main
objectionable constituents. Acid water with high sulfate content is
found in places. Shale has small, poorly connected openings, and ground-water
circulation is slow; however, the shale is commonly fractured to a depth
of at least 40 feet, and fractures form the main reservoir for water
in this formation.
Berea Sandstone (MDbb)
Topography
The sandstone forms steep walls and bluffs along the Ohio River and
tributaries.
Hydrology
The sandstone yields small amounts of water to springs. It may yield
100 to 500 gallons per day to wells where it occurs at and below stream level.
Water is soft.
Bedford Shale (MDbb)
Topography
The Bedford forms steep walls and bluffs of the Ohio River and tributary
valleys.
Hydrology
The Bedford yields little water to wells.
New Albany Shale (MDnb)
Topography
The shale forms steep hillsides and broad, flat valley bottoms.
Hydrology
The New Albany yields 100 to 500 gallons per day to drilled wells in valley
bottoms or on low hillsides. It yields some water to almost any dug
well, and small amounts of water to springs and seeps. Water quality
ranges from good to poor; salt, sulfate, hydrogen sulfide, and iron
are the main objectionable constituents. Acid water with high sulfate
content is found in places. Shale has small, poorly connected openings,
and ground-water circulation is slow; however , the shale is commonly
fractured to a depth of at least 40 feet, and fractures form the main
reservoir for water in this formation.
Boyle Dolomite (MDnb) / Bisher Limestone (Sb)
Topography
Prominent ledges along hillsides and lower edges of valleys.
Hydrology
Yields little water to wells; yields water to many small perennial springs.
Water is hard.
Crab Orchard Formation and Brassfield Dolomite (Scb)
Topography
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
These formations yield 100 to 500 gallons per day to wells in broad valley bottoms,
but almost no water to wells on hills. They do yield water to small
springs and seeps. Water is hard and locally contains magnesium and
calcium sulfate dissolved from epsom salt and selenite (gypsum) in the
shale. Dolomite beds yield hard water to small springs.
Drakes Formation (Od) / Bull Fork Formation (Ob)
Topography
The Drakes and Bull Fork form gently to moderately rolling uplands except
along large streams where there is considerable dissection, with slopes
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
These formations yield 100 to more than 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. These rocks do yield water
to small springs. Water is hard and in valley bottoms may contain salt
or hydrogen sulfide. Shale limits amount of water that has access to
thick limestone beds, and therefore restricts number of openings in
these beds enlarged by solution. As a result, the limestone beds yield
little water. In locations where ground water has ready access to thick
limestone beds along streams, wells and springs have larger yields.
Grant Lake Limestone/Fairview Formation (Oaf)
Topography
These formations create gently to moderately rolling upland except along
major streams, where there is considerable dissection that leaves steep
slopes. Thick limestone beds stand out as ledges on steep hillsides
and bluffs along streams; where present on uplands, they underlie broad,
flat valleys that may have small sinkholes and some underground drainage.
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. Yields are 100 to 500 gallons per day
to wells drilled into thick limestone beds along streams in uplands.
Thick limestone beds yield water to small springs along valley bottoms
and hillsides. Water is hard, and in valley bottoms may contain salt
or hydrogen sulfide.
The U.S. Geological Survey's Hydrologic Atlas Series, published cooperatively
with the
Kentucky Geological Survey, provides hydrologic information for the
entire state. Atlases for the
county are HA-17,
HA-73, HA-94.
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