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Alluvium (Qa)
Topography
The alluvium forms terraces and narrow floodplains of varying width
along streams.
Hydrology
The alluvium yields almost no water to drilled wells, but small quantities
to dug wells.
Breathitt Group (Pbl) (Pikeville Formation)
Topography
The topography of the Breathitt is rugged; sandstone forms narrow valleys
and cliffs or steep slopes on hillsides and shale forms wide valleys
and moderate or gentle slopes on hills. 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 the
wells in valley bottoms and very little to wells on hillsides and hilltops.
The most common aquifers are sandstone and shale, but coal supplies
water to a few wells. Near-vertical joints and openings along bedding
planes yield most of the water to wells. Waters are highly variable
in chemical character. It may contain salty water at depths less than
100 feet below the principal valley bottoms.
Grundy Formation (contains Lee-type sandstone of the former Lee
Formation) (Plc)
Topography
In the Grundy, some cliff-forming sandstone paleochannels have cut through
the Paragon Formation into limestone units of Late Mississippian age.
Hydrology
The Grundy yields more than 500 gallons per day to most wells drilled
in broad valley bottoms and smaller quantities of water to wells on
hillsides and hilltops. It yields 100 to 500 gallons per day on some
wide ridges, where water may be semiperched in sandstone on top of fireclay
that impedes downward percolation of water. Sandstone is the principal
aquifer, but shale yields water to some wells and coal to a few. Vertical
joints and openings along bedding planes, best developed in sandstones,
supply most of the water to wells. Intergranular openings yield water
to joints, and probably directly to some wells. Perched and semiperched
water tables are common. Waters are soft to moderately hard, and sometimes
contain noticeable amounts of iron, but generally have a low dissolved
solids content.
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 limestone in the Slade forms 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. The Slade 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; some springs 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. The Borden forms broad, flat valleys.
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 and sulfate 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. 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; steep,
dissected hillsides and bluffs form along streams.
Hydrology
The shale yields 100 to 500 gallons per day to drilled wells in valley
bottoms and on uplands, but little water to drilled wells on hillsides
and hilltops. It does yield water to small springs and seeps. Water
may be soft or highly mineralized. Salt, hydrogen sulfide, and iron
are the usual objectionable constituents. Acid water with high sulfate
content is found in places. Shale has small, poorly connected openings,
and groundwater 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)
Topography
The Boyle forms prominent ledges along hillsides and the lower edges
of valleys.
Hydrology
The Boyle yields little water to wells, but does yield water to many
small perennial springs. Water is hard.
Crab Orchard Formation and Brassfield Dolomite (Scb)
Topography
The 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
These rocks yield 100 to 500 gallons per day to wells in broad valley
bottoms, but almost no water to wells on hills; it yields 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, Odb)
Topography
The Drakes forms 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. 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 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. In
locations where groundwater has ready access to thick limestone beds
along streams, wells and springs have larger yields.
Grant Lake Limestone/Fairview Formation/Calloway Creek Limestone
(Oaf)
Topography
These formations lie in gently to moderately rolling uplands, 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 rocks 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 yield 100 to 500 gallons per day
to wells drilled into thick limestone beds along streams in uplands,
and thick limestone beds capping hills on 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.
Garrard Siltstone (Okc)
Topography
The Garrard forms prominent ledges in steep slopes and bluffs along
large streams.
Hydrology
The Garrard yields 100 to 500 gallons per day to drilled wells in valley bottoms,
but almost no water to wells on hillsides or ridgetops and almost no
water to springs. The well-cemented siltstone and fine-grained sandstone
do not provide many openings for water. Water is hard.
Clays Ferry Formation (Okc)
Topography
The Clays Ferry forms narrow, steep-sided ridges with narrow valleys
between.
Hydrology
The Clays Ferry yields 100 to 500 gallons per day to wells drilled in
valley bottoms. It also yields water to small springs. Water is hard,
and may contain salt or hydrogen sulfide.
Lexington Limestone (Ol)
Topography
The Lexington lies in valley bottoms.
Hydrology
The Lexington yields more than 500 gallons per day to wells in stream valleys
and as much as 150 gallons per minute in places. Water is hard and 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.
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