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Alluvium (Qa)
Topography
Forms narrow floodplains and underlies terraces. At least one well-developed
terrace is present along the principal streams of the region.
Hydrology
Where sandy material is present and saturated thickness great enough,
alluvium would yield more than 500 gallons per day to screened drilled
wells. Water is soft or moderately hard; it may contain large amounts
of iron at depth.
Breathitt Group (Pbu, Pbm, Pbl) (Princess Formation, Four Corners
Formation, Hyden Formation, 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.
Hydrology
The Breathitt yields more than 500 gallons per day to most wells in
valley bottoms and almost half the wells on hillsides, and smaller quantities
of water to wells on hilltops. Sandstone yields water to most wells.
Shale also yields 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.
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
Thick, resistant sandstone in the Grundy forms an extensive upland in
Morgan County. The upland is highly dissected and is characterized by
steep-sided ridges and cliffs 100 to 200 feet high. Waterfalls and rock
bridges, such as Natural Bridge and Sky Bridge, are common. Some cliff-forming
sandstone paleochannels have been cut through the Paragon Formation
into limestone units of Late Mississippian age.
Hydrology
Generally, the Grundy yields more than 500 gallons per day to most of
the wells drilled in valley bottoms. It yields more than 500 gallons
per day to about half of the wells on hillsides and more than 500 gallons
per day to almost three-quarters of the wells on hilltops. It also yields
water to small springs. 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.
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.
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, and limestone forms ledges on shale slopes. 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.
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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