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Alluvium (Qa)
Topography
The alluvium forms narrow floodplains.
Hydrology
Where sandy material is present and saturated thickness great enough,
the alluvium may 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 (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.
Hydrology
The Breathitt yields more than 500 gallons per day to almost half of
the wells drilled in valley bottoms, and less to wells on hillsides
and 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. The Breathitt 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.
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 the Upper Mississippian.
Hydrology
The Grundy yields more than 500 gallons per day of water to most wells
on hillsides and valley bottoms, and about half the wells drilled 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.
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. 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; 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, and limestone forms ledges on shale slopes. The Borden also
forms broad, flat valleys.
Hydrology
The Borden yields 100 to 500 gallons per day to wells in valleys, and
may yield more than 500 gallons per day to wells drilled in fractured
sandy rocks near streams in broad valley bottoms. 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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