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Alluvium (Qa)
Topography
Forms narrow floodplains and small terraces along the Kentucky River
and larger tributaries.
Hydrology
Yields 100 to 500 gallons per day to wells in thick deposits along the
Kentucky River; elsewhere, it is too thin and fine-grained to yield
much water. Water is hard.
Breathitt Group (Pikeville Formation) (Pbl)
Topography
The Breathitt Group underlies the valleys and forms 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 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 plains yield
most of the water to wells. Waters are highly variable in chemical character.
Grundy Formation (contains Lee-type sandstone of the former Lee
Formation) (Plc)
Topography
Shaly areas of the Grundy Formation form steep-sided, rounded hills
and ridges. Some cliff-forming sandstone paleochannels have been cut
through the Paragon Formation into limestone units of Late Mississippian
age.
Hydrology
In the eastern part of Estill County, the Grundy yields 100 to 500 gallons
per day to wells in thick deposits, and yields water to small springs.
Sandstone is the principal aquifer, but shale yields water to some wells.
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 (in southeastern corner) (Mpn)
Topography
These limestone beds form steep hillsides and prominent bluffs in sides
of ridges and knobs that are capped by rocks of Pennsylvanian age.
Hydrology
The Slade yields 100 to 500 gallons per day to drilled wells in the few places
where it occurs below stream level, but almost no water to wells on
narrow ridgetops or hillsides. It 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)
Topography
The Borden forms the main part of of the Mississippian escarpment, ridges,
and knobs. Shale forms dissected slopes, massive siltstone forms cliffs,
and limestone forms ledges on shale slopes. It forms broad, flat valleys
in the eastern part of the county.
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, but 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.
Boyle Dolomite (MDnb)
Topography
The Boyle Dolomite forms prominent ledges along hillsides.
Hydrology
The Boyle yields little water to wells, but some water to many small
perennial springs. Water is hard.
New Albany Shale (MDnb)
Topography
The New Albany forms broad, flat valleys and flat upland surfaces. Along
streams it forms steep, dissected hillsides and bluffs.
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.
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
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 provides dissected upland areas, 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.
The 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.
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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