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Alluvium (Qa)
Topography
The alluvium forms valley flats, floodplains, and, in Elkhorn Creek
valleys, terraces. Flats are dissected by short, steep-sided gullies
near tributaries.
Hydrology
The alluvium yields small to large quantities of water to drilled wells,
depending on texture and thickness of material. It yields as much as
20 gallons per minute from 44 feet of similar material in the valley
of Elkhorn Creek. It is too thin and fine grained elsewhere to yield
large amounts of water. Water is hard.
Garrard Siltstone (Okc)
Topography
The Garrard forms prominent ledges along hillsides.
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. It
yields little water to springs. The well-cemented siltstone and fine-grained
sandstone and siltstone do not provide many openings for water and yield
almost no water to wells. Water is hard.
Clays Ferry Formation (Okc) and Kope Formation (Okope)
Topography
These formations have rugged topography of narrow, steep-sided ridges
with narrow V-shaped
valleys of dendritic drainage. Shales on steep slopes erode easily and
are covered with thin
limestone slabs in many places. In the lower part of the formation topography
becomes more
gently to moderately rolling uplands, with small sinkholes and some
underground drainage
where limestone predominates.
Hydrology
These formations yield 100 to 500 gallons per day to drilled wells in
large valley bottoms along streams, but almost no water to drilled wells
on hillsides or ridgetops. They do yield water to small springs and
seeps. Water is hard in valley bottoms and may contain salt or hydrogen
sulfide. Shale has small, poorly connected openings, and groundwater
circulation is slow; as a result, little water is available to wells
and springs. On ridgetops the shale prevents downward percolation of
water, and creates small semiperched water bodies in the lower part
of the soil and the upper part of weathered bedrock.
Upper Part of Lexington Limestone (Ol) (Strodes Creek, Millersburg,
Tanglewood Limestone, Devils Hollow, Stamping Grounds, Sulfur Well,
Brannon Members)
Topography
The upper Lexington occurs in broad flat valleys in uplands. It has
well-developed subsurface
drainage and many sinkholes, with gently sloping hillsides adjacent
to small streams in upland.
The resistant shale and soft bentonite-rich beds form a subdued benchlike
topography along
hillsides and streams.
Hydrology
The upper Lexington yields 100 to 500 gallons per day to wells in valley
bottoms and along streams in uplands, and as much as 300 gallons per
minute in some places where thick limestone beds occur at or below stream
level along large streams. It yields water to springs in the Tanglewood
Limestone and Brannon Member. Generally, the upper part of the Lexington
Limestone contains more shale and yields less water compared to the
lower part, which is mostly limestone in many places. Water is hard
and may contain salt or hydrogen sulfide in some places. Water from
wells near fault zones may contain objectionable amounts of salt.
Lower Part of Lexington Limestone (Ol) (Grier, Logana, Curdsville
Members)
Topography
The lower Lexington occurs in rolling to dissected uplands. Sinkholes
are very common, the
large ones occurring in the Grier Limestone. Underground drainage is
well developed. Natural
outcrops are rare in the rolling uplands, but the resistant limestone
beneath hillslopes are evident
from the subdued benchlike or terrace-like appearance of the slopes.
Hydrology
The lower Lexington yields more than 500 gallons per day to wells in
valley bottoms and along streams in uplands. It yields up to 150 gallons
per minute from thick limestone beds in the Curdsville along large streams,
and yields water to many small and large springs. The amount of water
available in rocks of the Lexington Limestone is dependent on the amount
of shale. Generally, the upper part of the Lexington Limestone contains
more shale and yields less water compared to the lower part, which is
mostly limestone in many places. Water is hard and may contain salt
or hydrogen sulfide in some places. Water from wells near fault zones
may contain objectionable amounts of salt.
High Bridge Group (Ohb) (Tyrone Limestone, Oregon Formation, Camp
Nelson Limestone)
Topography
The High Bridge has no surface exposure in Scott County, but underlies
the entire county.
Hydrology
Wells drilled through the Tyrone into the Oregon and Camp Nelson limestones
produce very
little water, as impermeable bentonite beds in and at the top of the
Tyrone impede recharge of
underlying rocks. Water is hard.
Knox Group (Okx)
Topography
The Knox has no surface exposure in Kentucky, but underlies the entire
state at varying depths.
Hydrology
In the Inner Bluegrass Region of Kentucky, fresh water has been found
in the upper 100 to 250 feet of this largely untested dolomite-rich
aquifer. Wells often exceed 750 feet in total depth and have high concentrations
of dissolved solids in many areas. Average reported yields range in
the 10 to 20 gallon per minute range but are as high as 75 gallons per
minute.
You can find out more about the Knox
aquifer.
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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