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Alluvium (Qa)
Topography
The alluvium forms floodplains and terraces along tributaries. It is
too thin in tributary valleys to have distinctive topography.
Hydrology
The alluvium yields little water from fine-grained material.
Bull Fork Formation (Ob)
Topography
The Bull Fork forms gently to moderately rolling uplands where limestone
predominates; it is more dissected where shale predominates.
Hydrology
The Bull Fork yields 100 to 500 gallons per day to wells in valleys or on broad
ridges, but almost no water to drilled wells on narrow ridges or hilltops.
It yields water to dug wells and to small springs. Water is hard and
of good quality.
Grant Lake Limestone/Fairview Formation (Oaf)
Topography
These rocks form gently to moderately rolling uplands. The uplands are
moderately dissected where shale content increases. Ledges of thick
limestone beds occur on steep hillsides and bluffs along streams. Streams
in uplands produce broad, flat valleys where thick limestone beds are
present; the valleys may have small sinkholes with minor underground
drainage. Low hills on uplands also may be capped by thick limestone
beds. The lower part forms broad, flat ridges between steep-sided valleys
cut into the underlying shale of the Kope Formation.
Hydrology
These rocks yield 100 to 500 gallons per day to drilled wells in valley
bottoms and along streams on uplands, and more than 500 gallons per
day from thick limestone beds in broad valley bottoms. They yield almost
no water to wells on hillsides or hilltops, but may yield some water
to dug wells on ridgetops. They also yield water to small springs. They
yield little water from the sandy zone near the base of the formation
in Grant County. Small perennial springs occur in the lower Grant Lake
Limestone. Water is hard, and in valley bottoms may contain salt or
hydrogen sulfide. The relatively impermeable shale prevents circulation
of large quantities of groundwater in joints and bedding-plane openings
of underlying limestone. As a result, the limestone beds have few solutionally
enlarged openings, and little water is available to wells and springs.
Near the base of the Grant Lake is 25 feet or more of limestone with
small amounts of shale (Bellevue Limestone Member), however. Where this
limestone occurs at and below stream level in valley bottoms or along
streams on the uplands, fractures and bedding-plane openings have been
enlarged by solution; many small springs flow from outcrops, and some
drilled wells along streams yield more than 500 gallons per day.
Kope Formation (Okc)
Topography
The Kope forms rugged, much-dissected topography of long, narrow, steep-sided
ridges and narrow, winding, V-shaped valleys with dendritic drainage
patterns. Steep slopes are littered with thin limestone slabs that remain
as shale erodes and washes away. Contrast with less-rugged upland surfaces
of adjacent areas is marked, except near major streams, where change
is masked by dissection.
Hydrology
The Kope yields 100 to 500 gallons per day to drilled wells in valley
bottoms along large streams, but almost no water to drilled wells on
hillsides or ridgetops. It yields water to small springs and seeps.
It yields little water from the well-cemented sandy zone near the top
of the formation in Grant County. Water is hard in valley bottoms and
may contain salt or hydrogen sulfide. Shale units have small, poorly
connected openings that allow passage of only small quantities of water,
restricting yields to wells and springs and preventing recharge to underlying
rocks. The few thick limestone beds may yield water to small springs.
On ridgetops, shale impedes downward percolation of water and supports
water in the lower part of the soil and in the weathered-rock zone just
beneath the soil. High up on the sides of many ridges is a zone of seeps
and small springs; where the Grant Lake caps the ridges, the zone is
generally near or at the contact with the Kope Formation. Drilled wells
on these ridges obtain a little water at the contact between soil and
bedrock, but rarely at greater depths; if water is found at depth, it
is mainly in small quantities and of poor quality. Dug wells, with large
wall areas, are better suited for obtaining water from these bodies
of water; however, many go dry in late summer and fall.
Clays Ferry Formation and its Point Pleasant Tongue (Okc)
Topography
The Clays Ferry forms broad, flat valley bottoms along large streams
between steep, narrow ridges. Limestone has undergone solution and in
some areas is characterized by small sinkholes and subsurface drainage.
Smaller streams develop long, narrow, winding, V-shaped valleys similar
to the those of the Kope Formation.
Hydrology
These rocks yield more than 500 gallons per day to wells drilled in
the valley bottom, small amounts of water to wells on hillsides and
hilltops, and water to small springs. Water is hard or very hard and
may contain salt or hydrogen sulfide, particularly in wells in valley
bottoms; both, especially hydrogen sulfide, may be found in wells on
hillsides. Beneath broad interstream areas, much solutional enlargement
of fractures and bedding-plane openings has taken place in the soluble
zones beneath tributary streams, and many drilled wells produce 100
to 500 gallons per day. Some wide, flat areas have small sinkholes and
some underground drainage.
Lexington Limestone (Tanglewood Limestone, Grier, Logana Members)
(Ol)
Topography
The Lexington forms flat valley bottoms.
Hydrology
The Lexington yields more than 500 gallons per day to wells in valley bottoms
and as much as 150 gallons per minute in places. Water is hard and may contain
salt or hydrogen sulfide in some places.
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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