Alluvium (Qa), Glacial Sediments (Qg)
These sediments form floodplains and terraces of the Ohio River Valley
and tributaries. Highest terraces are about 100 feet above normal pool
level of the Ohio River. The sediments are too thin in tributary valleys
to have distinctive topography.
The sediments yield moderate to large quantities of water to drilled
wells in the Ohio River Valley, depending on thickness and texture of
the valley fill and type of well. They yield 200 to 500 gallons per
minute to ordinary tubular wells and as much as 1,000 gallons per minute
to gravel-packed wells. The sediments yield little water from fine-grained
material. Water is hard, and near the valley walls of the Ohio may have
a high iron content. Wells that penetrate the alluvium and enter bedrock
obtain little additional water, and this water may contain objectionable
amounts of salt or hydrogen sulfide.
Bull Fork Formation (Ob)
The Bull Fork forms gently to moderately rolling uplands where limestone
predominates, and is more dissected where shale predominates.
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 does yield water to dug wells and to small springs. Water is hard
and of good quality.
Grant Lake Limestone/Fairview Formation (Oaf)
These rocks form gently to moderately rolling uplands away from the
Ohio River. Where shale content increases, they form moderately dissected
uplands and steep dissected slopes along large streams. These rocks
also form ledges of thick limestone beds on steep hillsides and bluffs
along streams. Streams in uplands produce broad, flat valleys where
thick limestone beds are present; they 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.
These formations yield 100 to 500 gallons per day to drilled wells in
valley bottoms and along streams on uplands. They yield more than 500
gallons per day from thick limestone beds in broad valley bottoms, but
almost no water to wells on hillsides or hilltops. They may yield some
water to dug wells on ridgetops, and do yield water to small springs.
Small perennial springs occur in limestone 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 the 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, however, is 25 feet or more of limestone with
small amounts of shale (Bellevue limestone member). 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)
The Kope forms rugged, much dissected topography of long, narrow, steep-sided
ridges and narrow, winding, V-shaped valleys with dendritic drainage
pattern. 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.
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 does yield water to small springs and seeps.
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.
The U.S. Geological Survey's Hydrologic Atlas Series, published cooperatively
with the Kentucky Geological Survey, provides hydrologic information
for the entire state. Atlases covering Gallatin County areHA-23,
to "Groundwater Resources in Kentucky"