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Alluvium and Glacial Outwash Sediments (Qa)
Topography
These sediments form floodplains, valley bottoms, and terraces of the
Tennessee and Ohio Rivers and tributaries. Valley-train deposits occur
beneath terraces along the Ohio River.
Hydrology
These sediments yield several hundred gallons a minute to drilled wells
in the Ohio River Valley and in the valleys of its two main tributaries,
the Cumberland and Tennessee Rivers. They yield enough water for a modern
domestic supply (more than 500 gallons per day) to nearly all wells.
They yield practically no water to wells in small valleys where they
are thin and fine grained. Water ranges in hardness from 12 to 664 parts per million
and in dissolved solids from 53 to 1,220 parts per million. Iron may be present in
objectionable amounts.
Loess
Topography
Loess forms a thin mantle over alluvial deposits and bedrock over much
of the area near the Ohio River.
Hydrology
Loess is not an aquifer. It does yield small amounts of water to a few
wells. When saturated by rainfall, it transmits water to underlying
aquifers.
Terrace Gravel Deposits and Continental Deposits (QTcl)
Topography
These deposits occur on uplands and eroded edges of uplands above 370
feet.
Hydrology
These deposits yield small quantities of water suitable for household
use. One spring had a measured discharge of 47 gallons per minute. Most
wells yield less than 10 gallons per minute. The deposits yield sufficient
water west of Paducah for industrial demand, with maximum yields on
the order of 1,000 gallons per minute. Water-bearing gravel usually
overlies clay or indurated layers. Water ranges in hardness from 8 to
724 parts per million and in dissolved solids from 43 to 782 parts per
million. Iron content is generally low.
Claiborne (Tjc) and Wilcox (Tw) Formations
Topography
These formations provide uplands and high-level erosional surfaces over
most of county.
Hydrology
Sand yields enough water for domestic use near outcrop areas of the
Porters Creek Clay and in areas of perched water. Drilled wells penetrating
the main zone of saturation where beds are thick yield as much as 1,700
gallons per minute. Hardness of water ranges from 7 to 212 parts per
million, and dissolved solids from 28 to 431 parts per million. Iron
may be present in objectionable amounts.
Porters Creek Clay (Tp)
Topography
The Porters Creek Clay crops out along the Clarks River Valley and in
adjacent uplands from the Tennessee state line to Paducah. West of Paducah,
it is truncated and covered by alluvium.
Hydrology
The Porters Creek probably will yield a little water from joints and
from sandstone “dikes.” Water is probably hard and high in
iron. This formation is important as a confining layer.
Clayton and McNairy Formations (TKcm)
Topography
These formations crop out in uplands and dissected ridges between Kentucky
Lake and the Clarks River. West of Paducah, they are truncated and covered
by river alluvium.
Hydrology
These formations yield sufficient water for domestic use near outcrop
areas of Paleozoic bedrock and in areas of perched water. Where the
formation is thick, drilled wells yield as much as 830 gallons per minute.
In areas where the formations are mostly silt and clay, there may not
be sufficient saturated sand to furnish even a domestic supply. Hardness
of water ranges from 13 to 182 parts per million, and dissolved solids
from 62 to 275 parts per million. Iron may be present in objectionable
amounts.
Tuscaloosa Formation (Kt)
Topography
The Tuscaloosa may occur in remnants of a channel eroded into the surface
of the Paleozoic rocks. It underlies dissected ridges adjacent to Kentucky
Lake.
Hydrology
The Tuscaloosa is not significant as an aquifer. Most drilled wells
in the gravel of the Tuscaloosa are adequate for a bailer (more than
100 gallons per day). Yields are low, because of its clayey matrix and
poor sorting. Tripolitic clay is present locally, which tends to clog
well screens, and wells penetrating it are inadequate (less than 100
gallons per day). Hardness of water from two wells sampled was 26 and
57 parts per million, and dissolved solids content was 50 and 76 parts
per million. Yields adjacent to Kentucky Lake may exceed 5 gallons per
minute.
Chert Rubble
Topography
Chert rubble occurs mostly in the subsurface. The surface of the Paleozoic
rocks locally has been reduced to a chert rubble by pre-Late Cretaceous
weathering of the chert-bearing limestone.
Hydrology
Chert rubble probably will yield more than enough water for domestic
use; locally, it may yield sufficient water for small public supplies.
Yields are as large as 100 gallons per minute, varying with the saturated
thickness of the rubble and characteristics of the rubble’s matrix.
Hydrologic properties resemble those of gravel. The water level in the
rubble slopes downward from highs on the limestone surface toward collapse
structures (areas of thick chert rubble formed by solutional collapse
along fracture zones and former drainage channels). The water is soft
and has a low dissolved solids content, but may contain an objectionable
amount of iron, which probably is derived from the iron-rich clay that
commonly fills voids in the rubble.
Limestone, Chert, Shale (Paleozoic Bedrock)
Topography
These rocks occur mostly in the subsurface, below the unconsolidated
or poorly consolidated younger sediments.
Hydrology
These rocks usually yield sufficient water for domestic use, and are
known to yield 120 gallons per minute in some locations. Fresh water is found at
depths exceeding 1,000 feet. Hardness of water ranges from 17 to 238
parts per million, and dissolved solids from 39 to 273 parts per million.
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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