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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 beneath
terraces along 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. It yields enough water for a modern
domestic supply (more than 500 gallons per day) to nearly all wells. It yields
practically no water to wells in small valleys where it is thin and
fine-grained. Water ranges in hardness from 12 to 664 ppm and in dissolved
solids from 53 to 1,220 ppm. 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 in 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 ppm and in dissolved solids from 43
to 782 ppm. Iron content is generally low.
Claiborne (Tjc) & 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 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 ppm, and dissolved solids
from 28 to 431 ppm. Iron may be present in objectionable amounts.
Porters Creek Clay (Tp)
Topography
The Porters Creek clay crops out along Clarks River valley and in adjacent
uplands from 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. Formation is important as a confining layer.
Clayton and McNairy Formations (TKcm)
Topography
These formations outcrop in uplands and dissected ridges between Kentucky
Lake and Clarks River. West of Paducah, they is 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 formation is 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 ppm, and dissolved solids from 62 to 275 ppm.
Iron may be present in objectionable amounts.
Tuscaloosa Formation (Kt)
Topography
The Tuscaloosa may occur in remnants of a channel eroded into 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, owing to clayey matrix and poor sorting.
Tripolitic clay is present locally which tend 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 ppm, and dissolved solids,
50 and 76 ppm. 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 towards 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
content of dissolved solids 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
ppm, and dissolved solids from 39 to 273 ppm.
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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