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Alluvium (Qa) and Glacial Outwash Sediments (Qa)
Topography
These sediments form floodplains, valley bottoms, and terraces of the
Cumberland, Tennessee, and Mississippi Rivers and tributaries. Valley-train
deposits occur beneath terraces along the Mississippi River.
Hydrology
These sediments yield several hundred gallons a minute to drilled wells
in the alluvium of the Tennessee River Valley. They yield enough water
for a modern domestic supply (more than 500 gallons per day) to nearly
all wells, except in small valleys where the alluvium is 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 most uplands and gently sloping sides
of stream valleys. Thick deposits adjacent to the Mississippi River
thin to a veneer near Kentucky Lake. It forms steep bluffs where thick.
Many badlands or heavily eroded gullies occur in the uplands.
Hydrology
Loess is not an aquifer. It yields 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 measured discharge of 47 gallons per minute. Most
wells yield less than 10 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.
Jackson, Claiborne (Tjc), and Wilcox Formations (Tw)
Topography
These formations lie in uplands and high-level erosional surfaces over
most of the county.
Hydrology
Sand yields enough water for domestic use near the outcrop area 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 crops out along the Clarks River Valley and in adjacent
uplands from the Tennessee state line to Paducah.
Hydrology
The Porters Creek probably will yield a little water from joints and
from sandstone “dikes.” Water is probably hard and high in
iron. The formation is important as a confining layer.
Clayton and McNairy Formations (TKcm)
Topography
These formations create uplands and dissected ridges between Kentucky
Lake and the Clarks River. In southeastern Marshall County, badlands
are formed where McNairy sand crops out.
Hydrology
Yields are sufficient 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 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 parts per million, and dissolved solids from 62 to 275 parts
per million. Iron may be present in objectionable amounts. The best
potential for large yields to wells is in central and southern Marshall
County. The yields increase southward from central Marshall County to
Tennessee. Wells in northern Marshall County have lower yields, but
are adequate for domestic use.
Tuscaloosa Formation (Kt)
Topography
The Tuscaloosa may occur in remnants of 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 the 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, 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 around the periphery of
the embayment; its extent beneath the embayment is not known. 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. Yields vary 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 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.
Warsaw Limestone (Mw)
Topography
The Warsaw underlies dissected uplands and ridges adjacent to the Cumberland
and Tennessee Rivers.
Hydrology
In the Jackson Purchase Region west of Kentucky Lake, all wells in the
bedrock yield enough water for domestic use.
Fort Payne Formation (Mbf)
Topography
The Fort Payne underlies dissected ridges between the Tennessee and
Cumberland Rivers. It is present in fault blocks under the embayment
sediments.
Hydrology
In the Jackson Purchase Region west of Kentucky Lake, all wells in the
bedrock yield enough water for domestic use.
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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