GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
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142 <strong>GROUND</strong> <strong>WATER</strong> <strong>IN</strong> <strong>NORTH</strong>-<strong>CENTRAL</strong> <strong>TENNESSEE</strong><br />
is very uncertain. In general, however, wells must be drilled some<br />
what below the level of the near-by perennial drains in order to assure<br />
an adequate water supply. On the other hand, the likelihood of<br />
entering a water-bearing channeled zone seems to become materially<br />
less as a well is drilled much more than 75 feet below the perennial<br />
surface streams. In these comparatively rugged sections of the<br />
county springs are a relatively important source of water, especially<br />
the perennial tubular springs, which drain large volumes of channeled<br />
limestone. (See pp. 92-95.) The discharge of such a spring may vary<br />
widely during the year, however, so that its reliability can be deter<br />
mined only by periodic measurements of discharge over a period of<br />
several years.<br />
In the southern and eastern parts of the county several relatively<br />
deep wells have encountered a water-bearing stratum just above the<br />
Chattanooga shale, possibly in the lower part of the Fort Payne for<br />
mation. Among the wells that have tapped this stratum are Nos. 194,<br />
206, 216, 220, and 226 (pp. 144-146), of which Nos. 206 and 220 over<br />
flow at the surface by artesian pressure. However, the static level of<br />
the water confined in this bed is about 700 to 725 feet above sea level,<br />
so that the area within which flowing wells may be expected is not<br />
extensive and is limited to parts of the lower reaches of Turnbulland<br />
Jones Creeks. The specific capacity of wells that tap this stratum is<br />
relatively small, that of well 226, for example, being about 0.4 gallon<br />
a minute for each foot of drawdown. This water-bearing stratum<br />
seems to be discontinuous, for it was not found in wells 193, 205, and<br />
222, and a permeable bed is not known farther east where the strata<br />
at this horizon crop out in Cheatham County. Hence, the reliability<br />
of this stratum as a source of water throughout the region is limited.<br />
The chemical analysis of a sample from well 220 (pp. 114-115) shows<br />
that the water from this stratum, although rather hard, is not highly<br />
concentrated and is essentially free from sodium chloride (common salt).<br />
A few wells have been drilled into the beds that underlie the Chat<br />
tanooga shale in Dickson County, such as Nos. 194, 205, 207, 209,<br />
and 222. Of these, well 222 reaches the lowest stratigraphic horizon,<br />
about 1,260 feet below the Chattanooga shale. All such wells find<br />
these beds to be dry or to contain relatively small amounts of highly<br />
concentrated brine, as in well 194. Hence, deep drilling for water is<br />
not likely to be successful in this area.<br />
The chemical character of the ground waters of Dickson County is<br />
shown by the representative analyses tabulated on pages 112-115. It<br />
is noteworthy that the waters associated with the Fort Payne forma<br />
tion have a wide range in chemical composition, even in adjacent wells<br />
that reach approximately the same stratigraphic horizon, such as Nos.<br />
190 and 191. Of these two wells, No. 190 yields a moderately hard<br />
calcium bicarbonate water containing 222 parts per million of dissolved