GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
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120 <strong>GROUND</strong> <strong>WATER</strong> <strong>IN</strong> <strong>NORTH</strong>-<strong>CENTRAL</strong> <strong>TENNESSEE</strong><br />
REI^ATTON TO STRATIGRAPHY<br />
As is brought out in the following paragraph, the analyses of repre<br />
sentative ground waters tabulated above do not disclose any out<br />
standing relation between the chemical character of the ground waters<br />
and the stratigraphic horizon of the water-bearing beds. In general<br />
most of the waters fall into one of three classes first, slightly arid<br />
moderately concentrated calcium bicarbonate waters having moder<br />
ate carbonate hardness; second, highly concentrated calcium or<br />
calcium-magnesium sulphate waters with considerable noncarbonate<br />
hardness; third, highly concentrated brines or sodium chloride-sul<br />
phate waters. All members of the geologic column contain waters<br />
that fall into these three classes and have about the same range in<br />
concentration. The waters of the first class are those that circulate<br />
freely through permeable beds and channeled limestone at shallow<br />
or moderate depth and issue from most of the springs and from wells<br />
less than 200 feet deep. Most of them contain from 150 to 400 parts<br />
per million of dissolved mineral matter and from 125 to 325 parts<br />
per million of carbonate hardness. Usually they are/essentially free<br />
from iron and hydrogen sulphide. Hence they are suitable for all<br />
ordinary purposes if softened. The waters of the second and third<br />
classes, which can not be sharply discriminated, occur at greater<br />
depth in permeable beds or at moderate depth in beds of low per<br />
meability. The brines are probably connate or modified connate<br />
waters originating in an epoch of marine sedimentation. The cal<br />
cium sulphate waters owe their high concentration to slow percola<br />
tion or stagnation in strata containing soluble sulphates or possibly<br />
to reaction on limestone of sulphuric acid formed by oxidation- and<br />
hydrolysis of pyrite. These highly concentrated waters issue from<br />
a few springs and from some wells less than 50 feet deep, though<br />
generally they occur in strata more than 100 feet below the surface.<br />
So far as is known, the water in all strata more than 350 feet below<br />
the surface is highly concentrated and is not entirely satisfactory for<br />
most ordinary uses, especially for domestic consumption.<br />
The general character of the ground water associated with different<br />
stratigraphic units in north-central Tennessee is shown by the ac<br />
companying table of average, minimum, and maximum quantities of<br />
mineral constituents, which is based only on the 101 representative<br />
analyses. The accuracy of the relations suggested by this table is<br />
limited by several factors. It is impossible to tell the precise strati-<br />
graphic horizon of the water-bearing bed of some wells, because<br />
complete records of the strata penetrated are not available. This<br />
table shows the absolute minimum and maximum of each constituent<br />
"without reference to any other constituent. All the minima are not<br />
necessarily derived from the same analysis; neither are all the max<br />
ima necessarily derived from a single analysis. Some wells penetrate