GROUND WATER IN NORTH-CENTRAL TENNESSEE

102 GROUND WATER IN NORTH-CENTRAL TENNESSEE
Moderate quantities of sodium and potassium have little effect on
the suitability of a water for ordinary household use, inasmuch as
the salts of these elements do not impart hardness to the water. If
these constituents sum up to much more than 100 parts per million,
a water is likely to foam if used in a steam boiler unless it is conditioned
to prevent this reaction. Most of the ground water of north-central
Tennessee will cause little or no trouble in this way. More than
400 parts per million of sodium and potassium in a water make it
practically useless as boiler feed without preliminary conditioning.
Some natural waters contain so large quantities of sodium salts that
they are injurious to vegetation to which they may be applied, the
quantity that will be injurious depending upon the species of vegeta­
tion, the type of soil, and the drainage. The connate ground waters
of north-central Tennessee are generally so concentrated in sodium
and potassium as to be toxic to vegetation and hence can not be used
for watering crops and sprinkling lawns.
Carbonate and bicarbonate. The carbonate (CO3) and bicarbonate
(HCO3) in natural waters are derived by the solution of rock-forming
carbonate minerals largely through the action of carbon dioxide or
natural acids in the waters. Carbonate is not present in appreciable
quantities in most natural waters. All the rocks of north-central
Tennessee contain carbonate minerals in abundance, and the asso­
ciated ground waters are generally rather concentrated in bicarbonate.
Those of the representative samples that are moderately concentrated
contain from 30 to 400 or more parts per million of bicarbonate;
approximately half of them contain between 150 and 250 parts per
million. The bicarbonate as such has little effect on the use of a
water.
Sulphate.' Sulphate (SO4) in ground waters may be derived from
gypsum (calcium sulphate) associated with limestone and other
rocks, from the oxidation products of pyrite (iron disulphide) and
other sulphides, or from concentrated or desiccated brines inclosed
by marine sediments. The ground waters of north-central Tennessee
appear to have acquired sulphate from each of these sources. In
the moderately concentrated waters of this region sulphate is gener­
ally less abundant than bicarbonate, its approximate range being
from 2.5 to 350 parts per million; in two-thirds of them it is less than
25 parts per million. In most of the highly concentrated waters,
however, sulphate is more abundant than bicarbonate and may be
several thousand parts per million, as in analyses 260, 294, 311, 326,
and 390 (pp. 114-117).
The sulphates of sodium or magnesium if present in sufficient
quantity impart a bitter taste to water and may render it otherwise
unfit for domestic use. Several of the more concentrated waters of