GROUND WATER IN NORTH-CENTRAL TENNESSEE

QUALITY OF GROUND WATER 101
of dissolved solids it ranges from 8.6 to 163 parts per million but is
generally between 50 and 100 parts per million. Calcium is also rela­
tively abundant in the highly concentrated brines and other modified
connate waters that occur at depth in the marine sedimentary rocks
of this region. The greatest concentration of calcium in any of the
representative waters is 625 parts per million. (See analysis 260,
pp. 114-115.)
Calcium is the principal soap-consuming and scale-forming con­
stituent of the ground waters of north-central Tennessee. Except for
the difficulties arising from these properties, whoever, calcium has
little or no effect upon the suitability of the water for ordinary uses.
Magnesium. Magnesium (Mg) is usually taken into solution as the
bicarbonate by the reaction of waters containing carbon dioxide or
some natural acid with magnesium carbonate, which is present in
most of the rocks of north-central Tennessee, especially in the more
magnesian limestones. In most natural waters magnesium is much
less abundant than calcium, although in five of the samples analyzed
Nos 316, 326, 352, 427, and 433 magnesium exceeds calcium in
reacting value. In the moderately concentrated ground waters from
north-central Tennessee magnesium is commonly from one-third to
one-fifteenth as abundant as calcium. It ranges from about 2.5 to
about 50 parts per million but in more than half the samples does not
exceed 10 parts per million. Like calcium, magnesium occurs in large
quantity in the modified connate waters of this region. The greatest
concentration of magnesium in any of the representative waters is
533 parts per million (No. 352, pp. 116-117).
Magnesium is the only element other than calcium that causes
any appreciable amount of hardness in natural waters. If a water
contains several hundred parts per million of magnesium as the sul­
phate or chloride, like some of the more concentrated waters of north-
central Tennessee, it may be undesirable for drinking.
Sodium and potassium. Sodium (Na) and potassium (K) are dis­
solved in small quantities from practically all rocks but where present
in considerable amounts are derived chiefly from salts or concentrated
brines associated with rocks of marine origin. Potassium is generally
much less abundant than sodium. These elements constitute only
a small portion of the dissolved mineral matter in most of the ground
waters of north-central Tennessee and generally range from 1 to
about 50 parts per million. They amount to less than 5 parts per
million in two-thirds of the samples. In the highly concentrated
ground waters, however, sodium and potassium may be the most
abundant metallic elements and may sum up to several thousand parts
per million, as in analyses 260 and 352 (pp. 114-117).