GROUND WATER IN NORTH-CENTRAL TENNESSEE

QUALITY OF GROUND WATER 107
Temains in suspension in the water, gives the water an intense color,
and stains utensils. In the partly oxidized condition a concentrated
hydrogen sulphide water may corrode tanks, pipes, and other metallic
objects. Hydrogen sulphide may be removed from a water by aera­
tion, as in the treatment for the removal of iron, the products of oxi­
dation being finely divided sulphur and sulphate.
Many of the ground waters of north-central Tennessee, particularly
those that issue from the Chattanooga shale and from shaly facies of
certain limestones, contain small quantities of hydrogen sulphide.
Relatively little of the water, however, contains more than 5 parts per
million the smallest amount that can be determined quantitatively.
Those of the representative samples that contain determinable
quantities of hydrogen sulphide are for the most part highly concen­
trated waters in which the amount of sulphate is several times the
amount of bicarbonate and in which the magnesium: calcium ratio is
relatively large. On the other hand, some of the moderately con­
centrated bicarbonate waters contain appreciable amounts of hydro­
gen sulphide. The greatest concentration of hydrogen sulphide in
any of the representative samples is 379 parts per million. (See
analysis 120, pp. 112-113.)
Color. Ground waters are generally colorless, whereas surface
waters are likely to be noticeably colored even when quite free from
suspended matter. The organic matter that imparts this color is of
itself harmless, but decolorizing is one of the primary functions of all
plants for the purification of water for a public supply. Consumers
are generally more concerned over the slight color that may be per­
ceptible in water than over the unseen disease-bearing bacteria that
may be present in dangerous abundance.
The water that issues from some of the tubular springs and wells in
north-central Tennessee has a perceptible bluish opalescence, the color
probably being derived from decaying vegetation and other organic
matter with which the water was in contact before passing under­
ground into the limestone solution channels. Generally, however,
the color is not so intense that it is considered objectionable.
Suspended matter. Ground water that issues from porous rocks is
generally free from suspended matter, although an iron-bearing water
in contact with air may become turbid by formation of a reddish-brown
suspended precipitate of iron hydroxide. Sulphur waters may become
turbid by separation of sulphur through oxidation of the hydrogen
sulphide by the air or, if iron bearing, by separation of black iron
sulphide. Water of each of these classes is common in north-central
Tennessee, and the characteristic precipitates give rise to the local
designations "red sulphur water," "white sulphur water," and "black
sulphur water." ' '>