GROUND WATER IN NORTH-CENTRAL TENNESSEE

GROUND WATER IN NORTH-CENTRAL TENNESSEE
generally encounter concentrated salt water in the Ordovician rocks,
from which brine was formerly pumped and evaporated to obtain
salt for household use. In some wells the salty water contains a
small amount of oil. In the hilly area southeast of Cotton town
drilled wells encounter but little water, and that is inferior in quality
and is associated with natural gas; hence it is in some places difficult
or impossible to develop adequate household water supplies. Unfor­
tunately, strata bearing fresh water are not likely to occur below
those from which the salty and oil-bearing waters are obtained.
In the rolling country of the Nashville Basin, which constitutes the
southernmost part of the county, ground-water conditions differ so
greatly from place to place that it is impossible to predict the depth
and water-yielding capacity of the permeable zones. In the inter-
stream tracts many domestic water supplies are derived from drilled
wells, most of which are between 25 and 50 feet deep. However, not
all such wells obtain adequate supplies, and some are dry. Neither is
this shallow ground water satisfactory in chemical character at all
places, for it is generally high in noncarbonate hardness and may con­
tain an appreciable quantity of hydrogen sulphide. Analyses 131 and
132 (pp. 112-113) are representative. In a few places the water is ex­
tremely concentrated in sulphate, chloride, and hydrogen sulphide, like
that from Castalian Spring (analysis 137), and is quite unfit for all or­
dinary uses. Seemingly the earthy Middle Ordovician limestones that
occupy much of this area have never been extensively channeled, and
such permeable rocks as exist have been largely drained by the
tributaries of the Cumberland River. Several relatively deep wells
in Gallatin, such as Nos. 134, 135, and 136, reach a water-bearing
zone from 124 to about 200 feet below the surface, at approximately
the same altitude as the Cumberland River. The tested capacity of
these wells, which is reported as 80 to 150 gallons a minute, is much
greater than the capacity of any other known wells within the county.
Furthermore, the water is only moderately concentrated, has only a
very little noncarbonate hardness, and is suitable for all ordinary
purposes if softened. Within the meander belt of the Cumberland
River along the southern edge of the county the limestone is extremely
cavernous and contains many sink holes into which the water is
reported to rise from below when the river is in flood, the water level
fluctuating with the stage of the river. Hence there are in this area
systems of solution channels adjusted to the level of the river in its
present erosion cycle, and it is possible that the deep wells at Gallatin
tap a channeled zone that is tributary to one of these systems. If
such is the case, it may be that ground water of satisfactory chemical
character can be obtained at many other places south of the Highland
Rim escarpment by drilling to or slightly below the level of the
Cumberland River. However, no other wells as deep as those at