GROUND WATER IN NORTH-CENTRAL TENNESSEE

98 GROUND WATER IN NORTH-CENTRAL TENNESSEE
permanent hardness is rather high and renders the water objection­
able as a soap consumer and scale former. (See pp. 103-106.)
Analysis 220 (pp. 114-115) is typical. Again, the static level of the
ground water and the shape of its pressure-indicating surface are not
known exactly. Also, the artesian head may be due in part to the
presence of gas. Consequently the areas of flowing wells can not be
bounded definitely, although it is known that they are limited to the
bottoms of branches of Turnbull and Jones Creeks in the vicinity of
White Bluff. Obviously the artesian condition is local, for the
horizon of the water-bearing bed seems to be represented by imper­
meable material in the outcrops to the north, east, and south.
(See pi. 4.) To the west, the Highland Rim plateau rises far above
the static level of the ground water, and therefore flowing wells are
not to be expected. Artesian conditions also exist locally in a
stratum at the same stratigraphic horizon in the vicinity of a minor
structural dome in northeastern Sumner County. Well 120 (pp. 204-
205) is the only one in this district known to overflow at the sur­
face by artesian pressure. The water contains so much dissolved
mineral matter and hydrogen sulphide (see analysis 120, pp. 112-
113) that it is wholly unfit for all ordinary uses. The artesian head
is small and is doubtless due in part to the hydrogen sulphide gas in
the water.
Well 328 (pi. 4 and pp. 230-231), in northeastern Wilson County,
finds water confined in the Lebanon (?) limestone under so much head
that it rises to the surface in the well but does not overflow.
The water-bearing bed tapped by this well may be part of a zone of
channeling that seems to cut across several limestone formations and
yields water copiously to nonartesian wells at Lebanon, about 9
miles southwest. The possible extent and water-yielding capacity of
this zone are discussed on pages 222-227.
Artesian conditions exist locally at several points in north-central
Tennessee where small solution openings occur at shallow depth in
inclined thin-bedded limestone between shaly retaining beds. The
artesian head and yield at these places are usually very small. Wells
131 and 198-A (pp. 204, 144) typify this condition, which does not
depend upon regional structure but may occur in shaly limestone at
any place where its inclination is slightly more than that of the
topographic surface. Artesian conditions also exist in channeled lime­
stone above points at which the solution channels are obstructed by
clay or other debris, as represented by wells 275 and 365 (pp. 135, 215).
Under these conditions the static level of the ground water may fluc­
tuate according to the season, and the wells may overflow at the
surface only when the water table is in its highest position.