GROUND WATER IN NORTH-CENTRAL TENNESSEE

210 GKOUND WATEK IN NOKTH-CENTBAL TENNESSEE
limestone is also exposed in an area about 3% miles long in the West
Harpeth River Valley between the Columbia and Lewisburg pikes.
Both the Lowville and Lebanon limestones crop out in small areas.in
the south-central part of the county near the heads of the forks of
Rutherford Creek, a branch of the Duck River. No rocks older than
the Lebanon limestone are known to crop out within Williamson
County.
Inasmuch as Williamson County lies on the western flank of the
Nashville dome (pp. 62-63), its strata are generally inclined very
slightly westward. However, they do not constitute a true monocline
but are deformed by secondary open folds of small amplitude.
GROUND-WATER CONDITIONS
In Williamson County, as in other parts of north-central Tennessee,
none of the unweathered rocks are permeable, so that ground water
does not circulate in them except along joints or bedding planes or
through tubular solution channels in the limestone. The number and
size of the water-bearing openings of this sort are not uniform hi all
parts of the same stratum but are related to the geomorphologic his­
tory of the region (pp. 78-82). Hence ground-water conditions are in
large measure the. same throughout any one physiographic district.
On the remnants of the Highland Rim peneplain, in the western
part of the county, water supplies large enough for domestic purposes
are generally obtained from layers of chert debris in the residual
material that overlies the bedrock, as in wells 355 and 387 (pi. 4, also
pp. 215-217), or in the uppermost part of the bedrock itself. So far as
is known the wells on the peneplain remnants are between 30 and 95
feet deep, and all yield adequate supplies for household use. One
well (No. 386) that was drilled on the plateau in search of oil is re­
ported to be 1,060 feet deep and to have passed through water­
bearing beds at 33, 67, and 189 feet below the surface. It is reported
further that the yield from the upper two water-bearing beds was less
than could be removed with a 20-gallon bailer, whereas the yield from
the 189-foot bed was much greater, and that no water-bearing beds
were penetrated between 189 and 1,060 feet below the surface. The
chemical character of the water from the 189-foot bed is unknown,
although in other parts of north-central Tennessee the water associ­
ated with these rocks at such a depth is so highly concentrated that it
is wholly unfit for most uses. Some perennial seepage springs also
issue from the residual material in the heads of the minor drains.
Generally the residual clay and chert have been thoroughly leached,
so that the ground water associated with them is only slightly or mod­
erately concentrated and relatively soft, as is shown by analysis
387 (pp. 116-117).
On the Highland Rim escarpment and other slopes of'the dissected
parts of the plateau practically all water supplies are derived from