GROUND WATER IN NORTH-CENTRAL TENNESSEE

COUNTT
trated calcium bicarbonate water in beds from 30 to about 75 feet
below the surface and those which find more highly mineralized
waters containing sulphate, with or without hydrogen sulphide,
generally in beds between 100 and 135 feet below the surface. How­
ever, some wells more than 100 feet deep yield calcium bicarbonate
water of satisfactory quality, and some others less than 5Q feet deep
yield water that is much too highly concentrated to be fit for any
ordinary use. Analyses 365, 370, 376, and 390 (pp. 116-117) are
typical. Highly mineralized water that is unfit for most uses is found
in a relatively large proportion of the wells drilled in the Lowville and
Lebanon limestones on the upper reaches of the Harpeth and West
Harpeth Rivers. (See pi. 4.) Furthermore, adjacent wells may differ
greatly in depth to water-bearing beds and in the chemical character
of the water, and not all wells are successful, None have a reported
tested capacity exceeding 20 gallons a minute, and the ultimate capac­
ity of several is less than 1 gallon a minute. The water-bearing
properties of the deeply buried rocks are not known but may be in­
ferred to be similar to those disclosed by well 403, which is in Maury
County about 5 miles south of Allisona. This well on August 17, 1927,
was 870 feet deep. Beds ca>rrying potable water were penetrated at
25 and 60 feet below the surface, but the underlying strata were devoid
of water to a depth of 855 feet, where a very small amount of concen­
trated brine was found at the contact (unconformable?) between two
beds of limestone. Hence deep drilling for water in the east half of
the county is not likely to be successful. Furthermore, no rocks of
large water-yielding capacity are known to occur here at any depth.
It is reported that well 365 discharges by artesian pressure during
the winter from a solution crevice or unconformity 160 feet below
the surface. Presumably the artesian condition is local and due to
trapping of ground water above an obstruction in a solution channel
or in a discontinuous cavernous zone associated with an
unconformity.
QROTJND-WATER SUPPLIES
FranMin. The city of Franklin derives its municipal water supply front* 36
springs along the eastern base of Duck Rive? Bidge, froin 9 to 13 miles west and
southwest of the city (Nos. 3f>6, 379 to 385). The estimated minimum annual
discharge of these springs, as reported to the city officials by B. H. JOyee, con­
sulting engineer, of Nashville, is shown by the fallowing table.