GROUND WATER IN NORTH-CENTRAL TENNESSEE

RUTHERFORD COUNTY 183
tated as the black iron sulphide; it is known locally as "black
sulphur" water. Comparatively few wells derive water from the
Murfreesboro limestone in other parts of the county, so that it is
uncertain whether or not the water from this formation is everywhere
of similar chemical character. Unfortunately, in many places water
of satisfactory quality can not be obtained above or below the beds
that yield the sodium bicarbonate-sulphate waters.
MUNICIPAL QROUKD-WATER SUPPLIES
Murfreesboro. The municipal water supply of the county seat, Murfreesboro,
is derived from a tubular spring (No. 439, pi. 4 and p. 187), which issues from
several openings along a cavernous zone in the Murfreesboro limestone near the
southeast corner of the city. The cavernous zone follows a set of persistent
joints striking N. 55° W. From the downstream orifice, which is protected by
concrete cut-off walls sunk to the bedrock, the water is pumped to sedimentation
tanks, chlorinated, and then pumped to a 700,000-gallon steel tank at the south
edge of the town. Distribution is effected by gravity. The average daily con­
sumption is reported to be about 700,000 gallons; the maximum about 1,000,000
gallons. Usually the discharge of the spring is adequate for the total consumption,
although in the summer of 1925, a year of extreme drought, it reached a minimum
of 300,000 gallons a day. Furthermore, the discharge increases greatly and the
water becomes turbid from 6 to 12 hours after heavy rains in the vicinity of the
spring and along the belt of hills to the southeast. The chemical character
of the water is shown by the analysis tabulated on page 118 and graphically by
Figure 6.
During periods of drought the municipal supply is pumped from a gang of six
wells (No. 440) drilled in the cavernous limestone near the spring orifice, the
ground-water level being so depressed by pumping that the spring ceases to flow.
Of these wells one is 147 feet deep, and the other five from 200 to 211 feet. Each
is equipped with an air-lift pump. During the drought of 1925 two of these wells
(then 100 feet deep) were pumped continuously for six weeks, and the yield of
each declined gradually from 300 to about 250 gallons a minute, with a drawdown
of about 45 feet. Hence their specific capacity is moderate about 6 gallons a
minute for each foot of drawdown. In 1927, which was also a dry year, the yield
of the six wells was found to be more than the consumption, although the total
capacity of the gang was not determined.