GROUND WATER IN NORTH-CENTRAL TENNESSEE

SPKINGS
bearing channel very close to the spring outlet. Hence every tubular
spring is liable to permanent or intermittent pollution, so that the
water of each one that is used for municipal supply should be sterilized
thoroughly at all times, as a precaution against the transmission of
disease. The liability to pollution is quite independent of the tur­
bidity of the water discharged by the spring. Many of the tubular
springs yield clear water at all times, even though the discharge is
large and the source is known to be in a body of turbid surface water.
The system of solution channels that feeds such a spring has so large
a storage capacity and so low a gradient that the water flows slowly
and all its suspended matter is deposited. Tubular springs whose
flow responds quickly to local rainfall become extremely turbid at
high stages and may remain turbid for several days after the peak of
the storm discharge has passed. The system of solution channels
that feeds such a spring has little storage capacity, so that the sus-
'pended matter does not settle from the water. Naturally every
possible gradation exists between these two extremes. In order to
condition it for municipal and for many industrial uses, the turbid
spring water must be passed through a sedimentation basin, the capac­
ity of which should be based upon trustworthy information as to the
maximum possible turbidity of the spring water.
The water of the tubular springs is not highly concentrated in dis­
solved mineral matter and is generally of the calcium-magnesium
bicarbonate type. This is brought out by the accompanying diagram
(fig. 5) and by the corresponding analyses, which are summarized in
the following table and are tabulated on pages 110-119.
Average, minimum, and maximum quantities of mineral constituents in water from
tubular springs in north-central Tennessee °
[Parts per million]
Silica (SiOa)-..
Iron (Fe). . ___ . .. ...
Calcium (Ca)... ______ .
Sodium (Na) _________
Carbonate (COs) ______
Aver­
age
11 .6
49 as
2.0
.7
Mini­
mum
2.2
.02
8.6
4.0
1.0
.4
Maxi­
mum
21 4.6
93
146.0
1.2
Chloride (Cl) .
Nitrate (NO 3) _ . _
Aver­
age
155
10.9
2.0
1.9
161
139
Mini­
mum
31 3.7
.9
.2
50
31
Maxi­
mum
308
31 5.5
8.0
300
272
" Based upon analyses of water from 20 tubular springs which issue from Ordovician, Silurian, and Mis-
sissippian limestones. Samples taken at low or medium stage of spring flow.
The spring water is only slightly or moderately hard and contains
very little dissolved iron, so that it is suitable for most ordinary
purposes without softening. For some uses, however, softening may
be desirable. The water from the springs that vary in discharge
probably varies somewhat in hardness and in its content of dissolved
solids, so that the amount of reagents necessary to soften the water
will probably vary also.