GROUND WATER IN NORTH-CENTRAL TENNESSEE

QUALITY OF GROUND WATER 121
more than one water-bearing bed, so that the sample may not be
quite representative of the principal bed. Other wells may not be
adequately cased, or the casing may have deteriorated, so that water
from the surface or from a shallow water-bearing stratum may be
entering the well. Any particular stratigraphic unit may have con­
siderable lateral and vertical variations in the mineral character of its
component beds, so that the ground waters associated with it at
different depths and places may differ considerably in chemical
character. Wells that draw upon intensely channeled limestone may
yield water of different chemical character at different seasons.
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