REPORT OF INVESTIGATIONS No. 40


aquifer, as determined by the tests is 75,000 gpd per foot. The coefficient
ranged from 58,800 to 94,000 gpd per foot. This coefficient may be used
to calculate the effects of pumping on the water level near Pensacola.
The average coefficient of storage is 0.00055. This relatively low average
coefficient of storage indicates that an effective confining layer overlies
the sands from which the water is withdrawn. However, this confining
layer does not extend over a large area.
 The aquifer tests show that artesian conditions existed during the few
clays of the tests and perhaps artesian conditions would exist for as long
as a few weeks after continuous pumping started. Later, local recharge
by leakage from other parts of the sand-and-gravel aquifer would prob-
ably occur at the edges of and through the confining layers. This local
recharge would lessen the drawdown. Because of the effect of this re-
charge, it has been found by trial and error that reasonably accurate
drawdowns can be predicted using a storage coefficient of 0.15 in this
area. This coefficient of storage would give more reasonable time-distance-
drawdown figures than those calculated by using the average coefficient
obtained from the relatively short pumping tests. Jacob and Cooper
(1940, p. 48) calculated the "apparent coefficient of storage" to be 0.32 in
the upper sands in the Pensacola area. This calculated coefficient of
storage takes into consideration the effects of local recharge.
 In the fall of 1950, Heath and Clark (1951, p. 31-34) made an aquifer
test on the Gulf Breeze Peninsula in Santa Rosa County. The test area was
about half a mile east of the Gulf Breeze post office. The wells pene-
trated the upper part of the sand-and-gravel aquifer and the coefficients
that were determined apply to the upper 75 feet of the aquifer. This
part of the aquifer was found to have a coefficient of transmissibility of
84,000 gpd per foot and a coefficient of storage of 0.23. This relatively
high storage coefficient indicates nonartesian conditions. Several curves
relating pumping rates and well spacing to the resultant drawdowns are
given in the report.
 Several aquifer tests have been made during 1951-55 on some of the
Chemstrand Corporation's wells, about 13 miles north of Pensacola. Each
supply well is equipped with 110 feet of well screen, usually made up in
two sections. The screens are set in the most permeable zones in the sand-
and-gravel aquifer, between 170 and 380 feet below the sand surface.
The average value of the coefficients of transmissibility and storage de-
termined from these tests were about 150,000 gpd per foot and about
0.001, respectively.
 The coefficients of transmissibility and storage may differ consid-
erably from place to place; therefore, drawdowns at one place cannot