REPORT OF INVESTIGATIONS No. 40


 However, in certain areas these clay beds retard the encroachment
of salt water. For example, the clay bed 60 to 80 feet below the surface
in the vicinity of Gulf Breeze retards the vertical movement of the un-
derlying water when heavy pumping lowers water levels in the overly-
ing sands. The water just below the clay bed is salty near the shorelines
of the Gulf Breeze Peninsula.
 Another example of clay beds that prevent salt-water encroachment
is at Fort Pickens on the western tip of Santa Rosa Island. Here, the clay
and sandy clay beds are almost 300 feet thick. Below the clay beds is a
sand aquifer where fresh water for the Fort is obtained. The clay keeps
the salt water out even though the water level in this sand has been be-
low sea level since at least 1913. The chloride content of the water from
the wells at Fort Pickens is about 80 ppm and has not increased ap-
preciably since 1940. The fresh water in the sand is believed to come
from the mainland southwest of Pensacola and to move southward
under Pensacola Bay.
 4. Industrial wastes: Wastes from industrial plants can contaminate
 ground-water supplies when the wastes are discharged into ponds or on
 the ground. Wastes discharged into streams or rivers also can contami-
 nate ground-water supplies where pumping lowers the ground-water
 level below stream or river level.
 5. Residual salt water: Salt water that is not completely flushed
 from the sand-and-gravel aquifer is another limiting factor. This salt
 water probably entered the aquifer in the past when sea level stood
 higher than at present. Such salt water was found at a depth of 75 feet at
 Fair Point on Gulf Breeze Peninsula.

 FLORIDAN AQUIFER
 The Floridan aquifer is almost untapped by water wells in Escambia
 and Santa Rosa counties. A detailed appraisal of the possibility of devel-
 oping large supplies of potable water from this aquifer was not possible
 in 1962. Studies of well cuttings and electric logs from oil-test holes and
 deep water wells have established the location and thickness of the
 aquifer. Little is known of the ability of the upper limestone of the Flo-
 ridan aquifer to transmit water except in the southern part of Santa Rosa
 County. The water transmitting and water storing properties need to be
 determined by test drilling and aquifer tests. The chemical quality of
 the water needs to be determined from water samples collected during
 the test drilling.
 Wells drilled into the upper limestone of the Floridan aquifer in
 southern Santa Rosa County have large yields. The water is under artesian