REPORT OF INVESTIGATIONS No. 40


ride, and nitrate are negatively charged anionss). Chloride-type water is
indicated by chloride as the major anion and is generally accompanied
by a predominant sodium cation. Carbonate-type water is based on car-
bonate as the major anion and calcium, magnesium, and sodium, either
singularly or in various combinations, being the major cations.
Intermediate-type water is characterized by carbonate and chloride
being almost equal and usually shows no predominance in the cations.
 The chemical quality of the water from two wells located at Fort
Pickens State Park on the west end of Santa Rosa Island is distinctive.
They are the only two wells on Santa Rosa Island producing any quantity
of fresh water from the sand-and-gravel aquifer. The analysis of the wa-
ter from these two wells suggests the presence of a slight amount of
sea water. Sodium and chloride are among major ions present and the
magnesium exceeds the calcium, which is indicative of sea water. The
water has a pH slightly above neutral and a carbonate of 95 ppm, high
for this area. These two factors could be attributed to the action of the
usually acid water on fossil shells. This water is thought to cross under
the bay from the Pensacola area, separated from the salt water in Pensa-
cola Bay by an impermeable clay bed. The long exposure to clay could
account for the presence of high silica (20 ppm).
 On Fair Point Peninsula, Heath and Clark (1951) found two aquifers
 in the sand-and-gravel aquifer. The upper aquifer contains the more acid
 water (pH 5.2 to 5.9) which has sodium and chloride for the major con-
 stituents and is low in total mineralization. Water from the lower, more
 fossiliferous aquifer contains carbonate as the major constituent and has a
 pH of 7.2. A shallow well at Gulf Beach and a deeper well at Navarre
 show chemical characteristics similar to the deep well at Fair Point,
 whereas water from a shallow well at Santa Rosa Shores resembles the
 water from wells in the upper aquifer at Fair Point. Water from the
 sand-and-gravel aquifer in the southeastern part of Santa Rosa County
 away from the coast has a very low mineral content and shows no pre-
 dominant chemical constituents.
 In the section of Pensacola bordering closely on the bays, the water
 from this aquifer is generally very low in mineral content but shows a
 predominance of sodium and chloride ions. This slight salt-water en-
 croachment could be due to pumping in the area. Near Bayou Chico, an
 area of heavy pumping in close proximity to salt water, about 12 wells
 have been abandoned due to salt-water encroachment. This encroach-
 ment has been reduced by decreasing pumping near the salt water.
 The large Chemstrand plant on the Escambia River just north of
 Pensacola uses both river water and ground water from the sand-and-