58 REPORT OF INVESTIGATIONS NO. 50
conductance equals or exceeds values shown-in the St. Johns River near Cocoa from October 1953 to September 1963. For example, the conductance was 3,000 or greater for 2 percent of the time during the period of record. Figure 25 shows the relation of specific conductance to sodium, hardness, chloride and mineral content in water of the St. Johns River near Cocoa.
By using figure 24 in conjunction with figure 25 the percentage of time that the various constituents would exceed a given value can be estimated. For example, from figure 25, if the chloride content was 250 ppm, the specific conductance would be about 1,020 micromhos. From figure 24 a conductance of 1,020 micromhos or greater would occur about 18 percent of the time.
From October 1953 to September 1963, the mineral content and chloride concentration in water in the St. Johns River near Cocoa exceeded the U. S. Public Health Standards for drinking water during the following periods: April 21 to September 10, 1956; June 21 to July 31, 1961; October 13, 1961 to August 21, 1962;
4,000
3.500
I.o.),
0 HARDNESS
3, 000 ~SODIUM MINERAL CONTENTCHLORIDE
0
2 2000-0
M
o0.500e
z
0
U.500200 400 600 800 1,000 1,200 1,400 1.600 1800 PARTS PER MILLION
Figure 25. Relation of specific conductance to hardness, chloride, sodium, and mineral content for St. Johns River near Cocoa.