The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
In the absence of pollution, nutrient levels in the Upper Floridan Aquifer are generally
very low (SWFWMD 2001). Since their flows are dominated by groundwater discharge,
springs in largely pristine regions would be expected to have lower nutrient
concentrations than streams that receive overland runoff. The nutrient concentrations in
Sulphur Springs indicate nutrient enrichment of the groundwater sources that contribute
to the spring, which is not surprising given the location of the spring in a heavily
urbanized/industrialized setting.
Since monthly data collection began in 1991, Sulphur Springs has frequently exceeded
drinking water standards for chloride, sulfate, color and TDS. This had been particularly
the case for chloride and TDS, reflecting the brackish influence on the spring water
chemistry. Violations of potable water standards have been less frequent for sulfate
(33% of observations). Receiving water body standards for Class I (potable waters) are
listed in Table 2-3. Sulphur Springs periodically exceeds these standards for chloride,
TDS, and dissolved oxygen. However, as discussed later in this report, fall of the water
over the outlet structure at the spring effectively aerates the spring discharge.
As previously discussed, long-term data for specific conductance indicate the discharge
of Sulphur Springs has become increasingly mineralized over the last thirty years. Other
water quality parameters in the City of Tampa's monitoring program have shown
changes since 1991. Time series plots of parameters measured monthly by the City are
included in Appendix A, along with LOESS lines to indicate general trends in changes
over time. All parameters were plotted on a linear scale using the entire dataset. In
order to accommodate the range of values, some parameters were also plotted on a
log 10 axis, resulting in the censoring of zero concentration values. In addition, in a few
cases the upper limit of data was censured in the log scale portrayal in order to better
illustrate the temporal changes in the bulk of data.
Table 2-3. Comparison of monthly water quality data from spring pool
(1991-2002) with water quality standards.
Drinking
Water
Standard
Water Quality Criteria
– Class I
Number
Exceedances
pH 6.5 – 8.5 6.0 – 8.5 0 0%
NO 2 -N 1 mg/l 1 1%
NO 3 -N 10 mg/l 10 mg/l 0
Percent of
Exceedance
Dissolved
5.0 mg/l minimum 138 96%
Oxygen
Chloride 250 mg/l 250 mg/l 135 99%
SO 4 250 mg/l 45 33%
Color 15 pcu 59 41%
TDS 250 mg/l 1,000 mg/l 131 (1) 97%
(1) Drinking Water
Exceedances
2 -34