Source Number: 2.2.4
A 3-year study conducted from 1987 through 1989 encompassed about six square miles in Orlando's downtown urban area, and included water quality analyses from wells influenced by inflow from one or more drainage wells. The water quality data from the urban area were summarized and compared to water quality data from wells in the Orlando area but upgradient from the urban study area, and from wells in the Ocala National Forest located about 50 miles north of Orlando.
Data obtained from continuous monitoring of water quality in the vicinity of specific-use drainage wells (wells receiving lake overflow and stormwater runoff) were included in the study. Estimates of maximum inflow quantities ranged from 240,000 gallons per day (gpd) to the stormwater runoff well to more than 12 MGD to the lake overflow well. Average daily inflow during 1988 was about 9,000 gpd to the stormwater runoff well and about 2.1 MGD to the lake overflow well.
Water samples from the Upper Floridan aquifer in the urban Orlando area had tritium values ranging from 3 to 9.4 tritium units, indicating recent (1953 or later) recharge. Calcium, potassium, sodium, chloride, and ammonia are present in substantially higher concentrations in groundwater in Orlando than in groundwater from the background areas. The pH level is substantially lower, and the concentration of total organic carbon is substantially higher in groundwater upgradient from Orlando and in the urban Orlando area than in groundwater from the Ocala National Forest.
Organic compounds were detected in samples from 8 of the 11 wells in the urban Orlando area. Fluorocarbons were detected in samples from two wells. Most sources of the organic compounds are unknown; however, five of the wells sampled were within a hydrocarbon plume that likely originated as effluent from a former manufactured-gas plant.
One lake overflow drainage well injected an estimated 6,900 pounds of nitrogen and 450 pounds of phosphorus into the aquifer in 1988. Increasing calcium concentrations in groundwater downgradient from the drainage well indicate that dissolution of the limestone may be occurring. Higher sulfate concentrations in the groundwater were associated with the wet season and higher inflows to the drainage well, indicating that oxygenated inflow water may be converting hydrogen sulfide gas contained within the groundwater to sulfate. Specific conductance in the groundwater is lowered by incoming stormwater, but rises sharply to background values when inflow to the drainage well ceases.
Table 1 - Upper
Floridan Aquifer Wells in the Orlando Area Sampled as Part of the Study
Figure 1 - Study