Orlando, Florida

Source Number: 2.2.4

Source Description
Bradner, L. A. Water Quality in the Upper Floridan Aquifer in the Vicinity of Drainage Wells, Orlando, Florida. U.S. Geological Survey Water Resource Investigations Report 90-4175. Tallahassee, Florida. 1991.

Key Words
drainage wells; Floridan aquifer; groundwater sampling; water quality; urban runoff; stormwater runoff; surface water

Executive Summary
Since 1904, Orlando, Florida, and surrounding areas have used drainage wells to alleviate flooding and to control lake levels. In the greater Orlando area of approximately 75 square miles, about 310 drainage wells are presently injecting an average of approximately 23 million gallons per day (MGD) of surface water into the Upper Floridan aquifer, a zone of high transmissivity approximately 350-feet thick.

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.

Graphics and Tables
Many graphics and tables are included in the report. The following information is provided in a single Adobe .pdf file: Click here to download the file.

Table 1 - Upper Floridan Aquifer Wells in the Orlando Area Sampled as Part of the Study
Table 3 - Statistical Summary of Chemical Analyses of Water from 18 Wells Upgradient from Orlando and 9 Wells from the Ocala National Forest
Table 6 - Median Values of Selected Constituents and Physical Properties of Water from 11 Wells in the Urban Orlando Area, Well 16
Table 7 - Organic Compounds Detected in Water from Wells Within the Hydrocarbon Plume

Figure 1 - Study Areas
Figure 2 - Location of Drainage Wells and Public Supply Wells Within the Study Area
Figure 3 - Location of Wells Sampled Within the Urban Orlando Area
Figure 4 - Generalized Hydrogeologic Section in the Orlando Area
Figure 9b. - Factors that Affect Flow into the Lake Underhill Drainage Well
Figure 10 - Hydrograph Showing Stage and Outflow at Lake Underhill and Rainfall at Orlando, November 1987 through December 1988
Figure 11 - Map Showing Sites Where Organic Compounds Have Been Detected
Figure12 - Box Plots of Specific Conductance, Sodium, Chloride, and Calcium in Water from Wells in the Ocala National Forest, Upgradient from Orlando and the Urban Study Area
Figure13 - Box Plots of Total Organic Carbon, Potassium, Ammonia, and Phosphorus in Water from Wells in the Ocala National Forest, Upgradient from Orlando and the Urban Study Area
Figure 14 - Hydrograph Showing Specific Conductance of Water in the Gertrude Street Monitoring Well and the Lake Underhill Monitoring Well, Overflow from Lake Underhill, and Rainfall at Orlando
Figure 15 - Map Showing Approximate Extent of the Hydrocarbon Plume in the Urban Orlando Area
Figure 16 - Profiles of Acenaphthene, Naphthalene, and Benzene in Water from Wells in the Hydrocarbon Plume

Contact Information
Mr. Al Aikens
225 E. Robinson St., Suite 505
Orlando, FL 32801
407-423-0030 (v)
407-839-5901 (f)

Source Documents
Source document are not available electronically at this time.