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Orlando,
Florida
Source Number: 2.2.2 Source
Description Key Words Executive Summary Water injected by drainage wells is an important source of recharge to the Floridan aquifer. The wells bypass confining beds and likely allow more recharge to the Floridan aquifer than would occur under natural conditions. This recharge compensates for heavy withdrawals from the Floridan aquifer and helps maintain aquifer pressures that retard upward saltwater encroachment. At least 90 percent of the drainage wells inject storm water into the upper producing zone (100- to 600-foot depth) of the Floridan aquifer. The median depth of 314 drainage wells is about 400 feet; the range is 120 to 1,049 feet. The wells are used mainly to control lake levels and to dispose of urban storm runoff. About 50 percent of the drainage wells are used to dispose of street and other impervious-area runoff, about 35 percent to regulate lake levels, and about 15 percent to dispose of cooling, air-conditioning, and other miscellaneous wastewaters. Water injected by drainage wells moves downgradient towards supply wells. The distance between a drainage well and a supply well may be as short as several hundred feet. In addition, head difference allows water from drainage wells in the upper producing zone to move into the lower producing zone (1,100- to 1,500-foot depth), which is used for public water supply. About 65 percent of all water pumped from the Floridan aquifer is from the lower producing zone. Water samples from the Floridan aquifer were analyzed for selected major constituents, chemical and physical properties, nutrients, metals, and organic compounds to determine if water quality is affected by recharge through drainage wells. Sixty-five supply wells and 21 drainage wells, mostly within a 16-mile radius of Orlando, were sampled from September 1977 to June 1979. Based on water sample data, most constituent concentrations were slightly higher in water from drainage wells than in water from supply wells; this differential indicates at least a localized effect on aquifer water quality due to drainage well recharge. Bacteria count and total nitrogen concentration are the most notable differences between the waters from the two types of wells. For drainage wells, median values for total nitrogen and bacteria count were 1 milligram per liter (mg/l) and 39 colonies per 100 milliliters, respectively; for supply wells, median values were 0.27 mg/l and 0 colonies per 100 milliliters. However, with the exception of bacteria, water from drainage wells, without treatment, would likely meet the maximum contaminant standards established by the U.S. Environmental Protection Agency in 1975 and 1977 in the National Interim Primary and Proposed Secondary Drinking Water Regulations, and by the Rules of the Department of Environmental Protection in the Florida Administrative Code of 1978. The areal pattern of water quality variations did not relate statistically to the number of drainage wells in the vicinity of sampled supply wells. However, the high bacteria count in some drainage wells indicates a potential for contamination of supply wells by drainage well recharge if a supply well and a drainage well are hydraulically connected. Graphics and
Tables Figure 5 - Location
of Drainage Wells and Supply Wells Sampled for Water Quality Contact Information Source Documents |
