Effects of surface runoff and treated wastewater recharge on quality of water in the Floridan aquifer system, Gainesville Area, Alachua County, Florida

Rates of recharge to the Floridan aquifer system at four sites in Alachua County were estimated and water samples were analyzed to determine if the recharge water had any effects on the water quality of the aquifer. A total of about 33 million gal/day (mgd) recharges the upper part of the aquifer system at Haile Sink, Alachua Sink, and drainage wells near Lake Alice. At the Kanapaha Wastewater Treatment Plant, injection wells recharge an average of 6.1 mgd into the lower zone of the system. The samples of water entering the aquifer system collected at the four sites generally conformed to the drinking water standards recommended by the EPA in 1983. Bacteria and nutrient concentrations were more variable in the recharge water than were other constituents. Organic compounds such as diazinon, lindane, and malathion were occasionally detected in all recharge water, but concentrations never exceeded recommended limits. Bacteria were detected in most wells sampled near the Gainesville recharge sites. The highest counts were from wells near Alachua Sink. At only one site was there a significant difference between the quality of the recharge water and water from the wells sampled, although the recharge water tended to be lower in calcium and iron than water from the Floridan aquifer system. A sample from a well about 150 ft down-gradient of a drainage well near Lake Alice consisted of turbid water with a total phosphorus concentration of 75 mg/l and total nitrogen concentration of 57 ml/l. Water flowing into the drainage well from the lake had a total nitrogen concentration of 1.6 mg/l. Apparently, nutrient rich suspended sediment in inflow to the drainage well settles out of the water and accumulates in cavities in the limestone. Estimated loads entering the aquifer include 3,500 kg/d of chloride, < 0.4 kg/day of lead, 310 kg/day of nitrogen, and 150 kg/day of phosphorus. The effects of the loads were not detected in most monitor wells. Apparently, some of the constituents may settle out, some may be adsorbed by aquifer materials, and the remainder diluted and dispersed by the extremely large volume of water in the aquifer. (Author 's abstract)