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Comprehensive Plan Potable Water Sub-Element Community Development Department Indian River County 21 Upper Floridan aquifer Presently, the county potable water system receives its water supply from wells that have been installed into the Upper Floridan aquifer. Future county wells for both the south county plant and the north county plant will also tap the Upper Floridan aquifer. Due to geological conditions (the overlying Hawthorn Formation with its relatively low permeability), the Upper Floridan aquifer is less susceptible to contamination than the surficial aquifer. Although the Upper Floridan aquifer yields greater volumes of water than the surficial aquifer, the Upper Floridan aquifer contains higher concentrations of impurities (chlorides in excess of 250 milligrams per liter). Because water from a typical Upper Floridan aquifer well exceeds acceptable limits for impurities, treatment by reverse osmosis is necessary to make the water potable. With proper management, however, the Upper Floridan aquifer should provide a long-term, reliable water source for Indian River County. Surficial Aquifer Compared to the Upper Floridan aquifer, the surficial aquifer has a greater potential of being impacted by contamination and is a smaller volume producer. Qualitywise, water in the surficial aquifer is variable throughout the county. Although surficial aquifer water is of a quality acceptable for domestic consumption with limited treatment, water from a typical surficial aquifer well is hard and requires softening. Overall, the surficial aquifer is subject to several potential water quality problems. Among those problems are the following: • Trihalomethanes (THM). THM is a carcinogenic chemical formed when free chloride, which is used for disinfection, combines with organic materials that naturally occur in groundwater. The Florida Department of Environmental Protection (FDEP) standard for THMs is 0.08 mg/l. • Salt water intrusion. In an undisturbed state, natural discharge of an aquifer is sufficient to maintain the fresh water/salt water interface at or near the coastline. As water is withdrawn from the surficial aquifer in inland areas, however, this balance is disrupted. At high rates of groundwater extraction, the interface will move inland and contaminate fresh water zones with salt water. • Contamination from pesticides, herbicides and industrial wastes. The potential for such contamination is high, since the surficial aquifer receives its recharge directly from the surface.