Using Multiple Tracers to Evaluate Coastal Water Quality Impacts for Sewered and Non-Sewered Areas

When onsite treatment and disposal systems (OSTDS) are not properly sited or installed, they can be a potential risk to public health and a source of environmental degradation. There are estimated to be over 2.3 million onsite sewage treatment and disposal systems currently in use in Florida, serving approximately 4.5 million people. These systems discharge over 426 million gallons of treated effluent per day in to the subsurface soil environment. Nearly 40% of those systems are found along Florida's southeastern Atlantic coastline. Onsite system failure can result in problems that include direct exposure to inadequately treated sewage, ground and surface water pollution, and contamination of shellfish beds. Throughout the State of Florida, where the water table is high, septic tanks have proven to be problematic from a water resource perspective. Impacts are traced to a lack of regulation prior to the 1980s and to high densities of septic tanks on small lots. Moreover, many of these high-density developments were historically inhabited only in the winter months when the water table is low and performance optimal. When the water table is high, septic tanks cannot operate properly because the water table is above the drainage pipes, interfering with the normal hydraulic specifications and complicating pollutant migration modeling. Thus, the potential for groundwater and surface water contamination is increased, and clearly there is a need to quantify the contribution of environmental degradation attributable to OSTDS. The research team has investigated differences in sewered and non-sewered areas in Broward and Palm Beach Counties in Florida to attempt to quantify the nutrient loading contribution from septic tanks and also to determine the extent of observed nutrient contamination from other sources in a major urban setting. Recently, a unique opportunity to study a rural area in Taylor County, allowed the research team to investigate newer tracers. Taylor County (see Figure 1) is located in Northwest Florida along the Gulf of Mexico coastline directly south of Tallahassee. The total area of the County is 789,000 acres (3,191 km²), of which approximately 15% is comprised of water bodies. Taylor County has four rivers, numerous canals, creeks, and springs, and nearly 60 miles of Gulf of Mexico coastline. The major tourist attractions are fishing and scalloping, particularly from July through September. Half of its southern coast is part of the "Big Bend Sea Grasses Aquatic Preserve" and is classified as "Outstanding Florida Waters." Prior studies have been conducted by the Suwanee River Water Management District (SRWMD) and the Taylor County Health Department (TCHD) in Taylor County to determine if water quality criteria are being met. An ongoing beach monitoring program posts advisories approximately 46% of the time due to high concentration of indicator bacteria (>400 CFU/100mL for fecal coliform, >100 CFU/100mL for Enterococcus). Maintenance of the microbiological quality and safety of water systems used for drinking, for recreation, and for the harvesting of seafood is imperative. Contamination of these water systems can result in high risks to human health and significant economic losses due to closures of beaches and shellfish harvesting areas.