THERE IS ONLY ONE EVERGLADES: EVALUATION OF REGIONAL STORMWATER MANAGEMENT SYSTEMS TO ADDRESS THE GOALS OF THE EVERGLADES FOREVER ACT
The Everglades ecological system is endangered as a result of adverse changes in water quality, and in the quantity, distribution, and timing of flows. The Everglades not only contribute to South Florida's water supply, flood protection, and recreation, but serve as the habitat
for diverse species of wildlife and plant life. The system is unique in the world and is one of Florida's great treasures. In an effort to protect and restore the Everglades ecosystem, the Everglades Forever Act (EFA) was enacted in 1994 by the Florida legislature. A requirement of the
EFA is to identify and implement the optimal combination of source controls, treatment facilities, and/or regulatory programs to ensure that all waters discharged to the Everglades Protection Area (EPA) achieve long-term water quality goals by December 31, 2006. To facilitate the planning
and decision-making process, the District recently completed Basin Specific Feasibility Studies (October 2002). These studies combined the results of research and planning studies with regulatory programs and individual basin characteristics to identify optimal combinations of source controls,
basin-scale treatment, and diversion options to address long-term water quality objectives.
In support of the District's efforts, Brown and Caldwell conducted an evaluation of alternatives for addressing long-term water quality goals in stormwater runoff from six urban and tributary
basins discharging to the EPA. The alternatives considered the potential for source controls (best management practices) to reduce phosphorus levels at the source, as well as a variety of chemical treatment systems and natural treatment systems known as stormwater treatment areas (STAs) to
reduce phosphorus concentrations in stormwater runoff to very low levels prior to entering the EPA. The planning level target used in the evaluations was 10 parts per billion (ppb) total phosphorus (TP) in all discharges to the EPA. In some basins, stormwater diversion options were also considered
as alternatives to treatment systems. Each of the alternatives were evaluated based on ten evaluation criteria, consisting of five quantitative criteria (TP load reduction, long-term TP concentration achieved, implementation schedule, 50-year present worth and cost effectiveness) and five
qualitative criteria (operational flexibility, resiliency to extreme conditions, assessment of full-scale construction, management of side streams and improvement in non-phosphorus parameters). Rating of alternatives against the quantitative criteria was based upon the results of the technical
analyses performed as part of the Basin Specific Feasibility Studies. For the qualitative criteria, a numerical plus or minus (+/−) rating was assigned to an alternative based upon the results of the research conducted by the District, where applicable, and the best professional
judgment of the project team.
As a part of the technical analyses conducted for the Basin Specific Feasibility Studies, modeling of natural treatment systems, chemical treatment systems and diversion alternatives was performed to determine the sizing of facilities required to achieve the
water quality goals of the EFA. For example, the natural treatment system alternatives were analyzed using the Dynamic Model for Stormwater Treatment Areas (DMSTA). DMSTA is an unsteady state model that simulates phosphorous removal in STAs. DMSTA is calibrated with data from research studies
focused on phosphorus uptake by emergent vegetation, submerged aquatic vegetation and periphyton communities in natural and manmade wetlands. DMSTA was used to estimate the STA configuration in each basin that achieved the long-term water quality objective of 10 ppb TP using the least amount
of land and avoiding hydraulic bypass.
The Basin Specific Feasibility Studies represent a significant step toward satisfying the long-term water quality objective for future discharges to the EPA for the six ESP basins considered in this investigation. For the first time, historical (simulated)
flows and phosphorus loads in these basins were used to estimate the effectiveness of various phosphorus load reduction strategies and to estimate the long-term cost associated with implementation of those various strategies. The Basin Specific Feasibility Studies demonstrated that it is possible
to satisfy the long-term water quality goals set forth in the EFA in all six of the basins investigated. However, the implementation of some of the alternatives may extend beyond the December 31, 2006 deadline. Also, the projected cost of project implementation is very high in some basins,
due in large part to high land values in the urbanized areas of South Florida. Preliminary analyses indicate that total costs to meet the long-term planning level target of 10 ppb TP can be expected to range from about 275 to 380,000 per kilogram TP removed over the next 50 years depending
on the basin involved.
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