Lake Okeechobee Water Retention/Phosphorus Removal Critical Restoration Project Stormwater Treatment Areas (STAs)

This paper presents the details of the final design of a project developed through a partnership between the Jacksonville District U.S. Army Corps of Engineers (USACE) and the South Florida Water Management District (SFWMD, local sponsor). The project is the Lake Okeechobee Water Retention/Phosphorus Removal Critical Restoration and consists of two components, the Isolated Wetlands Restoration (IWR) and two constructed treatment wetlands known as Stormwater Treatment Areas (STAs). The goal of the project is to provide water retention through the IWR, and phosphorus reduction through the STAs. The subject of this document is the STAs component of the project to be constructed within the Taylor Creek/Nubbin Slough basin, this is one of the four priority basins in the Lake Okeechobee watershed, accountable for about 29 percent of phosphorus discharges to the Lake. The two STAs are: Taylor Creek, to be located at the former Grassy Island Ranch east of the Taylor Creek; and Nubbin Slough, to be located at the former Newcomer Dairy east of the Nubbin Slough. The STAs are expected to achieve phosphorous reduction by wetland emergent vegetation uptake and soil absorption. The stormwater will be pumped out of the natural stream into large constructed wetlands, and it will be treated and returned to the stream by gravity. Design issues included pumping rates (the highest phosphorus concentrations are found in peak flows), storage area, containment size and design, instrumentation and control, phosphorus removal rates, endangered species, and local areas of high residual phosphorus concentration. These issues were resolved during the design process in 2001 and 2002. The modeling performance predicted for the STAs, in terms of total phosphorus (TP) reduction, is the following. The Taylor Creek STA: 38.4 percent of the current TP mass load of 5.4 Metric Tons of phosphorus per year (MT P/yr); and the Nubbin Slough STA: 91.6 percent of the current TP mass load of 5.61 MT P/yr. Construction is scheduled to begin in 2003. Many of the features of this project are applicable to phosphorus removal programs being developed throughout the country.