As part of WGI’s continuing Environmental Consulting contract, Martin County hired WGI to provide feasibility design services for a water quality project within the Hog and Mapp Creek watersheds. Both watersheds have been identified by South Florida Water Management District as contributors of high concentrations of total nitrogen (TN), total phosphorus (TP), and copper into the St. Lucie River.

The initial focus of the study was to understand if Hog Creek could be diverted north towards Mapp Creek and a county-owned preserve area into a proposed combined stormwater treatment area (STA). Due to gradient limitations, the modeling performed showed that it would not be possible to locate the STA on county-owned land without active pumping. Alternative designs were prepared to identify the required size and preferred location for a combined STA for the county’s future interest.

Finally, WGI developed 30% design plans for a restoration of the Mapp Creek ditch within county-owned lands. The restoration plan proposes to approximately double the width of the ditch right-of-way to allow for the installation of planted littoral shelves along the banks of a sinusoidal center channel for an approximately one-mile length. The restoration will integrate bio-sorption-activated material (BAM) into the littoral shelves within the last 100 feet before a weir structure.

The 12-acre hybrid biological/chemical treatment will provide an effective and efficient treatment train for the 3,653-acre Mapp Creek watershed. The required Total Maximum Daily Loads (TMDLs) identified for the Mapp Creek watershed requires a 47.1% reduction in TN and a 61.8% reduction in TP. The proposed project is modeled to provide a load reduction of 70% for TN and 85% for TP.