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SFWMD Selects Alum as Water Treatment Component

September 22, 2021

By Leah Reidenbach, SCCF Research & Policy Associate

The 10,000-acre C-43 West Basin Reservoir in Hendry County on the Caloosahatchee is intended to store excess water during the wet season which can be used during the dry season to maintain minimum flows to the estuary. Concerns about the quality of the water coming out of the reservoir and directives in Gov. Ron DeSantis’ Executive Order 19-12 led to the initiation of a water quality treatment feasibility study in 2019. Last week, the South Florida Water Management District (SFWMD) announced the completion of the study and the selection of aluminum sulfate as the water treatment component of the C-43 Reservoir. 

Several water quality treatment technologies were compared and researched, including treatment wetlands which are effective, natural filtration systems that provide habitat for native plants and animals. However, the chemical technology using aluminum sulfate (alum) was selected as the prevailing plan for treatment of water stored in the C-43 West Basin Reservoir. It was primarily chosen because it has a smaller footprint, requiring less land, and is less expensive to implement. The concerns about this treatment, including increased aluminum and sulfate in treated water, were addressed in SFWMD studies and no impacts were found in their short-term experiments, prompting them to give the green light to select this technology for this project.

The treatment of stored water in the C-43 West Basin Reservoir is not a panacea for our water quality woes. While there will be a reduction of total nitrogen in the reservoir by about 30% and total phosphorous by about 62%, and a significant increase in water clarity, the water stored in the reservoir accounts for only 10% of basin flows.

In addition, the C-43 reservoir only accounts for approximately 38 to 42% of water storage needs for the Caloosahatchee watershed. This highlights the need for more water quality storage and treatment projects throughout the basin and for a balanced plan that supports the needs of the Caloosahatchee estuary during the U.S. Army Corps Lake Okeechobee System Operating Plan (LOSOM) optimization process.




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