The U.S. Army Corps of Engineers (USACE) Jacksonville District has announced a 30-day public comment period for the Draft Environmental Assessment (EA) and Proposed Finding of No Significant Impact (FONSI) for the approval of construction of an aluminum sulfate (alum) treatment system during the construction of the authorized C-43 West Basin Storage Reservoir (WBSR) in Hendry County, Florida. 

The reservoir will store water from the Caloosahatchee River during the wet season and release water back to the Caloosahatchee River in the dry season.  Use of the reservoir will help reduce extreme highs and extreme lows in the flow to the estuary.

USACE is evaluating the request from the South Florida Water Management District (SFWMD) to modify the C-43 WBSR Federal Civil Works project.

Comments are due June 5, 2023.

Due to concerns stemming from increased harmful algal blooms resulting from operation of the C-43 Basin (Caloosahatchee River basin), Executive Order 19-12, issued on Jan. 10, 2019, directed the Florida Department of Environmental Protection (FDEP) to “work with SFWMD to add a stormwater treatment component to the C-43 Reservoir to provide additional treatment and improve the quality of water leaving this important storage component” of the Comprehensive Everglades Restoration Plan (CERP). In response, a reservoir water quality treatment system at the S-470 pump station has been proposed.

In 2020, the SFWMD conducted the C-43 Water Quality Feasibility Study and identified alum treatment as the most cost-effective treatment technology for reducing phosphorous concentrations and improving water quality for water releases from the C-43 WBSR. It was determined that in-reservoir treatment using an inline injection of the alum had substantial water quality benefits and was compatible with the existing C-43 WBSR project compared to post-reservoir treatment of the reservoir outflow. Therefore, the proposed water quality treatment feature is an in-reservoir alum injection system that would be installed at the inflow of the C-43 WBSR. Though water quality improvement is not a project purpose, the potential exists for the reservoir to provide benefits from long-term nutrient (i.e., phosphorus and nitrogen) removal.

Inline injection of alum during reservoir filling is expected to be useful in suppressing potential nuisance algal growth within the reservoir while optimizing performance of the reservoir. A key advantage of the in-reservoir alum treatment system is its ability to be designed and constructed concurrently with construction of the C-43 WBSR. The in-reservoir alum treatment system proved to be the most cost-effective option that reduced nutrients and improved the quality of water leaving the C-43 WBSR to the Caloosahatchee River and its downstream estuary, while maintaining the current C-43 WBSR construction, design, schedule, and project purpose.

The Draft EA and Proposed FONSI evaluate the environmental effects of approving the construction of the proposed inline alum treatment system as part of the C-43 WBSR under the Corps Section 408 authority and are available for review at: www.saj.usace.army.mil/Sect408C-43WBSRAlum

Please submit comments on the Draft Environmental Assessment (EA) and Proposed FONSI via email to Jacob.S.Thompson@usace.army.mil (recommended subject: “Section 408 C-43 WBSR Alum EA Comments”) by June 5, 2023.