JACKSONVILLE — The U.S. Army Corps of Engineers, Jacksonville District, announces public comment on the Draft Supplemental Environmental Assessment (EA) and Proposed Finding of No Significant Impact (FONSI) for proposed design refinements to the Indian River Lagoon - South (IRL-S) Project, specifically to the C-23 and C-24 features in St. Lucie County. The IRL-S Project is one project that is part of the Comprehensive Everglades Restoration Plan (CERP). Public comments are due Wednesday, April 21.

The Draft Supplemental EA and Proposed FONSI are available for public review at: www.saj.usace.army.mil/IRLSC23C24

Please submit public comments to IRL-SComments@usace.army.mil by Wednesday, April 21, 2021 (recommended subject line “IRL-S C-23/C-24 EA Comments”).

“We are very excited that the construction on the first phase of the Indian River Lagoon – South Project, the C-44 Reservoir and Storm Water Treatment Area, will be complete by the end of the year,” said Project Manager Mike Drog. “Now, we are asking for public comment on the proposed design refinements for the next component of the project we are moving forward, the C-23 and C-24 Reservoirs and Stormwater Treatment Area.”

“The purpose of the Indian River Lagoon – South Project is to capture, store, and treat local basin runoff to restore the delicate balance of fresh and salt water in the St. Lucie River Estuary and the southern portion of the Indian River Lagoon, and revitalize degraded habitat,” said Drog. “As each component is completed and comes online, they will work together to protect and restore the Indian River Lagoon and the St. Lucie Estuary.”

The Record of Decision (ROD) approved for the 2004 IRL-S Final Integrated Project Implementation Report and Environmental Impact Statement (FIPIR/EIS) explained the selection of a Recommended Plan.

The C-23/24 Project features were reviewed following authorization, during the design phase. The project footprint was revised to incorporate available real estate and to avoid certain cultural resources sites, and further refinements were made to optimize the overall design.

The U. S. Army Corps of Engineers, Jacksonville District (USACE) has prepared a Supplemental EA to document the refinements made to the Recommended Plan that occurred during design that are different from what was described and evaluated in the original 2004 FIPIR/EIS and ROD. The revised design of the C-23/24 STA and Reservoirs is the Proposed Action analyzed in this Supplemental EA.

The Proposed Action consists of changes to the component footprints of the C-23/C-24 Stormwater Treatment Area (STA) and the North and South Reservoirs.

Consistent with the 2004 IRL-S FIPIR/EIS, the purpose of the proposed reservoirs is to capture and store large volumes of water flowing through the C-23 and C-24 canals during peak storm events, to reduce large inflows into the St. Lucie Estuary. Water is to be stored in two reservoirs. The North Reservoir encompasses 2,005 acres with a perimeter of approximately 8.4 miles and a 16.5-foot depth, and the South Reservoir includes 3,537 acres and a perimeter of approximately 11 miles and a 16.5-foot depth.

The stored water will be released into the C-23/24 STA to sequester nutrients from water conveyed from the North and South Reservoirs. The C-23/24 STA is designed to remove phosphorus from stormwater entering the C-23/24 Reservoirs.

Treated water is then released from the C-23/C-24 STA into the North St. Lucie Water Control District Canal 71, to flow into Ten Mile Creek (TMC) and, ultimately, the North Fork of the St. Lucie Estuary.

The purpose of the STA is to reduce sediment, phosphorus, and nitrogen going to the St. Lucie River Estuary and the southern portion of the Indian River Lagoon.

All components work together to improve conditions in the estuary by reducing turbidity and nutrient inflows and improving salinities.

Water from the North Reservoir can be routed to the C-23/24 STA or returned to Canal C-24 when there is a need to reclaim storage capacity or meet a water supply demand. Water from the South Reservoir can be returned to the C-23 or C-24 Canals when there is a need to reclaim storage capacity or meet a water supply demand.

The multi-cell STA will be located both east and west of County Road (CR) 613, and consist of 1,970 acres of effective treatment area spread among five cells within the approximately 10-mile perimeter: two cells of roughly 200 acres each and three cells at roughly 500 acres each, and will have a normal operating depth of about 1 to 2- feet, 260 cubic feet per second (cfs) inflow, and 200 cfs outflow. Inflowing water will be treated by filtering through emergent wetland vegetation.

The purpose of the C-23/24 Project components, as part of the larger IRL-S Project, is to provide design refinements to the Central and Southern Florida (C&SF) Project features in St. Lucie County, necessary to improve the quality of the environment, improve protection of the aquifer, and improve the integrity, capability, and conservation of urban and agricultural water supplies and other water-related purposes.

For additional information on the Indian River Lagoon – South C-23/C-24 Reservoirs and Stormwater Treatment Areas, including aerial maps and the 2004 Final Integrated Project Implementation Report and Environmental Impact Statement (FIPIR/EIS) for IRL-S visit: www.saj.usace.army.mil/IRLSC23C24

IRL-S is one of many Comprehensive Everglades Restoration Plan projects seeking to improve the quality, quality, timing, and distribution of water to restore the south Florida Everglades ecosystem.

The IRL-S Project includes approximately 9,000 acres of manmade wetlands and STAs, including the C-44, C-23/24 and C-25 STAs, 90,000 acres of natural storage and water quality areas, 90 acres of artificial submerged aquatic vegetation restoration, and 7.9 million cubic yards of muck removed from St. Lucie Estuary.

Additional information on the IRL-S Project is available on the IRL-S Project Fact Sheet at  https://usace.contentdm.oclc.org/utils/getfile/collection/p16021coll11/id/4904
and IRL-S Project Placemat at https://usace.contentdm.oclc.org/utils/getfile/collection/p16021coll11/id/4905
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