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USACE announces public comment on proposed seepage barrier wall in the 8.5 Square Mile Area as part of the Central Everglades Planning Project (New Water Phase)

Posted on August 17, 2022

The U.S. Army Corps of Engineers Jacksonville District announces a 30-day public comment period for the Draft Environmental Assessment (EA) and Proposed Finding of No Significant Impact (FONSI) for the proposed construction of a 5-mile-long seepage barrier wall in the L-357W levee at the 8.5 Square Mile Area (8.5 SMA), Miami-Dade County, Florida. The Corps is also evaluating a request from the South Florida Water Management District (SFWMD) to modify the Modified Waters Deliveries to Everglades National Park Federal Civil Works project pursuant to 33 U.S.C. 408 to construct the 5-mile-long seepage barrier wall in the 8.5 SMA.

Improved seepage management would allow for greater operational flexibility of the Central and Southern Florida Project. Comments are due September 12, 2022.

Review the Draft Environmental Assessment (EA) and Proposed FONSI at:

The proposed action is part of the multi-decade, multi-billion-dollar Comprehensive Everglades Restoration Plan (CERP). The 2014 Central Everglades Planning Project (CEPP, a component of CERP) Final Project Implementation Report/Environmental Impact Statement (PIR/EIS) Recommended Plan included construction of an approximately 4.2-mile-long, 35-foot-deep seepage barrier wall feature at the L-31N Levee, just south of Tamiami Trail, along properties to the east of Everglades National Park (ENP) as part of the CEPP (New Water Phase). In 2016, a 5-mile-long seepage barrier wall was constructed along the eastern toe of the L-31N Levee adjacent to ENP, in generally the same location as the Recommended Plan seepage barrier wall, by the Miami Dade Limestone Products Association (M-DLPA). This was a non-CERP effort completed as compensatory mitigation for wetland impacts regulated under Section 404 of the Clean Water Act for the same seepage management purposes.

Findings from the analysis of data from the M-DLPA wall and new information since the 2014 CEPP Final PIR/EIS, including changed conditions and additional technical analyses, as well as check of Savings Clause compliance indicates the need for a CEPP (New Water Phase) seepage barrier wall around the 8.5 SMA for CEPP purposes. The evaluation concludes that the existing 5-mile-long M-DLPA seepage barrier wall alone is not sufficient to ensure realization of the forecasted hydrologic and ecologic restoration benefits envisioned in the 2014 CEPP PIR/EIS. The findings indicate that to realize the maximum CEPP hydrologic and ecological restoration benefits, both the CEPP (New Water Phase) and the M-DLPA seepage barrier walls are necessary. The analysis determined that the CEPP (New Water Phase) seepage barrier wall is needed at the 8.5 SMA to afford increased system‐wide flexibility under future CEPP Water Control Plans (WCP) allowing for full accrual of ecological restoration benefits and maintain Savings Clause compliance. This is consistent with and addresses the recommended need identified in the 2014 CEPP Final PIR/EIS for construction of seepage management features (L-31N barrier wall), to prepare the system for future additional inflows from Lake Okeechobee to the south.

The CEPP New Water project Team (Corps/ SFWMD) has identified three alternatives for CEPP (New Water) seepage barrier wall lengths that will adjoin the 2.28-mile seepage barrier wall under construction by the SFWMD.  The three alternatives were evaluated relative to both existing COP water levels in Northeast Shark River Slough (NESRS) (e.g., 8.5 feet in the L-29 Canal) and future CERP water levels (maximum 9.7 feet in the L-29 Canal, but closer to 9.2 for prolonged wet periods). To ensure full accrual of the forecasted ecological restoration benefits, the Team determined that an additional 5-miles of seepage barrier wall around the perimeter of the 8.5 SMA is needed. This 5-mile CEPP (New Water) seepage barrier wall is recommended to address current and anticipated groundwater seepage into the 8.5 SMA and to afford greater operational flexibility within the Central and South Florida Project for management of water stages within Water Conservation Area-3A, ENP, and the ENP South Dade Conveyance System under the future projected ENP conditions with full CEPP build-out. The purpose of the CEPP (New Water Phase) seepage barrier wall remains unchanged from the CEPP Final PIR/EIS and is designed to manage seepage out of ENP.

The CEPP (New Water) 5-mile seepage barrier wall will adjoin a 2.28-mile seepage cutoff wall currently under construction by the SFWMD. The CEPP (New Water) 5-mile-long proposed seepage barrier wall will be made of a mix of soil, cement, and bentonite slurry along the L-357W levee northwest of the S-357 Pump Station. The seepage barrier wall would be constructed through the approximate center of the L-357W levee. The approximate depth of the curtain wall would be 55 to 65 feet deep, with an approximate thickness of 28 inches.

The enclosed Draft Environmental Assessment (EA) and Proposed Finding of No Significant Impact (FONSI) evaluates the effects of the construction of three seepage barrier wall alternatives and identifies a Preferred Alternative (ALT C, 5-mile-long seepage barrier wall).  The Preferred Alternative also incorporates the completed (2016) M-DLPA 5-mile-long seepage barrier wall as a CEPP feature and approves the SFWMD’s Section 408 Request to modify the Modified Water Deliveries to ENP Federal Project.

Please submit comments on the Draft Environmental Assessment (EA) and Proposed FONSI via email to (recommended subject: “8.5 SMA Seepage Barrier Wall EA Comments”) by September 12, 2022.


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