SFWMD to use alum to treat water in C-43 reservoir

Posted 9/14/21

The SFWMD will use an alum treatment system combined with a sand filter to improve water quality in the C-43 reservoir …

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SFWMD to use alum to treat water in C-43 reservoir


WEST PALM BEACH – The South Florida Water Management District (SFWMD) will use an alum treatment system combined with a sand filter to improve water quality in the C-43 reservoir, currently under construction.

Located on 10,700 acres of former farmland in Hendry County, west of LaBelle, the Caloosahatchee River West Basin Storage (C-43) Reservoir will hold approximately 170,000 acre-feet of water, with the maximum depth ranging from 15 feet to 25 feet across the expanse. When complete, the reservoir will capture and store local basin runoff as well as Lake Okeechobee regulatory releases in the wet season, to reduce damaging high levels of freshwater flows to the Caloosahatchee estuaries. This water can be released to the river during the dry season to maintain optimal salinity levels in the estuaries. Flows below 450 cfs (measured at the Franklin Lock) are considered harmful as the salinity levels in the estuaries are too high. Flows higher than 2,800 cfs are also considered harmful because the salinity levels drop too low. The ideal beneficial freshwater flow at the Franklin Lock advocated by estuary scientists is around 1,000 cfs, but the ideal salinity level varies for different parts of the estuaries.

“These are projects that have been a long time in the making,” said Jennifer Reynolds, SFWMD Director of Ecosystem Restoration and Capital Projects, during a Sept. 13 Zoom meeting about the project. The in-reservoir alum injection system was modeled to meet the phosphorus and nitrogen limits for the reservoir, she said.

“We’ve determined that an alum injection system will meet the goals set by Gov. DeSantis in his executive order where he told us to make sure that we would improve the water in, and leaving, the reservoir,” Reynolds explained. She said the process will also help prevent the growth of algae in the reservoir. The alum treatment process is the most cost-effective way they have found to meet that goal, she explained.

Alum (aluminum sulfate) is a nontoxic liquid that is commonly used in water treatment plants to clarify drinking water and reduce phosphorus levels in water.

Reynolds said she knows “a lot of folks are frustrated” because they wanted something more like a stomrwater treatment area (STA). A 5,000 acre STA was considered, but deemed non cost-effective with an estimated cost for construction and maintenance of $300 million, in addition to the cost of purchasing land. According the feasibility study, the cost of the using the alum treatment for 50 years was estimated at $84 million.

“We want to do more water quality treatment,” Reynolds explained. SFWMD estimates the reservoir will capture about 10% of the wet season river flow. She said the SFWMD is looking for additional water quality projects that will help the Caloosahatchee River, using available legislative dollars.

“We’re talking about spending a lot of money that will not do anything for the Caloosahatchee,” said Newton Cook of United Waterfowlers Florida.

“We’re taking one bite out of the elephant with this project,” said Kim Fikoski, SFWMD project manager for C-43 West Basin Reservoir. “We’re looking for other projects in the watershed.