STAs south of the lake have limited capacity to treat lake water

Posted 4/2/21

Moving water from Lake Okeechobee south depends on the capacity available in the Stormwater Treatment Areas (STAs)

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STAs south of the lake have limited capacity to treat lake water


WEST PALM BEACH -- Moving water from Lake Okeechobee south depends on the capacity available in the Stormwater Treatment Areas (STAs) south of the Everglades Agricultural Area (EAA).

STAs were the topic of dicsussion for the  South Florida Water Management District (SFWMD) Water Resources Accountability and Collaboration Forum (WRAC) held virtually on March 25, 2021.

“Lake Okeechobee is the heart of the South Florida water resources area,” explained SueLynn Kirkland of the SFWMD Office of Operations. She said the lake is only about one-fifth the size of the tributary basins that flow into the lake.

The lake can rise much more quickly than water can be released, she said.

The Everglades Agricultural Area (EAA) is between the lake the stormwater treatment areas (STAs.) Kirkland said the original Central and South Florida (C&SF) project did not include STAs or Flow Equalization Basins (FEBs).

When the system was first designed, runoff from the EAA and flow from the lake through canals discharged directly into the Central Everglades or backpumped into the lake. Over time, it was recognized the water needed to meet stricter water quality standards and backpumping was discontinued (except if needed to prevent flooding in the cities.)

STAs were built in what was then the southern portion of the EAA to clean the water before it is discharged south.

The Flow Equalization Benefits (FEBs) help the STAs by capturing runoff during peak rain events and holding the water until it can be released gradually to the STAs, she explained.

Canals run from the lake through the EAA. The canals serve a variety of purposes, she continued. At times the canal capacity is completely taken up by local basin runoff. The primary design purpose of the STAs and canals is to provide flood control to the local basins. Once flood conditions are alleviated, the canals may be able to send lake releases south.

The treatment capacity of the STAs is not unlimited and is another consideration of when and where to send lake releases south. Long periods of flow, especially high flow, will overload the cells and damage the vegetation, she warned.

She said three major projects needed to move water south are in progress or complete. When these are complete, an additional 370,000 acre feet of water can be sent south:

• Restoration Strategies was implemented so basin runoff and a limited amount of lake water can meet the final water quality standards.

• Modified Water Deliveries Project is complete and operating. However, additional flood mitigation efforts for the 8.5 square mile area (aka Las Palmas) to maximize water flow. In March 2021, the SFWMD governing board approved plans for a cutoff wall to keep water from Everglades National Park from seeping into the 8.5 square mile area development (which is west of the East Coast Protection Levee).

• The Central Everglades Planning Project (CEPP) is necessary to move more water south. Individual features are online or under construction.

Lawrence Glenn, director of the SFWMD Water Resources Division, explained the history of the STAs.

The STAs came about due to three primary actions, he said: the USA lawsuit, the Everglades Forever Act and the state’s Phosphorus Rule.

The USA lawsuit occurred in 1988 when the United States sued the Florida Department of Environmental Protect (FDEP) and SFWMD, claiming damage to federal property from EAA runoff. This was a federal case involving damages to federal lands including the Loxahatchee National Wildlife Refuge and Everglades National Park (ENP). A settlement agreement was reached in 1991 and a Consent Decree was approved in 1992, Glenn explained.

The goals of the Consent Decree are to reduce phosphorus loads from the EAA going into the Everglades Protection Area (EPA) including the Water Conservation Areas (WCAs). This was to be accomplished through the construction of the STAs – which are filter marshes with the sole purpose of extracting phosphorus from the water and implementation of Best Management Practices (BMPs) to create a 25% load reduction before the water leaves the EAA before it goes into the STAs, he explained. The Consent Decree also said water managers needed to conduct research and monitoring to determine the nutrient criteria for the Everglades.

The Consent Decree set the phosphorus limits for water that flows into ENP and the Refuge.

Phosphorus limits were set at the inflow to ENP. At Shark River Slough a range of 7.6 parts per billion (ppb) to 12.8 ppb was established. For Taylor Slough a fixed 11 ppb target was set.

In the Refuge, different phosphorus targets were set for 14 interior sites ranging from 7.2 to 17.5 ppb.

In 1994, the State of Florida adopted the Everglades Forever Act. It also called for BMPs and STAs to reduce phosphorus loads to the Everglades. The state wanted to extend water quality protections to the entire Everglades Protection Area including the water conservation areas (WCAs).

The Everglades Forever Act established the Agriculture Privilege Tax for the EAA and C-139 basins. In addition to other property taxes, farmers pay $25 per acre. (This tax generates about $11 million a year.)

In 2004, the Phosphorus Rule was adopted, establishing numeric phosphorus criteria in EPA. For the WCAs the level was set at 10 ppb for the WCAs and the Refuge. For Everglades National Park, the phosphorus criteria set at the level established in the Consent Decree.

“The next thing that came about was the Gold Case,” he continued. The Miccosukee Tribe of Indians of Florida sued the United States Environmental Protection Agency. The lawsuit challenged the 2003 Everglades Forever Act Amendment and the 2004 Phosphorus Rule. They claimed the U.S. Environmental Protection Agency violated the Clean Water Act because it did not consider the amendments to be a change in water quality standards and thus, did not evaluate them under the Clean Water Act before allowing the state to adopt the Phosphorus Rule. This led to Judge Gold saying ‘I need you to go back and evaluate them under the Clean Water Act and then provide a determination.’

A two part test was established the rule that “total phosphorus long-term flow weighted mean of 13 ppb, should not be exceeded more than three out of five years on a rolling basis, and the maximum total phosphorus annual flow weighted mean can not exceed 19 ppb in any water year.

To meet the limits on phosphorus, BMPs are used to reduce phosphorus in the water before it goes into the STAs. They found the STAs alone were not enough to meet the phosphorus levels, so Restoration Strategies were added.

Water coming out of the STAs is supposed to meet the 13 ppb level so as it moves through the marshes and is continued to be cleaned water in the marshes in the center of the Everglades will be below 10 ppb.

The 1998 settlement agreement states the “primary objective of the STAs is to treat EAA runoff,” Glenn continued. Secondary objectives are to treat runoff from the C-139 and C-51W basins, increase water sent to the Everglades.

Originally there were 40,000 acres of STAs, Glenn continued. They were designed to meet a discharge target of 50 ppb phosphorus. The total design average STA annual inflow volume was 1,162,700 acre feet of water. Because lake regulatory releases are not a primary objective, there was a calculation done to see how much lake water the STAs could accept and still meet the phosphorus goals. That capacity was determined to be about 250,000 acre feet.

Under Judge Goal’s order, the original plan could not meet the new standard set. There was an expansion to 64,000 acres of STAs and three FEBs providing 116,000 acre feet of storage. This brought the total design average annual STA inflow volume to 1,487,300 acre feet with a lake regulatory release capacity of about 58,300 acre feet.

The STAs are designed primarily to take runoff from the EAA, he said. How much capacity is available for lake water depends on where the rain falls. If there is more rainfall south of the lake, there is less capacity in the STAs for lake water. If there is less rainfall south of the lake, there is more capacity to move lake water through the STAs.

Current conditions in the STAs

SFWMD Chief Consulting Engineer of the Applied Sciences Bureau Tracy Piccone said STAs were designed to operate within the regional flood projection system.

“The STA inflow pump stations must operate to provide flood protection to the upstream agriculture, urban and residential areas,” she said.

“When it rains in the basin, the resulting runoff is discharged out of the basin canal into the district’s primary canal system, and this runoff water is then pumped out of the district’s canals into the STAs for treatment prior to discharge south to the Everglades.

STAs are man-made wetlands, she explained. As water is pumped into an STA, cattails and other emergent plants that thrive in high nutrient conditions are used to begin the treatment process. After the water flows through the cattails, more phosphorus is reduced by floating plants, submerged aquatic vegetation (SAV) algae and periphyton. If this cattail barrier of the wetland is damaged, water with higher phosphorus concentration enters the area that contains the SAV and algae that function best in water with lower nutrient levels.

STAs are very efficient at removing phosphorus from surface water as long as they contain healthy vegetation throughout the entire flow path. “ STAs store phosphorus in the sediment, she explained, Just like natural wetlands, STAs benefit from a dry season and shallower depths,” she continued. “Extended periods of water depth above 3 feet result in die-off of marsh vegetation, and instead of an STA, the area becomes like a pond, which cannot remove phosphorus as well as an STA,” she explained.

Deep water conditions also contribute to the develop of floating tussocks which degrade the STAs ability to remove nutrients.

She said currently only a small percentage of the STA vegetation is healthy. During the dry season, they need to go in and rehab the STAs. Over time, phosphorus builds up in the sediment and the STAs need to be dredged and replanted.