A decade ago, pumping treated wastewater into wetlands to nourish vegetation and counter salt water was viewed as a promising idea, one that the Lake Pontchartrain Basin Foundation fully supported.

Cities like Mandeville, Hammond and Breaux Bridge and parishes like St. Bernard and St. Charles were among nearly a dozen entities that launched what are known as wastewater assimilation   projects.

Discharging partially treated wastewater into natural wetlands would provide nutrients that would be taken up — or assimilated — by vegetation in marshes and swamps. Since the wastewater would not have to be treated to the same standard as water discharged into bodies of water, municipalities would save money.

The approach was thought to be a win-win.

But what was meant to help is actually harming wetlands, according to the Lake Pontchartrain Basin Foundation. The group is asking the state to stop issuing permits for new projects, and it's also raising concerns about existing ones, like Mandeville's, which is up for its five-year permit renewal.

Mandeville's permit will be the subject of a public hearing conducted by the Louisiana Department of Environmental Quality at 6 p.m. Thursday in the St. Tammany Parish Council chambers.

The Lake Pontchartrain Basin Foundation plans to oppose a proposed change in Mandeville's  permit that would increase the amount of solids allowed in the water that's being discharged into the Chinchuba Swamp and the East Tchefuncte Marsh.

"Ten years or so ago, we supported these kinds of projects," foundation Executive Director John Lopez said Friday. "In theory, it sounded like a good idea, considering how desperate our coastal situation is, in losing wetlands. Now, we have 10 years of information and projects."

Among other concerns, the foundation says that the continuous discharge of nutrients and water is overloading wetland ecosystems. Constant high water levels are essentially drowning the wetlands.

Wetlands are meant to have fluctuating water levels, Lopez said, and putting them into permanent flood is usually bad. It creates lower oxygen and stagnation that's bad for plants, he said.

Even areas that can pulse the discharge between two locations, like Mandeville, are less than ideal because Louisiana coastal wetlands are attuned to the annual cycle of spring floods and winter cold fronts that push water out. "If you just alternate to another, one will get high water when it's supposed to be low water," he said.

Other concerns include the introduction of chemicals into wetlands that are not monitored and pharmaceuticals and the lack of signage alerting people to the presence of partially treated wastewater.

Lopez also noted that the projects tend to be designed by commercial firms that are then contracted to monitor the site, rather than independent third-party scientists.

The negative consequences of the projects became clear at technical workshops the Lake Pontchartrain Basin Foundation held in 2010 and 2016.  A marsh just south of Ponchatoula where the city of Hammond was discharging treated wastewater had actually seen a loss in wetlands, Lopez said.

That project, which began in 2006, was the first to discharge wastewater into a marsh, Lopez said. Previous projects had been in swamps. At the 2010 workshop, scientists learned about the wetlands loss in the Hammond project, where 160 to 300 acres of marsh was converted to open water, Lopez said.

Initially that project had seemed to be functioning well, Lopez said. In the first two years, everyihing looked good and the marsh saw tremendous vegetation grlwoth. "The everything died off," he said.

That case prompted the Lake Pontchartrain Basic Foundation to ask the state not to approve any more wastewater discharges into marshes. The fear was that marshes were more vulnerable to the potential harm caused by such projects.

But now scientists are concerned about forested wetlands as well. In a marsh, grasses grow more quickly and died more quickly, Lopez  said. But if the growth of trees in a swamp slows, it's not as obvious, so ill effects don't show up as quickly.

That's why the foundation broadened its request to cover all new projects. But it also wants existing projects to be re-evaluated by independent scientists or engineers who would take an indeph look at the wetland site and treatment plant and its compliance history, among other things.

A policy paper released by the foundation last month recommends that independent reviews provide the basis for future decisions on managing and permitting such projects, including the possibility of abandoning existing projects.

The wastewater itself should be treated to the same level required for discharging into surface water, the policy paper says.

The new position that the foundation is not precipitated by Mandeville's permit renewal, Lopez said, but it does coincide with it. Kristi Trail, president of the Lake Pontchartrain Basin Foundation, said that the group plans to comment each time one of the wastewater projects comes up for renewal.

In the case of Mandeville, the group met with city officials on Sept. 1 to share concerns about the permit renewal. Trail also spoke at last week's Mandeville City Council meeting. She said that the proposed permit renewal would allow the city to have a higher level of total suspended solids in its wastewater, and the foundation is opposed to that because of fears that the ultra-violet light used to disinfect the wastewater will not be as effective.

The foundation wants Mandeville to be held to the more stringent level, she said.

At last week's meeting, Public Works Director David deGeneres said that Mandeville stays well below the permitted level it has now. He downplayed the change in the request and told the City Council that he's observed growth in the wetlands. "We've been planting cypress and they are growing like wildfire," deGeneres said.

Lopez said that the wetlands in Mandeville are generally in good health. But he credits the closing of the Mississippi River-Gulf Outlet, which had been stressing swamp around Lake Pontchartrain for decades. Salinity in water and in soils has been coming down since the closure in 2009, he said, and that has nothing to do with wastewater assimilation projects.

To the contrary, Lopez said reducing salinity was never a good argument for discharging wastewater since the volume of water was comparatively small. Now, he said, it's not necessary anymore.

"Once you have one of these plants discharging, they're often designed with no alternative," Lopez said. "You can never turn it off."

Brady Skaggs, on of the authors of the policy, said that as far as the foundation scientists know, Louisiana is the only place in the world using natural wetlands as a wastewater treating strategy and other. Those who've experimented with it have abandoned it in favor of using constructed wetlands.

The better solution, in the foundation's view, is to build wetlands where the hydrology can be controlled and optimum plants would be used. That would be at true extension of the treatment plant, Lopez said.

Follow Sara Pagones on Twitter, @spagonesadvocat.