Pollution in Falls Lake has long concerned environmentalists and others, even landing parts of the lake on North Carolina’s list of impaired waters. Now the city is pursuing an unconventional way to treat the lake’s water quality: algae.
The city plans to build an “algal floway” in the Falls Lake watershed, and is currently seeking a site for the project. Also known as an algal scrubber, an algal floway is a pollution control measure that uses algae to remove nutrients from water.
The council unanimously approved spending just over $1 million on the project at a February meeting. Local environmentalists and southern Durham residents, meanwhile, worry the project is a Band-Aid solution for the bigger issue of overdevelopment in southeastern Durham County.
“What has not been regulated heavily is the mass amounts of overdevelopment,” said Pam Andrews of Preserve Rural Durham, a group founded in 2022 to protect and conserve rural areas. The group has been on the losing end of rezoning decisions in southeast Durham, including approval for the construction of 100 new townhomes last summer.
Yet council members — even some who have opposed some developments in southeast Durham — say the city must act to reduce nitrogen levels in Falls Lake. And they say that even at $1 million, the algal floway is less expensive than other solutions, such as building treatment plants to treat the lake water.
“It’s concerning to me, all the development that’s happening in southeast Durham,” said Council Member Chelsea Cook, who voted against several area rezoning requests. “Do I wish historically that we had made different choices in southeast Durham? Perhaps.”
“Still, we have to meet the Falls Lake standards. The algal floway approach represents an innovative solution that could be a huge money-saver for the city.”
Trouble in the (drinking) water
Falls Lake pollution has drawn attention partly because the lake provides drinking water for Raleigh and other municipalities. Yet the lake also receives runoff from southeast Durham, where development has expanded in recent years.
Stormwater runoff carries dirt from construction sites into Falls Lake, allowing excess nutrients like nitrogen and phosphorus to enter the water supply, according to Neuse Riverkeeper Samantha Krop. The excess nutrients cause harmful algal blooms, depleting oxygen in the water and blocking sunlight.
Algal floways work by pumping polluted water onto a slab. Algae naturally grows over the top of the slab, absorbs the excess nutrients, and the cleaner water flows back to the lake. After two weeks, the algae is scrubbed off and laid out to dry before being composted or disposed of in a landfill.
Project Manager Jonathan Baker says the algal floway project will help the city comply with the Falls Lake Rules, established in 2011 to reduce the amount of pollution entering from upstream. The rules require a 40% reduction in total nitrogen and 77% reduction in total phosphorus by 2041.
The city will work with Gradient, a consulting firm specializing in stormwater management, to conduct the site selection evaluation for $1,046,376, with a contingency fund of $156,956. The project will be paid for using city stormwater utility fees.
The city will also lead public engagement efforts to inform Durham residents about the project.
It’s the second time Durham has tried to build one of the devices. In 2021, the city considered a potential site in Granville County, which sparked controversy, according to an article from the Butner Creedmoor News. Neighbors voiced concerns that the algal floway could create smells and noises and attract pests. The Granville site was eventually abandoned.
This time around, only property within Durham County limits will be considered. The city, which previously looked at only four-acre sites, will also expand its search to smaller tracts.
The project has been in the works since 2012, when the city first conducted a feasibility study. A small-scale pilot study followed from 2015 to 2017, which found that using the algal scrubber reduced nitrogen and phosphorus by 12% and 32%, respectively.
While algal floways are still uncommon throughout the country, Baker cites two similar projects in Vero Beach and Indian River, Florida as examples of successful implementations of the technology.
The ‘root of the problem’
Tina Motley-Pearson, another member of Preserve Rural Durham, questions the solution’s effectiveness. Motley-Pearson notes that a technological approach to pollution in another nearby lake was tried previously without success. In 2014, SolarBees were deployed in Jordan Lake. SolarBees are solar-powered devices designed to improve water quality by mixing and aerating the water. The over $1 million state project was intended to improve water quality in Jordan Lake, a body of water similarly affected by algae blooms, according to WRAL.
After two years of the pilot project, the state removed the much-criticized SolarBees from Jordan Lake. According to a release from the N.C. Department of Environmental Quality, the giant water mixers “indicated no significant improvement in water quality.”
Instead of technological fixes, Motley-Pearson wants a solution that tackles the problem upstream.
“They’re never gonna tell the developers like, ‘Hey, maybe you could, maybe you could develop in a way that wasn’t dumping so much nitrogen in,’” Motley-Pearson said.
Krop voiced similar concerns about the city addressing the water quality problem from only one angle. For example, preserving forested land helps improve water quality, Krop said. Forested areas can store and slowly release nutrients like nitrogen and phosphorus. Research from the UNC Collaboratory study on Falls Lake watershed shows that when forest cover drops below 70%, there are measurable declines in a watershed’s water quality.
The algal floway is “potentially something that could work, but I think it does not get at the root of the problem…,” Krop said. “The most low-hanging fruit solution is to protect the natural solutions that are currently in place on the landscape.”
Pam Andrews also expressed worry about potential smell and noise nuisances for the surrounding homes.
Baker said Vero Beach residents did not report any odors or an increased level of mosquitoes.
In line with City Council wishes, Baker is looking into turning the area near the algal floway into a site for recreational amenities such as hiking trails.
Cook said the city will continue to hold community engagement events as the project moves forward.
“If folks have concerns about the project as it progresses, the city is interested in hearing from them,” she said.
Above: Photo of Falls Lake courtesy of ncparks.gov.
