Eyeing a looming deadline to cut algae-feeding pollution in the St. Johns River, Jacksonville officials want to test new equipment to filter debris from rainwater in the city’s drainage systems.

The city’s Environmental Protection Board endorsed a $274,000 pilot project this week to measure how well a device with the unsexy name of a nutrient-separating baffle box will lower the amount of nitrogen and phosphorus flowing toward the Trout River (a St. Johns tributary) through a drainage line on Carbondale Drive East.

If the device works well there, baffle boxes might be considered as options in other areas to help the city reach a state-imposed goal that would cut nitrogen releases by about another 44 metric tons each year.

The goal for the pilot, which needs City Council approval before money from the protection board’s trust fund is spent, is just to test equipment that has been used in other Florida communities for years.

Baffle boxes are attached to drainage lines as a sort of catch-all to stop trash, leaf litter and other debris that flows into storm drains during hard rains. Debris builds up in holding areas until a vacuum truck empties them and hauls the contents to a landfill.

A heavy tree canopy can add to the amount of nitrogen-rich debris accumulating in a baffle box, and the site on Carbondale was picked partly because there’s a lot of tree cover in the areas upstream of the drainage line.

Florida’s Department of Environmental Protection routinely credits baffle boxes with removing about 19 percent of the nitrogen in stormwater, but two firms working with the city on the pilot idea pointed to a University of Central Florida study in Kissimmee showing a 54 percent reduction in one area.

Environmental Quality Division Chief Melissa Long told the protection board there are about 20 areas in Jacksonville where the devices might be particularly valuable for cutting nitrogen and phosphorus, the chemical nutrients that act like plant food to help algae grow in the river.

Very rough, back-of-the-envelope estimates suggest installing baffle boxes at those sites might collectively cost about $4 million and might cut the city’s nitrogen load by about nine metric tons each year.

But that’s all theoretical since Jacksonville hasn’t used devices like this before to remove nutrients, making the pilot project a real-world test that would have a see-through “observation cover” where people passing by could watch the system working. The protection board's plan doesn't commit any money except for the Carbondale site.

Jacksonville has a December 2023 deadline to cut its nutrient releases into the St. Johns under a 2008 plan the state negotiated with a string of Northeast Florida governments and businesses, but Long told the board in January that the city was on track to fall short of its commitment.

The pilot project won't be an instant fix, either. The one-year test might not be completed until late next year or 2024, but would at least help the city plan its next move.    

Jacksonville uses baffle boxes already to catch trash in some areas, but those weren’t made to hold nutrients, which is done with a feature called an upflow filter that’s hard to block.

The system will last decades, although the material used as a filter will has to be replaced from time to time at a cost of hundreds of dollars, not thousands, said Ted Smith, vice president of Central Pipe Rehab, a Jacksonville business that proposed the project to the city along with Ferguson Waterworks.