New Hanover County, N.C.
A decade ago, treated leachate from the New Hanover County, N.C., landfill was toxic enough in the wintertime that it was responsible for killing at least one fat-head minnow during a state toxicity test. Now, since the county has constructed the state’s first leachate-treatment wetlands, a variety of wildlife is thriving in an environment created to treat the effluent.
The New Hanover County, N.C., Department of Environmental Management (DEM) began investigating leachate-treatment options during the early 1990s, following the state test that revealed that effluent from the county’s landfill was too toxic to continue discharging to the Cape Fear River. Some engineers recommended that the department revamp its existing leachate-treatment plant by installing a costly mechanical pipe system whose upkeep would require constant maintenance for the next 50 years. But Ray Church, director of environmental management for the department, had a different idea.
“My degree is in biology,” Church explains, “so I like to ask, ‘Can nature do it?’ A friend of mine had been doing research on wetlands and suggested we could use them to treat the leachate.”
First, the department needed to determine which type of wetlands would be most effective at treating the leachate: surface-flow or subsurface-flow. After conducting a two-year test, researchers determined that the surface-flow wetlands worked better than the subsurface-flow wetlands, Church says. In a surface-flow wetland, microscopic organisms that live in the roots of bullrush and cattail plants break down ammonia and nitrogen, thus removing contaminants from the water. Wetlands also can clean and reduce the volume of leachate through “evapo-transpiration,” wherein a growing plant takes up water and releases it through its leaves.
Despite those discoveries, one question remained: After installing the wetlands, would the county continue to discharge treated leachate into the Cape Fear River, committing to labor-intensive monitoring and maintenance responsibilities for the foreseeable future? A member of Church’s staff found the answer, suggesting that the county install a spray-irrigation system that would use treated leachate to water and fertilize closed landfill cells. That solution would eliminate the need to discharge effluent into the river and create fertile ground for the landfill’s ultimate purpose: to become a wildlife park.
With positive results in hand, and a plan for reducing and someday ending the discharge of effluent into the Cape Fear River, the DEM secured a grant for $785,000 from the North Carolina Water Management Trust Fund to build wetlands to treat landfill runoff. That grant prompted the county’s Board of Commissioners to contribute a match grant of $243,500, bringing the project’s total budget to $1,028,500.
The county hired Cambridge, Mass.-based Camp, Dresser and McKee to retain permits and design the wetlands, and it contracted with Wilmington, N.C.-based Thompson & Co. to build the wetlands, which cover a 5-acre plot between a closed cell of the landfill and nearby natural wetlands. The wetlands can treat up to 60,000 gallons of leachate per day by passing the leachate through two parallel cells and discharging the treated water into a 0.6-acre effluent-retention pond.
North Carolina’s first leachate-treatment wetlands began operating in June. During its first few months, the wetlands attracted national as well as international guests, but some of its most important visitors came from the county’s own backyard, Church says. “We just had 70 eighth graders here,” he boasts, “and, on opening day, there were 15 water snakes having a good time out there. Although we haven’t seen an alligator yet, I’m sure it’s just a matter of time.”
Agencies/companies involved: Barbara Dohl, SeaGrant, Raleigh, N.C.; Billy’s Irrigation, Teachy, N.C.; Camp, Dresser & McKee, Raleigh; Coastal Area Management Agency, Raleigh; Michael Nelson, Nelson Environmental Consultants, Wilmington, N.C.; New Hanover County Boards of Commissioners, Wilmington; New Hanover County Department of Environmental Management, Wilmington; North Carolina Clean Water Management Trust Fund, Raleigh; North Carolina Department of Environment and Natural Resources, Solid Waste Section, Raleigh and Wilmington; North Carolina Department of Environmental and Natural Resources, Water Quality Section, Raleigh and Wilmington; Sarah Liehr, and Rober Rubin, North Carolina State University Biological and Agricultural Engineering Department, Raleigh; University of North Carolina at Wilmington, Ecology Club; Water Environment Research Foundation, Alexandria, Va.; Thompson & Co., Wilmington.