IN 2001, THE MOST FAMOUS landfill in America — Fresh Kills Landfill on Staten Island, N.Y. — closed for business. Local politicians hailed a “bright new beginning” for the beleaguered borough. Since then, New York City has engaged in a master-planning process that will guide the closed landfill's evolution during the next 30 years. In addition to dealing with such issues as landfill gas and leachate management, the city is working with private firms to redevelop the closed landfill as a public park, with areas for art, environmental education and recreation.
Although still in the early years of post-closure care, Fresh Kills Landfill may prove to be a model for landfill managers. As more and more landfills fill up and close, waste companies and other industry observers are studying landfill closure and post-closure procedures to determine ways to improve efficiency and environmental performance.
Landfill closure procedures have been in place for years. In 1991, the U.S. Environmental Protection Agency (EPA), Washington, promulgated regulations governing the disposal of nonhazardous wastes in landfills, including provisions for closure and post-closure, under Subtitle D. The regulations require careful capping and implementation of environmental monitoring systems, and the closed landfill must be monitored and maintained for 30 years.
Recent research, however, may change how the industry looks at Subtitle D regulations for landfill closure. For example, the Environmental Research and Education Foundation (EREF), Alexandria, Va., has funded a project to develop a performance-based system to evaluate post-closure care at landfills. Other projects such as bioreactors may also have long-term implications for landfill closure.
“You've got a whole bunch of facilities that have gone from 1991 to today that will close in the next few years,” says Ed Repa, director of environmental programs for the Washington-based National Solid Wastes Management Association. “Researchers are now looking at alternatives to [standard] post-closure care, so facilities can figure out how best to use their money to extend that amount of care or get to the end point.”
Closing a landfill involves several steps. Once a landfill cell or cells have reached capacity, a final cover must be installed. Those final covers may include a liner or multiple liners, the actual waste material, a soil layer, run-on and run-off control features, groundwater monitoring networks, and settlement monitoring markers.
Once the landfill is capped, the site owner/operator is required to provide post-closure care for a period of 30 years, although owners can file a request to terminate the post-closure period earlier if it can prove that the landfill is environmentally stable. During the post-closure period, the closed landfill is routinely monitored to ensure that erosion and settlement do not compromise the final cover system. Additionally, the landfill is tested for groundwater contamination and the migration of landfill gases.
Ft. Lauderdale, Fla.-based Republic Services, like many waste companies, closes its landfills one cell at a time. Currently, the company has about eight to 10 closure projects per year, varying in size from 10 to 20 acres. Generally, the company uses composite landfill caps that have a clay component or a geosynthetic clay liner, as well as a drainage blanket and a vegetative topsoil layer.
“We try to keep it at that size because of economies of scale with contractors and liner installers, etc.,” says Matt Davies, Republic's vice president of environmental engineering and compliance. “We've also tried to tie our capping projects to coincide with cell construction, if possible. A contractor is on site already, so [we're] able to save a few dollars in terms of mobilization if they can do both projects either simultaneously or back to back.”
The underlying implication of Subtitle D closure regulations, according to Dr. Morton Barlaz, a civil engineering professor at North Carolina State University in Raleigh, is that environmental monitoring will end after 30 years because the landfill will be stable. However, the EPA lacks technical criteria from which to define stability, Barlaz says. That makes it difficult for regulators to decide whether to extend or reduce the post-closure period. The need for technical data is even more important because of bioreactors, in which the waste decomposition process is accelerated, he says.
To address those issues, Barlaz has joined a team of researchers (including Ed Repa; Jeremy Morris and Mike Houlihan from GeoSyntec Consultants in Columbia, Md.; Steve Clarke and Dave Burt from Houston-based Waste Management Inc.; and Pat Sullivan from SCS Engineers in Sacramento, Calif.) to develop a conceptual Evaluation of Post-Closure Care (EPCC) model.
The model will evaluate the environmental risks associated with landfill closure and how those factors affect post-closure care. Using an integrated, modular approach, the EPCC model will regularly assess each of the four components of post-closure care, including leachate collection and treatment, landfill gas collection and treatment, environmental monitoring, and maintenance of the final cover, to determine the next steps.
“There is a growing realization that the concept of [studying] environmental performance made a lot of sense,” Barlaz says. “This project asks, ‘What do we need to do to evaluate whether a landfill is a potential threat to the environment?’ Then you use a ‘divide and conquer’ approach. Instead of talking about a landfill as a single entity, let's talk about the gas, the leachate, the ground cover and the groundwater as separate entities. You could show you were stable with respect to one or the other and determine how that would affect post-closure care. Post-closure monitoring costs money, and if we're going to spend money, let's spend it wisely.”
In the EPCC model, the performance and residual risks of each post-closure component can be evaluated continually or as-needed, allowing decisions to be made regarding continuation, reduction or elimination of each component's post-closure care requirements. For each module, an evaluation process was developed based on regulatory standards and site-specific performance criteria.
That approach, Barlaz says, represents a more realistic and environmentally protective strategy for the management of closed landfills than the standard “30 years and walk away” approach under Subtitle D. An important goal, Barlaz adds, is to encourage landfill designers and owner/operators to focus on reducing post-closure impacts by emphasizing the interrelation between the design, operation and post-closure periods of a landfill's lifecycle.
The researchers now are looking for a landfill project to use as the case study for the EPCC model. “In our model, the post-closure care management program is divided into fairly small chunks, each of which is pretty readily addressed,” Barlaz says.
“If you're showing your groundwater is clean, for example, doing expensive groundwater analyses doesn't make sense, so let's do something that's cost-effective,” he says. “If you wait to start thinking about this after the landfill's closed, you're going to waste time and money.”
Waste companies, EPA, municipalities and other entities also are investigating other methods to improve post-closure processes. The ongoing development of bioreactor technology, for one, has promising implications for the length and expense of the post-closure period. Bioreactor landfills use specific techniques, such as recirculating leachate and other liquids, to enhance a landfill's natural biodegradation process and stabilize organic components much quicker — ideally within five to 10 years — than a dry-tomb landfill. Bioreactor advocates claim that the technology will change post-closure care by reducing long-term environmental risks, producing less-harmful leachate, shortening the time periods during which air and water emissions are generated, and reducing costs associated with long-term care.
The waste industry also is examining the effect of alternative final covers (AFCs) on landfill closure. AFCs include asphalt covers, concrete covers, capillary barrier covers and evapotranspiration (ET) covers, which absorb and hold water until it evaporates. Depending on the specific site, those covers can be more cost-effective than traditional covers. Republic's Davies notes that with the rise in gas and oil prices, his company has noticed a 10 to 15 percent up-tick in the cost of geomembranes, a petroleum-based product.
“An initiative for us,” Davies says, “is we'd like to see more of the alternative caps. We're finding that in certain areas like arid environments, from a performance standpoint, it's not as important to have the geomembrane in the cap.” Another major challenge, Davies says, is erosion and sedimentation control at closed cells. “Probably our biggest challenge, once we get the dirt on the hill, is keeping it on the hill,” he says. “We are seeing some different products coming out that are economical and can help us in that area. In some cases, we've seen some covers that incorporate grass seed and mulching as part of that product as well. You roll this material out, and as long as you can get it hydrated with your initial installation, that vegetative material really takes off.”
Finally, both Barlaz and Davies advise landfill managers to factor proposed end-uses into their post-closure plans as early as possible. Evaluating an end-use strategy is a site-specific process that must consider local and federal brownfields regulations; long-term geotechnical, environmental and public health issues; and other community concerns as they arise, Barlaz notes.
“For an end-use strategy to be successful in the long-term, it will need to be considered in conjunction with the local community and regulator, as well as other local or regional public and private stakeholders and interested or affected parties,” he says.
Today, landfills have been redeveloped into parks, golf courses, botanical gardens, ski slopes and commercial centers. If the site is going to become a park, accommodations for a water supply and irrigation system should be taken into account. Flat areas can be engineered for heavier uses such as sports, while steeper areas could be used for natural vegetation.
“When we're talking about the end-use of a landfill, we need to be thinking about that when we're very early in the permitting process or shortly thereafter,” Davies says. “We don't want to go and put in a $100,000 per acre cap that six months from now we're just going to tear up so we can put more fill in or put a recreational use in. If you wait until the last minute when you're about to cap, it's really too late.”
Kim A. O'Connell is a contributing editor based in Arlington, Va.