Increasingly, closed landfills are being converted into recreational areas such as parks and golf courses. Although the unpredictable nature of waste decomposition can make this morphing tricky, we can determine the success of some of the older landfill conversions.
One such site, the Danehy Park landfill, Cambridge, Mass., once considered a yawning, derelict liability in the eyes of the surrounding community, has been open to the public as a recreation area since 1990. Housing three softball fields, three soccer fields, a multi-purpose playing field and other open spaces, the 50-acre park now provides more than two and a half miles of jogging, walking and biking paths, and parking for 300 cars. Additionally, a two-acre wetland serves as a collection point for stormwater runoff and 20 acres of slopes are generously planted with wild flowers and grasses.
The city of Cambridge began converting the Danehy landfill - formerly an old, excavated clay pit used as a municipal solid waste landfill and later as a repository for construction and demolition debris - into an asset in the late 1970s with the help of Cambridge-based Camp Dresser McKee (CDM).
One of the long-term concerns of closing any landfill is the build-up and venting of landfill gas, which is at peak production approximately seven to 10 years after dumping ceases. Most closed landfills now use active gas ventilation systems with flares. But at Danehy, a crushed stone passive venting trench was created around the perimeter of the landfill in the 1970s.
With this system, gas moves laterally beneath the cap, mixes with air in the porous spaces between the crushed stones and, once released, is undetectable within 2 feet of the trench, says John Kissida, CDM's project manager responsible for the landfill closure and conversion.
While the stone system works, another important environmental consideration when monitoring closed landfills is the settlement of decomposing trash, Kissida says.
This aspect posed a particular problem at Danehy. In the late '70s, the city allowed the Massachusetts Bay Transportation Authority (MBTA) to use the site as a construction staging area for a rapid transit line extension. In exchange, the MBTA awarded the city a $3.6 million grant to dump materials from the tunnel excavation on the top of the trash layer. This resulted in an effective cap of between 4 and 40 feet of fill over the entire site, which in turn was topped with an additional 1 foot to 2 feet of sand and loam. During the filling, some park areas settled more than 14 feet.
Today, some settlement continues to occur in certain areas, "but it's nothing we're concerned with," says Rich Rossi, deputy city manager for Cambridge and Danehy project manager. "We feel good about the predictability of the settlement."
To date, Danehy is hailed as a success. Compared to many "typical" reclaimed landfills that often plateau, the site is designed with fairly varied topography, which even includes a sledding hill. Overall, the park has boosted surrounding property values and spurred the construction of new, high-priced condominiums overlooking the site, and it has increased the city's open space by 20 percent.
"The passive recreation areas are lush, green and beautiful," Rossi says. And because the park sits on the opposite corner of a subsidized housing area, the Danehy site has become an equalizing force in the Cambridge community.
According to Rossi, the only problems have been wear and tear in certain play areas, which is being remedied in one section with the installation of artificial turf surface.
While landfill managers across the nation and the world - including people involved with New York's Fresh Kills landfill closure - look to Danehy as a model, the site continues to develop. For example, a recently completed glassphalt pathway winds toward an area devoted to public art.
Kissida and Rossi attribute their success to their strong working relationship. The two have been partners on the Danehy project since 1981. "Rich [Rossi] and I know the site, we also know all the players and all the decisions, and why those decisions were made," Kissida says. "There is an institutional memory related to the site."
Furthermore, securing a long-term relationship with consultants and the MBTA ensured that the people working on the site were committed to making it a success, and helped raise funds to pay for improvements. The MBTA agreement, and state and federal grants saved the city from using significant amounts of taxpayer money.
So, as it enters its 10th year of operation, the success of Danehy Park landfill has become a useful model for communities, solid waste managers and engineers involved in the process of closing landfills. "Too many times we look at a site and only see what's there," Kissida says, "but it does not have to stop there. We need to have a vision and look beyond current conditions."