The 12-acre Carver-Marion-Wareham (CMW) Landfill, overlooking the weather-prone Buzzard Bay, is just one of several closed landfill spaces that Covanta has to manage on the East Coast. These waste-to-energy ash landfills are traditional Subtitle D vegetation caps, meaning that Covanta is also responsible for overseeing monthly maintenance of mowing and the occasional reseeding.
Since 2012, the weather along the Atlantic coast has presented Covanta a unique challenge when it comes to the maintenance of the vegetative layer. While they are always on standby to manage any weather repercussions, the cost of those repairs has been significant. Especially when it comes to rebuilding slopes, replacing soil, and re-establishing vegetation.
With the upcoming closure of the CMV landfill, the site managers anticipated problems with the slopes, due to the extreme weather conditions. Slopes would weaken, become unstable, and require rebuilding. It was a process that might need to occur regularly.
The ClosureTurf® system offered a way to eliminate that risk.
“Once we did our research and evaluated other sites, we focused on the long-term aspects of the system,” said Melloni, “and found that ClosureTurf® required very little maintenance, if any, after installation. That was a slam dunk for us.”
The landfill closure system met and exceeded the EPA Subtitle D requirements. And, the three-component closure system did not require any soil coverage.
“We really liked that it provided around 12,000 cubic yards of extra capacity for ash,” said Melloni. “Because the two feet of soil is not required, we were able to use that space to our advantage.”
“With 30 mph winds, the main concern was getting the Super GripNet® geomembrane to lay down nice and tight in order to avoid wrinkles,” said Melloni. “The crew did an amazing job…. Another thing we experienced on site was when we began installing the engineered synthetic turf, gas began to build-up and we started to see pockets form. We eliminated this by installing a specialized [system-specific] gas vent on every acre. Once the relief values were in place, the turf laid down perfectly. We were able to incorporate this seamlessly with our traditional gas collection system.”
Underneath the geosynthetic cap, gas is generated and rises to the surface where a vacuum created by the differential pressures is vented through the surficial gas collection foot. This proved to be an efficient method of gas collection while reducing the amount of condensate that needed to be managed.
Because this would be the first use of ClosureTurf® in the state, the agency wanted some time to do its homework and fully evaluate each component of the system. With time constraints to complete the project looming, the DEP agreed to allow the system to be used on the 4-acre top deck but required the use of a traditional vegetation system on the side slopes.
To date, the site has performed exceptionally well.
“The last two summers have been some of our hottest and we have experienced some torrential downpours,” said Melloni. “The ClosureTurf® system has held up wonderfully with no maintenance to date.”
The Covanta team was so impressed with the CMW project that they specified the system on a separate site in Haverhill, Massachusetts.
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