Landfill innovations – down-in-the-dumps solutions
Looking for innovations on the current landfill scene is a bit like chasing the facts in a scandal: the key is to follow the money. Where the costs are greatest, that is where the push to improve efficiency in all stages of the landfill lifecycle can be found.
In both the public and private sector, landfill operators are seeking better ways to monitor their sites, deal with leachate and, perhaps most importantly, maximize their use of space.
This landfill space isno longer taken for granted in today’s environment of complex regulations and intense economic pressure.
“Landfills are under an incredible amount of pressure to be fiscally responsible, either to make a profit or bring in enough revenue to cover costs. It,s harder and harder to do that because it’s such a competitive environment,” says consulting engineer Neal Bolton, owner of Blue Ridge Solid Waste Consultants, Bozeman, Mont., and author of “The Handbook of Landfill Operations.”
“In the past, it never would have paid to haul garbage 1,000 miles because you could basically dig a hole and put garbage wherever you wanted to,” Bolton says.
But building a new facility is no bargain in the current environment, and sending waste out of town is often the cheapest, least painful option.
“Siting [a landfill] is a multi-year, multi-million dollar effort, and it’s a gamble at that,” Bolton says.
Bristol, Va., for example, spent the past eight years seeking a permit to build a regional landfill in an abandoned quarry. The site was unusual and the process involved a great amount of study, phone calls and trips to the state capital in Richmond. “I have lived, eaten, slept and breathed this project,” says Bill Dennison, the city’s assistant manager and lead staffer on the project.
The good news is that Bristol finally received its permit earlier this year and plans to begin accepting waste at the site from several counties in the area by late 1997.
Although in Bolton’s experience, most existing landfills continue to waste a lot of their precious air space, there is also a tremendous amount of work being done at landfills to make them more efficient and competitive.
“[Landfill operators] are trying to find ways to keep the revenues up, costs down and to use their air space as efficiently as possible,” he says.
Some of the space-saving innovations Bolton has seen at work in recent years include:
* alternative daily covers;
* improved initial compaction as well as recompaction;
* lowering of base grades when groundwater conditions allow; and
* proper and consistent management of garbage cells.
Bolton also mentions the possibility of negotiating with utility companies to re-route any utility rights-of-way that take up landfill space.
Mack Belue, head of the Dalton/Whitfield Solid Waste Management Authority in north Georgia, has seen the push to save landfill space in his community and else, where. In his service area, for example, refuse from the carpet industry makes up almost 50 percent of the waste stream, and in past years, 40 percent of this waste was sent to be landfilled loose rather than in bales.
However, Belue and the authority have slowly whittled away at this percentage by encouraging carpet manufacturers to bale wastes on-site, thereby increasing the density of garbage sent to the landfill. Meeting with industries and offering fee discounts for baled wastes have helped lower the amount of loose waste to 30 percent.
Kurt Thaus, Director of Environmental Central Services for WMX, Oak Brook, Ill., says more efficient use of space is also a key issue at his company’s facilities. The company is involved with 100 or so landfills in the United States and plays a variety of roles, from building and operating its own sites to managing facilities on contract with municipalities or other private waste companies.
“We’re seeing landfills become more [like] processing facilities,” Thaus says. “They,re no longer a place to just put trash.”
Within their boundaries, sites may have the capability for functions like the recovery of recyclables, incineration, composting and/or solidification of liquid wastes. Sites can thus accept a diverse waste stream and maximize revenues without using valuable landfill space for the entire tonnage.
UNIQUE SITE PROVIDES LONG-TERM
The landfill story in Bristol includes many of the issues and solutions described by Thaus and others. The story is one of both using existing space more efficiently and finding a new site altogether.
The city pursued the abandoned quarry as a landfill site with two main goals: it wanted a long-term destination for its solid waste, and, if possible, it wanted the facility to be locally controlled. The only other real option was to transfer waste to an outside site, a step the city hoped to avoid.
With this goal of “controlling its own destiny,” Bristol knew any new facility would have to accept waste from several area counties, since fees from the 70 tons per day generated by Bristol alone would not be enough to make the landfill financially viable, according to Dennison “It was either regionalize or transfer,” he says.
Bristol took the first step in this arduous process in 1988, when the city began discussions with the private company that had excavated the nearly 400-foot-deep quarry. By that time, the city had stretched the space in its existing Subtitle D landfill almost to the limit.
A large, national waste company had previously contracted with the quarry owner to explore the prospects for siting a landfill there, but backed off after its initial attempts at obtaining permits failed.
Thus, succeeding with the project would clearly be difficult, but the city was not as free as the waste company to dismiss the site so quickly. At the very least, officials figured that the quarry warranted a most in-depth look.
So, in 1989, Bristol hired Deerfield, Ill.-based STS Consultants to help make such a determination of feasibility, provide a cost analysis and later to obtain permits and create a design for a landfill at the quarry.
“We knew it would be a challenging project, and we didn’t tell [the city] anything less than that,” says Doug Hermann, the consulting firm’s project principal.
At that time, the city believed it was only about a year away from running out of space at its existing landfill, located adjacent to the quarry. Waste was being deposited at the site in a seven-acre working face, within an active cell of about 17 acres, according to Dennison. However, the city was able to buy itself a few years of space and time at the site through several measures, such as:
* upgrading to heavier waste compaction equipment;
* switching from soil cover to a synthetic daily cover that is removed each morning from the working face. Sheets of this cover have lasted up to eight months, Dennison says;
* transporting tree trimmings and brush to a wastewater treatment plant, where the materials are chipped, milled and mixed with sludge to create a dry compost;
* obtaining vertical expansion permits from the state in 1991 and 1993;
* beginning “landfill mining” at the site in 1994; and
* operating an incinerator as well as a tire chipper at the site. The city intends to use the chipped material as a daily cover additive and a medium for landfill gas (LFG) and leachate collection, although these uses have not yet been approved.
Since the quarry site, expected to open in late 1997, will take only baled waste, the city will continue to operate the old landfill for waste that is not easily baled and as “insurance space” in case baling equipment breaks down temporarily.
The state’s willingness to consider Bristol’s unusual and potentially problematic site was crucial from the beginning. “Ten years ago, I don’t think we would have gotten through the front door with this application,” Dennison says. “We got a fair hearing from the [state] agency, and without that we would have been dead in the water, no matter how much money and experience we had in hand.”
The city’s application made it through Part A of the process – a determination of the site’s feasibility – due largely to extensive study of conditions in the quarry. For example, the consulting firm used piezometers to look at groundwater flow at multiple levels in the quarry.
“One of the beauties of this site is that it’s nearly 200 feet below the groundwater table,” Hermann say. Thus, since groundwater flows into the site but not out, any potential polutants should remain on site where they can be monitored and collected.
Based on this data, the firm created a design that calls for a gradient control zone at the base, from which groundwater will be pumped to ensure its inward flow. Automated pumps will carry this groundwater to the area’s stormwater system.
Above this zone is a secondary clay liner – beyond what is required by Subtitle D – then a permeable “witness” or monitoring zone, the primary clay liner and then a synthetic liner. A leachate collection system installed above this synthetic barrier will channel leachate, via gravity, to a shaft, from which it will be pumped to the surface and transported to a waste-water treatment plant.
The firm designed an alternate liner for the quarry’s steep sides, including wire mesh on the rock face to minimize falling rock, then a permeable geotextile, an impermeable geomembrane, a layer for leachate drainage and a buffer zone of “select waste” that will prevent larger pieces of baled waste from damaging the geomembrane layer. The firm used computer modeling to demonstrate that this alternate liner would provide the same performance as the type of liner normally required by regulations.
Finally, the design includes a gas extraction system that will be active during the landfill’s operation. A blower will pull LFG through horizontal piping and vent the gas away from the working area.
As with siting and operation, closure is also a time in the lifecycle of landfills when innovation is key. In late 1992, deciding the fate of its Flanders Road landfill, 46-acre Subtitle D site, was the initial challenge for Groton, Conn. The landfill could have remained open under federal rules, but the state Department of Environmental Protection (DEP) was pushing for closure, according to Dan Duffy, project manager for Camp Dresser & McKee, Cambridge, Mass., engineering consultants for the city.
“It was sort of a mutual understanding that the state wanted it closed,” Duffy says.
The Flanders Road site was an unlined landfill for which the city had never gotten a state leachate discharge permit, according to Duffy. Although the site had been permitted before this discharge requirement was enacted, the state saw potential problems and readied a consent order that would have required the closure even if Subtitle D did not.
In April 1993, at the advice of its consultant, Groton decided to close the landfill rather than force the state’s hand. Timing then became everything, and the crucial date was Oct. 9, 1994. If the site’s cap was in place by this deadline, the city could avoid Subtitle D requirements for financial assurances and post-closure monitoring. After this date, the state’s order would have taken effect.
Finding money for the closure was the biggest obstacle to meeting the deadline, and the fact that Groton had planned to operate the facility into the next century meant two things: the city had not set aside a lot of funds for such a closure, and the flat site had not yet been built up to the necessary closure grades.
Past methods of operation at the landfill also made closure difficult. “To put it bluntly, we messed up all 46 acres at once [during operation], rather than closing down one cell at a time,” says Public Works Director Gary Schneider. “It kind of looked like a moonscape out there.”
The city and its consultant found a single solution to these issues by deciding to accept out-of-town waste at the landfill. Between May 1993 and September 1994, the city took in 1,000 tons to 1,500 tons per day, raising the level of the site and generating around $6.5 million in tipping fees, enough to fund the entire closure.
Thus, Groton avoided the trials of a bond issue to raise funds, as well as the cost of bringing in large amounts of clean fill material to grade the site. Also, differential settling and maintenance problems would have been likely with the use of this material, which tends to be much more dense than waste, according to Duffy.
In accordance with Subtitle D rules, Groton accepted municipal solid waste, largely from New York City, at the site until October 1993. The city then began taking only shredded bulky waste – which is not regulated by Subtitle D – until September 1994. Closure work began in July 1994, as waste was still coming into the site, and the contractor had the barrier layer in place just in time to meet the October deadline.
Finding enough waste to meet closure needs at the Flanders Road site was not a problem throughout the process. When the landfill opened each morning at six o’clock, a long line of trucks waited at the gate to pay the $20 to $25 fee.
“Up here in New England, if you have a site that is available, you can get stuff coming out of your ears,” Schneider says.
However, as Duffy acknowledges, “It is never a popular decision to start bringing in 18-wheelers full of New York and New Jersey waste.”
There was concern that materials such as medical wastes, tires and batteries might slip into the landfill, but assurances from the public works department that loads of waste would be monitored closely helped win vital support from the city council. Groton ended up with a surprisingly clean stream of waste flowing into the site, according to Schneider.
“I think the important thing was having a good plan up front, with all the issues identified and answers for these issues,” Schneider says.
The department used a broker to find haulers and required them to pay in advance by certified check. Staff did frequent spot inspections of loads and kept detailed logs.
“We weren’t a Superfund site, but if we became one we wanted to have a good, detailed list of who brought what in and the tonnage,” Schneider says. “We had a good accounting of the [incoming] waste.
“We were watching, and we could cut off the flow of waste at any time,” he says. “[And], when you demand the money up front, you’re usually getting people with a good cash flow.”
Along with the public work department’s vigilance, the environmentally concerned bent of the city council was key to the project’s success, according to Schneider.
“Our council has always been on the pro-environmental side, the green side,” he says. “It is very concerned about meeting permit requirements because it expects [local] industries and other towns around Groton to meet these requirements.”
Finally, in spite of its threat of a consent order, the state DEP was responsive, open-minded and supportive of the closure project, according to Duffy. “It was one of those few projects where everybody gets together and cooperates to get the job done,” he says.
Other noteworthy elements of the Flanders Road closure project include:
* the use of a geomembrane layer rather than a clay cap. The city went beyond closure requirements in installing this layer in order to minimize the chance of future problems;
* the use of a blend of sand and composted sewage sludge as the top soil layer. The contractor had difficulty finding enough clean soil to create a six-inch cover over the 46-acre site, and thus proposed this blend as a solution when a large volume of composted sludge was found to be available at a Massachusetts facility. “It has worked out tremendously,” Duffy says. “The blend has grown the best grass I’ve ever seen in any closure;”
* the installation of a landfill gas extraction system, including 30 wells buried from 30 feet to 80 feet into the waste, two miles of header pipe, a condensate tank, blower *and temporary candlestick flare; and
* the connection of an experimental fuel cell to this gas extraction system. The phosphoric acid cell functions much like a battery, using methane to produce both electricity and heat, and is part of an EPA demonstration project. Groton signed a MOU this summer with investor-owned Northeast Utilities, Berlin, Conn., to host the fuel cell project for at least 18 months.
“We’re in the process of looking right now at what is out there beyond those 18 months,” Schneider says. “Groton would definitely like to keep the cell here. Maybe there is something we can do with the research to help promote the use of landfill gas.”
The cell uses about 80 cubic feet per minute (cfm) of LFG, while the remainder of the 400 cfm to 700 cfm that the Flanders Road site produces is flared off. The cell generates around 140 kilowatts to 160 kilowatts of power that goes into the utility’s grid. For its part, the utility paid for $300,000 worth of improvements to the site’s LFG system – fencing, outbuildings, a flare pad – that will remain in place even if the cell is removed.
In the competitive, uncertain landfill business of today, efficiency is more important than ever. Measures like those implemented in Groton and Bristol will help local governments meet this challenge into the next century.