Digging up the Dirt

Landfill mining at Fauquier County is scheduled three to six months per year to balance fines generation with landfill cover soil requirements.

Today’s landfill mining projects range from efforts to recover valuable material fractions, such as ferrous scrap, to attempts to save space and reuse landfill cover dirt. Local economics and infrastructure can lend themselves to the mining concept, as some success stories illustrate.

One such project was conducted on a 2.5-acre site at the Perdido Landfill in Escambia County, Fla. That area, an unlined cell, was mined as a pilot project between June and November 2008. According to the county, 54,300 yards of the landfill were mined. Different processing techniques were used to evaluate the ability to segregate the fines fraction (consisting mostly of soil and degraded waste) from the oversized fraction.

At Perdido, directly screening excavated materials using a trommel was found to be more effective than shredding the material and passing it over a vibratory screen. However, recyclable commodities eventually were no longer separated, says Pradeep Jain, project manager with Innovative Waste Consulting Services, Gainesville, Fla. He says the quality of the materials did not justify sorting.

Still, 38,000 cubic yards of soil was reclaimed as a result of the project. The reclaimed soil was recycled daily as intermediate cover on the internal slopes of the active landfill cell.

“We tried to recover material, but the quality of the material was not good enough for us to process,” Jain says.

Landfill mining will continue because land use is becoming increasingly restrictive, but local situations always will determine the need and viability of such a project, says Michael T. Dorsey, Fauquier County director of environmental services, Warrenton, Va.

“The justification for landfill mining will vary by community and specific situation,” Dorsey says. “Materials recovery for recyclable sales may not offset expenses, but if a community operates a WTE (waste to energy) [facility] with unused capacity, creating airspace via mining may be viable. Another community may find it difficult or impossible to site a new landfill, so a mining operation may be a practical solution. Fauquier County’s landfill needs additional cover soil, so fines recovery is very important,” he adds.

Fauquier County is trying to beneficially use recovered fines. “Mining is scheduled only three to six months per year to balance fines generation with landfill cover soil requirements,” Dorsey says. “We’re in our second year of a pilot demonstration period and, if successful, plan a long-term seasonal operation.”

Hidden Below
Materials recovered from MSW (municipal solid waste) are typically ferrous metals, plastic, wood, rubber and a fines fraction. A limited number of studies have characterized material recovered from an MSW landfill with respect to composition. Cover soil and degraded organic waste constitute 50 percent to 85 percent of the recovered material on a weight basis. This is based on analysis done in Alachua County, Fla.

“There are lots of opportunities to recover commodities if the market is right,” says Bob Wallace, principal and vice president of client solutions for WIH Resource Group Inc. (WIH) and Waste Savings Inc., Phoenix. He sees a focus on plastics and metals, in particular, in older landfills prior to the introduction of recycling efforts.

At Perdido Landfill, Jain says the plan was to dig up the garbage, run it through a trommel to screen out the soil and sort for ferrous, plastics and other salable products. “Most of the volume was plastics,” he says. “Ferrous was not a lot volume-wise but by weight it represented a decent fraction.”

Because recyclable material was heavily intermingled with the dirt, it presented a challenge. The material also was quite wet when it was mined.

Herein lies lesson one for those considering reclamation of recyclables in an existing landfill. Jain says, “Unless you have a MRF (material recovery facility) on site and you can co-process the incoming waste stream with the reclamation material, it will be difficult to do.”

Dorsey agrees. “Typically, landfill mining as a stand-alone operation is not economical,” he says.

“Recovering and selling recyclables from mining can partially offset operating expenses, but other landfill mining justifications/benefits include recovering landfill capacity, cover material, environmental remediation and possibly deferring closure expenses,” Dorsey continues.

In short, those people with experience in landfill mining projects suggest that landfill operators keep their eyes open for other related savings targets.

Big Savings
Collier County, Fla., saved roughly $350 million in valuable landfill air space as part of a landfill mining and reclamation project. The county did its own work targeted at reclamation and lays claim to having the first planned reclamation project, conceived in the 1980s. Reclamation work, however, did not begin until the 21st century.

Originally, cells one and two of the Collier County Landfill were unlined disposal areas covering 32 acres. The cells are near the northeast corner of the landfill and were filled with solid waste from 1976 through 1979. They have subsequently been closed by the county and covered with a soil cap.

Full-scale reclamation of the 22-acre landfill was underway in December 2007 and was successfully completed ahead of schedule and within the allotted budget, at less than $7 million, in September 2008.

The Collier County project was so successful that the Solid Waste Management Department received two awards for the reclamation of cells one and two. The department earned the Solid Waste Association of North America

(SWANA) 2010 Landfill Reuse Excellence Award and was recipient of the Sustainable Florida Collins Center for Public Policy 2010 Best Practice Award.

About 10 acres of the southwest corner of cells one and two were mined. The project recovered 50,000 tons of soil suitable for landfill cover. The total volume of waste and soil buried was estimated to be 378,922 bulk cubic yards, and the total volume of waste and soil excavated was estimated to be 473,715 loose cubic yards.

At Perdido, the overall soil fraction of excavated material was more than 70 percent, suggesting that substantial airspace may be recycled for additional waste disposal at the site and that some of the site’s daily cover procurement costs may be avoided by using screened fines during a full-scale mining, thus offsetting some of the large-scale mining project costs.

WIH Resource Group’s research finds that landfill mining is not typically motivated by materials recovery in the traditional sense of turning aluminum to cash. Instead, landfill mining is often motivated by more than one goal or desired outcome of the mining project, Wallace says.

“Projects would be more viable if they accomplished more than one thing—for example, recovery of metals, providing fuel for a waste-to-energy facility, postponing a landfill closure and/or remediating a landfill with environmental problems,” he states. “Most projects will only find a small subset of these benefits to be relevant—of course, everything is subject to change,” Wallace adds.

Fuel Production
Landfill mining also has been considered to recover refuse-derived fuel (RDF) from a landfill site for combustion at a waste-to-energy (WTE) facility. For example, the Frey Farm Landfill in Lancaster County, Pa., mined a lined cell. Recovered material from the site was sent to a nearby WTE facility to be converted to fuel.

In Ohio, several operations have been established to provide RDF for energy recovery. However, most of them are sourcing their materials from the original waste stream.

Landfill mining also has been proposed as a step subsequent to a bioreactor landfill operation.

The economic viability of RDF is a cost issue and will vary by community, Dorsey says. “In Fauquier County’s situation, recovered material will not achieve the high quality that’s required for RDF, and disposal via WTE is not economical with associated hauling and disposal expenses.”

However, Dorsey adds that if a community has ready access to a WTE facility, RDF may be viable for energy and volume reduction.

Jain notes that the Lancaster County project set out to recover waste for WTE from the outset.

Like most WTE plants, the county’s facility was designed to process more material than would be available early in the plant’s life cycle. The county started mining the landfill to provide an additional source of WTE material.

Research found that the Btu (British thermal unit) content of the reclaimed waste was lower than the Btu content of fresh material. However, when the waste stream catches up with the plant’s capacity in a decade, much of the usable material in the landfill will have been profitably used.

Although landfill mining has not caught fire across the United States, Wallace finds that in Europe, where they have a need for property in certain areas, the idea has been embraced.

“It is also great for a small (closed) landfill—less than 10 acres—that can be removed and developed into a better end use,” he says, pointing to examples such as a project in Oxnard, Calif., where a developer wanted to move a 4-acre closed landfill to construct condos on the site.

“In our experience as an industry consulting firm based in the USA and through our independent research, with current technology and prices, landfill mining is generally not economically viable here,” Wallace says. “The benefits, such as revenue from sale of recovered metals [and] reduction in regulatory costs, generally do not outweigh the costs,” he adds.

Other Concerns
WIH Resource Group has done some small studies on the subject for both public and private sector clients.

“We have watched private sector clients move waste during construction at their landfills and in some remedial situations, but it is not a common procedure for private companies,” according to Wallace. “It’s very expensive, causes odors and disrupts landfill operations of active sites.”

Heavy metals and contaminants always are a concern at landfills. Digging into an old landfill profile in an attempt to recover material can awaken sleeping dogs in the form of dangerous materials, sources warn.

Metals and hazardous waste has not been an issue to date in Fauquier County’s mining operation. “However, TPH (total petroleum hydrocarbons) have been higher in the fines fraction than what is considered ‘clean’ fill,” Dorsey says. The source could be oil filters, asphalt shingles or pavement, he offers.

“Our approach is to use the fines as landfill cover with continued testing over time to evaluate how this material changes (breaks down),” Dorsey says.

At Perdido, that was not a major problem, either. “We screened soil to recover the active area,” Jain says. Because the soil did not leave the landfill, there was no real concern.

In work at a different landfill in Florida, however, samples collected for analysis showed elevated levels of arsenic. “Overall, it was not too bad,” Jain says of the results. Still, possible contaminants are another area to check before going full-tilt into any recovery operation.

Transportation costs are increasing because of higher equipment and fuel costs. Despite that, trucking is typically the only practical hauling method for material relocation, according to sources contacted.

Since Fauquier County is only in its second year of its pilot landfill mining operation, Dorsey says he does not yet have a firm handle on the project’s costs. He continues to adjust the project’s operations plan.

“We’re trying to recover 1.3 million cubic yards of landfilled airspace to combine with another 2.7 million cubic yards to develop future landfill capacity of 4 million cubic yards,” Dorsey says. This would extend the landfill’s life by 20 or more years—and that’s the sort of payoff that has more operations looking at landfill mining.

“Higher tipping fees might make the process more economical, however,” Wallace says. Higher costs for landfill closures might help.

“If the prices for secondary materials increase further, it might make landfill mining more feasible,” he says. “The single largest thing that could enhance landfill mining would be a breakthrough in the cost of remediation and processing of the materials with value for resale in the commodities markets.”

Most efforts at landfill mining reflect circumstances specific to a particular location or facility. “Because costs often outweigh benefits, landfill mining on a commercial scale will probably not catch on in the near future,” Wallace concludes.

The author is a freelance writer based in Cleveland and can be contacted at curt@curtharler.com.