LANDFIL L Landfill Mining: Current Trends Landfill mining is a term used to describe a process whereby landfilled solid waste is excavated and processed for beneficial purposes. BY BRUCE CLAR:<. ALYSOI~ DAGLY, AND "!ARC ROGOFF he beneficial purposes can Table 1. Landfill Mining/Reclamation Considerations include recovery of recyclable materials, recovery of soils for use as daily or intermediate Nuisances caused during mining (i.e., construction Gain additional airspace for active waste filling coverT in active landfills, or recovery of land traffic, fugitive dust) · Potential presence of hazardous materials, area for redevelopment. As urban sprawl Recycling potential of certain materials extra cost and delays has continued in many metropolitan areas, Recovery of cover soil for reuse Escape of leachate and/or nuisance odors during landfills-which previously were located in (if uncontaminated) mining operations areas relatively distant from the population Potential for recovery of materials that Few regulatory laws or standards centers-are less so, and the value of those could be used for energy production properties for redevelopment have increased. Land reclamation Projected volume of recyclables may not materialize In the US, however, the term "landfill Remediation of soil and Relatively long process that requires Owner's oversight mining" has increasingly become a mis- groundwater contamination and management commitment nomer, as the primary driver has been to reclaim the old footprint and develop it to meet current Subtitle C regulations (i.e., What About Recyclables? The production of a landfill mining typically at a minimum installing a bottom- Some landfill owners have opted to separate operation is mainly dependent on the lining system with leachate controls) and and sell recyclables obtained from a recla- size and number of pieces of equipment gain valuable additional airspace for active mation project; however, the value of these deployed, the types of soils used during waste filling. The reclamation of recyclable materials is elusive. Cal Recovery, Hercules, landfill operations (e.g., sandy versus clayey materials-like plastics, metals, and glass, CA, conducted a study for EPA of the Collier materials), the types of waste disposed, and plastics and paper for energy recovery- County, FL, landfill mining demonstration weather conditions, liquid levels in the are secondary and do not typically justify the process in 1993, and concluded that plastic landfill, and gas emissions. More equipment total cost to reclaim them with natural gas and metal were the only viable recyclables, but means more production, but more equip- energy, both abundant and relatively "cheap." were not of acceptable quality for the resale ment also means additional capital costs. As pointed out in the recent International market. They indicated that the actual "cost" Certain types of waste are more difficult Solid Waste Association (ISWA) publication of mining and separating the recyclables was to excavate and process than others, which on landfill mining, the concept of mining about $115 per ton. Extrapolating that cost to can slow productivity. High liquid levels and landfills is not new. Some 60 examples have today's dollars would cost approximately $250 highly saturated wastes require additional been cited in solid waste literature since the per ton. This cost is high, relative to the price steps to excavate and process, which, again, first reported project in Israel in the 1950s. being paid for recyclables as discussed in the slows production. Inclement weather is a less Landfill mining is a practice not unique to section on benefit-cost. controllable factor; however, the timing of any particular country or even region. The major excavation efforts can be scheduled to practice has both advantages and disadvan- Construction Timeframe take advantage of seasons with less inclem- tages, which are summarized in Table 1. Basic landfill mining equipment may include ent weather. Lastly, health and safety issues the following: associated with gas emissions such as com- Planning Aspects • Waste excavation: hydraulic excavators bustible gases, odorous gases, and such must An overview of the entire landfill mining (backhoes) be considered and can negatively impact process is helpful to be able to properly • Waste screening (large objects): surrounding properties if not controlled plan all of the parts of the process and have grizzly screen properly, ultimately impacting the excava- contingency plans ready if something does • Waste screening (smaller objects): tion and processing activities. not go according to plan. Table 2 presents a trommel screen Equipment involved in the waste excava- summary overview of the overall aspects to • Screen feed: front -end loader tion activities typically limits the actual consider on a mining project. • Waste hauling: dump trucks capacity of an operation. This equipment 56 MSW MANAGEMENT [ SEPTEMBER/OCTOBER 2016 ] A drilling and test pit program is usually An accurate waste thickness profile Baseline waste necessary to obtain a reasonable and a representative description of the characterization understanding of the depth of the wastes in-place waste ofthe waste is desirable. and the main materials. Soil and/or Can remediation be completed prior to Many proven new techniques are available groundwater that can relatively quickly remediate certain constructing a new landfill cell? contamination common types of contamination. Identify former areas used for disposal Special waste areas of asbestos, sludge, etc. Special health Develop a Contingency Plan for managing and safety issues will apply. these wastes if encountered. Large amounts of plastics could potentially Identify specific materials; soil, metals, Materials desired go to a WTE plant. Soil should be tested if plastics, etc. that are desired for reuse for separation on site (soil) or disposal offsite. any concern it may be contaminated and unsuitable for reuse as daily cover. Plan for waste disposal tonnage to Space required for your active cell to increase, potentially Assume low volume of cover soil excavated and all other materials filled back into relocated waste significantly, on a temporary basis, operating cell. with refilling of some old waste. Space required for Some old landfills can contain up to Ideally, the reclaimed cover soil should temporary storage 40% of cover soil. If soil has to be stored be transported from the screener of excavated temporarily, a significant area could be directly to your current soil source area. cover soil needed. Always a potential to discover this, Have a Contingency Plan for managing Hazardous wastes typically in drums. Special health these wastes if encountered. and safety issues will apply. is involved in excavating compacted waste, to stockpile recovered soils near or with other loading trucks, and moving as the excavation onsite cover stockpiles in order to handle the progresses. The other machines in a landfill materials only once. However, this approach mining operation, such as shredders, screens, may not always be feasible. If that is the case, magnets, and conveyors are generally static all of the mined soil may have to be tempo- (i.e., they are not moved for periods of rarily stockpiled separately. Soils can make time), and are processing materials that have up to 40% of the materials mined from old had some loosening and separation, and are landfills. In our previous example, that would for one function only, so their capacity usu- amount to approximately 153,000 cubic ally does not limit the operation. yards of soil, which would be equivalent to a If you are considering implementing a 4-acre stockpile area 40 feet high. landfill mining project, you should be real- istic about the time it will take to complete Benefit-Cost Assessment the project. This timeline needs to coordi- A benefit-cost assessment should be con- nated with the overalllandfilling activities ducted to justify pursuing a landfill mining of a site, assuming it's an active landfill, and project. One way to approach a benefit--cost remaining site life calculations. A mining assessment is to compare the estimated cost project and the necessity to dispose of much of mining the landfill cell against the value of the excavated materials back into the new of the "new" airspace that created by mining landfill can temporarily increase the landfill and used for future landfilling (Table 3), tonnage by up to 80% over your normal or the value of the reclaimed property. We throughput, if everything except the cover typically would not include the value of soils are put back in the landfill. any separated recyclables, because the value Take for example, an old landfill 40 feet of these recovered materials generally is high with a base dimension of 800 feet long inconsequential. by 500 feet wide, about a 9-acre footprint. That landfill will contain Table 3. Projected "Value" of New Airspace approximately 383,000 cubic yards Item Amount of material. Working with three Total volume 383,000 CY large bucket excavators (total bucket capacity 36 cubic feet), it Less reclaimed soil ~ 20% 76,600 CY would take at least a year, or more, Less all other materials ~ 42% 160,000 CY to complete excavating, working Net new airspace 146,400CY nine hours a day, 6 days a week, 102,500 tons without bad weather delay. Volume new waste at 1,400/CY The most efficient approach is "Value" of new airspace at $42/ton $4,305,000 [ www.mswmanagement.com l MSW MANAGEMENT 57 LANDFILL Table 2 summarizes a simple cost analysis x $4 per cubic yard) is equal to $1,532,000. Contrasting that to $250 per ton for mining for an example landfill mining project at Clearly, in this example, the reclamation and separation extrapolated from the Collier an active landfill based on the following benefit far outweighs the cost. If cover soil County study, plastic reclamation would not assumptions: has to be purchased from an outside source, provide any significant monetary benefit. • Landfill cell volume = 383,000 yd'. there could be another savings benefit by • Volume of reclaimed soil = 20% of reusing the recovered soil.