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1 May 2018

Hot landfills – prevention, detection and solutions

The issue of hot landfills has become a significant challenge to the waste industry over the last ten years. When a landfill’s temperature begins to elevate significantly, rapid response is necessary to minimize impacts to the public and costs to the owner. Each hot landfill is unique and I wanted to share the experience gained from these sites to educate others on the prevention, detection, and solutions to manage these facilities. Design of odor, gas, and leachate controls for these sites are outside the norm and the lessons learned are valuable for efficiently managing new hot landfills and reducing the associated cost.

What is a hot landfill and what are its impacts?

Landfills are generally considered to be hot landfills when temperatures exceed 140°F, although there can be some site and regional conditions that might explain higher “normal” temperatures. However, temperatures of up to 250°F have been measured in municipal solid waste landfills when they are undergoing a subsurface reaction. High heat has even been measured in saturated waste. At these temperatures, “thermal runaway” can occur. This means the increased temperature changes conditions in a way that causes even further increases, often leading to destructive results.

One potential casualty of hot landfills is high-density polyethylene (HDPE), which is a common element in landfills, where it is used for liners and pipes. HDPE loses half its strength at every 60°F rise in temperature. At 140°F, HDPE will buckle at a very small load, and at 260°F the HDPE melts.

Hot landfills lead to significantly more landfill gas (LFG), so much that operators can have difficulty keeping up with it. This condition may also lead to large scale settlement, which may allow more rainwater to enter the landfill. There is often a large increase in odors – and with them neighbor complaints. Leachate volumes can also increase significantly and there may not be enough storage for efficient management. Finally, a hot landfill may produce high strength leachate, which may be difficult and expensive to treat and dispose.

Not every hot landfill is considered a fire. For example, in the left-hand photo below, what looks like smoke is really steam and hydrogen gas with moderate carbon monoxide (CO) levels resulting from exposure of a gas well for remedial activities. The photo on the right is an actual fire, in which one or two landfill gas wells are involved. This fire photo shows a shallow event, with a melted wellhead, smoke, and high CO levels.

 An ounce of prevention

When it comes to hot landfills, an ounce of prevention is worth a ton of cure. Wastes to be especially cautious of include aluminum dross and other metal waste, sulfur treatment media, hot loads, and lime materials. Chemical reactions from mixtures of these materials can contribute to heat accumulation at localized areas within a landfill.  

Unfortunately, toxicity characteristic leaching procedure (TCLP) tests on special wastes do not tell the whole story! Be sure to add ASTM C-1702 (Standard Test Method for Measurement of Heat of Hydration of Hydraulic Cementitious Materials Using Isothermal Conduction Calorimetry) to your special waste testing protocol before you consider accepting special wastes. Also, be sure to keep liquids and gas under control (not allowing them to build leachate head or pressure at depth in the waste mass), and keep a close watch on your LFG chemistry. Calculate the CH4/CO2 ratio at every LFG well – if it is less than 1.0, take action. Finally, make sure the hydrogen levels in LFG wells are less than 0.5 percent by volume.

Additional causes of excessive heat in a landfill

Aside from materials that tend to overheat, there are a few other causes of heat in landfills. First off, there’s actions taken for NSPS compliance, for example, tuning wells down to stay in compliance with 131°F criteria, or pulling too hard to stay below the 500 parts per million by volume (ppmv) methane concentration for surface emission monitoring (SEM).

Then there are operations that lead to perched leachate, which retains heat and impairs landfill gas removal. These include not stripping out old roads prior to filling; not stripping out intermediate cover; using clay or silt for daily cover; and recirculating too much leachate.

Management strategies for heat in landfills

The two most effective strategies for managing heat in landfills include getting the liquids out – 1 gallon per minute at 150°F = 949 BTU/minute; and then getting the LFG out; where 30 cubic feet per minute at 145°F = 387 BTU/minute!

Here’s a suggested progression of remedial activities for a hot landfill:

  1.  Increase the number of LFG wells with dewatering capabilities where necessary
  2.  Construct localized capping for target control of odor and air intrusion
  3.  Increase operations and maintenance (O&M) activities as challenges arise to assure uninterrupted gas and leachate collection
  4.  Add LFG and leachate piping to critical areas
  5.  Upgrade GCCS headers to accommodate additional wells
  6. Upgrade flare as necessary
  7. Repair excessive settlement to prevent ponding and control infiltration
  8. Add air and forcemain upgrades as dewatering wells are added
  9. Expand capping for control of odor and air intrusion if necessary
  10. Consider separation of clean and dirty gas and leachate systems for improved liquids management
  11. Implement leachate & GCCS treatment when the quality warrants improvement
  12. Finally, prepare Operation, Maintenance and Monitoring (OM&M) plan once systems are in place and in a controlled state.

Examples to think about

Operators would do well to take a very proactive approach to preventing hot landfills. Otherwise, the results can prove extremely expensive. Here are just a few impacts of hot landfills that I have seen:

  • Loss of 5 million cubic yards of airspace
  •  $10 million fine
  •  $65 million of remediation and O&M costs
  •  65 gas well seals for a geomembrane cap broken overnight due to temperature fluctuation
  •  $400,000 remediation for a leachate pipe leak on a capped landfill to a stormwater pond
  •  3 wells per acre needed at a landfill for GCCS control rather than the typical 1 well per acre
  •  400,000 cubic yards of waste excavation to create an isolation break
  •  Construction of 4 one-million gallon storage tanks and a $12 million WWTP to manage leachate
  •  Flare capacity for one landfill requiring 5 operating flares + 2 standby flares

It can take a very long time for a landfill to cool off – and millions of dollars to remediate! At one landfill I’m familiar with, the hot landfill condition cost more than $100 million dollars, about 100 times more than it would have cost to prevent. And that does not even include other lasting impacts, such as loss of public trust and loss of airspace. At this site, control and containment was the long-term resolution. Eleven years ago at one hot landfill, landfill gas was measured at 280°F, while it is now at 200°F. Odor, gas and leachate are under control, but there are continued settlement effects that need to be dealt with. The facility is operated in a controlled manner and operators have implemented an OM&M plan for management.

What has been your experience with hot landfills?

James Walker, PE, is a Client Manager in Cornerstone’s Farmington Hills, MI office. He earned his degree in Civil Engineering and has 30 years of experience with Subtitle D landfill design and construction projects across the US.

Categories: Biogas and Landfill Gas, Environmental Remediation, Landfill Engineering and Design, Operations and Maintenance, Solid Waste
Posted By James Walker, PE at 11:30 AM  |  No Comments on Hot landfills – prevention, detection and solutions

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