Preparing for the closure and long-term care of a municipal solid waste landfill (MSWLF) can be an inordinate undertaking. Whether public or private, all landfills eventually reach the end of their active lifecycle. Before closure, a landfill must meet a series of criteria as determined by Subtitle D of the Resource Conservation and Recovery Act (RCRA). Following closure, those same regulations also require a minimum 30-year care period of monitoring and maintaining the landfill after it no longer generates income, thus requiring a postclosure fund – typically a pledge of revenue from public agencies or a trust fund from private site owners.
If the regulations weren’t complicated enough, controlling the environmental issues related to landfill closure are numerous, and the impacts of failure are expensive. Among those, leachate and landfill gas generated from landfill waste always poses a threat to groundwater pollution. Inability to control landfill slope stability can also have drastic impacts as well.
With both the threat and the responsibility high, the importance of proper landfill closure cannot be overstated. How can landfill owners and operators properly prepare? This blog addresses the major considerations in landfill closure and post-closure care.
Planning for Landfill Closure
It has been said that a small, 100-acre landfill has a capacity four to six times the volume of the Great Pyramid at Giza. Like those great pyramids, modern landfills are not immune to the effects of age. Proper landfill closure requires extensive planning, design, and careful installation, not to mention active management during post-closure care.
The EPA (under 40CFR Part 258.60(c)) requires every MSWLF to prepare a written closure plan that describes the steps necessary to close the unit. This plan must include:
- A description of the final cover design and its installation methods and procedures.
- An estimate of the largest area of the landfill requiring a final cover.
- An estimate of the maximum inventory of waste on site during the landfill’s active life.
- A schedule for completing all required closure activities.
Among the many design hurdles facing proper landfill closure, arguably the biggest design issue may be slope stability.
Slope Stability
Slope stability can be difficult to evaluate, as there are several failure mechanisms.
The effects of slope failure can be financially catastrophic at a closed site with no income stream other than the postclosure maintenance fund. As repair funds are gathered, final cover failures can allow surface water into the waste mass causing increased leachate generation, release of significant landfill gas emissions, into the atmosphere, among other environmental issues. In addition, the remediation and reconstruction of these challenges can be expensive, impinge the reputation of responsible parties, and lead to lawsuits. While the majority of waste facilities have not experienced slope failure, there has been enough documentation to tell us how and why slope failures occur. To put it simply, gravity has the highest effect on a slope’s stability: steep side slopes and flat side slopes.
Steep side slopes maximize the amount of volume a landfill can hold but come at a higher risk of a slope failure – global and within the final cover veneer. Alternatively, flat side slopes are safer but produce less volume. Even the slightest slope changes can have significant impacts on the amount of volume (and income) the landfill can generate. To understand the right decision, it is necessary to conduct slope stability analysis, a calculation method similar to the one used for levees, dams and natural slopes.
The basic concept of slope stability analysis is easy enough to understand. Landfill materials want to fall downhill under the influence of gravity, and it is the job of the closure system to hold the material in place. This necessitates driving forces being less than resisting forces. The stability of the slope is measured by the ratio of those forces and regulators often require a 1.5 safety factor in favor of the resisting forces.
The Responsibilities of Post-Closure Care
Subtitle D of RCRA determines the minimum design requirements following landfill closure. Post-closure costs can be divided into four broad categories: site security maintenance, landfill cover and mechanical systems maintenance, monitoring wells and gas probes, and environmental monitoring.
Among those requirements, the post-closure responsibilities include:
- Maintaining the integrity and effectiveness of any final cover
- Maintaining and operating the leachate collection system
- Monitoring the groundwater and maintaining the groundwater monitoring system
- Maintaining and operating the gas-monitoring and control (if required) system
The financial obligations of the landfill owner during the post-closure care period are high and, during this time, the landfill is no longer generating income. The proper landfill closure solution anticipates these long-term responsibilities and seeks to reduce postclosure costs while maximizing its effectiveness.
Determining the Right Closure Solution
To meet Subtitle D requirements (40 CFR Part 258.60), MSWLF unit operators must install a final cover system that is “designed to minimize infiltration and erosion.” This final cover system must be designed and constructed to:
Have a permeability less than or equal to the permeability of any bottom liner system or natural subsoils present, or a permeability no greater than 1×10−5cm/sec, whichever is less
Minimize infiltration through the closed MSWLF by the use of an infiltration layer that contains a minimum 18-inches of earthen material, and
Minimize erosion of the final cover by the use of an erosion layer that contains a minimum 6- inches of earthen material that is capable of sustaining native plant growth.
ClosureTurf®, produced in partnership with WatershedGeo, is an easy-to-install three-component landfill closure system that exceeds this “prescriptive standard,” and significantly reduces postclosure maintenance costs versus the prescriptive standard.
ClosureTurf® vs Traditional Final Cover Systems
The use of geosynthetic products in landfill design is nothing new. There is over a half-century of case histories and documentation that give credence to the positive impacts of geosynthetic material in landfill closure. ClosureTurf®, however, introduces an alternative to traditional cover systems that not only decreases construction and maintenance costs but lowers the carbon footprint and improves gas collection systems.
ClosureTurf® also reduces the post-closure maintenance costs. Since ClosureTurf® requires no mowing or soil, there is very little to maintain. On average, post-closure maintenance savings are $1500 per acre per year. That is $4.5 million saved for a 100-acre site during the 30-year post-closure care period.
Throughout your life, you may never need the assistance of a fireman. If you’re lucky, you may never need the assistance of the police. But, you’ll need the garbageman at least once a week. If you’re planning a landfill closure, consider a closure solution that protects our environment while reducing construction and operational costs.
