May 2011

The Long-Term Management and Care of Closed Subtitle D Landfills

In 2010, the SWANA Applied Research Foundation (ARF) developed a report to identify, characterize and address the issues associated with the long-term management and care of closed Subtitle D landfills. This research need was submitted by the city of Winston-Salem, North Carolina, and voted on for selection by the ARF’s FY2010 Disposal Group. This article presents highlights and conclusions from the 64-page report that was prepared by the SWANA ARF staff with input and guidance provided by the ARF Disposal Group Subscribers, who are listed in Table 1. (The SWANA Applied Research Foundation was founded in 2001 with the purpose of conducting collectively defined and funded applied research on pressing solid waste issues. It is funded by local governments and other organizations that contribute a “penny per ton” of waste managed to the foundation on an annual basis. For more information on the SWANA Applied Research Foundation, please contact Jeremy O’Brien, director of applied research, at 301-585-2898.)

Perspective of State Regulators
Federal RCRA landfill regulations are codified in Part 258 of Title 40 of the Code of Federal Regulations (CFR). These regulations, which are often referred to as “Subtitle D” regulations, were promulgated by the United States Environmental Protection Agency (USEPA) in 1991 and include prescriptive requirements for monitoring and maintaining landfills for a period of 30 years following closure—i.e., the postclosure care (PCC) period. These requirements include the following:

• Maintaining the integrity and effectiveness of the final cover system
• Maintaining and operating the leachate collection system
• Monitoring the groundwater in the vicinity of the site and maintaining the groundwater monitoring system
• Maintaining and operating the gas-monitoring system.

The length of the PCC period may be decreased by the state agency that issued the landfill permit if the landfill owner demonstrates that the reduced period is sufficient to protect human health and the environment. Alternatively, the state permitting agency may increase the PCC period if it determines that the lengthened period is necessary to protect human health and the environment. (US Code of Federal Regulations [40 CFR §258.61.)

In the process of developing new postclosure financial assurance regulations, the state of California conducted a survey in 2009 to identify the policies that other states had or were developing with respect to extending or shortening the PCC period. The state compiled the following information based on the 49 responses received:

• Forty-seven states have not changed the 30-year PCC period.
• Two states have changed the 30-year PCC period:
• Nebraska decreased the period for 1 MSWLF to 18 years.
• Tennessee increased the period of 1 MSWLF to 50 years.
• Six states (Indiana, Minnesota, Nebraska, Ohio, Utah, and Virginia) are considering criteria to change the postclosure maintenance (PCM) period.
• Wisconsin has increased the financial assurance requirement to a minimum of 40 years and requires the landfill owner to assume responsibility for the “perpetual long-term care” of the landfill.

In July 2010, the state of California adopted new postclosure regulations requiring landfill owners to fund PCC “until the waste no longer poses a threat to human health and the environment.” In addition, landfill owners must include funding for a reasonably expected postclosure remediation action such as the eventual replacement of the final cover.

Based on the California as well as other surveys, it is apparent that the majority of state regulatory agencies have not addressed the issue of the monitoring, maintenance, and funding requirements for the long-term care of Subtitle D landfills after the 30-year PCC period. Of the states that have addressed this issue, it appears that the prevailing option is to extend the PCC period and, in the case of California, to continue it indefinitely.

In light of these findings, it is imperative that the solid waste industry continue to conduct basic and applied research on this issue as well as develop models and methodologies to guide the states in the development of prudent policies and regulations that protect human health and the environment in a cost-effective manner.

*Interstate Technology and Regulatory Council. Evaluating, Optimizing, or Ending Post-Closure Care at MSW Landfills Based on Site-Specific Data Evaluations. ALT-4. Washington, D.C.: Interstate Technology & Regulatory Council, Alternative Landfill Technologies Team. 2006. www.itrcweb.org.

Performance-Based Post-Closure Care
Current regulations for Subtitle D landfills require that the same monitoring procedures be followed each year during the 30-year PCC period—regardless of what the monitoring results indicate with respect to the performance of the environmental system being monitored. For example, groundwater wells must be sampled semiannually for the entire 30-years, even if no groundwater pollution is detected. No guidance is given in the regulations on how to modify monitoring based on system performance.

The Evaluation of Post Closure Care (EPCC) Methodology—developed by GeoSyntec Consultants Inc., with funding from the Environmental Research and Education Foundation (EREF)—presents a scientifically based method for determining the types and timing of monitoring activities that should be conducted during the PCC period. (See Figure 1).

The EPCC methodology has been peer reviewed by a large team of technical experts and leading researchers and has been endorsed by the Interstate Technology and Regulatory Council (ITRC)—a state-led national coalition of personnel from environmental regulatory agencies of some 40 states.

Documented case studies of landfills at which the EPCC methodology was applied indicate significant reductions may be justifiable with respect to sampling for many of the regulated parameters and that the 30-year postclosure care period may be too long for some Subtitle D landfills. Based on this research, it may behoove landfill owners to consider using the EPCC methodology and to take steps to meet the data and other requirements for its application to their facilities.

Biostabilization in the PCC Period
Subtitle D landfill regulations were promulgated by the USEPA in 1991. As a result, a number of landfills constructed in accordance with Subtitle D requirements are reaching the end of their service lives and managers are beginning to investigate PCC and long-term management strategies for these sites. One possible method of shortening the PCC and long-term management periods for Subtitle D landfills involves the biostabilization of the landfilled waste during the 30-year PCC period.

This option would involve delaying the installation of the final cover and, instead, installing an interim final cover that would allow infiltration of precipitation into the landfilled waste during the PCC period. It would also require the installation of a liquids recirculation system for adding leachate and other liquids to the landfilled waste.

The primary objective of this method would be to biostabilize a majority of the landfilled waste during the PCC period, thus minimizing or possibly eliminating the long-term environmental risks associated with the closed landfill site. Based on recent research, it appears that traditional landfills can be effectively retrofitted as bioreactors. (Bareither, C. et al. Performance of North American Bioreactor Landfill. (Draft – 12-30-08: 74 pp.))

Recent research also indicates that the biostabilization of the landfilled waste during the PCC period is likely to result in costs that are on the order of 10% higher than traditional landfills. (Hinkley Center for Solid and Hazardous Waste Management. Bioreactor Landfill Costs and Benefits (Volume 9). Gainesville, FL: Hinkley Center, July 1, 2008.) Landfill owners will have to figure the value of realizing potential long-term management cost savings following the PCC period compared with the higher costs of retrofitting the landfill to achieve biostabilization during the PCC period.

The “Landfill Organic Stability Rule” promulgated by the state of Wisconsin indicates the importance that at least one state gives to the goal of the biostabilization of the landfilled waste by the end of the PCC period. The state has promulgated this rule to address the risks associated with landfilled organic materials that remain potentially bioactive past the period for which proof of financial responsibility from the landfill owner for PCC is required.

Federal PCC regulations—as well as most state PCC regulations—discourage landfill owners from considering biostabilization by not providing regulatory flexibility to allow the installation of interim final covers. Furthermore, other than Wisconsin, states have not adopted policies that encourage the biostabilization of landfilled waste before the end of the PCC period. In light of its environmental benefits and higher costs, state regulators should provide clear regulatory policies and should consider could providing economic and other incentives to landfill owners to biostabilize landfilled waste during the PCC period.

Long-Term Care Options
The maintenance and monitoring activities for a closed Subtitle D Landfill following the 30-year regulatory PCC period can be referred to as “long-term care.”

Long-term care of landfills is intended to protect human health and the environment and consists of maintenance of the landfill’s final cover system to contain the waste and to ensure that the outcomes anticipated for groundwater quality, LFG generation, and leachate collection during the postclosure period are achieved and maintained. It also includes such traditional site maintenance activities as mowing or fence repair. The long-term care options reviewed in the ARF report are listed in Table 2.

Of the four long-term care options reviewed in the SWANA report, one was proposed by a research team, another was developed by a consultant and adopted by the ITRC, and two were developed by state regulatory agencies (Minnesota and California). A comparison of the four long-term care options yields the following observations:

• All of the options rely on the proper functioning and perpetual maintenance of the final cover system.
• One state requires financial assurance for eventual replacement of the landfill’s final cover system (California) while the other (Minnesota) assumed replacement of a 3-acre section.
• Neither state assumes a reduction in monitoring and maintenance costs if and when the landfill transitions from the PCC period to the long-term care period.
• The research team, the ITRC, and one of the states (Minnesota) envision a point in a landfill’s long-term care period when monitoring and maintenance activities can be reduced significantly.
• The two state options involve the continuation of the state’s regulatory oversight of the long-term care of the closed landfill site while the ITRC option ends the state regulatory oversight and transfers responsibility to local government planning/building departments. The research team is silent on this issue.

2 Bonaparte, R., D. Daniel, and R. Koerner. 2002. Assessment and Recommendations for Improving the Performance of Waste Containment Systems. (EPA/600/R-02/099). Cincinnati, OH: EPA National Risk Management Research Laboratory. 3 GeoSyntec Consultants.2006. Performance-Based System for Post-Closure Care at MSW Landfi lls: A Procedure for Providing Long-Term Stewardship under RCRA Subtitle D. Alexandria, VA: Environmental Research and Education Foundation. 4 Minnesota Pollution Control Agency. Minnesota MMSW Landfi ll Liability Report: Findings and Options. January 1998. http://www.pca.state.mn.us/index.php/download-document.html?gid=95 5 CalRecycle. Final Statement of Reasons, Long-Term Post-Closure Maintenance, Corrective Action and Financial Assurances. February 2010.

Need for Final Cover System Replacement
All of the long-term care options proposed for Subtitle D landfills require the proper functioning of a robust final cover system. The state of California is requiring that financial assurance requirements for Subtitle D landfills include the costs associated with the replacement of the final cover system at the end of its service life.

According to a 2007 study by the National Research Council on engineered waste containment barriers, the service life for final cover geomembranes installed in landfills located in a temperate climate, with a mean ambient temperature of less than 30°C, should be on the order of several hundred years. (Committee to Assess the Performance of Engineered Barriers, National Research Council. 2007. Assessment of the Performance of Engineered Waste Containment Barriers. (ISBN: 0-309-10810-1). Washington, DC: National Academic Press.)

Even if breaching of the geomembrane occurs at the end of its service life, a well-constructed cap is a system consisting not only of the geomembrane but also a compacted clay layer overlain by a vegetative support soil layer. This system will continue to serve as a barrier to prevent the infiltration of moisture into the landfilled waste mass.

For these reasons, it is not at all certain that the final cover geomembrane will need to be replaced in its entirety at the end of its service life for the final cover system to continue to function effectively. Even if it is found necessary to replace the geomembrane, it is reasonable to assume that the replacement will not be needed for hundreds of years. During such a time frame, it is likely that many regulatory and other aspects of managing closed Subtitle D landfills will change, new technologies will develop, and natural resource needs may change to the point of making the recovery of the landfilled resources economically attractive.

In light of the above considerations, it can be reasonably concluded that the financial assurance requirements for the long-term care of Subtitle D landfills would not necessarily need to include financing for the replacement of the final cover system.

Need for Final Cover System Leak-Detection
Subtitle D regulations require that landfill caps provide an overall permeability of less than or equal to the bottom liner system of the landfill. This usually means that a geomembrane is employed as a component of the landfill capping system unless the landfill is located in an extremely arid environment. (Committee to Assess the Performance of Engineered Barriers, National Research Council. 2007. Assessment of the Performance of Engineered Waste Containment Barriers. (ISBN: 0-309-10810-1). Washington, DC: National Academic Press.)

As illustrated in Figure 2, the installation of the final cover system begins by the placement of 18 inches of low-permeability clay over the intermediate cover soil (typically 12 inches in depth) that covers the final layer of the landfilled waste. The geomembrane panels are then rolled out on top of the infiltration layer and seamed together. Construction and quality insurance (CQA) programs then typically require that the ultimate tensile strength of the geomembrane seams be tested. Ironically, this testing involves the destruction of various sections of the geomembrane seams to test tensile strength, after which patches are placed over the tested seams.

Visual examination of the geomembrane is a basic element of CQA during installation. However, after the drainage and soil layers are installed, a visual evaluation of the final cover geomembrane is not possible since these layers are placed directly on top of the geomembrane. (Pegg, I., Phaneuf, R. and Sieracke, M. “Factors Influencing the Quality of Geoelectric Liner Integrity and Leak Location Surveys.”)

The placement of the soil cover over the geomembrane can occur on relatively steep slopes. The steeper the slope, the more difficult soil placement becomes, making equipment damage far more likely. (Hansen, R. and Beck, A. Electrical Leak Location Surveys For Landfill Caps. Grass Valley, CA: Vector Engineering, Inc.) If damage is done to the geomembrane during installation of the protective layer, it typically goes unnoticed, since the damaged area is in the process of being covered with soil.

Figure 2. Typical Subtitle D Final Cover System6 INDUSTRY STANDARD FINAL COVER SYSTEM 6 Source: http://garrett-moore.com/index.php/projects/solid_waste/ horry_county/

A landfill liner system is similar to a final cover system and is installed at the bottom of the landfill so that leachate can be collected and substantially prevented from exiting the bottom of the landfill. It has been documented that the vast majority of landfill liner system defects are construction-related. In this regard, a research team reported that two research papers published in 1996 and 2000 summarized the results of more than 300 electrical resistivity surveys that collectively evaluated more than 3 million square meters of geomembrane liners in 11 countries. (Phaneuf, R. and Peggs, I. “Landfill Construction Quality: Lessons Learned from Electrical Resistivity Testing of Geomembrane Liners.” GFR Magazine, Vol. 19, No. 3, April 2001.) The 1996 paper concluded that 73% of the damage to the geomembrane resulted from placement of the protective layer over the geomembrane. For this reason, CQC/CQA procedures and soil material specifications need to better address how protective or drainage soils are placed in the field to minimize damage to the geomembrane liner. (Ibid.) Even with improved CQC/CQA procedures, the conduct of liner integrity surveys to locate liner defects is the only way from preventing construction-related liner defects from going unnoticed and unrepaired. (Pegg, I., Phaneuf, R. and Sieracke, M. “Factors Influencing the Quality of Geoelectric Liner Integrity and Leak Location Surveys.”) It is likely that the construction-related defects issue associated with landfill liner systems will raise similar concerns for final cover systems.

The importance of the integrity of the final cover system in minimizing the long-term environmental impacts of Subtitle D landfills has been clearly established in the published research literature. In addition, as discussed above, there has been a growing recognition of the need to test the integrity of the final cover system after the placement of the protective layer of soil over the geomembrane. Finally, it would be beneficial to be able to periodically test the integrity of the final cover geomembrane following the closure of the landfill. For all of these reasons, landfill managers should consider the option of installing a leak detecting and monitoring method for the final cover system when closing Subtitle D landfills.

Long-Term Oversight
One of the primary issues regarding long-term care of a closed Subtitle D landfill is whether or not regulatory oversight is needed during this phase of the landfill lifecycle. In this regard, the state of California concluded that state regulatory oversight is needed due to the lack of experience and expertise of local government planning boards and/or building departments and the need to ensure that financial assurance is provided for long-term care activities.

Alternatively, the ITRC has concluded that long-term care requirements can be included in the site deed; and therefore, regulatory oversight by the state can be ended. To support their position, they reference redeveloped brownfield sites, which have addressed long-term care issues in this manner.

State governments may decide to continue their roles in providing regulatory oversight for closed Subtitle D landfill sites following the 30-year PCC period. In this regard, the USEPA and state regulators may want to consider the creation of a new regulatory phase called “long-term care” to distinguish it from Subtitle D PCC. State regulatory agencies could issue a certificate that the closed Subtitle D landfill has successfully met its Subtitle D PCC requirements and has entered the long-term care phase for the site.

Conclusions
Subtitle D landfill regulations were promulgated by the USEPA 20 years ago. As a result, some Subtitle D landfills are reaching the end of their service lives and are beginning to enter the PCC phase. The Subtitle D regulations allow for state regulatory agencies to extend or shorten the 30-year PCC period prescribed in the regulations as deemed necessary. The regulations do not address how closed Subtitle D landfill sites should be maintained and monitored if and when the PCC period has ended.

The findings of relevant research reviewed by the SWANA Applied Research Foundation have been presented in this article to shed light on some of the key issues associated with the long-term maintenance and monitoring of closed Subtitle D landfills. It is hoped that this effort will foster discussions between regulatory agencies, the landfill industry and environmental and community organizations that will lead to the establishment of environmentally protective and economically sound policies and management strategies to provide for the long-term care of these facilities.

Jeremy K. O’Brien, P.E., is director of applied research for the Solid Waste Association of North America. For more information about this report or the ARF, he may be contacted at jobrien@swana.org.