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September 28, 2017

30 years and beyond: caring for landfills post closure

  • For landfill owners and operators, an ounce of prevention can be worth hundreds of thousands of dollars of cure.
    Aspect Consulting


    Landfills have a finite operational and economic life. When waste can no longer be accepted and the facility closes, it transitions from an income source to a financial and environmental liability.

    Recognizing this, EPA’s Resource Conservation and Recovery Act (RCRA) outlines requirements for post-closure care (PCC) and long-term management for landfills. For landfill owners, strategic end-use planning for the facility, early data collection, and predictive modeling of landfill changes will reduce near- and long-term costs.

    Based on experience with active and closed landfills throughout the Pacific Northwest, let’s take a look at regulatory requirements and owner strategies for planning long-term management of permitted waste facilities and ways to reduce the PCC period.

    Closure without ‘closure’

    Closure of a facility ends its operational life accepting waste and marks the transition to the PCC period.

    PCC can be defined as the time after closure when the owners actively monitor and maintain systems designed to prevent releases of contaminants to the environment (e.g., landfill cover, landfill gas extraction system and leachate collection system).

    N.J. Department of Environmental Protection (modified and used with permission) [enlarge]
    The amount of post-closure care decreases as a landfill becomes functionally stable.

    RCRA established that PCC should be conducted for a presumptive period of 30 years by the owner or operator of a waste facility. The PCC period is generally considered complete when the landfill no longer presents a threat to human health or the environment. However, in practice, the PCC period is typically much longer than 30 years, especially for legacy facilities (i.e., unlined “sanitary landfill” facilities or open dumps) developed prior to advances in landfill design and operation requirements.

    Newer landfills were designed to more effectively manage risk, reduce threats to human health and environment, and stabilize the waste more efficiently.

    The owner is financially responsible for any contaminant release that poses a threat to human health and environment until the PCC period ends. And this is true even when the facility is transitioned to reuse (i.e., custodial care). RCRA requires owners of waste facilities to demonstrate “financial assurance” for the required maintenance and monitoring activities during the PCC period, and any corrective action needed to control releases of contaminants into the environment.

    The greatest risk to incurring long-term financial obligations is generally a release to groundwater from leachate or landfill gas. Corrective action for a groundwater impact can be costly and take years of additional effort and expenditures to characterize, investigate and clean up.

    The monitoring and maintenance programs for the PCC period need to be designed carefully during the closure process to be both protective of the environment but also cost efficient based on the potential long-term financial obligations of a closed facility.

    Functional stability

    Determining how long to continue PCC monitoring and when a landfill no longer poses a threat to human health and environment is challenging for both owners and regulators. Also daunting is successfully planning for the post-PCC finish line — i.e., the sustainable transfer of a facility back to beneficial reuse — while trying to avoid threats to landfill health over the next 30 years.

    In Washington, the Department of Ecology adopted a “functional stability” model to clarify the more arbitrary 30-year presumptive PCC period for permitted municipal landfills. These standards allow owners to determine the time needed for a permitted landfill to become “functionally stable” and update financial assurance estimates. Threats are evaluated based on leachate quality and quantity, landfill gas production, cover system integrity and groundwater quality.

    The criteria for demonstrating functional stability are not specifically stated in Ecology guidance because the ability to demonstrate functional stability is site-specific and dependent on several factors. Landfill design, waste type and age, local geology, hydrogeology, nearby land use and other considerations such as potential long-term beneficial reuse of the facility all affect the evaluation of the potential impacts or threats.

    A case for less monitoring

    Methodical data collection is key to set the stage for regulatory compliance in both new and legacy landfills.

    For newer landfill facilities, leachate characteristics, landfill gas characteristics, background water quality and, in some instances, potential contamination to groundwater should be adequately characterized. Unfortunately, this may not always be possible for legacy facilities that are already in post closure.

    In either case, steps to take early in the post-closure planning process include:

    • Evaluating the groundwater monitoring program design

    • Defining leachate, landfill gas and groundwater sampling methods

    • Evaluating the waste management area point of compliance boundaries

    • Confirming performance of control systems

    • Performing statistical and trend analysis of historical leachate, gas and water quality data trends

    As an example, an owner of a currently active regional facility evaluated how to significantly reduce the monitoring frequency and number of locations by reducing the number of deep wells monitored. They demonstrated that hydrogeologic conditions didn’t support a threat to deeper groundwater. This reduction in monitoring requirements will carry over during PCC.

    Performance-driven reductions and long-term monitoring program optimization (such as decreasing monitoring frequency from quarterly to bi-annual or decreasing the number of locations in the monitoring program) can only be done when supported by sufficient data to show reduced threat due to progress towards functional stability.

    Invest now to save later

    For landfill owners and operators, an ounce of prevention can be worth hundreds of thousands of dollars of cure. Data to evaluate functional stability indicators is critical to assess time frames and predict measures of functional stability like leachate quality and landfill gas emissions, which pose the greatest threats to human health and environment.

    Adequate data collection and characterization will allow development of predictive modeling of a potential release.

    Predictive modeling that demonstrates progress towards functional stability can persuasively support the case made to regulatory agencies for reducing the PCC period from the presumptive 30 years — thus reducing the owner’s financial obligations.

    Additionally, the ability to periodically evaluate and verify functional stability of the landfill will allow optimization of the post-closure monitoring program and more rapid transition from costly active controls to passive controls, reduce monitoring and decrease the PCC period based on performance-driven evaluation of cover integrity, leachate, landfill gas and groundwater quality.

    Christopher Augustine is a senior hydrogeologist in Aspect Consulting’s Portland office. Augustine has performed hydrogeologic investigations and supported operations, groundwater monitoring programs, regulatory compliance, permitting, and remedial investigations at municipal and hazardous waste landfills for over 16 years throughout Washington and Oregon.

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