Seeking (Effective Landfill) Closure

Seeking (Effective Landfill) Closure

The way you operate your landfill now will have a big impact on the site’s post-closure period.

You’re a landfill operator and you’re thinking that once you close your site, it will be time to kick back and relax, right? Think again. You will be required to maintain and monitor your landfill for up to 30 years after closing, and doing so can be quite time-consuming
and expensive.

However, the actions you take while your landfill is still operating can have a significant impact on the costs and effectiveness of the post-closure period. In fact, an effective closure only can be accomplished if a landfill’s daily operations are executed properly while the site is open. Implementing certain best operational and maintenance practices can improve a landfill operator’s ability to control the major areas of concern during the post-closure care period, which include:

  • Waste settlement;
  • Final cover system integrity;
  • Maintenance of the vegetative cover component of the final cover;
  • Erosion and stormwater control; and
  • Leachate and landfill gas control.

By paying close attention to such operational details as compaction, soil and stormwater management, leachate recirculation and waste stream management, you will maximize the chances of a successful post-closure period.

Compaction in Action

Maximizing waste density not only improves the bottom line of your facility during its operational life, but also during the post-closure period. Better compaction of waste will result in less settlement after closure. This in turn results in less maintenance and will help decrease the potential for stormwater damage to the cap system due to low spots or ponding water.

Effective compaction will reduce waste volume to the smallest practicable size and minimize the airspace consumed. Maximizing compaction requires an appropriately sized compactor, the right compactor wheels and cleats, a consistent maintenance program to ensure that the machine remains up to the task and proper operating practices.

Generally, the heavier the compactor, the greater the waste compaction that can be achieved. Equipment is important, but the operating procedures that a landfill operator uses also will make a real impact on available airspace. Waste coming into the landfill should be placed in no more than 2-foot vertical lifts in order for the compactor to have the greatest effect. The compactor should make between three and five passes over each area of placed waste. The equipment operator should move over one wheel width to the left or right and then make three to five passes over the next section.

Minimizing the area of the working face and tipping deck can help extend a facility’s life by reducing the amount of material required to cover the face at the end of each day. It also allows a more concentrated path for the compactor so that more passes can be made and compaction of the entire working face ensured.

Soil Management

Soils should be stockpiled during a facility’s operation. These soils will be used as part of the final cap construction. Stockpiled soils should include low permeability soils to be used in the infiltration layer, and soils that will support the vegetative cover while resisting erosion from wind and water. Soils should be stockpiled on top of areas that have received waste to increase waste settlement with minimal effort.

Soils are used within the landfill for a variety of purposes and structures, including the construction of interim haul roads, temporary berms and daily/intermediate covers. However, using soil for these purposes can take up valuable airspace and can create pockets of perched water in the landfill, increasing the potential for leachate seeps during the site’s operating life and after its closing.

Soils used for these purposes should be stripped prior to the placing of new wastes in order to minimize this problem. The stripped soils can then be re-used as daily and intermediate cover, which will minimize the amount of clean soil needed during the landfill’s operation.

An alternate daily cover (ADC) can be used to minimize the amount of soil in the landfill and achieve greater compaction. Many types of ADCs are available: they include natural or artificial materials that can be sprayed or broadcast onto the working face at the end of the day. The material will break down when the next layer of waste is placed. A tarp also can be spread across the working face at the close of business each day and removed the following morning to allow waste placement to begin again. This method is also one of the fastest ways to close and re-open the facility each day. The lower your daily intake volume, the greater the impact an ADC will have on your available airspace and your overall waste compaction.

Stormwater Management

Perimeter ditches, diversion berms, stormwater culverts and sedimentation basins all are critical features that protect the final cover as well as other operational features of the closed facility. During the operations of the landfill, areas that may be subject to increased erosion due to stormwater runoff can be identified and corrected prior to facility closure. This is the opportunity to tweak design plans and make field adjustments to the locations, sizes and lengths of downslope drains and other stormwater control devices. These adjustments during a facility’s operation establish the features required for better performance during post-closure care and can minimize the amount of maintenance required after closure.

Leachate Recirculation

Authorization can be obtained to recirculate leachate during landfill operations. When done well — that’s another story for another day — leachate recirculation can result in greater waste compaction, quicker waste decomposition and the acceleration of landfill gas production. All of these serve to stabilize a landfill more quickly and can help reduce the post-closure care time frame.

Leachate recirculation is a practice that has been around since the 1970s and is one that can significantly extend a landfill’s life. Leachate from the landfill is pumped to a storage location and then broadcast on the working face of the operation. This leachate also can be introduced into a landfill through a series of perforated pipes or trenches that are placed throughout the waste mass. The moisture added to the waste can greatly enhance the compaction operation. Waste densities of more than 2,000 pounds per cubic yard can be attained when moisture is added to the waste prior to compaction. This moisture also accelerates the decomposition and stabilization of the waste mass. Additional airspace is obtained as the waste mass is consolidated as a result of these processes.

Another result is the accelerated generation of landfill gas, which can become another source of revenue through landfill gas-to-energy facilities.

During the post-closure care period, the owner or operator may petition the state to stop managing the leachate if he can demonstrate that the leachate no longer poses a threat to human health and the environment; this is perhaps more likely to be the case in a bioreactor landfill.

Waste Stream Management

During the operating life of the facility it is important to manage the incoming waste stream and also operate a well-defined fill sequencing plan. By properly managing the placement of different waste streams, compaction can be improved, which will help with the overall settlement of the landfill. In addition, thoughtful haul road placement can help improve compaction of the waste as well as minimize how often the road needs to be moved, which will save on the cost of road-building materials.

Maintaining Closed Portions

Most facilities will perform closure construction in phases to manage financial assurance requirements and address other concerns. These areas will not be considered to be in the post-closure care period until the entire site is certified as closed. However, it is imperative that these areas be well maintained and inspected often. These areas are opportunities to get a head start on post-closure care, as they can help you identify stormwater management practices that work best on your site, identify seed mixes and types of vegetation and fertilizers that stand up best over the seasons, and confirm the effectiveness of the other techniques employed during operations to try to stabilize the waste mass prior to closure.

Conclusion

You will be required to maintain and monitor your landfill for up to 30 years after final closure. However, the actions you take now can have a significant impact on the closure costs you could see in the future. Be smart: pay attention to the operational details, and keep a lot of those future dollars in your pocket.

Jeffrey M. Fantell is a senior technical consultant with Richmond, Va.-based Joyce Engineering. Jerry L. McGraner, P.E., is a regional manager with the firm.

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