Designing A Better Alternative for Post-Closure Care
After a landfill has reached the end of its service phase, federal law requires owners to install a final soil cover and maintain it over the next 30 years. This is the traditional strategy that most landfill owners employ and represents a significant cost of business. When all the layers are tallied together, the capping and post-closure period can cost up to $400,000 for a small, 100-acre landfill. With advancements in geosynthetics over the past half-century, however, there is a viable alternative.
The U.S. Environmental Protection Agency (EPA) allows for alternative post-closure care solutions at the discretion of each state’s solid waste director. As long as the alternative meets EPA standards, states can accept other post-closure strategies from landfill owners.
Proposed by Dr. Robert M Koerner, director emeritus of the Geosynthetic Institute, exposed geomembranes offer a triple-threat advantage with faster installation, lower project costs, and a smaller environmental footprint. With this approach, the final cover is only installed after the 30-year maintenance period, giving landfill owners the flexibility to reopen a portion of the landfill, if necessary. Exactly how much does it save? Of course, outcomes will depend on site-specific conditions but, by some estimates, exposed geomembranes clock in at about one third of the cost of traditional cover solutions.
Sustainability and Costs Advantages of Exposed Geomembranes
When compared with a traditional landfill cover, an exposed geomembrane cover eliminates the need for a surface layer, protection layer, and drainage layer. The topsoil and protection layer are both significant costs, so their removal from the equation favors the exposed geomembrane solution, as shown in Table 1 [a cost analysis of a landfill cover from (1)].
Table 1. Cost Analysis of a Traditional Landfill Cover vs. Exposed Geomembrane
|Layer (top to bottom)||Traditional Landfill ($/m2)||Exposed Geomembrane Cover ($/m2)|
|Seeding and vegetation||0.90||–|
|Topsoil; 150 mm||36.00||–|
|Protection soil; 750 mm||28.00||–|
|Drainage composite; 6.3 mm||7.30||–|
|Geomembrane; 1.0 and 1.5 mm||6.50||9.20|
|Geotextile; 520 g/m2||3.80||3.80|
|Soil foundation layer||9.20||9.20|
|Waste proof rolling||0.90||0.90|
Beyond cost, exposed geomembranes also leave behind a much smaller carbon footprint. That’s because installing a traditional landfill cover requires almost a meter of soil, a huge mass that must be transported to the site. In terms of CO2 emissions, diesel fuel for transportation is one of the most “expensive” components in landfill closures. By eliminating the two topsoil layers, the landfill post-closure care phase becomes far more sustainable.
How do you get started? By selecting a resin type that meets your project needs and receiving approval by the appropriate state environmental agency.
Exceeding EPA Standards
Once you are convinced that an exposed geomembrane strategy is appropriate for your site, you must create a design that meets all EPA regulations. The U.S. Environmental Protection Agency’s (EPA) municipal solid waste regulations for the final cover have the follow requirements:
- The cover’s permeability (hydraulic conductivity) must be less than either 1 x 10-5 cm/sec or that of the liner beneath the waste mass.
- The cover must minimize infiltration.
- The cover must minimize erosion.
- It must be placed within one-year after the last waste is deposited.
Currently, there are four different types of exposed geomembranes resins that are capable of meeting EPA’s solid waste regulations for post-closure care. They are high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), flexible polypropylene (fPP) and ethylene propylene diene monomer (EPDM). Each of these geomembranes can satisfy the 30-year time required for post-closure of landfills, with HDPE displaying the highest potential lifetime at about 42 years.
Choosing an Exposed Geomembranes Solution
There are many factors that can alter the economic differences between traditional landfill covers and exposed geomembranes. For instance, exposed geomembranes must be thicker than the type utilized under the traditional soil layer, and geomembranes still require a gas collection layer and an underlying foundation layer. These costs vary project-to-project.
Finally, site-specific conditions can further alter the cost advantage between the two approaches. At some sites, waste can settle much more over the 30-year period. In these cases, the settlement allows for additional waste placement if an exposed geomembrane was used rather than a traditional cover. All these considerations, on top of EPA regulations and the need for state approval, makes designing an appropriate geomembrane solution somewhat of a challenge.
For the best geosynthetic materials, partner with an experienced manufacturer such as Agru America. Agru America offers a range of HDPE and LLDPE geomembranes suitable for post-closure, including HDPE resin that meets Geosynthetic Institute’s GM 13 quality control protocol. Moreover, their technical support provides expert guidance to engineers, owners and installation contractors during the project design and construction phases.