You have a full landfill cell that isn’t receiving anymore waste and the final design specifications for the closure cap is pending. What do you do? An intermediate cover, often in the form of soil, is required to prevent rainfall infiltration into the waste, and hence reduce leachate generation. But cover soil can be logistically expensive to ship and place and is subject to erosion damage, which will cause the soil to diminish in effectiveness over time. If the cover soil isn’t constantly monitored, maintained, and repaired, there is an increased risk of leachate generation.
Recently, builders have been using temporary exposed geomembrane cover (TEGC) to block rainfall from infiltrating buried waste and generating leachate. This approach has been recommended by the Geosynthetic Institute to allow grade adjustments due to landfill settlement before the considerably more expensive final cover is applied. With a service life of about five years, TEGC is a more cost-effective temporary cover solution compared with cover soil in many situations. We will describe the scenarios that would benefit from using TEGC, what to look for in a TEGC product, and discuss the advantages of using our own AGRU Drain Liner as a temporary exposed geomembrane cover.
TEGC: Use cases and benefits
Federal regulations (SubTitle D) require an interim cover for exposed waste that isn’t expected to have a final covered installed within 180 days. In the past, installers turned to soil as a temporary cover solution. Between 12 and 24 inches of soil would be brought in and compacted to cover the bulk of the waste. Over time, the effectiveness of this cover soil in preventing rainfall infiltration diminished significantly without constant care. Often to the point where the amount of generated leachate matches the amount that would be generated by uncovered waste.
The cost of controlling leachate buildup can easily exceed $10,000 per acre a year in site operating costs. If a cell isn’t expected to receive its final cap within a few years, then a better solution is certainly warranted. Temporary exposed geomembrane covers are better suited for the role of a temporary cover. TEGCs are synthetic materials that are designed as impermeable barriers that block rainwater from contributing to leachate generation. Installation is relatively simple. A thin layer of cover soil is placed above the waste material before the geomembrane is positioned to protect it from puncture by the underlying waste.
TEGCs have many uses besides leachate cost-reductions. Geomembranes are also capable of capturing gas, reducing odor and greenhouse emissions in the environment. Furthermore, the captured gas can be repurposed for other uses. TEGCs can also help delay the permanent closure of a cell that is expected to have some use in the near future.
Selecting the right product for use as a temporary cover
Selecting the right TEGC for your project requires a number of considerations. First, what is the amount of expected rainfall each year? How many years is the TEGC expected to function before a permanent cover solution is installed? What is the expected top wind speed in the area? What is the size of the area that must be covered?
Determining the average amount of rainfall each year will help you identify the approximate thickness that your TEGC should possess as well as whether or not a studded surface is necessary. The lifespan of the temporary cover will determine the material type to be used, either high-density polyethylene (HDPE) or linear low-density polyethylene (LLDPE).
Knowing the wind speed will help you choose the best anchoring solution against wind uplift. Sandbags are a typical and straightforward solution, but they are susceptible to weathering. Earth percussion anchors are another option. Having an accurate gauge of the top wind speed in the area will enable you to calculate the optimal distance between anchor points. Finally, the size of the area to be covered is important. If its relatively small, prefabricating a smaller set of large TEGC pieces can reduce welding needs and therefore reduce installation time.