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As any landfill operator knows all too well, many MSW challenges do not emerge until the waste is compacted and set to rest in a landfill. At that point, deposited materials—like food and other solid waste—break down, creating a variety of chemical and bacterial components that interact in an assortment of ways detrimental to the leachate collection and drainage systems. The magnitude, degree, and extent of clogging appear to depend on the variety of wastes found in a landfill, as well as on its operational procedures and the performance of the leachate collection system. In some instances, frequent jetting and cleaning of leachate collection piping will maintain the system. In other cases, no matter how frequently an operator flushes a landfill leachate collection system with acid washes or other cleansers, precipitates continue to collect, creating a persistent problem. |
Regions that experience dry weather often have few encounters with clogged pipes, but communities in a warm, high-precipitation state like Virginia can spend in excess of $100,000 a year maintaining their drainage systems. Some landfill operators work a continuous remediation cycle; by the time they finish flushing the leachate collection system of each cell, it is time to begin the process all over again. Prompted by widespread clogging phenomena in landfills, a team of researchers and industry professionals from the University of South Florida and Cambridge, MA-based CDM analyzed the deposits that clogged the drainage pipes at the landfill site. They also studied laboratory-induced clogging to understand the mechanisms that lead to clogging so they could develop strategies to mitigate or control this all-too-common problem. |
Documented cases of clogged leachate collection systems date back to the early 1970s, when the USEPA raised concerns about the clogging of landfill leachate collection systems. This prompted the EPA to conduct research on test cells at the Boone County landfill in Kentucky. By the 1990s, landfills in Germany, England, Canada, and the United States were experiencing clogging problems. Aside from the cost and amount of labor involved in flushing leachate pipes, there are a variety of genuine environmental risks associated with clogged pipes. As long as a landfill remains free of such fluid build-up and continues to drain properly, there is no problem. |
When the components of these draining systems clog—either with biogeochemical deposits, silt and biofilms, or precipitating minerals—the leachate can build up within a landfill, creating the potential to leak or seep into the groundwater or cause landfill slope instability, which occurs when liquid accumulates in a landfill, exerting pressure on its side.
When rainfall percolates through a landfill’s waste layers, leachate develops, causing the liquid’s constituent elements to clog drainage pipes. Heavy nutrient loading—associated with the movement of leachate initially through the waste matrix and then through the leachate collection system—inevitably causes microbial activity. In turn, the growth of these microorganisms fosters an environment where the biologically induced precipitation of minerals thrives. These minerals, which are present in leachate and form the clogging material, can potentially affect the drainage system’s performance.
After the waste is saturated to capacity, it releases its excess moisture. This is a continuous exchange, since decomposing waste is in a constant flux of absorption and degradation. Once released, leachate percolates through the landfill until it reaches the liner.
Abdul Mulla-Saleh*
With accepted landfilling practices unlikely to change in the near future, solid waste professionals should address these issues now. Waste will continue to be collected and its elements will continue to react to create clogging. Monofilling and co-disposal practices should be assessed further to prevent the formation of precipitates.
Although landfill operators can flush a drainage system with biocides and cleaning agents to control mineral formation and biofilm, this technique is unlikely to prevent future clogs.
*Abdul Mulla-Saleh is an associate and solid waste specialist in CDM’s Tampa, FL, office.
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