Landfill operators are making significant investments developing comprehensive lining systems to protect human health and the environment. These lining systems are normally equipped with drainage layers to convey leachate reaching the lining system to collection pipes and sumps for removal from the landfill. Landfill operators are also heavily investing in collecting and removing landfill gas for disposal or conversion to renewable energy.
After three decades of experience with these systems, landfill liquids may still accumulate in some gas wells adversely impacting gas removal efficiencies. In these situations installing a pneumatic submersible pump in the gas well to lower the liquid head in the well, restoring gas removal efficiencies is standard practice. However, this remediation technique requires additional capital investment.
An Alternative Solution Exists
A more recent alternative, constructing vertical drains from the bottom up where gas wells are located, may be a better solution. Construction of a vertical drain/gas well begins by constructing a gravel pad at the bottom of the landfill after completion of the lining system and placement of the protective soil cover over the lining system. The gravel pad may be 15 ft. by 15 ft. in lateral dimensions by 10 ft. in height. Gravel pads are normally constructed where future vertical wells are planned to be drilled. The center of each pad is surveyed, and the information is used to locate future gas wells at some vertical distance above waste that is placed in the new cell over time. The gas well drilling continues until it reaches the gravel pad at the bottom of the landfill. The connection between the gas well gravel pack and the gravel pad at the bottom makes it possible for landfill liquids to flow down and drain directly into the leachate collection system below the gas well.
Vertical drains help landfill liquids reaching the gas well gravel pack to flow to the leachate collection system at the bottom of the landfill; thus preventing watering out the gas wells. This sustainable alternative keeps gas production efficient and is environmentally sound, requiring less capital investment.
About the Author: Dr. Ali Khatami
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