If you are using a gravity under drain leachate collection system, are you likely to need additional pumping of the leachate?

The short answer is yes, there is still a need to dewater the gas wells even with a functioning under drain system for leachate. Liquid leachate in the waste mass should migrate downward to the under drain system, however, the gas wells aren’t connected to that system. The gas wells typically terminate anywhere from two to three meters off the bottom of the landfill site. Regardless of a functioning under drain system, the gas wells tend to accumulate liquid. We had a site in Iowa that was being told by the regulators that they had exceeded their maximum liquid level against the liner because they had roughly 10 meters of liquid building up in the gas wells, and the regulators were convinced that was the liquid level in the entire landfill site. There was an excellent paper written by Terry Johnson with Waste Management published in 2007 describing how they excavated about 15 meters in the landfill site all the way down to the drainage wire and then were able to identify that they had as little as two to three centimeters of liquid in the under drain system even though they still had as much as 10 meters of liquid accumulated in the gas wells.