Do you have information on the causes of forming leachate, and geysers?

There have been several papers published in the U.S., as well as a couple of International Solid Waste Association (ISWA) conferences on the topic of sudden gas pressures and problems with leachate seeps both out of the sides of landfills as well as pulling or pounding on top of the landfill. The formation is related to two things, the age of the leachate itself (as it ages it tends to form more), but also the amount of gas that is accumulated in the sides. In general, what we see is an interesting cycle of very high shut-in gas pressure so the wells are dewatered, but when they’re dewatered more gas starts flowing into the wells and then gas and liquids are literally being blown out of the wells, even where the pumps are installed. This sort of a cycle of continued dewatering followed by pulling of gas needs to occur to get the system to settle down.  Eventually the liquid levels get down low enough that there will be a nice and steady gas flow and the foaming and surging problems will be eliminated.