Blackhawk side-slopes take over for crusty submersibles after hot, aging landfill adds gas system

A large, older landfill in a Southern state was baffled by significant changes in its operating characteristics after installing a landfill gas system.

The conscientiously well-run site, opened more than 20 years ago, always has been challenging — extremely harsh, hot and highly volatile. The regional gas manager called it more than a typical landfill, with high variability and breadth in the stream of accepted waste — 40-50 percent trash, 10 percent construction debris, plus significant amounts of industrial waste, bio solids, sludges, solidified liquids, offset products, ash and heavy metals. Industrial waste and fill are used as cover. There is little oxygen and no leachate fingerprint, the manager says.

The introduction of a gas system more than five years ago tested every experience the manager and the regional engineer held about landfill dynamics and leachate pumping. Although contrary to the "science," high dynamic head began to tax the leachate collection system, and liquids began behaving and moving in unexpected ways. High-flow electric submersible pumps began failing, victims of two forces — a "crusty crud" in the leachate that fouled the pumps’ motors, and leachate wells that seemed to be drying out, which burned up the exposed submersibles.

Pneumatics offered surprising low-flow solution.

The engineer reasoned that if the gas-extraction wells were moving liquids first, there would not be much liquid left for leachate wells in some area of the landfill. Yet when submersibles were pulled, liquids again appeared in the leachate wells. "In the beginning, we tried to fix things in standard ways but the problems multiplied," the engineer said. "Liquids were moving in opposite directions from what we expected."

"The electric pumps were breaking down," the manager said. "They required lots of effort just to keep going." Plus the electrics were expensive to run, their motors were good only to 105° F., and there were transducer issues in the hot sun. The two pros were stumped.