When are gas collection systems typically constructed?

Gas collection systems are typically constructed after waste is in place or during cell construction because this timing allows for the effective capture of landfill gas as it begins to be generated from the decomposition of waste. As waste accumulates, anaerobic conditions develop, resulting in the production of methane and other gases.

Building the gas collection system during cell construction enables the integration of gas wells and piping into the landfill design, ensuring efficient collection as soon as gas generation begins. It also allows the landfill operators to manage the gas emissions effectively and mitigate potential environmental impacts right from the start of waste placement.

Other options suggest constructing gas collection systems either before the landfill's opening, which wouldn’t facilitate gas capture as waste has not yet been placed, or only after the landfill closure, which would not address the gas issues during the active life of the landfill. The choice indicating construction during the planning phase of landfill expansion overlooks the practical necessity of having active waste along with a gas collection system to create a functional operation.