Landfills are getting larger in height and greater in footprint area, but the location of leachate tanks, leachate ponds, or discharge points to an on-site or off-site leachate treatment plant usually don’t change.
A larger footprint means leachate force mains are getting longer and pumps have to work harder to push leachate through the system to a target point. Some operators carry on with the same pumps for decades and don’t monitor the performance of the pumps after expanding the landfill footprint.
SCS highly recommends that you evaluate the performance of the existing pumps again. Such an evaluation may require hydraulic analysis of the entire network of pipes along with pumps, or whatever segment of the network that is affected by the expansion. The effort is minimal in retrospect, but the operator makes sure that the system will function in an optimized zone with minimal wear on the pumps.
Sometimes the hydraulic evaluation may require up-sizing all or certain pumps in leachate sumps because not enough flow can go through the force main due to high friction loss in the expanded leachate force main. Up-sizing pumps may be achievable depending on the type of the leachate sump, i.e., riser system or vertical manholes. If the up-sized pump in a riser system is too long to fit inside a riser system or too long to the point of making routine maintenance too cumbersome, your engineer needs to come up with another idea.
Booster pumps along an expanded leachate force main can certainly be an option. Booster pumps can be the inline or offline type. Install the inline pumps on the actual force main, and position the offline type on the side so that liquids go through bends and elbows to reach the pump, and again through bends and elbows to get back in the force main. In either case, the booster pump adds hydraulic energy to the flow inside the force main to push the liquids at a higher pressure and velocity through the remainder of the force main and to the target point.
Operators need to be aware of the dynamic nature of the leachate piping network and the role of booster pumps in dynamic environments. After landfill expansion, with new cells coming online -increasing leachate generation, and when closing landfill slopes -decreasing leachate generation over time, the flow in the force main may change. Sometimes booster pumps have to be up-sized or down-sized depending on flow and pressure in the system.
Questions? Contact the author Ali Khatami.