Landfill operators may add a casing pipe to their leachate force main for additional environmental protection. Consequently, the leachate force main is entirely located inside a casing pipe where the leachate force main is below ground. In the event of a leak from the leachate force main, liquids stay inside the casing pipe preventing leakage into the ground. During monitoring, checking for the presence of leachate inside of the casing pipes is routine.
For many years, I designed the installation of an HDPE monitoring manhole at each leachate removal sump station. Designed at the top of the perimeter berm, where the leachate force main is normally located, these manholes normally remain dry. The leachate force main crosses through the manhole without discharging into it. The casing pipes connecting to the manholes are open-ended at the manhole, draining directly into it. Easy to monitor, if liquids are present, you probably have a leak.
Using field operations experience, we improved the design.
A blind casing pipe above the surface leaves the leachate line exposed for piping purposes. In this design, the casing pipe does not connect to any vessel for monitoring; instead, it has a pressure gauge or small valve on it for pressure monitoring.
If the gauge reads pressure in the casing pipe, it is indicating there is liquid inside the casing pipe; leachate is leaking from the force main and filling the casing pipe causing the pressure to build. If using a valve, monitoring is opening the valve to look for liquid coming out of the casing pipe. Regularly monitored pressure gauges or valves is a standard operating procedure and easily accomplished.
