flow capacity

March 2, 2016

The benefits of implementing these cleaning recommendations for leachate collection pipes will help keep the pipes clean and fully functioning; helping landfill operators prevent the potentially serious complications of clogged pipes and immovable leachate.

By Dr. Ali Khatami, P.E., SCS Engineers

Some states require that leachate collection pipes be cleaned with high-pressure jets on a regular basis (for example, every ten years or even more frequently); however, the rules don’t clarify or set forth the specific conditions under which the jet cleaning should be performed. Some landfills have undertaken jet cleaning while the pipes are partially or fully submerged in leachate above the liner. Unfortunately, jetting under water may drastically reduce the effectiveness of the pressurized jet, resulting in a pipe that is not cleaned properly. This is even more important when the jetting is intended to remove biological growth on the pipe walls and in the perforation openings.

The self-propelling equipment that carries the nozzle through the pipe.
The self-propelling equipment that carries the nozzle through the pipe.

In addition, many states do not require videotaping the pipe after jetting. Videotaping is the best way to verify that the pipe was cleaned successfully. If the leachate collection pipes are not properly cleaned, then over a period of 20 years or so, they can be adversely impacted by severe biological growth and buildup in the pipe perforations to the point that liquid can no longer enter the pipe.
Another shortcoming is that the rules do not specifically require that the riser pipes (where the submersible pumps are located) be cleaned or videotaped. Therefore, due to the added costs, some landfill operators may not clean the riser pipes as part of the required cleaning events, or they may delay such cleanings for an extended period. This can prevent leachate from flowing into the riser with the direct and serious consequence that leachate cannot be removed from the sump.

Shown here, the high pressure nozzle at the inlet to the cleanout riser.
Shown here, the high-pressure nozzle at the inlet to the cleanout riser.

Another issue to consider is that pressurized jet cleaning procedures do not necessarily push the solids that separate from the pipe wall out of the pipe inlet opening through which the cleaning nozzle entered the pipe. As a result, these solids flow out of the pipe and into the gravel bedding on the outside of the pipe, and can potentially clog the void within the gravel pack around the pipe or in the sump. Clogging the sump gravel can mean reduced flow capacity from the leachate collection pipe to the riser pipe and the submersible pumps.
To resolve these issues, SCS recommends the following:

  • Before inserting the pressured jet cleaning nozzle into the pipe, remove as much leachate as possible from the leachate collection pipe and the sump
  • Clean both the leachate collection pipes and the riser pipes during each cleaning event
  • Use a vacuum truck to remove liquids that reach the lowest point in the leachate collection pipes or riser pipes during the jetting
  • After each 10-year (or more frequent) jetting event, videotape the pipes to ensure that the perforations in the leachate collection pipe and riser pipes were cleaned properly
  • Repeat the jetting if there are indications that additional cleaning is needed. This is important as conditions inside the pipe will become more severe over the years if the pipes are left uncleaned and buildup accumulates.

The benefits of implementing these recommendations will help keep the pipes clean and fully functioning. These suggestions help prevent potentially serious complications that the landfill operator may have to address if the pipes are clogged and leachate cannot be removed.

Questions? Contact Ali Khatami, PhD, PE, LEP, CGC, is a Project Director and a Vice President of SCS Engineers. He is also our National Expert for Landfill Design and Construction Quality Assurance. He has nearly 40 years of research and professional experience in mechanical, structural, and civil engineering. Dr. Khatami has acquired extensive experience and knowledge in the areas of geology, hydrogeology, hydrology, hydraulics, construction methods, material science, construction quality assurance (CQA), and stability of earth systems. Dr. Khatami has applied this experience in the siting of numerous landfills and the remediation of hazardous waste contaminated sites.


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Posted by Diane Samuels at 3:27 pm