Municipalities nationwide are taking a proactive and preventive approach to sewer maintenance by implementing a standard operating procedure (SOP) that includes aggressive sewer cleaning methods as an integral element. Aggressive cleaning extends the service life of the entire system while reducing sanitary sewer overflows (SSOs).
Common, controllable causes of SSOs include fats, oils and grease (FOG), roots, debris and structural anomalies, such as protruding taps. The Environmental Protection Agency (EPA) recognizes that all sewer pipe materials are susceptible to SSOs due to these common causes. The objective when cleaning a line must be to remove anything that obstructs full flow. This is especially important when the sewer pipe to be cleaned is on a three, five, or seven-year maintenance rotation and the completed cleaning must last through the full rotation.
In a style of cleaning that is a throwback to the adoption of the hydro-flushing trucks of the 1930s, passive cleaning incorporates low gallons per minute (gpm) and low pounds per square inch (psi) delivered to the inside of the pipe. Pressures of less than 1,800 psi and flows of less than 50 gpm are considered passive. Most municipal sewer hydro-jetters operate between 2,000 to 3,000 psi and 50 to 125 gpm. These more aggressive pressure and flow ranges are needed to effectively clean sanitary sewers. The final psi and gpm settings are selected based on the pipe sizes to be cleaned and the tools to be used.
Passive cleaning techniques combine nozzles that usually have smaller jet angles and nozzles with smaller outside diameters to facilitate faster cleaning times while increasing “completed” cleaning footage without considering whether a pipe has been returned to an acceptable level of operational capacity. Another common passive technique, “catfishing,” is the process of dragging a sewer nozzle on the bottom of a pipe without using a nozzle centralizer or “proofing skid.”