It may seem impossible that a two-inch build up can rob the pipe of 75% of its capacity, but the two inches of build up is around the entire circumference of the pipe. The eight-inch pipe is now a four-inch pipe. (See illustration.) A pipe’s carrying capacity is calculated by using the area of the pipe multiplied by the velocity of the flow. The area of an eight-inch pipe is 50.24 square inches, while the area of a four-inch pipe is only 12.56 square inches.
Even at this reduced capacity of 6,000 gallons per hour, the normal sanitary flow is easily handled, but problems can occur when the rains begin. The reduced carrying capacity of the pipe is not always able to handle the added flow produced by the stormwater runoff, and the excess flow can back up in basements and/or area manholes.
The Public Utilities Maintenance Department implemented a sewer-jetting program in 2004 to address this problem. Jetting a sewer involves sending a large amount of water, under a great deal of pressure, through the sewer line. This helps to clean some of the build up from the inside of the pipe.
The accumulated fats, oils and grease (FOGs) must then be sucked out of the pump station wet wells with the Vactor truck as they create havoc with the level controls and pumping equipment. Maintenance superintendent, Tim Patrick reported, “The Department’s goal is to jet ever inch of sewer line in the City.” “And then we will start over and do it all again. It is an ongoing process that must be done on a continuing basis in order to produce results.” The program also involves a monthly jetting schedule in the identified problem areas of the City as well as any blockages as they arise.
The program has produced results. Sanitary sewer overflows and back-ups have declined significantly since the program began. The following are a few steps area residents can take to keep FOGs out of the sewer pipes and maintain a free flowing sewer system:
- Be aware of the “hidden oils” such as salad dressings, cheese, cookies and pastries, and the sauces and gravies. Scrap plates and bowls or wipe with a paper towel for disposal in the trash, not down the sink.
- Never pour fats, oils or grease down the drain. No amount of hot water will keep it from sticking to the inside of the pipes.
- Wipe out greasy pots and pans with a paper towel before washing. Even a small amount of FOG will become a thick layer of build up over time.
Educate family, friends and neighbors. We are all served by the same system, and what is being put down the drain upstream may be clogging up your pipes.