The lack of carrying capacity created by the fats, oils and grease discharged to the sewer system is most evident during heavy rain events when a substantial amount of runoff is entering the system in a short period of time. Residential sewer pipe, in the City of Moberly, is mainly eight inches in diameter. The pipe is laid at a grade that allows for the wastewater to gravity flow at approximately 2.5 feet per second.
This translates into around 400 gallons per minute carrying capacity or nearly 24,000 gallons per hour with a full pipe. A one-inch build up of FOGs will decrease the flow by 25%, resulting in a carrying capacity of 18,00 gallons per hour. A two-inch build up will reduce the carrying capacity by 75%, allowing only 6,000 gallons per hour.