What is a Gravity Sewer System?
Conventional gravity sewers convey raw, untreated sewage through pipelines to a treatment facility or lift station. The sewer lines are straight and installed on a specific horizontal and vertical alignment, with interspaced manholes placed at set intervals, at pipe intersections and at changes in pipeline direction. The pipes are installed with uniform gradients sufficient to create a self-cleansing velocity of two feet per second. Concrete manholes allow access for inspection, cleaning, and repair. Construction of these systems on flat terrain typically requires deep excavations (6 to 12 feet below grade) and proper preparation and bedding materials are required in the pipeline trenches. Sarasota County standards restrict the depth of burial to 18 feet, at which point a lift station is built to pump wastewater to another location, such as another pump station or a wastewater treatment plant through a force main. The sewers and manholes are most typically installed along the centerlin
