Building a Prioritized Force Main Assessment Program

Since sanitary sewer force mains are under pressure to push wastewater flow, they typically run a higher risk of failure than their gravity sewer counterparts. Force mains usually require continuous pumping operation and have few access points, which makes typical inspection and maintenance technologies non-applicable. Consequently, force mains are often not included in regular assessment and maintenance programs. The City of Naperville chose a proactive route, instituting a force main inspection and preventative maintenance program with the assistance of RJN's investigation team.

The multi-year force main inspection program evaluates conditions and supports O&M and repair planning initiatives. Our engineers performed a historical data review and desktop analysis; investigated the route and structural condition of the pipe; led the force main condition screening using Pipers®, a multi-sensor inspection technology, to identify air and gas pockets, measure debris and record pressures, and changes in bulk wall thickness. With this data, RJN engineers were able to ascertain pipeline conditions and develop long- and short-term solutions for the maintenance and improvement of the City's force main network. 

Acoustic data overlaid with force main elevation

• Diagnostics collected from multi-sensor Pipers® include acoustical data, leak detection, magnetic flux, and hydrostatic pressure analytics. 
• Our engineers manage the 5-year force main inspection program on the City's behalf (4 force mains evaluated per year) to proactively assess and remediate threats to the system and evaluate rehabilitation, repair, and O&M options.
• RESULTS: Through 2024, RJN identified 86 air pockets, and one leak across thirteen force mains. Two of the assessed force mains were not pressurized and were at risk of reduced capacity and hydrogen sulfide corrosion. Structural assessments revealed submerged air release valves on two force mains, with debris accumulation found in every force main, sometimes exceeding 35%. Overall, 29 high-risk and 115 medium-risk anomalies were identified. As a result, RJN recommended to the City that $4.35 million be allocated for trenchless rehabilitation, partial replacement, and cleaning maintenance.