How Much Rainwater Are You Treating? Solutions and Budgeting for I&I Reduction

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Kendall Ryan

Water/Wastewater Engineer

This article is a preview of a presentation recorded for the Collection Systems Digital Conference presented by the Water Environment Federation. 

Treating large volumes of rainwater due to inflow and infiltration (I&I) in the wastewater collection system is a shared experience of many utilities across the US. The City of Conroe, Texas, is facing the same challenge with their aging wastewater infrastructure serving 87,000+ residents. The issue is not limited to treatment costs; I&I reduces the wastewater system’s capacity, increases risk of sewer overflows, and can result in expensive capital improvement projects that vie for a share of the City’s budget. Conroe’s story is a valuable case study for utilities of all sizes in proactively tackling this issue.

The City launched a sanitary sewer evaluation study (SSES) project to tie together I&I reduction efforts and the ongoing sanitary sewer overflow (SSO) initiative. The SSES effort involved flow monitoring for 100 days using 30 flow monitors and two level-only monitors. Data collected by the meters helped qualify I&I volume and rank collection system basins to narrow down areas for field survey and investigations, including CCTV inspections of sewer line segments and NASSCO MACP inspections of manholes. A combination of technologies was employed to visualize and analyze the field collected data.

Detailed rehabilitation recommendations were developed following the analysis of manhole and line inspection results. An easy-to-implement rehab decision tree matrix was developed and utilized for this step. These findings led to the final step of the project, identifying areas of future SSO initiative work. To address financial constraints, a calculation tool was developed to easily identify future SSO initiative areas that maximized rehab efforts within the City’s allocated annual budget.

Learn more about this project at the WEF Collection Systems Digital Conference, an online course featuring recorded presentations originally planned for the 2020 Collection Systems Conference. This presentation, which is available to view now, covers analysis tools, time-saving lessons learned, and more ideas to address the challenges of wastewater collection systems. Registration is required and PDHs are available.

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Kendall Ryan, PE, is a Water/Wastewater Engineer in Pearland.