Sewer Monitoring Series · Water Environment Federation · 2025
Data-Driven Consent Decree Navigation Using Sewer Flow Monitoring
Reducing a $28M Corrective Action Program to $4.44M Through Targeted RDII Characterization
“I can defend every dollar I spend — because I have the data to prove why I spent it.”
Sewer flow monitoring provides quantified, field-measured data for credible consent decree corrective action plans. By characterizing actual RDII sources and SSO volumes, utilities can propose targeted, cost-effective corrective action programs instead of broad replacements based mainly on estimates.
Abstract
This case study follows a public works director responding to a state Notice of Violation and threatened consent decree for recurring sanitary sewer overflows. An 18-month, 31-meter monitoring program with rainfall capture characterized RDII sources at each SSO location and replaced broad estimates with measured evidence.
The monitoring-driven corrective action plan reduced the contemplated program from $28 million to $4.44 million, avoided a larger rate increase, and supported a plan that could be explained to regulators, elected officials, and ratepayers.
Background
A sanitary sewer overflow occurs when untreated wastewater escapes the collection system before reaching treatment. Recurring SSOs can expose utilities to enforcement action, stipulated penalties, and legally binding compliance schedules.
The whitepaper centers on the decision-maker’s dilemma: EPA expects a credible corrective action plan, council resists rate increases, the public expects accountability, and the utility needs a technical basis for every recommendation. Without data, every major project is easier to challenge.
Methodology
The monitoring program had two explicit objectives: characterize actual RDII sources at each SSO location and establish quantified SSO volume baselines. That structure allowed the utility to replace estimated overflow volumes with measured reporting.
Meters were placed upstream and downstream of SSO structures for mass-balance calculations, while additional meters characterized RDII at the contributing sewershed level. EPA reviewers were given read-only dashboard access, improving transparency during review.
Results
The strongest finding came from the commercial district, where the prior engineering estimate recommended expensive interceptor replacement. Monitoring showed the dominant problem was fast inflow from private property cross-connections, not the pipe capacity deficiency originally assumed.
That diagnosis changed the corrective action from an $8.4 million replacement concept to a $340,000 cross-connection enforcement and assistance program. Across the program, the measured data allowed the city to match each SSO location with a more appropriate fix.
Engineering Significance
Quantified RDII sources enable targeted enforcement and targeted rehabilitation. When the dominant source is private inflow, pipe replacement may cost millions without solving the actual wet-weather problem.
Measurement-based SSO volume reporting also changes the regulatory conversation. Accurate measurement documents actual conditions, tracks progress objectively, and signals good-faith engagement to technical reviewers.
Conclusion & Next Steps
For public works leaders facing SSO enforcement pressure, sewer flow monitoring is both an engineering tool and a governance tool. It gives leaders a defensible basis for capital planning, rate discussions, public communication, and compliance milestones.