Non-stormwater contributions to our stormwater drainage infrastructure, whether from private, municipal, commercial, or industrial sources, can quietly degrade water quality, impact public health, and erode community trust. Sanitary wastewater (human sources of waste) leaking into or improperly connected to stormwater infrastructure is an often underappreciated, insidious, and widespread issue, with illicit discharges likely present in nearly any community served by a sanitary sewer system. While many municipalities have Illicit Discharge Detection and Elimination (IDDE) programs in place due to regulatory requirements, not all approaches provide the insight needed to drive meaningful action.
Across regions, we often see a gap between compliance-based programs and those that truly illuminate what is happening within a stormwater system. At Woodard & Curran, we work alongside communities to close that gap, moving IDDE from a checklist to a strategic, data-informed program that supports long-term water quality goals.
Why IDDE Work Rarely Follows a Straight Line
IDDE is rarely as simple as it appears on paper. Stormwater systems are complex, aging, and shaped by decades of development. Illicit discharges often appear intermittently, with signals that can be subtle, inconsistent, or influenced by weather and seasonal conditions. Some municipalities have also inherited combined sewer systems from previous generations where what you flush, and what enters catch basins, mix in the same conveyance pipes. As those combined pipes are repurposed or abandoned their impact on existing stormwater networks further complicating the IDDE process.
We approach IDDE as an investigation — one grounded in curiosity, field experience, and collaboration with our clients. By combining field observations, system knowledge, and data analysis, our teams can interpret ambiguous results, test assumptions, and adjust strategies in real time. This adaptive approach helps uncover issues that might otherwise go undetected and positions communities to act with greater confidence.
