Loudoun County Illicit Discharge Detection and Elimination (IDDE) Program Methods for Long Term Tracking and Follow-up of Outfalls with Suspect Discharges

Loudoun County’s Illicit Discharge Detection and Elimination (IDDE) program dates back almost 20 years.  The County is one of the fastest growing communities in the Country, and its stormwater network of 3,000 outfalls is continually increasing.  As the outfall inventory grows and land uses change, it is imperative that the County adjust its procedures to ensure that illicit discharges are identified and eliminated efficiently. The County, with GKY’s assistance, has refined it’s IDDE procedures using iterative processes to enhance its screening and follow up methods.

The County’s IDDE program successfully uses a combination of drainage area tracing, field testing, and laboratory testing results to identify illicit discharges, allowing Loudoun County to eliminate these sources of pollution through public education and municipal code enforcement. In addition to obvious illicit discharges, Loudoun County’s dry weather screening program identifies an even larger number of suspicious sources of potential non-stormwater flow or other indicators of pollution. Generally, these sources are not clearly identified during dry weather screening and require additional investigation. To streamline the process, the follow up requirements are separated into different categories. This allows follow-up efforts to be prioritized, moving the analysis of lower risk suspect flows from the field to the desktop. Tracking and analysis of historical data informs the County when prioritizing outfalls for future screening efforts and suspect discharge follow-up.