Elimination of Discovered Nutrient Discharges from Grey Infrastructure BMP Expert Panel Report

Description

"Nutrient Discharges" refers to the complex range of non-stormwater flows that export nutrients and other pollutants into urban receiving waters during dry weather conditions due to spills, leaks, and overflows from grey infrastructure. These discharges are created by the interaction of pollutant generating activities/sources with aging grey infrastructure (sanitary sewers, drinking water pipes and storm sewers) via stormwater runoff and groundwater migration. 

Many nutrient discharges from grey infrastructure are regulated under MS4 permit requirements for illicit discharge detection and elimination (IDDE) and NPDES wastewater permit requirements to abate sanitary sewer overflows (SSO). More than 1,000 communities across the Bay watershed are now subject to one or both permits, but to date, most have not utilized their programs to specifically focus on potential nutrient reductions. Nutrient discharges from grey infrastructure are not explicitly simulated in the current version of the Chesapeake Bay Watershed Model (CBWM), and no pollutant reduction credits are currently available to states and localities that invest in finding and eliminating them. 

The Panel reviewed 15 different types of nutrient discharges from grey urban infrastructure, and concluded that they collectively can contribute a significant portion of the dry weather nutrient loads in urban watersheds, although their share of the total load is extremely variable in both space and time. The Panel reasoned that nutrient reduction credits could be assigned when certain types of individual discharges are permanently eliminated, as confirmed by actual monitoring data. Recommendations from the Expert Panel are outlined in this report.