Green Infrastructure in Municipal Separate Storm Sewer Systems

Section 502 of the Clean Water Act defines green infrastructure as 'the range of measures that use plant or soil systems, permeable pavement or other permeable surfaces or substrates, stormwater harvest and reuse, or landscaping to store, infiltrate, or evapotranspirate stormwater and reduce flows to sewer systems or to surface waters.' Although there are numerous examples of municipalities that prioritize green infrastructure in their approaches to stormwater management, the national extent of green infrastructure adoption within compliance frameworks has been difficult to assess. To address this need, EPA conducted a review of final individual and general National Pollutant Discharge Elimination System MS4 permits issued by states and EPA through May 2020. EPA reviewed 67 MS4 permits. Out of those, EPA found clear, specific and measurable examples of permit language requiring or encouraging green infrastructure in 23 permits across 19 states. Permit excerpts were categorized according to typical permitting requirements: public education and outreach, public involvement/participation, illicit discharge detection and elimination, construction site stormwater runoff control, post-construction stormwater management in new development and redevelopment, pollution prevention/good housekeeping for municipal operations, and monitoring. The review also identified examples of how green infrastructure is being used to address specific pollutants of concern such as mercury and polychlorinated biphenyls. This analysis catalogued a wide variety of methods states and EPA use to incorporate green infrastructure into MS4 permits, including, but not limited to, performance standards that address post-construction stormwater discharges; requiring that green infrastructure be considered or implemented as part of local building and site development approval processes; and establishing a ceiling on new impervious area. EPA's presentation at the 2021 Stormwater Summit will synthesize the results of this permit review, provide national perspective on how states are incorporating green infrastructure requirements into their MS4 permit programs, and highlight successful implementation examples at the municipal and regional levels. By sharing these results with state and municipal stakeholders, EPA hopes to foster information exchange and the continued development of permitting approaches that support resilient, vibrant, and livable communities.