Nonpoint source (NPS) pollution is a leading cause of water quality degradation in the United States. In the Piscataqua Region watershed, 67% of the nitrogen entering the Great Bay Estuary comes from nonpoint sources and roughly 40% is delivered through stormwater (PREP, 2017). Nutrients like nitrogen are the primary cause of water body impairments in the Great Bay Estuary (NHDES, 2014). EPA Region 1 recently released the Great Bay Total Nitrogen General Permit (General Permit) designed to comprehensively regulate nitrogen loading from 13 wastewater treatment facilities at a watershed scale that promotes innovative and adaptive approaches to achieving water quality standards including voluntary nonpoint source nitrogen reductions. Local governments subject to the General Permit and other MS4 permits have raised concerns about meeting pollutant reduction targets for total nitrogen, total phosphorus, and total suspended solids. Street sweeping and seasonal leaf collection are emerging methods to maintain and mitigate water quality threats and control nitrogen. These nonstructural best management practices (BMPs) have historically received inconsistent pollutant removal credits under regulatory permits. However, recent science indicates these BMPs may be much more effective at removing pollutants than previously expected, especially during certain times of the year. Developed and implemented by the Chesapeake Bay Program (CBP) and piloted around buffers in the Great Bay watershed in 2018, the expert panel process is a defensible method for establishing and updating nutrient reduction credits. Building off these previous efforts, Clean Sweep implemented the expert panel process to develop consensus-based recommendations for pollutant load reductions for street cleaning with a focus on removal of organic materials during peak deposition. The goal of this project was to ensure that the credit received under regulatory permits is commensurate with the latest science. Results yielded an innovative crediting system accommodating both modeled and measured nutrient load reduction accounting approaches.
