The MS4 permitting structure was implemented in two phases: Phase I (implemented in 1990) required individual NPDES permits for MS4s serving over 100,000 people, while Phase II (implemented in 1999) required general permits for all MS4s not covered by Phase I. Water quality standards are intended to be supplementary provisions to ensure that waters meet minimum water quality standards, regardless of individual compliance with technology-based limitations. The water quality standard is determined based on the intended use of the impaired water. waters by urban runoff, the federal Clean Water Act (CWA) regulates MS4s through NPDES (National Pollutant Discharge Elimination System) permits that are allocated to the sewer network based on ambient, state-controlled water quality standards, rather than effluent limitations. Environmental Protection Agency (USEPA) estimates that urban runoff is the leading cause of impairment related to human activities for ocean shoreline waters, and has led to significant degradation of nearly 30,000 miles of river. While stormwater is typically less highly contaminated than raw sanitary waste, stormwater discharges can carry a variety of different contaminants. MS4s use separate networks for sanitary waste and for stormwater the sanitary waste is sent to a wastewater treatment plant, while stormwater is discharged directly into the local waterbody. In this analysis, we model different stormwater management approaches for a hypothetical representative municipal separated storm sewer network (MS4) located in an impaired watershed. The increasing frequency of high-intensity rainfall events caused by climate change is expected to exacerbate these water quality challenges. Runoff from roads, roofs, and lawns often carries contaminants including suspended sediments, polycyclic aromatic hydrocarbons (PAHs), heavy metals, and fertilizers and pesticides. The rapid increase in impervious area has caused less infiltration and more runoff. The spread of metropolitan areas has led to increases in the twin issues of poor water quality and localized flooding. Results also reveal that policy impacts are highly dependent on agents' spatial position within the stormwater network, leading to important questions of social equity and environmental justice. Large, downstream agents have a disproportionate share of bargaining power. However, the choice of the “best” regulatory approach will depend on a variety of different factors including politics and financial considerations. The results indicate that municipal regulation leads to the greatest reduction in pollutant loading. We used a cooperative game theory framework to investigate the potential impacts of different policy strategies used to incentivize green infrastructure installation. Game theory, an analysis framework that has historically been under-utilized within the context of stormwater management, is uniquely suited to address this policy question.
However, there is little consensus on what policy strategies can be used to best incentivize green infrastructure adoption by private landowners. Green stormwater infrastructure has been demonstrated as an innovative water resources management approach that addresses multiple challenges facing urban environments.
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