Integrating Green Infrastructure Into Stormwater Policy: Reliability, Watershed Management, and Environmental Psychology as Holistic Tools for Success.

• Author: William, Reshmina

INTRODUCTION

More than half of the global population lives in cites; consequently, the management of urban areas has been heralded as one of the most important development challenges of the twenty-first century. (1) As the size and density of urban areas increase, the growth of paved areas has led to a sharp rise in issues of degraded water quality and localized flooding. (2) Overall, the impairment of U.S. waters by urban runoff constitutes nearly five thousand square miles of estuaries, 1.4 million acres of lakes, and thirty thousand miles of rivers across the country. (3) In some watersheds, the impact of urban runoff can be even more concentrated. For example, urban runoff constitutes sixteen percent of the nitrogen entering the Chesapeake Bay watershed and is the only nitrogen source that is still increasing. (4)

To address some of these challenges, many urban areas are turning to green infrastructure, a low-cost, distributed, flexible alternative to traditional (grey) infrastructure. Green stormwater infrastructure (GSI) is the use of natural processes to filter, capture, treat, and store stormwater runoff at its source. (5) GSI includes bioretention, green roofs, and permeable pavements. These different interventions use a combination of vegetated surfaces and artificially enhanced infiltration to reduce runoff in urban areas. (6) However, the efficiency of green infrastructure benefits is highly variable and contingent upon a number of factors. (7) Not surprisingly, GSI better mitigates runoff from smaller storms with shorter return periods than high intensity events. (8) Moreover, green infrastructure capability scales nonlinearly with catchment size. In other words, the layout of existing stormwater networks, and the location of green infrastructure within those networks play important roles in the runoff reduction effectiveness of green infrastructure.

A game theoretic study of municipal policies governed by economic stimuli suggests that the efficiency of private green infrastructure at the catchment scale is determined by network location, with important environmental justice implications. (9) To mitigate some of these challenges, we build upon these game theory results by applying aspects of environmental psychology within the context of green infrastructure implementation. This inclusion of environmental psychology enables us to better frame green infrastructure solutions for municipal separate storm sewer (MS4) regulatory regimes and provide a more holistic perspective for addressing watershed-scale challenges.

1. TECHNICAL ASPECTS OF GREEN STORMWATER INFRASTRUCTURE (GSI)

   Green infrastructure mitigates urban runoff by attenuating stormwater volume and reducing or delaying peak flows. (10) In many instances, the substantial reductions in runoff volume in dense urban environments achieved by combinations of GSI present a viable, cost-effective alternative to traditional grey infrastructure, (11) and in years of high rainfall could exceed grey infrastructure performance. (12)

   From a pollution-prevention perspective, GSI can remove heavy metals, sediment, excess nutrients, and other contaminants commonly found in urban runoff. (13) In addition to water quality and flood mitigation benefits, GSI has other positive externalities, including mitigation of urban heat island effects and air quality improvements, (14) as well as social benefits associated with increased urban green space such as improvements in mental and physical health, (15) decreases in violent crime, (16) and environmental equity. (17) As a result of these benefits, several medium to large cities are exploring GSI to meet Municipal Separate Storm Sewer Systems (MS4) (18) permit requirements and/or improve urban sustainability. For example, Madison, Wisconsin has committed to the installation of one thousand rain gardens throughout the city, (19) Philadelphia, Pennsylvania has adopted a twenty-five-year GSI plan to reduce annual pollution entering surface waters by eighty five percent, (20) and Chicago, Illinois has pledged fifty million dollars to the installation of an additional ten million gallons of green stormwater storage. (21)

   Public perception of GSI as a risky investment persists, however, despite the benefits outlined above. A lack of data to quantify variability in GSI performance reinforces these perceptions. Soil type and condition, current land uses, vegetation type, existing soil moisture, and water table height all impact the performance of GSI. (22) Most importantly, rainfall distribution, specifically the prevalence of high intensity rainfall events, predicts GSI failure rates. (23) Because of this variability of GSI performance across space and time, it is important to develop and implement a risk-based evaluation of flood and water quality infrastructure to the regulatory environment of urban stormwater. (24)

   At the catchment scale, green infrastructure layout makes a significant difference in runoff reduction effectiveness. The relative placement within a network is a significant contributor to its collective success; however, because investment in green infrastructure requires multiple instances of private actions for a public good, public policy mechanisms need to be developed to nudge optimal GSI placement by private actors within a watershed.

   In other words, the net effect is contingent on private citizens' willingness to implement GSI on their own properties. The following Part explores some of the policy, psychological, and legal implications of this private-public integration of green infrastructure performance. We begin by evaluating the implications of green infrastructure within the current legal framework of the Clean Water Act's (CWA) MS4 regulations. To better understand these findings, we explore the implementation of green infrastructure at the private, individual scale. As previously discussed, a game theoretic study of municipal stormwater management practices suggests that not only does network layout play a key role in the effectiveness of green infrastructure policy, but that this finding has significant environmental justice implications. (25) Accordingly, we propose an alternative framework for human motivation, and suggest some practical methods to integrate a psychological model to influence and optimize green infrastructure uptake as part of the CWA's MS4 program.

2. LEGAL IMPLICATIONS FOR GREEN STORMWATER INFRASTRUCTURE

   1. Current Framework for Stormwater Regulations

      The aim of the CWA is to protect "the physical, chemical, and biological integrity of the nation's waters." (26) Despite this broad mandate, it took a surprisingly long time for urban stormwater, a significant source of pollution for many streams, lakes, and rivers, to come under the Act's purview. The court's ruling in NRDC v. Costle (27) eventually forced the EPA to include urban stormwater as a part of the National Pollutant Discharge Elimination System (NPDES) permitting process. (28) It took an additional ten years for Congress to pass substantial amendments to section 402 of the statute that specifies NPDES permitting requirements for storm sewer systems. (29) As a result, the first set of MS4 regulations did not come into effect until 1990. (30)

      The EPA defines stormwater as all "stormwater runoff, snow melt runoff, and surface runoff and drainage," not including infiltration into pipes or street wash waters. (31) From a civil engineering perspective, urban stormwater is classified as a non-point source pollutant (i.e., water that is distributed rather than channeled). (32) Several legal interpretations concur with the hydrological approach adopted in the engineering disciplines. (33) For example, in Ecological Rights Foundation v. Pacific Gas and Electric Company, (34) the court found that leachate from urban utility poles containing toxic substances could not be regulated under the CWA because the discharge was not from a point source (i.e., utility poles), but rather, from stormwater. (35) Once stormwater flows into an MS4, however, the legal nature of the water is transformed into a point source. In other words, MS4 discharges are regulated under the CWA through the same permitting process that is used to regulate wastewater treatment plants and other industrial discharges. (36)

      The EPA regulates MS4s through NPDES permits allocated to the sewer network on a system- or jurisdiction-wide basis. (37) Permit requirements are based on ambient, state-controlled water quality standards and require controls to reduce the discharge of pollutants to the maximum extent practicable (MEP), rather than technology-based effluent limitations. (38) The EPA implemented the MS4 permitting structure in two phases: Phase I (implemented in 1990) required individual NPDES permits for MS4s serving over one hundred thousand people, (39) while Phase II (implemented in 1999) provided general permits for all MS4s not covered by Phase I. (40) While Phase I permittees are required to submit detailed information and quantitative data sampling of stormwater discharges collected during storm events, Phase II permit requirements are significantly less stringent, requiring either an individual permit application or the filing of a notice of intent to comply with a general permit. (41) Both Phase I and Phase II MS4s are required to meet six minimum control measures: i) public education and outreach, ii) public participation, iii) illicit discharge detection and elimination, iv) construction runoff control, v) postconstruction runoff control and pollution prevention, and vi) good housekeeping. (42) The final measure, good housekeeping, is intended to create protocols for municipalities to inspect whether control practices are working in the longterm, as designed. These measures are recorded and updated in a municipal stormwater management plan. As discussed below, successful longterm implementation of GSI requires a degree of...