Clean Water Act Compliance During Wet Weather: Lessons and Recommendations

The Water Research Foundation (WRF) funded a study (WRF 5123 Establishing Seasonal Targets for Receiving Waters: Rethinking Wet Weather versus Dry Weather Expectations) to evaluate the requirements of the Clean Water Act as they apply to wet weather discharges, including municipal separate storm sewer systems (MS4s) and combined sewer systems (CSSs), which convey both sanitary wastewater and stormwater. The study involved working with 17 utilities (see Figure 1) and a technical advisory committee to survey permit and program requirements for wet weather discharges. The study confirmed that regulatory programs are challenging to develop and implement because of the unique and highly variable conditions that occur during wet weather events. Permittees are concerned about requirements they perceive to be stringent and inflexible, leading to a focus on permit compliance rather than improved water quality outcomes-concerns that may be exacerbated by future requirements to address climate change, constituents of emerging concern (such as PFAS), and measures of receiving water quality (such as biological objectives). This presentation summarizes the WRF research and provides recommendations for regulatory agencies and permittees to improve CWA regulatory programs and water quality outcomes for wet weather discharges. BACKGROUND The Clean Water Act (CWA) was adopted in 1977 to promote the goals that the nation's waters should be 'fishable' and 'swimmable.' The CWA required the development of water quality standards, established the National Pollutant Discharge Elimination System (NPDES) permit program, and provided for periodic assessments to identify 'impaired waters' and develop Total Maximum Daily Loads (TMDLs). The 1987 CWA amendments added a program for stormwater discharges, including MS4s and discharges determined to contribute to exceedances of water quality standards. Beginning in the 1980s, EPA developed standard procedures for evaluating 'reasonable potential' and computing effluent limitations for traditional point source discharges such as wastewater treatment plants, considering the frequency, magnitude, and duration components of water quality standards. However, because wet weather discharges typically exhibit far greater variability than traditional point sources in flow rates, flow volumes, and constituent concentrations, they often violate the assumptions of EPA's procedures. Neither EPA nor the states have developed alternative procedures that are appropriate for wet weather. CURRENT APPROACHES TO REGULATING WET WEATHER DISCHARGES Despite decades of progress in improving water quality, many of the nation's waters still do not meet water quality standards, particularly during wet weather conditions, and regulation of wet weather discharges has become increasingly stringent. As shown in Figure 2, regulatory options include best management practices (BMPs), numeric action levels (NALs), and numeric effluent limitations in the form of both technology-based effluent limitations (TBELs) and water quality-based effluent limitations (WQBELs). All four options have been used for MS4 discharges-in some cases, water quality standards have been applied directly as numeric effluent limitations. For CSOs, numeric limits and other implementation measures are being required even after successful implementation of minimum controls and long-term control plans (LTCPs). These regulatory approaches raise concerns about consistency with EPA guidance and water quality standards, dischargers' ability to comply with permit requirements, and the availability of suitable treatment technologies. The study shows that regulatory agencies have attempted to address these concerns by working with permittees to modify water quality standards (e.g., to suspend recreational uses during high flows, develop site-specific objectives for metals, or eliminate permit requirements not supported by science). Wet weather permit approaches identified in the study include watershed management programs, trading, variances, compliance schedules, multiple pathways to demonstrate compliance, and integrated permits that combine wastewater and stormwater obligation. The study also identified enforcement orders and citizens' suits for both MS4 and CSS permittees. While helpful, these approaches do not address comprehensive concerns about CWA implementation during wet weather. RECOMMENDATIONS The study recommends that EPA invest in and develop guidance for CWA programs, including evaluating water quality standards and how to translate the frequency, magnitude, and duration aspects of water quality standards for wet weather discharges. Guidance is needed regarding the use of Financial Capability Assessments (FCAs) to prioritize permit implementation over time and enable use of sustainable, nature-based solutions. Dedicated funding sources and research into the efficacy of treatment technologies for wet weather conditions are critical. Finally, guidance will be needed regarding the implementation of requirements for CECs, climate change, and integrative water quality measures.