A Guide to Performing Reasonable Assurance Analyses to Inform Municipal Stormwater Planning: “The Wheel is Turning and You Can’t Slow Down”
Since the beginning of the storm water regulatory program in the early 1990’s, there has been considerable discussion regarding the NPDES permit requirement that dischargers must not cause or contribute to exceedances of water quality standards. This discussion was further expanded to address TMDL implementation requirements. Dischargers, permitting authorities, and other stakeholders agree that it is very challenging to develop long-term stormwater management plans that provide sufficient information to support findings that the plans will result in timely compliance with water quality standards and associated TMDL provisions. Recent MS4 permitting efforts in CA have attempted to address this challenge. MS4 permits in the Lake Tahoe basin incorporate a TMDL implementation approach that provides for both near term progress and long term certainty required to plan and implement TMDL requirements. Both the LA County MS4 permit and the San Diego Regional MS4 permit include similar alternative approaches for municipalities to use in demonstrating compliance with the permit. The San Francisco Bay Municipal Regional MS4 Permit also provides examples incorporating TMDL requirements through permit provisions. Fundamental to the use and success of these compliance pathways is the requirement to conduct a Reasonable Assurance Analysis (RAA) to quantifiably demonstrate that the implementation of a stormwater management plan (e.g., Watershed Management Programs in LA, Water Quality Improvement Plans in San Diego, Green Infrastructure Plans in San Francisco) will result in attainment of MS4 permit WQBELs or TMDL wasteload allocations. The requirements for RAAs vary for different MS4 permits depending on the pollutants addressed, preferences of each Regional Board, the availability and previous investment in local modeling tools, and technical understanding of permittees and other stakeholders. As a result, a wide range of modeling approaches have been developed to address the specific needs of individual permittees to meet requirements of individual permits. As new MS4 permits are adopted that include similar RAA requirements, municipalities will benefit from the many lessons learned and technological advancements throughout CA and the U.S. that have successfully completed RAAs. EPA is cooperating with the State Board and various Regional Boards to develop a guide for performing RAAs that will help ensure these plans provide “reasonable assurance” to address the near term needs of regulatory agencies and other stakeholders in reviewing stormwater management plans, and the communities’ future program management and capital improvement planning efforts. The goal of this guide is to summarize permit requirements and approaches used in those regions that have successfully completed RAAs, outline the basic elements that have resulted in their success, and document lessons learned to support those municipalities embarking on new RAAs. The guide will assist municipalities in the selection of technical frameworks for RAAs that best suit their permit requirements and stormwater program planning needs. Looking past the RAAs and stormwater management plans, the guide will also consider how efforts can provide meaningful information to support capital improvement planning, asset management planning, or the investigation of funding needs. As the schedule for meeting pollutant reductions are often based on TMDL compliance schedules, the ability of a stormwater management plan to outline capital and funding needs will greatly inform future assessments of the feasibility to meet these schedules. As a result, selection of approaches for performing RAAs should not only consider the minimum requirements of the MS4 permit, but provide capability to support broader discussions regarding feasible compliance schedules and the ability of a municipality to responsibly meet pollutant reduction goals given other funding and logistical challenges.
David Smith is the Manager of the NPDES Permits Office at EPA Region 9 in San Francisco. Prior to moving to permits, Dave managed Region 9’s Wetlands and TMDL programs, and worked on watershed planning, water quality standards, and grants management. Dave has also worked for the State of California, the Congressional Budget Office, and several environmental consultants. He also worked in real estate development and managed his family’s buffalo-cattle ranch in Oklahoma. He holds degrees from UC-Berkeley and Wesleyan University.