2020 Facilities Plan Facilities Plan Report Appendix 9F Sanitary Sewer Overflow Level of Protection Definitions and Recommendation 9F-i 2020 Facilities Plan Facilities Plan Report Table of Contents APPENDIX 9F: SANITARY SEWER OVERFLOW LEVEL OF PROTECTION DEFINITION AND RECOMMENDATIONS......................................................................9F-1 9F.1 Introduction....................................................................................................................9F-2 9F.2 Definitions......................................................................................................................9F-2 9F.2.1 Sanitary Sewer Overflow Definition .............................................................................9F-2 9F.2.2 Level of Protection Definition .......................................................................................9F-3 9F.3 Approaches and Methods for Defining Level of Protection..........................................9F-3 9F.3.1 Approaches ....................................................................................................................9F-3 9F.3.2 Methods..........................................................................................................................9F-5 9F.4 Applicable Law..............................................................................................................9F-8 9F.4.1 U.S. Environmental Protection Agency – Current Federal Rules and Withdrawn Draft of Sanitary Sewer Overflow Rule ......................................................................................9F-8 9F.4.2 U.S. Environmental Protection Agency – Water Quality Standards for Coastal and Great Lakes Recreation Waters ...............................................................................................9F-9 9F.4.3 U.S. Environmental Protection Agency – Watershed Approach...................................9F-9 9F4.4 State of Wisconsin – Sanitary Sewer Overflow Requirements ...................................9F-12 9F.5 Previous Milwaukee Metropolitan Sewerage District Level of Protection Standards 9F-13 9F.5.1 Water Pollution Abatement Program...........................................................................9F-13 9F.5.2 The Milwaukee Harbor Estuary Study (1987).............................................................9F-14 9F.5.3 2010 Facilities Plan Sizing Criteria .............................................................................9F-14 9F.5.4 2020 Facilities Plan Level of Protection/Design Criteria Tools ..................................9F-15 9F.6 Data on Other Metro Areas’ Level of Protection/Design Criteria...............................9F-15 9F.6.1 Wisconsin Agencies.....................................................................................................9F-15 9F.6.2 U.S. Environmental Protection Agency Region 5 .......................................................9F-17 9F.6.3 Non-U.S. Environmental Protection Agency Region 5...............................................9F-20 9F.6.4 AMSA Wet Weather Survey Final Report, May 2003................................................9F-23 9F.6.5 U.S. Environmental Protection Agency Study – 1998 ................................................9F-25 9F.6.6 Summary of Available Data on Level of Protection....................................................9F-28 9F.6.7 Recommended Approach, Method and Standard for the 2020 Facilities Plan............9F-28 9F-ii 2020 Facilities Plan Facilities Plan Report Appendix 9F Figures 9F-1 USEPA Watershed Approach......................................................................................9F-11 Appendix 9F Tables 9F-1 Level of Protection Approaches.....................................................................................9F-4 9F-2 Comparison of Level of Protection Methods.................................................................9F-6 9F-3 USEPA Region 5 Level of Protection Data.................................................................9F-18 9F-4 Level of Protection/Design Criteria in Metro Areas Outside of USEPA Region 5.....9F-21 9F-5 Year 1998 U.S. Environmental Protection Agency Sanitary Sewer Overflow Survey ..........................................................................................................................9F-26 9F-iii 2020 Facilities Plan Facilities Plan Report Appendix 9F: Sanitary Sewer Overflow Level of Protection Definitions and Recommendation 9F.1 Introduction The Milwaukee Metropolitan Sewerage District (MMSD) is developing its 2020 Facilities Plan (2020 FP) in conjunction with the Southeastern Wisconsin Regional Planning Commission (SEWRPC) Regional Water Quality Management Plan Update (RWQMPU); this is referred to as the Water Quality Initiative (WQI) for the region. This planning effort employs the watershed approach, in which the primary focus is to determine the facilities, programs, operational improvements and policies (FPOPs) that result in the most cost effective improvement in water quality and address stakeholder inspired goals and objectives. One of the goals and objectives of the WQI is to meet the regulatory requirements as set by the U.S. Environmental Protection Agency (USEPA) and the Wisconsin Department of Natural Resources (WDNR). A key regulatory goal that has evolved from the current regulations involves the selection of a level of protection (LOP), or design criteria, for sanitary sewer overflows (SSOs). This appendix presents the recommendation of the 2020 technical team (the team of consultants providing technical analysis to both the RWQMPU and the 2020 FP) with respect to LOP for SSOs. It presents a definition for LOP, describes the current laws and regulations governing SSO LOP, reviews historical decisions by MMSD in establishing LOP, and summarizes approaches taken by other wastewater authorities in circumstances similar to MMSD. This appendix concludes with a recommended approach for determining LOP for the WQI. 9F.2 Definitions This section provides definitions for SSOs and LOP. 9F.2.1 Sanitary Sewer Overflow Definition In general, SSOs are discharges of untreated wastewater from a sanitary sewer system. Current WDNR and USEPA regulations do not clearly define SSOs; however, the term “discharge” as currently defined under Wisconsin regulations includes any release of pollutants from the wastewater system that reach waters of the state, including groundwater. In addition, the term “bypass” is defined under federal regulations as “the intentional diversion of waste streams from any portion of a treatment facility.” (40 CFR sec. 122.41(m)(1)(i)). Under this regulation, bypasses in the form of SSOs are prohibited under the Clean Water Act (CWA), subject to “exceptional circumstances” and “no feasible alternative” language incorporated into discharge permits pursuant to federal and state regulations. The general regulatory approach to SSOs can be described as “prohibition with exceptions.” The basic purpose of the LOP definition is to define the feasible level of control of SSOs for which the wastewater system should be planned, designed and built. 9F-1 2020 Facilities Plan Facilities Plan Report The LOS is determined by defining the peak wastewater flow to be accommodated and the desired (or required) LOP against overflows or exceedances of water quality objectives. The peak wastewater flow to be accommodated is a function of many factors including population, land use, sewers system condition, and the many weather factors involved including antecedent conditions. 9F.2.2 Level of Protection Definition In general, LOP means the protection against sanitary sewer overflows provided by the conveyance, storage, and treatment systems. In principle, a definition of LOP should be directly related to the probability of an SSO; however, in practice, common definitions for LOP are often indirectly related to the risk of the outcome. Defining the LOP for a particular wastewater treatment system requires an approach, a method, and a standard for the desired outcome. The approach provides the context for the LOP definition; it is a general statement of the priorities and values to be used in the process of defining the LOP. The LOP methodology sets forth an analytical method that can be applied to evaluate the performance of the system. The standard is a specific definition of the performance goal in numerical terms. For example, the approach may be to comply with regulatory requirements. The analytical method may be to use a rainfall design storm to size facilities. The standard may be 5-year recurrence interval for the input rainfall using a 24-hour duration. The following sections provide more detail on these aspects of LOP definition. 9F.3 Approaches and Methods for Defining Level of Protection This section details LOP approaches and methods. 9F.3.1 Approaches An LOP definition starts with an approach that is a statement of the values and priorities that guide the subsequent methods and standards. There are at least four types of approaches for selecting the LOP. Some are scientifically based, while others are not. The LOP approaches are typically one of the following: ♦ Regulatory requirements ♦ Stakeholder expectations (rate payers, environmentalists, etc.) ♦ Cost effective point of diminishing return (so called “knee-of-the-curve” determination) ♦ Water quality standards Table 9F-1 provides a comparison of strengths and weaknesses of each of these LOP approaches. 9F-2 LOP Approaches Example Strengths Weaknesses Regulatory