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2023 Fact Sheet NPDES Permit No. MA0103284 Page 1 of 195 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY NEW ENGLAND - REGION 1 5 POST OFFICE SQUARE, SUITE 100 BOSTON, MASSACHUSETTS 02109-3912 FACT SHEET DRAFT NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES) PERMIT TO DISCHARGE TO WATERS OF THE UNITED STATES PURSUANT TO THE CLEAN WATER ACT (CWA) NPDES PERMIT NUMBER: MA0103284 [This Draft Permit is also integrating existing permits MA0101192, MA0101974, MA0101877, MA0101982 1 ] PUBLIC NOTICE START AND END DATES: May 31, 2023 – July 31, 2023 NAME AND MAILING ADDRESS OF APPLICANT: Massachusetts Water Resources Authority (MWRA) Deer Island 33 Tafts Avenue Boston, MA 02128 The Massachusetts municipalities listed below are Combined Sewer Overflow (CSO)- responsible Co-permittees: MAC053284 MAC093284 MAC113284 MAC303284 City of Boston Boston Water and Sewer Commission 980 Harrison Avenue Boston, MA 02119 City of Cambridge Department of Public Works 147 Hampshire Street Cambridge, MA 02139 City of Chelsea Department of Public Works 380 Beacham Street Chelsea, MA 02150 City of Somerville Department of Public Works 1 Franey Road Somerville, MA 02144 and responsible for Parts I.B., I.C., I.D., I.E., I.F, and I.J of the Draft Permit. The Massachusetts municipalities in Appendix A are Co-permittees for specific activities required by the Draft Permit as described in Section 5.6. of this Fact Sheet and as set forth in Parts I.C., I.E., I.F, and I.J of the Draft Permit. NAME AND ADDRESS OF FACILITY WHERE DISCHARGE OCCURS: MWRA Deer Island Treatment Plant (“DITP”) 190 Tafts Avenue Winthrop, MA 02152 1 See Section 5.7, Combined Sewer Overflows 2023 Fact Sheet NPDES Permit No. MA0103284 Page 2 of 195 and from 4 Combined Sewer Overflows (CSO) Treatment Facilities with 5 outfalls and from 6 CSO Outfalls owned and operated by MWRA as well as 41 CSO Outfalls owned and operated by the CSO-responsible Co-permittees (Boston, Cambridge, Chelsea and Somerville) (see Appendix B). NOTE: The former near shore DITP outfalls: 001, 002, 003, 004 and 005, are not authorized by the Draft Permit. The Draft Permit no longer requires the Permittee to maintain these nearshore Deer Island outfalls as a contingency option. RECEIVING WATERS AND CLASSIFICATIONS: Massachusetts Bay (no defined segment, North Coastal Drainage Area, see 314 CMR 4.06, Table 23), Class SA, Shellfishing Boston Inner Harbor (MA70-02), Class SB (CSO) Dorchester Bay (MA70-03), Class SB - Shellfishing Chelsea River (also known as Chelsea Creek) (MA71-06), Class SB (CSO) Charles River Basin (MA72-38), Class B, warm water fishery – with CSO variance Back Bay Fens (Muddy River) (MA72-11), Class B, warm water fishery (CSO Upper Mystic River (MA71-02), Class B, warm water fishery – with CSO variance Lower Mystic River, below Earhart Dam (MA71-03), Class SB – CSO, Shellfishing Alewife Brook (MA71-20), Class B, warm water fishery – with CSO variance Little River (MA71-22), Class B, warm water fishery – with CSO variance 2023 Fact Sheet NPDES Permit No. MA0103284 Page 3 of 195 Table of Contents 1.0 Proposed Action ................................................................................................................ 10 2.0 Statutory and Regulatory Authority .................................................................................. 12 2.1 Technology-Based Requirements ................................................................................. 13 2.2 Water Quality Based Requirements .............................................................................. 13 2.2.1 Water Quality Standards ......................................................................................... 13 2.2.2 Antidegradation....................................................................................................... 14 2.2.3 Assessment and Listing of Waters and Total Maximum Daily Loads. .................. 14 2.2.4 Reasonable Potential ............................................................................................... 15 2.2.5 State Certification ................................................................................................... 15 2.3 Effluent Flow Requirements ......................................................................................... 16 2.4 Monitoring and Reporting Requirements ..................................................................... 18 2.4.1 Monitoring Requirements ....................................................................................... 18 2.4.2 Reporting Requirements ......................................................................................... 19 2.5 Standard Conditions ...................................................................................................... 19 2.6 Anti-backsliding ............................................................................................................ 19 3.0 Description of Facility and Discharge .............................................................................. 20 3.1 Location and Type of Facility ....................................................................................... 20 3.1.1 Treatment Process Description ............................................................................... 21 3.1.2 Collection System Description ............................................................................... 22 4.0 Description of Receiving Water and Dilution .................................................................. 23 4.1 Receiving Waters .......................................................................................................... 23 4.1.1 Massachusetts Bay .................................................................................................. 23 4.1.2 Boston Inner Harbor ............................................................................................... 23 4.1.3 Dorchester Bay........................................................................................................ 26 4.1.4 Chelsea River .......................................................................................................... 28 4.1.5 Charles River .......................................................................................................... 30 4.1.6 Muddy River (Back Bay Fens) ............................................................................... 34 4.1.7 Mystic River............................................................................................................ 36 4.1.8 Little River and Alewife Brook .............................................................................. 39 4.2 Ambient Data ................................................................................................................ 42 4.3 Available Dilution......................................................................................................... 42 5.0 Proposed Effluent Limitations and Conditions ................................................................. 44 5.1 Effluent Limitations and Monitoring Requirements ..................................................... 44 5.1.1 Effluent Flow .......................................................................................................... 44 5.1.2 Carbonaceous Biochemical Oxygen Demand (CBOD5) ........................................ 45 5.1.3 Total Suspended Solids (TSS) ................................................................................ 45 5.1.4 Eighty-Five Percent (85%) CBOD5 and TSS Removal Requirement.................... 46 5.1.5 pH............................................................................................................................ 46 5.1.6 Bacteria ................................................................................................................... 47 5.1.7 Total Residual Chlorine .......................................................................................... 54 5.1.8 Oil and Grease......................................................................................................... 55 5.1.9 Ammonia................................................................................................................. 55 5.1.10 Nutrients .................................................................................................................. 56 5.1.11 Metals ...................................................................................................................... 80 5.1.12 Other Toxics............................................................................................................ 81 2023 Fact Sheet NPDES Permit No. MA0103284 Page 4 of 195 5.1.13 Whole Effluent Toxicity ......................................................................................... 87 5.1.14 Per- and polyfluoroalkyl substances (PFAS) .......................................................... 88 5.1.15 Contaminants of Emerging Concern (CECs) .......................................................... 91 5.2 Industrial Pretreatment Program ................................................................................... 95 5.3 Sludge Conditions ......................................................................................................... 96 5.4 Infiltration/Inflow (I/I) .................................................................................................. 96 5.5 Unauthorized Discharges ............................................................................................ 100 5.6 Operation and Maintenance ........................................................................................ 100 5.6.1 Operation and Maintenance of the Wastewater Treatment Facility ..................... 102 5.6.2 Operation and Maintenance of the Sewer System ................................................ 102 5.7 Combined Sewer Overflows ....................................................................................... 103 5.7.1 Numerical Effluent Limitations and Reporting Requirements for MWRA CSO Treatment Facilities, Outfalls MWR201, 203, 205/205A and 215 ..................................... 115 5.7.2 Conditions for Discharge ...................................................................................... 127 5.7.3 Reopener/Additional CSO Control Measures ....................................................... 127 5.7.4 Relationship with CSO Communities ................................................................... 127 5.8 Best Management Practices Plan (BMP Plan) ............................................................ 128 5.9 Assurance of Compliance with 436 MGD Flow Limit............................................... 128 5.10 Pollution Prevention Plan ........................................................................................... 129 5.11 Groundwater Remediation Site Waters ...................................................................... 130 5.12 Ambient Monitoring Plan ........................................................................................... 130 5.12.1 Effluent Monitoring .............................................................................................. 133 5.12.2 Water Column Monitoring .................................................................................... 136 5.12.3 Benthic Monitoring ............................................................................................... 150 5.12.4 Fish and Shellfish Monitoring .............................................................................. 156 5.12.5 Additional Tasks/Studies Related to Ambient Monitoring Program .................... 164 5.13 Contingency Plan (CP) ............................................................................................... 165 5.14 Outfall Monitoring Science Advisory Panel ............................................................... 168 5.15 Standard Conditions .................................................................................................... 168 6.0 Federal Permitting Requirements ................................................................................... 168 6.1 Endangered Species Act ............................................................................................. 168 6.1.1 Introduction ........................................................................................................... 169 6.1.2 USFWS Protected Species .................................................................................... 169 6.1.3 NOAA Fisheries Protected Species ...................................................................... 171 6.2 Essential Fish Habitat ................................................................................................. 172 6.2.1 Introduction ........................................................................................................... 172 6.2.2 EPA’s Finding of All Potential Impacts to EFH Species ..................................... 175 6.3 National Marine Sanctuary Act .................................................................................. 176 6.4 Coastal Zone Management (CZM) Consistency Review ........................................... 178 6.5 Environmental Justice (EJ) ......................................................................................... 178 7.0 Public Comments, Hearing Requests and Permit Appeals ............................................. 180 8.0 Administrative Record .................................................................................................... 182 2023 Fact Sheet NPDES Permit No. MA0103284 Page 5 of 195 Tables Table 1: Supplemental application and data request submittals ................................................... 10 Table 2: Summary of Designated Uses and Listing Status for Segment MA70-02, Boston Inner Harbor , ........................................................................................................................................... 26 Table 3: Summary of Designated Uses and Listing Status for Segment MA70-03, Dorchester Bay , ............................................................................................................................................... 27 Table 4: Summary of Designated Uses and Listing Status for Segment MA71-06, Chelsea River , ....................................................................................................................................................... 29 Table 5: Summary of Designated Uses and Listing Status for Segment MA72-38, Lower Charles River , ............................................................................................................................................. 31 Table 6: Summary of Designated Uses and Listing Status for Segment MA72-36, Charles River , ....................................................................................................................................................... 33 Table 7: Summary of Designated Uses and Listing Status for Segment MA72-11, Muddy River , ....................................................................................................................................................... 35 Table 8: Summary of Designated Uses and Listing Status for Segment MA71-02, Mystic River , ....................................................................................................................................................... 37 Table 9: Summary of Designated Uses and Listing Status for Segment MA71-03, Mystic River , ....................................................................................................................................................... 39 Table 10: Summary of Designated Uses and Listing Status for Segment MA71-04, Alewife Brook , ............................................................................................................................................ 41 Table 11: Alternate effluent bacteria limits if MA Marine Fisheries and/or USFDA deem necessary. ...................................................................................................................................... 54 Table 12: Contingency Plan Thresholds related to nitrogen and its potential impacts ................. 57 Table 13: Bottom Water DO Survey Mean Concentrations (mg/L) ............................................. 65 Table 14: Bottom Water DO Survey Mean Percent Saturation (%) ............................................. 66 Table 15: Bottom water DO rate of decline/oxygen depletion rate .............................................. 67 Table 16: Ambient Chlorophyll a (nearfield mean, mg m -2 ) ........................................................ 68 Table 17: Alexandrium catenella (nearfield, cells L) ................................................................... 70 Table 18: Nine Minimum Control Plans for MWRA and CSO Communities. .......................... 105 Table 19: CSO discharges authorized to Boston Inner Harbor, Class SB – CSO ...................... 112 2023 Fact Sheet NPDES Permit No. MA0103284 Page 6 of 195 Table 20: CSO outfalls authorized to Charles River, Class B -Variance for CSO outfalls ........ 113 Table 21: CSO outfalls authorized to Alewife Brook/Little River, Class B -Variance for CSO outfalls......................................................................................................................................... 114 Table 22:CSO outfalls authorized to Mystic River, Class B -Variance for CSO outfalls .......... 115 Table 23: MWRA DITP Dry Day Flow ..................................................................................... 129 Table 24: Removal rates for MWRA DITP from 2020 Outfall Monitoring Overview. ............. 136 Table 25: Harmful Algal Blooms to be enumerated and identified with thresholds for rapid response surveys. ........................................................................................................................ 148 Table 26: Nuisance Algal Species to be Monitored and Reported ............................................. 150 Table 27: 2021 AMP Revision 2.1 Fish and Shellfish Monitoring Requirements ..................... 156 Table 28. Species and life stages with designated EFH and one Habitat Area of Particular Concern in the vicinity of the MWRA Deer Island Treatment Plant Outfall T01 and 47 CSO Discharges. .................................................................................................................................. 174 2023 Fact Sheet NPDES Permit No. MA0103284 Page 7 of 195 Figures Figure 1: Water Column Monitoring: Number of Surveys and Stations with each Ambient Monitoring Plan Revision ........................................................................................................... 137 Figure 2: Annual mean ammonium by area 1992-2009 from MWRA Ambient Monitoring Plan Revision 2.1, August 2021 .......................................................................................................... 141 Figure 3: Nearfield bottom water dissolved oxygen concentration results from MWRA Ambient Monitoring Plan Revision 2.1, August 2021 .............................................................................. 142 Figure 4: Benthic Monitoring: Number of Surveys and Stations with each Ambient Monitoring Plan Revision .............................................................................................................................. 150 Figure 5: From 2020 Outfall Benthic Monitoring Results ......................................................... 152 Figure 6: From AMP Revision 2.1, August 2021. ...................................................................... 153 Figure 7: Fish and Shellfish Monitoring: Number of Surveys per year and Stations with each Ambient Monitoring Plan Revision ............................................................................................ 157 Figure 8: Comparison of average mid-June to mid-August air and surface water temperature (C) at Buoy 44013 in the vicinity of the nearfield from 1992-2020 from MWRA 2020 Water Column Monitoring Results, October 2021 .............................................................................................. 163 Figure 9: MWRA DITP and Outfall T01 locations. ................................................................... 183 Figure 10: Extent of MWRA Collection System ........................................................................ 184 Figure 11: Flow diagram ............................................................................................................. 185 Figure 12: CSO outfall locations from MWRA .......................................................................... 186 Figure 13: Locations of Ambient Bacteria Monitoring Sites ..................................................... 187 Figure 14: Geography, bathymetry, schematic long-term mean circulation, adapted from https://www.mwra.com/harbor/enquad/pdf/2017-13.pdf ........................................................... 188 Figure 15: Expanded nutrient enrichment model. Source: Bricker et al. 1999........................... 189 Figure 16: Depth-averaged dissolved nitrate (μM) at Station N18. The shaded areas are the data ranges from 1992-2020 with the trend as the darker color in the center of the shading. The line with the dots represents the actual 2020 values from MWRA 2020 Water Column Monitoring Report.......................................................................................................................................... 190 Figure 17: Infiltration as a percentage of average daily flow for all MWRA sewer communities averaged. From MWRA Annual I/I Reports for Calendar Years 2001-2020............................. 191 Figure 18: Inflow as a percentage of average daily flow for all MWRA sewer communities 2023 Fact Sheet NPDES Permit No. MA0103284 Page 8 of 195 averaged. From MWRA Annual I/I Reports for Calendar Years 2001-2020............................. 191 Figure 19: MWRA DITP Daily Maximum Flow compared to non-excessive infiltration/inflow standard. ...................................................................................................................................... 192 Figure 20: MWRA DITP Dry Day Flows compares to non-excessive infiltration (dry weather) standard. ...................................................................................................................................... 193 Figure 21: Stellwagen Bank National Marine Sanctuary Boundary and location of the MWRA DITP Outfall T01. ....................................................................................................................... 194 2023 Fact Sheet Page 9 of 195 NPDES Permit No. MA0103284 Appendices Appendix A – MWRA Member Communities named as Co-permittees Appendix B – CSO Treatment Facilities and CSO Outfalls Appendix C – DITP DMR Data Appendix D – Permitting Approach for POTWs with Co-permittees Appendix E - Ambient Data Summary Appendix F –Additional MWRA Data Appendix G - Reasonable Potential and Limits Calculations Appendix H – CSO Treatment Facility Effluent Data Summary Appendix I – Summary of CSO Activations and Volumes 2023 Fact Sheet Page 10 of 195 NPDES Permit No. MA0103284 1.0 Proposed Action The above-named applicant, MWRA (the Permittee), has applied to the U.S. Environmental Protection Agency (EPA) for reissuance of a National Pollutant Discharge Elimination System (NPDES) Permit to discharge from the Deer Island Treatment Plant (DITP, the Facility) into Massachusetts Bay (the Bay). The permit currently in effect, was issued on May 20, 1999, and subsequently modified on July 10, 2000. The Permit and modification became effective on August 10, 2000 and expired on August 10, 2005 (the 2000 Permit). The Permittee filed an application for permit reissuance with EPA, dated February 8, 2005, as required by 40 Code of Federal Regulations (CFR) § 122.6. Since the permit application was deemed timely and complete by EPA on April 26, 2005, the Facility’s 2000 Permit has been administratively continued pursuant to 40 CFR § 122.6 and § 122.21(d). The Permittee has continued to provide updated data and information to EPA upon request (See Table 1). EPA and the State conducted a virtual site visit with meetings occuring on May 18, 2022, August 31, 2022, and October 18, 2022. Table 1: Supplemental application and data request submittals Date Submittal 4/18/2023 Email. Wendy Leo, MWRA to Michele Barden, EPA. Subject: Updated values - DITP NPDES 2/13/2023 Email. Betsy Reilley, MWRA to Michele Barden, EPA. Subject: Update to sludge information 8/23/2022 CSO design/engineering details 7/15/2022 Email. Betsy Reilley, MWRA to Michele Barden, EPA. Subject: Discussion of Color/Clarity in Ambient Monitoring 7/15/2022 Email. Betsy Reilley, MWRA to Michele Barden, EPA. Subject: Design/Engineering Details for CSOs 6/2/2022 Rolling average dry day flow calculation 5/31/2022 MWRA Deer Island Treatment Plant pH Adjustment Demonstration 5/6/2022 List of Water Column Reports and Quality Assurance Project Plans; Plankton and ammonium data 1992-present 3/4/2022 CSO facility initial dilution 1/28/2022 Effluent sampling for bacteria and chlorine residual 1/6/2022 DP-29 Secondary Treatment Facilities Recommended Plan for Completion of the Deer Island Facilities 9/14/2021 Phytoplankton data 2016-2020 9/13/2021 Division of Marine Fisheries MOU Bacteria Data 2015-2021 8/26/2021 Zooplankton data 2016-2018 8/13/2021 Email. Betsy Reilley, MWRA to Michele Barden, EPA. Subject: RE: % of sludge that is sold as fertilizer 8/13/2021 Email. Betsy Reilley, MWRA to Michele Barden, EPA. Subject: RE: Oil & Grease data 7/28/2021 Email. Betsy Reilley, MWRA to Michele Barden, EPA. Subject: EPA Data Request for DITP NPDES. • Updated effluent data pollutants listed in Table C of Application Form 2023 Fact Sheet NPDES Permit No. MA0103284 Page 11 of 195 Date Submittal 2A; • Ambient data for Station N21 from 2016 through 2020; • Sediment organic carbon data from 2020 Benthic Monitoring; • 2020 results for phytoplankton and zooplankton abundance. 12/4/2017 Letter. Michael J. Hornbrook, MWRA to Michele Cobban Barden, EPA and Susannah King, MassDEP. RE: Supplement to Massachusetts Water Resources Authority’s Application for Renewal of NPDES Permit No. MA0103284 for Deer Island Wastewater Treatment Plant and Combined Sewer Overflows – section I.1a, T01 Effluent Limitations and Monitoring Requirements – Blending 12/4/2017 Letter. Michael J. Hornbrook, MWRA to Michele Cobban Barden, EPA and Susannah King, MassDEP. RE: Supplement to Massachusetts Water Resources Authority’s Application for Renewal of NPDES Permit No. MA0103284 for Deer Island Wastewater Treatment Plant and Combined Sewer Overflows – section I.1a, T01 Effluent Limitations and Monitoring Requirements – Indicator Bacteria 7/24/2017 Letter. Michael J. Hornbrook, MWRA to Michele Barden, EPA and Susannah King, MassDEP. RE: Supplement to Massachusetts Water Resources Authority’s Application for Renewal of NPDES Permit No. MA0103284 for Deer Island Wastewater Treatment Plant and Combined Sewer Overflows - updated diagrams and attachments 6/30/2017 Letter. Michael J. Hornbrook, MWRA to Michele Barden, EPA and Susannah King, MassDEP. RE: Supplement to Massachusetts Water Resources Authority’s Application for Renewal of NPDES Permit No. MA0103284 for Deer Island Wastewater Treatment Plant and Combined Sewer Overflows 12/7/2009 Letter. Andrea C. Rex, MWRA to Michele Cobban Barden, EPA. RE: Effluent data update and spreadsheet 2/25/2009 Letter. Michael J. Hornbrook, MWRA to Stephen Perkins, EPA and Glenn Haas, MassDEP. RE: Supplement to Massachusetts Water Resources Authority’s Application for Renewal of its Deer Island Wastewater Treatment Plant NPDES Permit Number MA0103284 - CSO 3/4/2008 Letter. Michael J. Hornbrook, MWRA to Stephen Perkins, EPA and Glenn Haas, MassDEP. RE: Supplement to Massachusetts Water Resources Authority’s Application for Renewal of NPDES Permit No. MA0103284 for Deer Island Wastewater Treatment Plant 11/13/2006 Letter. Andrea Rex, MWRA to Michele Cobban Barden, EPA. RE: Effluent chemistry results and spreadsheet 7/7/2006 Letter. Michael J. Hornbrook, MWRA to Michele Cobban Barden, EPA. RE: Design flow of Deer Island Treatment Plant 9/6/2005 Letter. Andrea C. Rex, Ph.D., MWRA to Michele Barden, EPA and Glenn Hass, MassDEP. RE: Massachusetts Water Resources Authority, NPDES Permit Number MA0103284, Permit Renewal Negotiations 5/18/2005 Expanded Effluent Testing Data – 2005 Application, Form 2A 2023 Fact Sheet NPDES Permit No. MA0103284 Page 12 of 195 EPA is also incorporating the individual NPDES permits for the municipalities of Boston (as Boston Water and Sewer Commission (BWSC)) (MA0101192), Cambridge (MA0101974), Chelsea (MA0101877), and Somerville (MA0101982) into the Draft Permit as the individual permits regulate discharges from CSOs that are part of the collection system that conveys wastewater to the DITP for treatment. These Permittees will be referred to as CSO-responsible Co-permittees in this Fact Sheet and the Draft Permit to help clarify their specific responsibilities (See Part I.B and I.D of the Draft Permit). The CSO outfalls regulated by these permits will now be authorized under this Permit with specific conditions applicable to each CSO-responsible Co- permittee who owns and operates a CSO discharge. Permit applications for each of the individual CSO permits were submitted, respectively, by BWSC on November 26, 2007 and deemed complete on February 17, 2009; the City of Cambridge on May 29, 2014 and deemed complete on October 1, 2014; the City of Chelsea on July 27, 2018 and deemed complete on December 19, 2018; and the City of Somerville on July 6, 2017 and deemed complete on July 11, 2017. These CSO-responsible Co-permittees are also responsible for all the obligations applicable to Co- permittees (See Parts I.C., I.E., I.F., and I.J. of the Draft Permit). EPA is also adding the thirty-nine (39) municipalities that own and operate collections systems that convey flows to the DITP for treatment as Co-permittees to the Draft Permit. These municipalities are Co-permittees for certain activities pertaining to proper operation and maintenance of their respective collection systems (See Parts I.C., I.E., I.F., and I.J. of the Draft Permit). Adding them to the Draft Permit ensures that they comply with requirements to operate and maintain the collection systems to avoid discharges of sewage from the collection system. These Co-permittees did not apply for permit coverage; with letters sent on March 8, 2023, EPA waived the application requirements for the thirty-nine (39) Co-permittees that own and operate sanitary collection systems. The legal basis for including municipal satellite collection systems as Co-permittees is described in In re Charles River Pollution Control District , 16 E.A.D. 623 (EAB 2015) 2 (Also see Appendix D). When EPA refers to “Permittees” in the Draft Permit’s Part II, Standard Conditions, the term “Permittees” includes MWRA, the CSO-responsible Co- permittees, and the 39 municipalities identified as Co-permittees. 2.0 Statutory and Regulatory Authority Congress enacted the Federal Water Pollution Control Act, codified at 33 U.S.C. § 1251-1387 and commonly known as the Clean Water Act (CWA), “to restore and maintain the chemical, physical, and biological integrity of the Nation’s waters.” CWA § 101(a). To achieve this objective, the CWA makes it unlawful for any person to discharge any pollutant into the waters of the United States from any point source, except as authorized by specific permitting sections of the CWA, one of which is § 402. See CWA §§ 301(a), 402(a). Section 402(a) established one of the CWA’s principal permitting programs, the NPDES Permit Program. Under this section, EPA may “issue a permit for the discharge of any pollutant or combination of pollutants” in accordance with certain conditions. CWA § 402(a). NPDES permits generally contain discharge limitations and establish related monitoring and reporting requirements. See CWA § 402(a)(1) 2 The decision is available at: https://yosemite.epa.gov/oa/EAB_Web_Docket.nsf/Published%20and%20Unpublished%20Decisions/F89699D1A0 710BCF85257DE200717A93/$File/Charles%20River%20Decision%20Vol%2016.pdf 2023 Fact Sheet NPDES Permit No. MA0103284 Page 13 of 195 and (2). The regulations governing EPA’s NPDES permit program are generally found in 40 CFR §§ 122, 124, 125, and 136. “Congress has vested in the Administrator [of EPA] broad discretion to establish conditions for NPDES permits” in order to achieve the statutory mandates of Section 301 and 402. Arkansas v. Oklahoma, 503 U.S. 91, 105 (1992). See also 40 CFR §§ 122.4(d), 122.44(d)(1), 122.44(d)(5). CWA §§ 301 and 306 provide for two types of effluent limitations to be included in NPDES permits: “technology-based” effluent limitations (TBELs) and “water quality-based” effluent limitations (WQBELs). See CWA §§ 301, and 304(d); 40 CFR Parts 122, 125, 131. 2.1 Technology-Based Requirements Technology-based limitations, generally developed on an industry-by-industry basis, reflect a specified level of pollutant reducing technology available and economically achievable for the type of facility being permitted. See CWA § 301(b). As a class, publicly owned treatment works (POTWs) must meet performance-based requirements based on available wastewater treatment technology. See CWA § 301(b)(1)(B). The performance level for POTWs is referred to as “secondary treatment.” Secondary treatment is comprised of technology-based requirements expressed in terms of biochemical oxygen demand (BOD5), total suspended solids (TSS) and pH. See 40 CFR Part 133. Under CWA § 301(b)(1), POTWs must have achieved effluent limits based upon secondary treatment technology by July 1, 1977. Since all statutory deadlines for meeting various treatment technology-based effluent limitations established pursuant to the CWA have expired, when technology-based effluent limits are included in a permit, compliance with those limitations is from the date the issued permit becomes effective. See 40 CFR § 125.3(a)(1). 2.2 Water Quality Based Requirements The CWA and federal regulations also require that permit effluent limits based on water quality considerations be established for point source discharges when such limitations are necessary to meet state or federal water quality standards that are applicable to the designated receiving water. This is necessary when less stringent TBELs would interfere with the attainment or maintenance of water quality criteria in the receiving water. See CWA § 301(b)(1)(C) and 40 CFR §§ 122.44(d)(1), 122.44(d)(5). 2.2.1 Water Quality Standards The CWA requires that each state develop water quality standards (WQSs) for all water bodies within the State. See CWA § 303 and 40 CFR § 131.10-12. Generally, WQSs consist of three parts: 1) the designated use or uses assigned for a water body or a segment of a water body; 2) numeric or narrative water quality criteria sufficient to protect the assigned designated use(s); and 3) antidegradation requirements to ensure that once a use is attained it will not be degraded and to protect high quality and National resource waters. See CWA § 303(c)(2)(A) and 40 CFR § 131.12. The applicable State WQSs can be found in 314 of the Code of Massachusetts Regulations, Chapter 4 (314 CMR 4.00). 2023 Fact Sheet NPDES Permit No. MA0103284 Page 14 of 195 As a matter of state law, state WQSs specify different water body classifications, each of which is associated with certain designated uses and numeric and narrative water quality criteria. When using chemical-specific numeric criteria to develop permit limitations, acute and chronic aquatic life criteria and human health criteria are used and expressed in terms of maximum allowable in- stream pollutant concentrations. In general, aquatic-life acute criteria are considered applicable to daily time periods (maximum daily limit) and aquatic-life chronic criteria are considered applicable to monthly time periods (average monthly limit). Chemical-specific human health criteria are typically based on lifetime chronic exposure and, therefore, are typically applicable to average monthly limits. When permit effluent limitation(s) are necessary to ensure that the receiving water meets narrative water quality criteria, the permitting authority must establish effluent limits in one of the following three ways: 1) based on a “calculated numeric criterion for the pollutant which the permitting authority demonstrates will attain and maintain applicable narrative water quality criteria and fully protect the designated use,” 2) based on a “case-by-case basis” using CWA § 304(a) recommended water quality criteria, supplemented as necessary by other relevant information; or, 3) in certain circumstances, based on use of an indicator parameter. See 40 CFR § 122.44(d)(1)(vi)(A-C). 2.2.2 Antidegradation Federal regulations found at 40 CFR § 131.12 require states to develop and adopt a statewide antidegradation policy that maintains and protects existing in-stream water uses and the level of water quality necessary to protect these existing uses. In addition, the antidegradation policy ensures maintenance of high-quality waters which exceed levels necessary to support propagation of fish, shellfish, and wildlife and to support recreation in and on the water, unless the State finds that allowing degradation is necessary to accommodate important economic or social development in the area in which the waters are located. Massachusetts’ statewide antidegradation policy, entitled “Antidegradation Provisions” is found in the State’s WQSs at 314 CMR 4.04. Massachusetts guidance for the implementation of this policy is in an associated document entitled “Implementation Procedure for the Anti-Degradation Provisions of the State Water Quality Standards,” dated October 21, 2009. According to the policy, no lowering of water quality is allowed, except in accordance with the antidegradation policy, and all existing in-stream uses, and the level of water quality necessary to protect the existing uses, of a receiving water body must be maintained and protected. This permit is being reissued with effluent limitations sufficiently stringent to satisfy the State’s antidegradation requirements, including the protection of the existing uses of the receiving water. 2.2.3 Assessment and Listing of Waters and Total Maximum Daily Loads. The objective of the CWA is to restore and maintain the chemical, physical and biological integrity of the Nation’s waters. To meet this goal, the CWA requires states to develop information on the quality of their water resources and report this information to EPA, the U.S. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 15 of 195 Congress, and the public. To this end, EPA released guidance on November 19, 2001, for the preparation of an integrated “List of Waters” that could combine reporting elements of both § 305(b) and § 303(d) of the CWA. The integrated list format allows states to provide the status of all their assessed waters in one list. States choosing this option must list each water body or segment in one of the following five categories: 1) unimpaired and not threatened for all designated uses; 2) unimpaired waters for some uses and not assessed for others; 3) insufficient information to make assessments for any uses; 4) impaired or threatened for one or more uses but not requiring the calculation of a Total Maximum Daily Load (TMDL); and 5) impaired or threatened for one or more uses and requiring a TMDL. A TMDL is a planning tool and potential starting point for restoration activities with the ultimate goal of attaining water quality standards. A TMDL essentially provides a pollution budget designed to restore the health of an impaired water body. A TMDL typically identifies the source(s) of the pollutant from point sources and non-point sources, determines the maximum load of the pollutant that the water body can tolerate while still attaining WQSs for the designated uses, and allocates that load among to the various sources, including point source discharges, subject to NPDES permits. See 40 CFR § 130.7. For impaired waters where a TMDL has been developed for a particular pollutant and the TMDL includes a waste load allocation (WLA) for a NPDES permitted discharge, the effluent limitation in the permit must be “consistent with the assumptions and requirements of any available WLA.” 40 CFR § 122.44(d)(1)(vii)(B). 2.2.4 Reasonable Potential Pursuant to CWA § 301(b)(1)(C) and 40 CFR § 122.44(d)(1), NPDES permits must contain any requirements in addition to TBELs that are necessary to achieve water quality standards established under § 303 of the CWA. See also 33 U.S.C. § 1311(b)(1)(C). In addition, limitations “must control any pollutant or pollutant parameter (conventional, non-conventional, or toxic) which the permitting authority determines are or may be discharged at a level which will cause, have the reasonable potential to cause, or contribute to an excursion above any water quality standard, including State narrative criteria for water quality.” 40 CFR § 122.44(d)(1)(i). To determine if the discharge causes, or has the reasonable potential to cause, or contribute to an excursion above any WQS, EPA considers: 1) existing controls on point and non-point sources of pollution; 2) the variability of the pollutant or pollutant parameter in the effluent; 3) the sensitivity of the species to toxicity testing (when evaluating whole effluent toxicity); and 4) where appropriate, the dilution of the effluent by the receiving water. See 40 CFR § 122.44(d)(1)(ii). If the permitting authority determines that the discharge of a pollutant will cause, has the reasonable potential to cause, or contribute to an excursion above WQSs, the permit must contain WQBELs for that pollutant. See 40 CFR § 122.44(d)(1)(i). 2.2.5 State Certification 2023 Fact Sheet NPDES Permit No. MA0103284 Page 16 of 195 EPA may not issue a permit unless the State Water Pollution Control Agency with jurisdiction over the receiving water(s) either certifies that the effluent limitations contained in the permit are stringent enough to assure that the discharge will not cause the receiving water to violate the State WQSs, the State waives, or is deemed to have waived, its right to certify. See 33 U.S.C. § 1341(a)(1). Regulations governing state certification are set forth in 40 CFR §§ 124.53 and 124.55. EPA has requested permit certification by the State pursuant to 40 CFR § 124.53 and expects that the Draft Permit will be certified. If the State believes that conditions more stringent than those contained in the Draft Permit are necessary to meet the requirements of either CWA §§ 208(e), 301, 302, 303, 306 and 307 or applicable requirements of State law, the State should include such conditions in its certification and, in each case, cite the CWA or State law provisions upon which that condition is based. Failure to provide such a citation waives the right to certify as to that condition. EPA includes properly supported State certification conditions in the NPDES permit. The only exception to this is that the permit conditions/requirements regulating sewage sludge management and implementing CWA § 405(d) are not subject to the State certification requirements. Reviews and appeals of limitations and conditions attributable to State certification shall be made through the applicable procedures of the State and may not be made through EPA’s permit appeal procedures of 40 CFR Part 124. In addition, the State should provide a statement of the extent to which any condition of the Draft Permit can be made less stringent without violating the requirements of State law. Since the State’s certification is provided prior to final permit issuance, any failure by the State to provide this statement waives the State’s right to certify or object to any less stringent condition. It should be noted that under CWA § 401, EPA’s duty to defer to considerations of State law is intended to prevent EPA from relaxing any requirements, limitations or conditions imposed by State law. Therefore, “[a] State may not condition or deny a certification on the grounds that State law allows a less stringent permit condition.” 40 CFR § 124.55(c). In such an instance, the regulation provides that, “The Regional Administrator shall disregard any such certification conditions or denials as waivers of certification.” Id. EPA regulations pertaining to permit limitations based upon WQSs and State requirements are contained in 40 CFR §§ 122.4 (d) and 122.44(d). 2.3 Effluent Flow Requirements Sewage treatment plant discharge is encompassed within the definition of “pollutant” and is subject to regulation under the CWA. The CWA defines “pollutant” to mean, inter alia , “municipal...waste” and “sewage…discharged into water.” 33 U.S.C. § 1362(6). Generally, EPA uses effluent flow both to determine whether an NPDES permit needs certain effluent limitations and to calculate the limitations themselves. EPA practice is to use effluent flow as a reasonable and important worst-case condition in EPA’s reasonable potential and WQBEL calculations to ensure compliance with WQSs under § 301(b)(1)(C). Should the effluent flow exceed the flow assumed in these calculations, the in-stream dilution would be reduced, and the calculated effluent limitations may not be sufficiently protective (i.e., might not 2023 Fact Sheet NPDES Permit No. MA0103284 Page 17 of 195 meet WQSs). Further, pollutants that do not have the reasonable potential to exceed WQSs at the lower discharge flow may have reasonable potential at a higher flow due to the decreased dilution. In order to ensure that the assumptions underlying the EPA’s reasonable potential analyses and permit effluent limitation derivations remain sound for the duration of the permit, EPA may ensure the validity of its “worst-case” wastewater effluent flow assumptions through imposition of permit conditions for effluent flow. 3 In this regard, the effluent flow limitation is a component of WQBELs because the WQBELs are premised on a maximum level flow. The effluent flow limit is also necessary to ensure that other pollutants remain at levels that do not have a reasonable potential to exceed WQSs. The limitation on wastewater effluent flow is within EPA’s authority to condition a permit to carry out the objectives of the Act. See CWA §§ 402(a)(2) and 301(b)(1)(C); 40 CFR §§ 122.4(a) and (d); 122.43 and 122.44(d). A condition on the discharge designed to ensure the WQBEL and reasonable potential calculations account for “worst case” conditions is encompassed by the references to “condition” and “limitations” in CWA §§ 402 and 301 and implementing regulations, as they are designed to assure compliance with applicable water quality regulations, including antidegradation. Regulating the quantity of pollutants in the discharge through a restriction on the quantity of wastewater effluent is consistent with the overall structure and purposes of the CWA. In addition, as provided in Part II.B.1 of this permit and 40 CFR § 122.41(e), the Permittee is required to properly operate and maintain all facilities and systems of treatment and control. Operating the facilities wastewater treatment systems as designed includes operating within the facility’s design wastewater effluent flow. EPA has also included the effluent flow limit in the Permit to minimize or prevent infiltration and inflow (I/I) that may result in unauthorized discharges and compromise proper operation and maintenance of the facility. Improper operation and maintenance may result in non-compliance with permit effluent limitations. Infiltration is groundwater that enters the collection system though physical defects such as cracked pipes or deteriorated joints. Inflow is extraneous flow added to the collection system that enters the collection system through point sources such as roof leaders, yard and area drains, sump pumps, manhole covers, tide gates, and cross connections from storm water systems. Significant I/I in a collection system may displace sanitary flow, reducing the capacity available for treatment and the operating efficiency of the treatment works and to properly operate and maintain the treatment works. Furthermore, the extraneous flow due to significant I/I greatly increases the potential for sanitary sewer overflows (SSOs) in separate systems. Consequently, the effluent flow limit is a permit condition that relates to the Permittee’s duty to mitigate ( i.e. , minimize or prevent any discharge in violation of the permit that has a reasonable likelihood of adversely affecting human health or 3 EPA’s regulations regarding “reasonable potential” require EPA to consider “where appropriate, the dilution of the effluent in the receiving water,” id 40 C.F.R. §122.44(d)(1)(ii). Both the effluent flow and receiving water flow may be considered when assessing reasonable potential. In re Upper Blackstone Water Pollution Abatement Dist., 14 E.A.D. 577. 599 (EAB 2010). EPA guidance directs that this “reasonable potential: analysis be based on “worst- case” conditions. See In re Washington Aquaduct Water Supply Sys. 11 E.A.D. 565, 584 (EAB 2004) 2023 Fact Sheet NPDES Permit No. MA0103284 Page 18 of 195 the environment) and to properly operate and maintain the treatment works. See 40 CFR §§ 122.41(d), (e). 2.4 Monitoring and Reporting Requirements 2.4.1 Monitoring Requirements Sections 308(a) and 402(a)(2) of the CWA and the implementing regulations at 40 CFR Parts 122, 124, 125, and 136 authorize EPA to include monitoring and reporting requirements in NPDES permits. The monitoring requirements included in this Permit have been established to yield data representative of the Facility’s discharges in accordance with CWA §§ 308(a) and 402(a)(2), and consistent with 40 CFR §§ 122.41(j), 122.43(a), 122.44(i) and 122.48. The Draft Permit specifies routine sampling and analysis requirements to provide ongoing, representative information on the levels of regulated constituents in the wastewater discharges. The monitoring program is needed to enable EPA and the State to assess the characteristics of the Facility’s effluent, whether Facility discharges are complying with permit limits, and whether different permit conditions may be necessary in the future to ensure compliance with technology-based and water quality-based standards under the CWA. EPA and/or the State may use the results of the chemical analyses conducted pursuant to this permit, as well as national water quality criteria developed pursuant to CWA § 304(a)(1), State water quality criteria, and any other appropriate information or data, to develop numerical effluent limitations for any pollutants, including, but not limited to, those pollutants listed in Appendix D of 40 CFR Part 122. NPDES permits require that the approved analytical procedures found in 40 CFR Part 136 be used for sampling and analysis unless other procedures are explicitly specified. Permits also include requirements necessary to comply with the National Pollutant Discharge Elimination System (NPDES): Use of Sufficiently Sensitive Test Methods for Permit Applications and Reporting Rule . 4 This Rule requires that where EPA-approved methods exist, NPDES applicants must use sufficiently sensitive EPA-approved analytical methods when quantifying the presence of pollutants in a discharge. Further, the permitting authority must prescribe that only sufficiently sensitive EPA-approved methods be used for analyses of pollutants or pollutant parameters under the permit. The NPDES regulations at 40 CFR § 122.21(e)(3) (completeness), 40 CFR § 122.44(i)(1)(iv) (monitoring requirements) and/or as cross referenced at 40 CFR § 136.1(c) (applicability) indicate that an EPA-approved method is sufficiently sensitive where: • The method minimum level 5 (ML) is at or below the level of the effluent limitation established in the permit for the measured pollutant or pollutant parameter; or 4 Fed. Reg. 49,001 (Aug 19, 2014). 5 The term “minimum level” refers to either the sample concentration equivalent to the lowest calibration point in a method or a multiple of the method detection limit (MDL). Minimum levels may be obtained in several ways: They may be published in a method; they may be sample concentrations equivalent to the lowest acceptable calibration point used by a laboratory; or they may be calculated by multiplying the MDL in a method, or the MDL determined by a lab, by a factor. EPA is considering the following terms related to analytical method sensitivity to be synonymous: “quantitation limit,” “reporting limit,” “level of quantitation,” and “minimum level.” See Fed. Reg. 49,001 (Aug. 19, 2014). 2023 Fact Sheet NPDES Permit No. MA0103284 Page 19 of 195 • In the case of permit applications, the ML is above the applicable water quality criterion, but the amount of the pollutant or pollutant parameter in a facility’s discharge is high enough that the method detects and quantifies the level of the pollutant or parameter in the discharge; or • The method has the lowest ML of the analytical methods approved under 40 CFR Part 136 or required under 40 CFR chapter I, subchapter N or O for the measured pollutant or pollutant parameter. 2.4.2 Reporting Requirements The Draft Permit requires the Permittee and Co-permittees to report monitoring results obtained during each calendar month to EPA and the State electronically using NetDMR. The Permittee and CSO-responsible Co-permittees must submit a Discharge Monitoring Report (DMR) for each calendar month no later than the 15 th day of the month following the completed reporting period. NetDMR is a national web-based tool enabling regulated CWA Permittees to submit DMRs electronically via a secure internet application to EPA through the Environmental Information Exchange Network. NetDMR has eliminated the need for participants to mail in paper forms to EPA under 40 CFR §§ 122.41 and 403.12. NetDMR is accessible through EPA’s Central Data Exchange at https://cdx.epa.gov/ . Further information about NetDMR can be found on EPA’s NetDMR support portal webpage. 6 With the use of NetDMR, the Permittee is no longer required to submit hard copies of DMRs and reports to EPA and the State unless otherwise specified in the Draft Permit. In most cases, reports required under the Permit shall be submitted to EPA as an electronic attachment through NetDMR. Certain exceptions are provided in the Permit, such as for providing written notifications required under the Part II Standard Conditions. 2.5 Standard Conditions The standard conditions, included as Part II of the Draft Permit, are based on applicable regulations found in the Code of Federal Regulations. See generally 40 CFR Part 122. 2.6 Anti-backsliding The CWA’s anti-backsliding requirements prohibit a permit from being renewed, reissued or modified to include less stringent limitations or conditions than those contained in a previous permit except in compliance with one of the specified exceptions to those requirements. See CWA §§ 402(o) and 303(d)(4) and 40 CFR § 122.44(l). Anti-backsliding provisions apply to effluent limits based on technology, water quality and/or state certification requirements. 6 https://netdmr.zendesk.com/hc/en-us/articles/209616266-EPA-Region-1-NetDMR-Information 2023 Fact Sheet NPDES Permit No. MA0103284 Page 20 of 195 All proposed limitations in the Draft Permit are at least as stringent as limitations included in the 2000 Permit unless specific conditions exist to justify relaxation in accordance with CWA § 402(o) or § 303(d)(4). Discussion of any less stringent limitations and corresponding exceptions to anti-backsliding provisions is provided in the sections that follow. 3.0 Description of Facility and Discharge 3.1 Location and Type of Facility The locations of the Deer Island Treatment Plant (DITP) and Outfall T01 to Massachusetts Bay are shown in Figure 9 . The latitude and longitude of the outfall diffuser begins approximately 8 miles offshore of the DITP at 42° 23’ 3.2” N latitude / 70° 48’ 13.5” W longitude and ends at 42° 23’ 19.6” N latitude / 70° 46’ 48.4” W longitude. The DITP is a secondary wastewater treatment facility that is engaged in the collection and treatment of municipal and industrial wastewater. Flow is conveyed from the treatment facility, through an outfall tunnel that is approximately 9.5 miles in length and discharged into Massachusetts Bay. A diffuser comprises the last 1.25 miles of the outfall tunnel and consists of 55 riser pipes installed perpendicular to the tunnel and each riser is capped with an eight (8) port diffuser head (on average 5 of 8 ports have been opened per diffuser head). Currently, the Facility serves about 2,300,000 residents in the metropolitan Boston area. The regional collection system is operated in part by MWRA and in part by each of the 43 member communities (See Figure 10 and Appendix A). The Facility has a design flow of 361 MGD 7 , the annual average daily flow reported in the 2005 application was 356 MGD and the monthly average median for the review period (January 2018- December 2022) was 322 MGD (and a dry weather median of 298 MGD). The Facility has a peak treatment capacity of 1.27 billion gallons. Wastewater is comprised of domestic sewage with commercial and industrial sewage and some septage. The Facility receives flows from 69 categorical industrial users (CIUs) and 109 non-categorical significant industrial users (SIUs). 8 A quantitative description of the Outfall T01 discharge in terms of effluent parameters, based on monitoring data submitted by the Permittee from January 2018 through December 2022 is provided in Appendix C of this Fact Sheet. Additionally, EPA is adding forty-three (43) Co-permittees to the Draft Permit. The Massachusetts municipalities in Appendix A own and operate wastewater collection systems that discharge flows to the DITP for treatment. These municipalities are Co-permittees for certain activities pertaining to proper operation and maintenance of their respective collection systems. Adding them to the Draft Permit ensures that they comply with requirements to operate and 7 Camp Dresser & McKee, 1995, Massachusetts Water Resources Authority, DP-29 Secondary Treatment Facilities, Recommended Plan for Completion of the Deer Island Facilities , pp. 2-21 and 2-23. 8 EMAIL. Betsy Reilley, MWRA to Michele Barden, EPA. July 28, 2021. Subject: EPA Data Request for DITP NPDES. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 21 of 195 maintain the collection systems to avoid discharges of sewage from the collection system. EPA did not require these Co-permittees (with the exception of Boston (BWSC), Cambridge, Chelsea, and Somerville) to apply for permit coverage; with letters sent March 8, 2023, EPA waived application requirements for 39 of the Co-permittees. The legal basis for including municipal satellite collection systems as Co-permittees is described in In re Charles River Pollution Control District , 16 E.A.D. 623 (EAB 2015) 9 (Also see Appendix D). The cities of the Boston (BWSC), Cambridge, Chelsea and Somerville are currently Permittees under individual NPDES Permits for their respective CSO outfalls. On March 8, 2023, EPA informed each of these Cities by letter that they would be included as CSO-responsible Co- permittees in the Draft Permit and that they would retain the obligation to submit NPDES applications in the future. (See Section 5.7 of this Fact Sheet for more detail.) As a general matter and as explained further in the Permit, the Permittee, the CSO-responsible Co-permittees, and each Co-permittee are severally liable for their own activities under the Standard Conditions of Part II, Parts I.C, I.E, I.F, and required reporting under Part I.J with respect to the portions of the POTW that they own or operate. This means that they are not liable for violations of the Standard Conditions of Part II, Parts I.C, I.E, I.F and Part I.J committed by others relative to the portions of the collection system owned and operated by others. Nor are they responsible for any reporting that is required of other Permittees under the Standard Conditions of Part II, Part I.C, Part I.E, Part I.F, and Part I.J. EPA welcomes public comments on the clarity of the several liability for the Permittee, the CSO-responsible Co-permittees, and each other Co-permittee with respect to Standard Conditions of Part II, Parts I.C, I.E, I.F and Part I.J. 3.1.1 Treatment Process Description The DITP is a secondary treatment facility with chlorine disinfection and dechlorination. Influent enters the Facility from the North and South Systems and flows through the primary clarifiers A- D, followed by three batteries of secondary treatment and then the final clarifiers. During high flows, primary treated flows, in excess of 700 MGD, 10 may bypass the secondary batteries and final clarifiers and then be added back to main treatment train. All flows are combined prior to disinfection and dechlorination before discharge to Massachusetts Bay. A flow diagram of the Treatment Facility is shown in Figure 11 . Raw primary and secondary sludge are combined and anaerobically digested at the treatment plant. The digested sludge is thickened by centrifuges, then pumped via an underground harbor tunnel to the biosolids plant in Quincy. There, the liquid sludge is pumped into storage tanks prior to further mechanical dewatering. The dewatered cake is heat-dried and pelletized in rotary drum dryers. The final product is fertilizer and is stored in silos prior to shipment. In 2022, DITP 9 The decision is available at: https://yosemite.epa.gov/oa/EAB_Web_Docket.nsf/Published%20and%20Unpublished%20Decisions/F89699D1A0 710BCF85257DE200717A93/$File/Charles%20River%20Decision%20Vol%2016.pdf 10 700 MGD is the secondary process limit for the DITP as required by the Stipulation and Order in United States of America v. Massachusetts Water Resources Authority and Commonwealth of Massachusetts. Case 1:85-cv- 004890RGS, Document 1707, Filed 09/08/2008, 18 pages. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 22 of 195 generated 27,263 dry metric tons of sludge at the pellet plant. 11 Most of the fertilizer, 94%, is used in commercial agriculture or blended with other fertilizer products. A small percentage (6%) is bagged and used for smaller applications. Any material that is not beneficially used is disposed of at municipal solid waste landfills. The Permit requires monthly monitoring of the pelletized product and contains conditions for each use or disposal practice by MWRA. 3.1.2 Collection System Description Although the collection system includes combined sewers, the majority of the system is a separate system with only 5% 12 of the system being combined sewers. 13 The MWRA-owned portion of the collection system consists of four (4) CSO treatment facilities with five (5) outfalls and six (6) additional CSO outfalls and approximately 225 miles of sewers. (See Appendix B and Figure 12.) Four of the 43 Co-permittee municipalities own and operate CSO discharges which are currently authorized to discharge under separate NPDES permits. These permits will be terminated following the effective date of the Final MWRA DITP Permit which will include the CSO discharges from all four CSO communities. The City of Boston, as the Boston Water and Sewer Commission (BWSC), is currently permitted under NPDES permit number MA0101192 14 to discharge from 26 CSO outfalls with MWRA as a Co-permittee for CSO Treatment Facility MWR215. The discharges permitted under the BWSC Permit are to Boston Inner Harbor including the Chelsea River, Little Mystic Channel, Mystic River, Fort Point Channel, Reserved Channel, Dorchester Bay, and the Muddy River. The City of Cambridge is currently permitted under NPDES permit number MA0101974 15 to discharge from 12 CSO outfalls to the Little River (formerly listed as Alewife Brook) and the Charles River. The City of Chelsea is authorized under NPDES permit number MA0101877 16 to discharge from 4 CSO outfalls to the Boston Inner Harbor including the Chelsea River. The City of Somerville is currently authorized for 2 CSO outfalls that discharge to Alewife Brook and the Mystic River under NPDES permit number MA0101982 17 . The DITP collection system is divided into two distinct systems, the North System and the South System. There are 43 municipalities that own and operate individual municipal sewer systems that make up the larger collection system along with the interceptor system owned and operated by MWRA. Flows from the North System (~214 MGD 18 as a monthly average) begin treatment at the North System Grit Facility at Deer Island. South System flows (~114 MGD 19 as a monthly 11 EMAIL. Betsy Reilley, MWRA to Michele Barden, EPA. February 13, 2023. Subject: Update to sludge information 12 EMAIL. Wendy Leo, MWRA to Michele Barden, EPA. April 18, 2023. Subject: Updated values - DITP NPDES 13 A combined sewer conveys domestic, industrial, and commercial sewage, in addition to stormwater. A separate sanitary sewer conveys domestic, industrial, and commercial sewage, but not stormwater. 14 https://www3.epa.gov/region1/npdes/permits/2007/finalma0101192permitmod.pdf , https://www3.epa.gov/region1/npdes/permits/2003/bostonwspermit.pdf 15 https://www3.epa.gov/region1/npdes/permits/2009/finalma0101974permit.pdf 16 https://www3.epa.gov/region1/npdes/permits/2013/finalma0101877permit.pdf 17 https://www3.epa.gov/region1/npdes/permits/2012/finalma0101982permit.pdf 18 EMAIL. Wendy Leo, MWRA to Michele Barden, EPA. April 18, 2023. Subject: Updated values - DITP NPDES 19 EMAIL. Wendy Leo, MWRA to Michele Barden, EPA. April 18, 2023. Subject: Updated values - DITP NPDES 2023 Fact Sheet NPDES Permit No. MA0103284 Page 23 of 195 average) are degritted at the Nut Island Pump Station in Quincy prior to pumping to the Deer Island Treatment Plant via the Inter-Island Tunnel. The South System flows enter the Deer Island Treatment Plant immediately following the North System Grit Facility. 4.0 Description of Receiving Water and Dilution 4.1 Receiving Waters 4.1.1 Massachusetts Bay The DITP discharges through Outfall T01 into Massachusetts Bay. The DITP outfall diffuser begins approximately 8 miles offshore and extends 1.25 miles into Massachusetts Bay. Massachusetts Bay is classified as a Class SA water and designated for shellfishing in the MA WQS. 20 The MA WQS at 314 CMR 4.05(4)(a) state that Class SA are: “Those coastal and marine waters so designated pursuant to 314 CMR 4.06; including, without limitation, 314 CMR 4.06(2) and (5), and certain qualified waters designated in 314 CMR 4.06(6)(b). These waters are designated as an excellent habitat for fish, other aquatic life and wildlife, including for their reproduction, migration, growth and other critical functions, and for primary and secondary contact recreation. In certain waters, excellent habitat for fish, other aquatic life and wildlife may include, but is not limited to, seagrass. Where designated for shellfishing in 314 CMR 4.06(6)(b), these waters shall be suitable for shellfish harvesting without depuration (Approved and Conditionally Approved Shellfish Areas). These waters shall have excellent aesthetic value.” The receiving waters for Outfall T01 have not been included in the Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle 21 (2018/2020 Integrated List) and do not have a segment number. 22 4.1.2 Boston Inner Harbor The Draft Permit authorizes the MWRA to discharge from the CSO Treatment Facilities: Prison Point (MWR203) and Union Park (MWR215), into Boston Inner Harbor within Segment MA70- 02. The Draft Permit also authorizes the City of Boston for the following CSO outfalls: BOS003, BOS004, BOS009, BOS010, BOS012, BOS013, BOS014, BOS057, BOS060, BOS062, BOS064, BOS065, BOS068, BOS070, BOS073, BOS076, BOS078, BOS079 and BOS080 that discharge into Boston Inner Harbor within Segment MA70-02. CSO outfalls BOS060, BOS064, 20 314 CMR 4.06, Table 19, https://www.mass.gov/doc/314-cmr-400/download 21 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 22 EMAIL. Claire Golden, MassDEP to Michele Barden, EPA. November 3, 2022. Subject: Request for Segment Number. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 24 of 195 BOS68, and BOS073 all have an activation frequency of 0 and a volume of 0 during a Typical Year 23 as defined in the Long-Term Control Plan (LTCP). 24 Previously authorized CSO outfalls BOS005, BOS006, BOS007 and BOS072 have been closed. 25 , 26 The Boston Inner Harbor segment is 2.56 square miles and encompasses the “Entire inner harbor, inclusive of the Reserved, Fort Point and Little Mystic channels, from the respective mouths of the Charles, Mystic and Chelsea rivers, southeasterly to its seaward boundary formed by a straight line drawn from the southern tip of Governors Island to Fort Independence, Boston.” 27 This segment of the Boston Harbor is classified in the MA WQS as Class SB (CSO) which denotes that all the designated uses that normally apply to Class SB waters are also designated for Class SB (CSO), except as described in the partial use description. The MA WQS at 314 CMR 4.02 define Class SB (CSO) waters as “Those Class SB partial use Coastal and Marine Waters so designated in accordance with 314 CMR 4.06(1)(d)11. and (6)(b).” The partial designated use is further described in 314 CMR 4.06(1)(d)11 as follows: Partial Use, B(CSO) and SB(CSO) denotes those waters occasionally subject to short- term impairment of swimming or other recreational uses due to untreated CSO discharges in a typical year, and the aquatic life community may suffer adverse impact yet is still generally viable. In these waters, the uses for Class B and SB waters are maintained after the implementation of long-term control measures described in the approved CSO long- term control plan, except as identified in such plan. The Department may designate a segment partial use, B(CSO) or SB(CSO), provided that: a. a Department approved long-term control plan provides justification for the overflows; b. the Department finds through a use attainability analysis, and EPA concurs, that achieving a greater level of CSO control is not feasible for one of the reasons specified at 314 CMR 4.03(4); c. existing uses and the level of water quality necessary to protect the existing uses shall 23 Typical Year Rainfall or Typical Year: The performance objectives of MWRA’s approved Long-Term CSO Control Plan include annual frequency and volume of CSO discharge at each outfall based on “Typical Year” rainfall from 40 years of rainfall records at Logan Airport, 1949-1987 plus 1992. The Typical Year was a specifically constructed rainfall series that was based primarily on a single year (1992) that was close to the 40-year average in total rainfall and distribution of rainfall events of different sizes. The rainfall series was adjusted by adding and subtracting certain storms to make the series closer to the actual averages in annual precipitation, number of storms within different ranges of depth and storm intensities. The development of the Typical Year is described in MWRA’s System Master Plan Baseline Assessment, June 15, 1994. The Typical Year consists of 93 storms with a total precipitation of 46.8 inches. 24 MWRA remains subject to orders of the United States Court for the District of Massachusetts, Civil Action Nos. 85-04890MA and 83-1614-MA, including amended Schedule Seven, dated October, 2011 (the “Federal Court Order”) regarding its implementation of the revised Long-Term Control Plan (LTCP). 25 Boston Water and Sewer Commission. January 2023. Combined Sewer Overflow Final Public Notification Plan, Attachment A, page 1. 26 Boston Water and Sewer Commission. April 2022. CSO Monitoring Report 2021.Table 1. 27 Massachusetts Surface Water Quality Standards, December 10, 2021. 314 CMR 4.06, Table 2. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 25 of 195 be maintained and protected; and d. public notice is provided through procedures for permit reissuance under M.G.L. c. 21, §§ 26 through 53 and regulations promulgated pursuant to M.G.L. c. 30A. In addition, the Department will publish a notice in the Environmental Monitor. Other combined sewer overflows may be eligible for a variance granted pursuant to 314 CMR 4.03(4). When a variance is not appropriate, partial use may be designated for the segment after public notice and opportunity for a public hearing in accordance with M.G.L. c 30A. For CSO outfalls that MWRA did not believe could be eliminated, such as the CSO Treatment Facilities: Prison Point and Union Park, the Long-Term Control Plan 28 includes information to support a Use Attainability Analysis (UAA) pursuant to 40 CFR 131.10(g). A UAA is defined as a “structured scientific assessment of the factors affecting the attainment of the use that [can] include physical, chemical, biological and economic factors as described in 40 CFR 131.10(g).” The evaluation is conducted by the state and supports removal of a National Use Goal based on criteria such as costs and impacts associated with attaining that use. Massachusetts submitted its final administrative determinations, including an UAA 29 , to EPA for approval on December 31, 1997. On February 27, 1998, EPA approved the state’s changes to water quality standards, which included a SB (CSO) designation for Boston Inner Harbor 30 . MassDEP’s 2018/2020 Integrated List 31 includes this segment of the Boston Harbor as a Massachusetts Category 5 Water and in need of a TMDL due to contaminants in fish and/or shellfish, dissolved oxygen, Enterococcus , fecal coliform and PCBs in fish tissue. A Pathogen TMDL 32 has been completed for Boston Harbor and the contributing watersheds. 28 The MWRA Long-Term Control Plan consists of numerous MWRA studies and reports but is best defined by Exhibit B of the Second Stipulation, March 15, 2006, “Second Stipulation of the United States and the Massachusetts Water Resources Authority on Responsibility and Legal Liability for Combined Sewer Overflow Control, as amended on April 30, 2008”. 29 LETTER. Arleen O’Donnell, MassDEP to Ron Manfredonia, EPA. December 31, 1997. Re: MWRA, Combined Sewer Overflow Final Facilities Plan/Environmental Impact Report: State Administrative Determinations for Certain CSO-Impacted Waters; Use Attainability Analysis. 30 LETTER. John P. DeVillars, EPA to David Struhs, MassDEP. February 27, 1998. 31 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 32 MassDEP, EPA Region 1 and ENSR International, 2018, Final Pathogen TMDL for Boston Harbor, Weymouth- Weir, and Mystic Watersheds, https://www.mass.gov/doc/final-pathogen-tmdl-report-for-the-boston-harbor- weymouth-weir-and-mystic-watersheds/download 2023 Fact Sheet NPDES Permit No. MA0103284 Page 26 of 195 Table 2: Summary of Designated Uses and Listing Status for Segment MA70-02, Boston Inner Harbor 33 , 34 Designated Use Status Aquatic Life Support with exception of the Fort Point Channel Fort Point Channel: Impaired – Cause(s): low DO; Source(s): unknown; Suspected source(s): industrial point source discharge, Wet Weather Discharges (Point Source and Combination of Stormwater, SSO or CSO), Discharges from Municipal Separate Storm Sewer Systems (MS4). Fish Consumption Impaired/TMDL Completed – Cause(s): elevated PCB in fish tissue and other contaminants in fish/shellfish. Source(s): upstream sources, contaminated sediments, wet weather discharges (point source and combination of stormwater, sanitary sewer overflow - SSO or combined sewer overflow - CSO), discharges from biosolids (sludge) storage, application or disposal. Primary Contact Recreation Support with exception of Fort Point Channel Fort Point Channel: Impaired – Cause(s): Elevated Enterococci bacteria Source(s): Wet Weather Discharges (Point Source and Combination of Stormwater, SSO or CSO), Discharges from Municipal Separate Storm Sewer Systems (MS4) Secondary Contact Recreation Support with exception of Fort Point Channel Fort Point Channel: Impaired – Cause(s): Elevated Enterococci bacteria Source(s): Wet Weather Discharges (Point Source and Combination of Stormwater, SSO or CSO), Discharges from Municipal Separate Storm Sewer Systems (MS4) Shellfish Harvesting Impaired – Cause(s): Elevated fecal coliform bacteria Source(s): Wet Weather Discharges (Point Source and Combination of Stormwater, SSO or CSO), Discharges from Municipal Separate Storm Sewer Systems (MS4) Aesthetics Not Assessed 4.1.3 Dorchester Bay The Draft Permit authorizes the City of Boston for CSO outfalls: BOS081, BOS082, BOS084, BOS085, and BOS086 that discharge into Dorchester Bay which is identified as Segment MA70- 03. The Boston CSO outfalls are located along the South Boston beaches. MWRA’s CSO storage tunnel provides a 25-year storm level of CSO control and a 5-year storm level of separate stormwater control for the Boston Outfalls BOS081, BOS082, BOS084, BOS085, and BOS086. 33 MassDEP, 2010, Boston Harbor 2004-2008 Water Quality Assessment Report, https://www.mass.gov/doc/boston- harbor-2004-2008-water-quality-assessment-report-0/download 34 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 2023 Fact Sheet NPDES Permit No. MA0103284 Page 27 of 195 Previously authorized outfalls BOS083 and BOS087 were closed in 2011 as a result of the construction of the storage tunnel. Other previously authorized outfalls BOS088, BOS089, BOS090, BOS093 and BOS095 have been closed. 35 The remaining CSO outfalls achieve the goals in the LTCP. This segment is 3.46 square miles and is defined in 314 CMR 4.06, Table 2 as “Entire bay, from the mouth of the Neponset River, Boston/Quincy, northeasterly to the bay’s seaward boundary formed by straight lines drawn from the southerly tip of Head Island, Boston, to the north side of Thompson Island, Boston; and from the southerly tip of Thompson Island to Chapel Rocks, Quincy.” Dorchester Bay is classified in the MA WQS as Class SB – Shellfishing. The MA WQS at 314 CMR 4.02 define Class SB waters as “those coastal and marine waters so designated pursuant to 314 CMR 4.06; including, without limitation, 314 CMR 4.06(2) and (5), and certain qualified waters designated in 314 CMR 4.06(6)(b). These waters are designated as a habitat for fish, other aquatic life and wildlife, including for their reproduction, migration, growth and other critical functions, and for primary and secondary contact recreation. In certain waters, habitat for fish, other aquatic life and wildlife may include, but is not limited to, seagrass. Where designated for shellfishing in 314 CMR 4.06(6)(b), these waters shall be suitable for shellfish harvesting with depuration (Restricted and Conditionally Restricted Shellfishing Areas). These waters shall have consistently good aesthetic value.” Table 3: Summary of Designated Uses and Listing Status for Segment MA70-03, Dorchester Bay 36 , 37 Designated Use Status Aquatic Life Support Fish Consumption Impaired; Causes: Elevated PBCs in fish tissue and other contaminants in fish and/or shellfish; Sources: upstream sources, contaminated sediment, wet weather discharges (point source and combination of stormwater, sanitary sewer overflow-SSO or combined sewer overflow-CSO), discharges from biosolids (sludge) storage, application or disposal. Shellfishing Impaired; Causes: Elevated fecal coliform bacteria; Sources: Discharges from municipal storm sewer systems (MS4), unspecified urban stormwater. Primary Contact Recreation Impaired; Causes: Elevated Enterococci bacteria; Sources: Discharges from Municipal Separate Storm Sewer Systems (MS4), Unspecified urban stormwater. Secondary Contact Recreation Support Aesthetics Not Assessed 35 Boston Water and Sewer Commission. April 2022. CSO Monitoring Report 2021. Table 1 and p.9 36 MassDEP. 2010. Boston Harbor 2004-2008 Water Quality Assessment Report, https://www.mass.gov/doc/boston- harbor-2004-2008-water-quality-assessment-report-0/download 37 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 2023 Fact Sheet NPDES Permit No. MA0103284 Page 28 of 195 MassDEP’s 2018/2020 Integrated List 38 includes Dorchester Bay as a Massachusetts Category 5 Water and in need of a TMDL due to cause unknown (contaminants in fish and/or shellfish); dissolved oxygen, Enterococcus , fecal coliform, and PCBs in fish tissue. A Pathogen TMDL 39 has been completed for Boston Harbor and the contributing watersheds and includes Dorchester Bay. 4.1.4 Chelsea River The Draft Permit authorizes the City of Chelsea to discharge from CSO outfalls: CHE003, CHE004, CHE008, into the Chelsea River in Segment MA71-06. The Draft Permit also authorizes the City of Boston for CSO outfalls: BOS013 and BOS014, that discharge into the Chelsea River in Segment MA71-06. This segment is 0.37 miles in length and travels from the confluence of Mill Creek, Chelsea/Revere to confluence with Boston Inner Harbor, Chelsea/East Boston. CSO Outfall CHE008 has an activation frequency of 0 and a volume of 0 for a “Typical Year” under the LTCP. The Chelsea River is classified in the MA WQS as Class SB (CSO). The MA WQS at 314 CMR 4.02 define Class SB (CSO) waters as “those Class SB partial use coastal and marine waters so designated in accordance with 314 CMR 4.06(1)(d)11. and (6)(b). Partial Use, B(CSO) and SB(CSO) denotes those waters occasionally subject to short- term impairment of swimming or other recreational uses due to untreated CSO discharges in a typical year, and the aquatic life community may suffer adverse impact yet is still generally viable. In these waters, the uses for Class B and SB waters are maintained after the implementation of long-term control measures described in the approved CSO long- term control plan, except as identified in such a plan. The Department may designate a segment partial use, B(CSO) or SB(CSO), provided that: a. a Department approved long-term control plan provides justification for the overflows; b. the Department finds through a use attainability analysis, and EPA concurs, that achieving a greater level of CSO control is not feasible for one of the reasons specified at 314 CMR 4.03(4); c. existing uses and the level of water quality necessary to protect the existing uses shall be maintained and protected; and d. public notice is provided through procedures for permit reissuance under M.G.L. c. 21, §§ 26 through 53 and regulations promulgated pursuant to M.G.L. c. 30A. In addition, the Department will publish a notice in the 38 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 39 MassDEP, EPA Region 1 and ENSR International, 2018, Final Pathogen TMDL for Boston Harbor, Weymouth- Weir, and Mystic Watersheds, https://www.mass.gov/doc/final-pathogen-tmdl-report-for-the-boston-harbor- weymouth-weir-and-mystic-watersheds/download 2023 Fact Sheet NPDES Permit No. MA0103284 Page 29 of 195 Environmental Monitor. Other combined sewer overflows may be eligible for a variance granted pursuant to 314 CMR 4.03(4). When a variance is not appropriate, partial use may be designated for the segment after public notice and opportunity for a public hearing in accordance with M.G.L. c 30A. 314 CMR 4.06(1)(d)11. Table 4: Summary of Designated Uses and Listing Status for Segment MA71-06, Chelsea River 40 , 41 Designated Use Status Aquatic Life Impaired; Causes: Sediment Screening Value, Petroleum; Source: Contaminated Sediments, Above Ground Storage Tank Leaks (Tank Farms), Accidental release/spill, Cargo loading/unloading, Municipal (Urbanized High Density Area) Fish Consumption Impaired; Causes: PCBs in Fish Tissue, Other (contaminants in fish and shellfish); Sources: Unknown Shellfishing Impaired; Causes: Fecal Coliform, Source: Unknown Primary Contact Recreation Impaired; Causes: Petroleum; Source: Above Ground Storage Tank Leaks (Tank Farms), Accidental release/spill, Cargo loading/unloading, Municipal (Urbanized High Density Area) Secondary Contact Recreation Impaired; Causes: Petroleum; Source: Above Ground Storage Tank Leaks (Tank Farms), Accidental release/spill, Cargo loading/unloading, Municipal (Urbanized High Density Area) Aesthetics Impaired; Causes: Petroleum; Source: Above Ground Storage Tank Leaks (Tank Farms), Accidental release/spill, Cargo loading/unloading, Municipal (Urbanized High Density Area) For CSO outfalls that MWRA did not believe could be eliminated, such as the CHE003, CHE004, CHE008, BOS013 and BOS014, the Long-Term Control Plan 42 includes information to support a Use Attainability Analysis (UAA) pursuant to 40 CFR § 131.10(g). A UAA is defined as a “structured scientific assessment of the factors affecting the attainment of the use that [can] include physical, chemical, biological and economic factors as described in 40 CFR § 131.10(g).” The evaluation is conducted by the state and supports removal of a National Use Goal based on criteria such as costs and impacts associated with attaining that use. Massachusetts submitted its final administrative determinations, including an UAA 43 , to EPA for approval on December 31, 1997. On February 27, 1998, EPA approved the State’s changes to 40 MassDEP, March 2010, Mystic River Watershed and Coastal Drainage Area, 2004-2008 Water Quality Assessment Report. 41 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 42 The MWRA Long-Term Control Plan consists of numerous MWRA studies and reports but is best defined by Exhibit B of the Second Stipulation, March 15, 2006, “Second Stipulation of the United States and the Massachusetts Water Resources Authority on Responsibility and Legal Liability for Combined Sewer Overflow Control, as amended on April 30, 2008.” 43 LETTER. Arleen O’Donnell, MassDEP to Ron Manfredonia, EPA. December 31, 1997. Re: MWRA, Combined Sewer Overflow Final Facilities Plan/Environmental Impact Report: State Administrative Determinations for Certain CSO-Impacted Waters; Use Attainability Analysis. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 30 of 195 water quality standards, which included a SB (CSO) designation for Boston Inner Harbor 44 including the Chelsea River. The MassDEP’s 2018/2020 Integrated List 45 includes the Chelsea River as a Massachusetts Category 5 Water and in need of a TMDL due to debris, ammonia, un-ionized, cause unknown (contaminants in fish and/or shellfish; sediment screening value exceedance), fecal coliform, odor, PCBs in fish tissue, petroleum hydrocarbons, trash and turbidity. A Pathogen TMDL 46 has been completed for Boston Harbor and the contributing watersheds and includes the Chelsea River. 4.1.5 Charles River Segment MA72-38 The Draft Permit authorizes MWRA to discharge from the CSO Treatment Facility Cottage Farm (MWR201) and the CSO discharges: MWR010, MWR018, MWR019, MWR020 and MWR023, into the Charles River within Segment MA72-38. This segment, also referred to as the Charles River Basin, is 3.10 miles in length and travels from the Boston University Bridge, Boston/Cambridge to mouth at the New Charles River Dam, Boston. CSO Outfalls MWR010, MWR018, MWR019 and MWR020 each have an activation frequency of 0 and a volume of 0 under the LTCP. The City of Cambridge is currently authorized for CSO discharges: CAM009, CAM011, and CAM017, that also discharge to the Charles River in Segment MA72-38. CAM-011 has an activation frequency of 0 and volume of 0 in a “Typical Year” under the LTCP. Previously authorized CSO outfalls, MWR021 and MWR022 have been closed. 47 The Charles River Basin has been classified in the MA WQS as Class B, warm water fishery with a variance for the CSO discharges. A variance is a temporary modification of surface water quality standards pursuant to 314 CMR 4.03(4). The current variance 48 for the Charles River Basin was adopted by MassDEP on August 30, 2019, approved by EPA on May 29, 2020 49 and ends on August 31, 2024. The MA WQS at 314 CMR 4.05(3)(b) states that Class B waters are 44 LETTER. John P. DeVillars, EPA to David Struhs, MassDEP. February 27, 1998. 45 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 46 MassDEP, EPA Region 1 and ENSR International, 2018, Final Pathogen TMDL for Boston Harbor, Weymouth- Weir, and Mystic Watersheds, https://www.mass.gov/doc/final-pathogen-tmdl-report-for-the-boston-harbor- weymouth-weir-and-mystic-watersheds/download 47 https://www.mwra.com/03sewer/html/sewcso.htm#1819floatables 48 Kathleen M. Baskin, MassDEP, August 30, 2019, Final Determination to Adopt a Variance for Combined Sewer Overflow Discharges to Charles River Basin, https://www.mass.gov/doc/final-determination-to-adopt-a-variance- for-combined-sewer-overflow-discharges-to-the-charles/download 49 LETTER. Ken Moraff, EPA to Martin Suuberg, MassDEP, May 29, 2020, RE: Lower Charles River/Charles Basin and Alewife Brook/Upper Mystic River Water Quality Standard Variances for Certain CSO Discharges, https://www.mass.gov/doc/epa-approval-of-the-massdep-adoption-of-the-2019-cso-variances/download 2023 Fact Sheet NPDES Permit No. MA0103284 Page 31 of 195 “those inland waters so designated pursuant to 314 CMR 4.06; including, without limitation, certain wetlands designated 314 CMR 4.06(2); certain other waters designated in 314 CMR 4.06(5); and certain qualified waters designated in 314 CMR 4.06(6)(b). These waters are designated as a habitat for fish, other aquatic life, and wildlife, including for their reproduction, migration, growth, and other critical functions, and for primary and secondary contact recreation. Where designated in 314 CMR 4.06(1)(d)6. and (6)(b), as a “Treated Water Supply” they shall be suitable as a source of public water supply with appropriate treatment. Class B waters shall be suitable for irrigation and other agricultural uses and for compatible industrial cooling and process uses. These waters shall have consistently good aesthetic value.” During wet-weather conditions, Class B requirements for bacteria, solids, color and turbidity, and taste and odor may not be met. 50 The variance requires continued implementation of the revised LTCP and implementation as required by the Federal Court Order, as modified. The MassDEP’s 2018/2020 Integrated List 51 includes this segment of the Charles River as a Massachusetts Category 5 Water and in need of a TMDL due to fish passage barrier, flow regime modification, cause unknown (sediment screening value exceedance), chlorophyll a, combined biota/habitat bioassessments, DDT in fish tissue, dissolved oxygen, dissolved oxygen supersaturation, Escherichia Coli ( E. coli) , harmful algal blooms, nutrient/eutrophication biological indicators, odor, oil and grease, PCBs in fish tissue, total phosphorus, salinity, temperature, and transparency/clarity. A TMDL 52 has been developed for nutrients (phosphorus) in the lower Charles River basin. A Pathogen TMDL 53 for E. coli has also been completed for the Charles River Watershed. A regional TMDL 54 has been completed for the atmospheric deposition of mercury which is one impairment of the fish consumption use. Table 5: Summary of Designated Uses and Listing Status for Segment MA72-38, Lower Charles River 55 , 56 Designated Use Status Aquatic Life Impaired – Causes: Elevated water temperatures, combined biota/habitat bioassessment, salinity, biological indicators of nutrient enrichment, blue-green algal bloom, low dissolved oxygen, elevated saturation of dissolved oxygen, elevated 50 Kathleen M. Baskin, MassDEP, August 30, 2019, Final Determination to Adopt a Variance for Combined Sewer Overflow Discharges to Charles River Basin, https://www.mass.gov/doc/final-determination-to-adopt-a-variance- for-combined-sewer-overflow-discharges-to-the-charles/download 51 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 52 MassDEP, USEPA and Tetra Tech, Inc. 2007. Final Total Maximum Daily Load for Nutrients in the Lower Charles River Basin, Massachusetts . CN 301.0, https://www.mass.gov/doc/final-phosphorus-tmdl-report-for-the- lower-charles-river-basin/download 53 MassDEP, EPA Region 1 and ENSR International, 2007, Final Pathogen TMDL for the Charles River Watershed. CN0156.0 . https://www.mass.gov/doc/final-pathogen-tmdl-reports-for-the-charles-river-watershed-0/download 54 New England Interstate Water Pollution Control Commission (NEWIPCC) in cooperation with the states of Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island, and Vermont, 2007, Northeast Regional Mercury Total Maximum Daily Load, https://neiwpcc.org/wp-content/uploads/2020/08/FINAL-Northeast-Regional-Mercury-TMDL.pdf 55 MassDEP, 2008, Charles River Watershed, 2002-2006 Water Quality Assessment Report, https://www.mass.gov/doc/charles-river-watershed-2002-2006-water-quality-assessment-report-0/download 56 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 2023 Fact Sheet NPDES Permit No. MA0103284 Page 32 of 195 Designated Use Status chlorophyll a, poor Secchi disk transparency, elevated total phosphorus, other flow regime alterations associated with dams/impoundments, sediment contamination (sediment screening values exceeded) Sources: Thermal discharge, habitat modification from thermal discharge, entrainment from cooling water intake structure, habitat alteration associated with dams/impoundments, changes in ordinary stratification and bottom water hypoxia/anoxia, contaminated sediments, upstream sources, discharges from municipal separate storm sewer systems, unspecified urban stormwater, urban runoff/storm sewers Fish Consumption Impaired/TMDL Completed – Causes: Elevated PCB in fish tissue, pesticides (total DDT) Source: Unknown Suspected source: Contaminated sediments Primary Contact Recreation Impaired – Causes: Blue-green algal bloom, poor Secchi disk transparency Sources: Upstream sources, discharges from municipal separate storm sewer systems, unspecified urban stormwater, urban runoff/storm sewers. Secondary Contact Recreation Aesthetics Segment MA72-36 The Draft Permit authorizes the City of Cambridge to discharge from CSO outfalls: CAM005, CAM007, CAM009 and CAM011 to the Charles River in Segment MA72-36. CAM-005 has an activation frequency of 3 and volume of 0.84 MG and CAM007 has an activation frequency of 1 and volume of 0.03 MG in a “Typical Year” under the LTCP. CAM009 and CAM011 have been temporarily closed but remained authorized by the Draft Permit. 57 This segment of the Charles River is 6.10 miles in length and travels from the Watertown Dam, Watertown to the Boston University Bridge, Boston/Cambridge. It is classified in the MA WQS as Class B, warm water fishery with a variance for the CSO discharges. A variance is a temporary modification of surface water quality standards pursuant to 314 CMR 4.03(4). The current variance 58 for the Charles River Basin was adopted by MassDEP on August 30, 2019, approved by EPA on May 29, 2020 59 and ends on August 31, 2024. The MA WQS at 314 CMR 57 City of Cambridge , Department of Public Works. April 29, 2022, 2021 Annual Report National Pollutant Elimination System for the City of Cambridge, Massachusetts, Combined Sewer Overflow Permit #MA0101974, p.6 58 Kathleen M. Baskin, MassDEP, August 30, 2019, Final Determination to Adopt a Variance for Combined Sewer Overflow Discharges to Charles River Basin, https://www.mass.gov/doc/final-determination-to-adopt-a-variance- for-combined-sewer-overflow-discharges-to-the-charles/download 59 LETTER. Ken Moraff, EPA to Martin Suuberg, MassDEP, May 29, 2020, RE: Lower Charles River/Charles Basin and Alewife Brook/Upper Mystic River Water Quality Standard Variances for Certain CSO Discharges, https://www.mass.gov/doc/epa-approval-of-the-massdep-adoption-of-the-2019-cso-variances/download 2023 Fact Sheet NPDES Permit No. MA0103284 Page 33 of 195 4.05(3)(b) states that Class B waters are “those inland waters so designated pursuant to 314 CMR 4.06; including, without limitation, certain wetlands designated 314 CMR 4.06(2); certain other waters designated in 314 CMR 4.06(5); and certain qualified waters designated in 314 CMR 4.06(6)(b). These waters are designated as a habitat for fish, other aquatic life, and wildlife, including for their reproduction, migration, growth, and other critical functions, and for primary and secondary contact recreation. Where designated in 314 CMR 4.06(1)(d)6. and (6)(b), as a “Treated Water Supply” they shall be suitable as a source of public water supply with appropriate treatment. Class B waters shall be suitable for irrigation and other agricultural uses and for compatible industrial cooling and process uses. These waters shall have consistently good aesthetic value.” During wet-weather conditions, Class B requirements for bacteria, solids, color and turbidity, and taste and odor may not be met. 60 The variance requires continued implementation of the revised LTCP and implementation as required by the Federal Court Order, as modified. The MassDEP’s 2018/2020 Integrated List 61 includes this segment of the Charles River as a Massachusetts Category 5 Water and in need of a TMDL due to fish passage barrier, flow regime modification, non-native fish/shellfish/zooplankton, water chestnut, chlorophyll a, DDT in fish tissue, dissolved oxygen, Escherichia Coli ( E. coli) , fish bioassessments, harmful algal blooms, nutrient/eutrophication biological indicators, oil and grease, PCBs in fish tissue, high pH, total phosphorus, sediment bioassay (acute toxicity freshwater), transparency/clarity and unspecified metals in sediments. A TMDL 62 has been developed for nutrients (phosphorus) in the lower Charles River basin. A Pathogen TMDL 63 for E. coli has also been completed for the Charles River Watershed. A regional TMDL 64 has been completed for the atmospheric deposition of mercury which is one impairment of the fish consumption use. Table 6: Summary of Designated Uses and Listing Status for Segment MA72-36, Charles River 65 , 66 Designated Use Status Aquatic Life Impaired – Causes: Elevated water temperatures, combined biota/habitat bioassessment, salinity, biological indicators of 60 Kathleen M. Baskin, MassDEP, August 30, 2019, Final Determination to Adopt a Variance for Combined Sewer Overflow Discharges to Charles River Basin, https://www.mass.gov/doc/final-determination-to-adopt-a-variance- for-combined-sewer-overflow-discharges-to-the-charles/download 61 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 62 MassDEP, USEPA and Tetra Tech, Inc. 2007. Final Total Maximum Daily Load for Nutrients in the Lower Charles River Basin, Massachusetts . CN 301.0, https://www.mass.gov/doc/final-phosphorus-tmdl-report-for-the- lower-charles-river-basin/download 63 MassDEP, EPA Region 1 and ENSR International, 2007, Final Pathogen TMDL for the Charles River Watershed. CN0156.0 . https://www.mass.gov/doc/final-pathogen-tmdl-reports-for-the-charles-river-watershed-0/download 64 New England Interstate Water Pollution Control Commission (NEWIPCC) in cooperation with the states of Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island, and Vermont, 2007, Northeast Regional Mercury Total Maximum Daily Load, https://neiwpcc.org/wp-content/uploads/2020/08/FINAL-Northeast-Regional-Mercury-TMDL.pdf 65 MassDEP, 2008, Charles River Watershed, 2002-2006 Water Quality Assessment Report, https://www.mass.gov/doc/charles-river-watershed-2002-2006-water-quality-assessment-report-0/download 66 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 2023 Fact Sheet NPDES Permit No. MA0103284 Page 34 of 195 Designated Use Status nutrient enrichment, blue-green algal bloom, low dissolved oxygen, elevated saturation of dissolved oxygen, elevated chlorophyll a, poor Secchi disk transparency, elevated total phosphorus, other flow regime alterations associated with dams/impoundments, sediment contamination (sediment screening values exceeded) Sources: Thermal discharge, habitat modification from thermal discharge, entrainment from cooling water intake structure, habitat alteration associated with dams/impoundments, changes in ordinary stratification and bottom water hypoxia/anoxia, contaminated sediments, upstream sources, discharges from municipal separate storm sewer systems, unspecified urban stormwater, urban runoff/storm sewers Fish Consumption Impaired/TMDL Completed – Causes: Elevated PCB and pesticides (total DDT) in fish tissue, Source: Contaminated sediments and/or unknown Primary Contact Recreation Impaired – Causes: Elevated E. coli, poor Secchi disk transparency. Sources: Upstream sources, discharges from municipal separate storm sewer systems, unspecified urban stormwater, urban runoff/storm sewers Secondary Contact Recreation Aesthetics 4.1.6 Muddy River (Back Bay Fens) The Draft Permit authorizes the City of Boston CSO discharge, BOS046, into the Back Bay Fens portion of the Muddy River within Segment MA72-11. The segment is 3.6 miles long and travels from the headwaters at the outlet Ward Pond in Olmsted Park, Boston through Leverett Pond, Boston/Brookline to confluence with Charles River, Boston (four culverted portions totaling approximately 2200 feet (0.42 mile)). The segment had been classified in the MA WQS as Class B (CSO), warm water fishery. The MA WQS at 314 CMR 4.02 define Class B (CSO) waters as those Class B partial use Inland Waters so designated in accordance with 314 CMR 4.06(1)(d)11. and (6)(b). Partial Use, B(CSO) and SBO (CSO) denotes those waters occasionally subject to short- term impairment of swimming or other recreational uses due to untreated CSO discharges in a typical year, and the aquatic life community may suffer adverse impact yet is still generally viable. In these waters, the uses for Class B and SB waters are maintained after the implementation of long-term control measures described in the approved CSO long- term control plan, except as identified in such a plan. The Department may designate a segment partial use, B(CSO) or SB(CSO), provided that: a. a Department approved long-term control plan provides justification for the overflows; 2023 Fact Sheet NPDES Permit No. MA0103284 Page 35 of 195 b. the Department finds through a use attainability analysis, and EPA concurs, that achieving a greater level of CSO control is not feasible for one of the reasons specified at 314 CMR 4.03(4); c. existing uses and the level of water quality necessary to protect the existing uses shall be maintained and protected; and d. public notice is provided through procedures for permit reissuance under M.G.L. c. 21, §§ 26 through 53 and regulations promulgated pursuant to M.G.L. c. 30A. In addition, the Department will publish a notice in the Environmental Monitor. Other combined sewer overflows may be eligible for a variance granted pursuant to 314 CMR 4.03(4). When a variance is not appropriate, partial use may be designated for the segment after public notice and opportunity for a public hearing in accordance with M.G.L. c 30A. 314 CMR 4.06(1)(d)11. The MassDEP’s 2018/2020 Integrated List 67 includes this segment of the Muddy River as a Massachusetts Category 5 Water and in need of a TMDL due to bottom deposits, flow regime modification, non-native aquatic plants, physical substrate habitat alterations, DDT in fish tissue, dissolved oxygen, Escherichia Coli ( E. Coli ), odor, oil and grease, PCBs in fish tissue, total phosphorus, turbidity, and unspecified metals in sediment. A Pathogen TMDL 68 for E. coli has also been completed for the Charles River Watershed. Table 7: Summary of Designated Uses and Listing Status for Segment MA72-11, Muddy River 69 , 70 Designated Use Status Aquatic Life Impaired – Causes: Bottoms deposits of sediment and silt, physical substrate habitat alteration, flow regime alterations, elevated total phosphorus, and the dense infestation of Phragmites australis , and other contamination including elevated concentrations of trace metals and organic compounds in sediment. Sources: Wet weather discharges (point source and combination of stormwater, sanitary sewer overflow (SSO) or combined sewer overflow (CSO), channelization, sediment contamination, the loss of riparian habitat Fish Consumption Impaired – Causes: Elevated PCB in fish tissue (carp, bullhead, and American eel); Source: Unknown and contaminated sediments 67 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 68 MassDEP, EPA Region 1 and ENSR International, 2007, Final Pathogen TMDL for the Charles River Watershed. CN0156.0 . https://www.mass.gov/doc/final-pathogen-tmdl-reports-for-the-charles-river-watershed-0/download 69 MassDEP, 2008, Charles River Watershed, 2002-2006 Water Quality Assessment Report, https://www.mass.gov/doc/charles-river-watershed-2002-2006-water-quality-assessment-report-0/download 70 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 2023 Fact Sheet NPDES Permit No. MA0103284 Page 36 of 195 Designated Use Status Primary Contact Recreation Impaired – Causes: Elevated E. coli ., turbidity; Sources: Wet weather discharges (point source and combination of stormwater, SSO or CSO), illicit connections/hookups to storm sewers. Suspected Sources: Channelization, loss of riparian habitat Secondary Contact Recreation Impaired – Causes: Turbidity; Sources: Wet weather discharges (point source and combination of stormwater, SSO or CSO), illicit connections/hookups to storm sewers. Suspected Sources: Channelization, loss of riparian habitat Aesthetics Impaired – Causes: Turbidity; Sources: Wet weather discharges (point source and combination of stormwater, SSO or CSO), illicit connections/hookups to storm sewers. Suspected Sources: Channelization, loss of riparian habitat 4.1.7 Mystic River Segment MA71-02 The Draft Permit authorizes MWRA CSO Treatment Facility Outfall MWR205A to discharge into the Mystic River within Segment MA71-02. MWR205A is only activated during wet weather events, when high tide prevents the discharge of flows from MWR205. This segment is 5.0 miles in length and travels from the outlet of Lower Mystic Lake, Arlington/Medford to the Amelia Earhart Dam, Somerville/Everett. The Draft Permit authorizes the City of Somerville to discharge from CSO outfall SOM007A into the Mystic River via the same outfall as MWR205A. This segment of the Mystic River has been classified in the MA WQS as Class B, warm water with a variance for CSO discharges. A variance is a temporary modification of surface water quality standards. The latest variance 71 for the Mystic River was adopted by MassDEP on August 30, 2019, approved by EPA on May 29, 2020 72 and ends on August 31, 2024. The MA WQS at 314 CMR 4.05(3)(b) states that Class B waters are “those Inland Waters so designated pursuant to 314 CMR 4.06; including, without limitation, certain wetlands designated in 314 CMR 4.06(2); certain other waters designated in 314 CMR 4.06(5); and certain qualified waters designated in 314 CMR 4.06(6)(b).” These waters are designated as a habitat for fish, other aquatic life, and wildlife, including for their reproduction, migration, growth, and other critical functions, and for primary and secondary contact recreation. Where designated in 314 CMR 4.06(1)(d)6. and (6)(b), they shall be suitable as a source of public water supply with appropriate treatment (“Treated Water Supply”). Class B waters shall be suitable for irrigation and other agricultural uses and for compatible industrial cooling and process uses. These waters shall have consistently good aesthetic value.” The variance for this segment authorizes limited CSO 71 Kathleen M. Baskin, MassDEP, August 30, 2019, Final Determination to Adopt a Variance for Combined Sewer Overflow Discharges to Alewife Brook/Upper Mystic River Basin, https://www.mass.gov/doc/final-determination- to-adopt-a-variance-for-combined-sewer-overflow-discharges-to-alewife/download 72 LETTER. Ken Moraff, EPA to Martin Suuberg, MassDEP, May 29, 2020. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 37 of 195 discharges. The variance requires continued implementation of the LTCP Plan and implementation as required by the Federal Court Order, as modified. The MassDEP’s 2018/2020 Integrated List 73 includes this segment of the Mystic River as a Massachusetts Category 5 Water and in need of a TMDL due to Eurasian Water Milfoil, Myriophyllum Spicatum , non-native aquatic plants, water chestnut, arsenic, chlordane in fish tissue, chlorophyll a, DDT in fish tissue, dissolved oxygen, dissolved oxygen supersaturation, Escherichia Coli ( E. coli) , PCBs in fish tissue, high pH, , total phosphorus, sediment bioassay (chronic toxicity freshwater), and transparency/clarity. TMDLs 74 , 75 have been developed for phosphorus management and bacteria. A regional TMDL 76 has been completed for the atmospheric deposition of mercury which is one impairment of the fish consumption use. Table 8: Summary of Designated Uses and Listing Status for Segment MA71-02, Mystic River 77 , 78 Designated Use Status Aquatic Life Impaired – Causes: Chlorophyll-a, DO saturation, fish- passage barrier, sediment bioassays -- chronic toxicity freshwater, elevated total phosphorus Sources: Contaminated sediments, hydrostructure impacts on fish passage, unspecified urban stormwater Fish Consumption Impaired – Causes: DDT, chlordane, and PCBs in fish tissue Source: Unknown Primary Contact Recreation Impaired – Causes: E. coli , secchi disk transparency Source: Unspecified urban stormwater Secondary Contact Recreation Impaired – Causes: secchi disk transparency Source: Unspecified urban stormwater Aesthetics Impaired – Causes: secchi disk transparency Source: Unspecified urban stormwater Segment MA71-03 73 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 74 Eastern Research Group, Inc. for EPA, Region 1, January 2020, Mystic River Watershed Alternative TMDL Development for Phosphorus Management – Final Report, https://www.epa.gov/sites/production/files/2020- 06/documents/mystic-river-tmdl-report.pdf 75 MassDEP, EPA Region 1, & ENSR International, October 2018, Final Pathogen TMDL for the Boston Harbor, Weymouth-Weir, and Mystic Watersheds, (Control Number CN 157.1), https://www.mass.gov/doc/final-pathogen- tmdl-report-for-the-boston-harbor-weymouth-weir-and-mystic-watersheds/download 76 New England Interstate Water Pollution Control Commission (NEWIPCC) in cooperation with the states of Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island, and Vermont, 2007, Northeast Regional Mercury Total Maximum Daily Load, https://neiwpcc.org/wp-content/uploads/2020/08/FINAL-Northeast- Regional-Mercury-TMDL.pdf 77 MassDEP, March 2010, Mystic River Watershed and Coastal Drainage Area, 2004-2008 Water Quality Assessment Report, https://www.mass.gov/doc/mystic-river-watershed-2004-2008-water-quality-assessment-report- 0/download 78 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 2023 Fact Sheet NPDES Permit No. MA0103284 Page 38 of 195 The Draft Permit authorizes the MWRA to discharge from CSO Treatment Facility Outfall MWR205, the primary discharge from the Somerville Marginal Treatment Facility, into the Mystic River Segment MA71-03. The segment is 0.49 square miles and travels from the Amelia Earhart Dam, Somerville/Everett to confluence with Boston Inner Harbor Chelsea/Charlestown (Includes Island End River). The Draft Permit also authorizes the City of Boston to discharge from CSO outfall BOS017 into the Mystic River Segment MA71-03. This segment of the Mystic River is classified in the MA WQS as a Class SB (CSO) water. The MA WQS at 314 CMR 4.02 define Class SB (CSO) waters as “those Class SB partial use coastal and marine waters so designated in accordance with 314 CMR 4.06(1)(d)11. and (6)(b)”. Partial Use, B (CSO) and SB(CSO) denotes those waters occasionally subject to short- term impairment of swimming or other recreational uses due to untreated CSO discharges in a typical year, and the aquatic life community may suffer adverse impact yet is still generally viable. In these waters, the uses for Class B and SB waters are maintained after the implementation of long-term control measures described in the approved CSO long- term control plan, except as identified in such a plan. The Department may designate a segment partial use, B(CSO) or SB(CSO), provided that: a. a Department approved long-term control plan provides justification for the overflows; b. the Department finds through a use attainability analysis, and EPA concurs, that achieving a greater level of CSO control is not feasible for one of the reasons specified at 314 CMR 4.03(4); c. existing uses and the level of water quality necessary to protect the existing uses shall be maintained and protected; and d. public notice is provided through procedures for permit reissuance under M.G.L. c. 21, §§ 26 through 53 and regulations promulgated pursuant to M.G.L. c. 30A. In addition, the Department will publish a notice in the Environmental Monitor. Other combined sewer overflows may be eligible for a variance granted pursuant to 314 CMR 4.03(4). When a variance is not appropriate, partial use may be designated for the segment after public notice and opportunity for a public hearing in accordance with M.G.L. c 30A.” 314 CMR 4.06(1)(d)11. The MassDEP’s 2018/2020 Integrated List 79 includes this segment of the Mystic River as a Massachusetts Category 5 Water and in need of a TMDL due to ammonia (un-ionized), cause unknown (contaminants in fish and shellfish); sediment screening value (exceedance), dissolved oxygen, fecal coliform, flocculant masses, nutrient/eutrophication biological indicators, odor, oil 79 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 2023 Fact Sheet NPDES Permit No. MA0103284 Page 39 of 195 and grease, PCBs in fish tissue, petroleum hydrocarbons, and scum/foam. TMDLs 80 , 81 have been developed for dissolved oxygen, flocculant masses, nutrient/eutrophication biological indicators, and fecal coliform bacteria. A regional TMDL 82 has been completed for the atmospheric deposition of mercury which is one impairment of the fish consumption use. Table 9: Summary of Designated Uses and Listing Status for Segment MA71-03, Mystic River 83 , 84 Designated Use Status Aquatic Life Impaired – Causes: Sediment Bioassays – Chronic Toxicity Freshwater Sources: Contaminated sediments Fish Consumption Not Assessed Shellfish Impaired – Causes: Fecal Coliform; Sources: Unknown Primary Contact Recreation Support Secondary Contact Recreation Support Aesthetics Not assessed due to lack of data 4.1.8 Little River and Alewife Brook Segment MA71-22 - Little River The Draft Permit authorizes MWRA for CSO discharge, MWR003, that discharges to the Little River which is identified as Segment MA71-22 (formerly part of Segment MA71-04 85 ). This segment is 0.03 miles in length and travels from MWRA CSO Outfall MWR003, approximately 150 feet upstream from the mouth, Cambridge to mouth at the confluence with Alewife Brook, Cambridge. The Draft Permit also authorizes the City of Cambridge to discharge from CSO outfall, CAM401A into the Little River. CSO discharge CAM004 has been closed. 86 80 Eastern Research Group, Inc. for EPA, Region 1, January 2020, Mystic River Watershed Alternative TMDL Development for Phosphorus Management – Final Report, https://www.epa.gov/sites/production/files/2020- 06/documents/mystic-river-tmdl-report.pdf 81 MassDEP, EPA Region 1, & ENSR International, October 2018, Final Pathogen TMDL for the Boston Harbor, Weymouth-Weir, and Mystic Watersheds, (Control Number CN 157.1), https://www.mass.gov/doc/final-pathogen- tmdl-report-for-the-boston-harbor-weymouth-weir-and-mystic-watersheds/download 82 New England Interstate Water Pollution Control Commission (NEWIPCC) in cooperation with the states of Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island, and Vermont, 2007, Northeast Regional Mercury Total Maximum Daily Load, https://neiwpcc.org/wp-content/uploads/2020/08/FINAL-Northeast- Regional-Mercury-TMDL.pdf 83 MassDEP, March 2010, Mystic River Watershed and Coastal Drainage Area, 2004-2008 Water Quality Assessment Report. 84 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 85 MassDEP re-defined Segment MA71-04 in the 2018/2020 Integrated List of Waters. 86 City of Cambridge , Department of Public Works. April 29, 2022, 2021 Annual Report National Pollutant Elimination System for the City of Cambridge, Massachusetts, Combined Sewer Overflow Permit #MA0101974, p.6. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 40 of 195 This segment of Little River has been classified in the MA WQS as a Class B, warm water with a variance for CSO discharges. The latest variance 87 for the Alewife Brook (which previously included Little River) was approved by EPA on May 29, 2020. 88 The MA WQS at 314 CMR 4.05(3)(b) states that Class B waters are “those Inland Waters so designated pursuant to 314 CMR 4.06; including, without limitation, certain wetlands designated in 314 CMR 4.06(2); certain other waters designated in 314 CMR 4.06(5); and certain qualified waters designated in 314 CMR 4.06(6)(b). These waters are designated as a habitat for fish, other aquatic life, and wildlife, including for their reproduction, migration, growth, and other critical functions, and for primary and secondary contact recreation. Where designated in 314 CMR 4.06(1)(d)6 and (6)(b), they shall be suitable as a source of public water supply with appropriate treatment (“Treated Water Supply”). Class B waters shall be suitable for irrigation and other agricultural uses and for compatible industrial cooling and process uses. These waters shall have consistently good aesthetic value.” A variance is a temporary modification of surface water quality standards. The variance for this segment authorizes limited CSO discharges. The variance requires continued implementation of the LTCP and implementation as required by the Federal Court Order, as modified. The MassDEP’s 2018/2019 Integrated List 89 includes this segment of the Little River as a Massachusetts Category 5 Water and in need of a TMDL due to debris, copper in sediment, DO, E.coli , flocculant masses, lead in sediment, odor, oil and grease, PCBs in fish tissue, total phosphorus, scum/foam, transparency/clarity and trash. Segment MA71-20 - Alewife Brook The Draft Permit authorizes the City of Cambridge to discharge from CSO outfall CAM001, CAM002, and CAM401B into Alewife Brook. CAM001 has an activation frequency of 0 and volume of 0 in a “Typical Year” under the LTCP. CSO discharge CAM400 has been closed. 90 The Draft Permit authorizes the City of Somerville to discharge from CSO outfall, SOM001A, into Alewife Brook. Alewife Brook is identified as Segment MA71-20 (formerly part of Segment MA71-04). This segment is 1.6 miles in length and begins at the emergence north of Cambridgepark Drive, Cambridge to mouth at confluence with the Mystic River, Arlington/Somerville. 87 Kathleen M. Baskin, MassDEP, August 30, 2019, Final Determination to Adopt a Variance for Combined Sewer Overflow Discharges to Alewife Brook/Upper Mystic River Basin, https://www.mass.gov/doc/final-determination- to-adopt-a-variance-for-combined-sewer-overflow-discharges-to-alewife/download 88 LETTER. Ken Moraff, EPA to Martin Suuberg, MassDEP, May 29, 2020. 89 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 90 City of Cambridge , Department of Public Works. April 29, 2022, 2021 Annual Report National Pollutant Elimination System for the City of Cambridge, Massachusetts, Combined Sewer Overflow Permit #MA0101974, p.6. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 41 of 195 Alewife Brook is classified in the MA WQS as a Class B, warm water with a variance for CSO discharge. The latest variance 91 for Alewife Brook was approved by EPA on May 29, 2020. 92 The MA WQS at 314 CMR 4.05(3)(b) states that Class B waters are “those Inland Waters so designated pursuant to 314 CMR 4.06; including, without limitation, certain wetlands designated in 314 CMR 4.06(2); certain other waters designated in 314 CMR 4.06(5); and certain qualified waters designated in 314 CMR 4.06(6)(b). These waters are designated as a habitat for fish, other aquatic life, and wildlife, including for their reproduction, migration, growth, and other critical functions, and for primary and secondary contact recreation. Where designated in 314 CMR 4.06(1)(d)6 and (6)(b), they shall be suitable as a source of public water supply with appropriate treatment (“Treated Water Supply”). Class B waters shall be suitable for irrigation and other agricultural uses and for compatible industrial cooling and process uses. These waters shall have consistently good aesthetic value.” A variance is a temporary modification of surface water quality standards. The variance for this segment authorizes limited CSO discharges. The variance requires continued implementation of the LTCP and implementation as required by the Federal Court Order, as modified. The MassDEP’s 2018/2020 Integrated List 93 includes Alewife Brook (including Little River) as a Massachusetts Category 5 Water and in need of a TMDL due to debris, water chestnuts, chloride, trash, copper in sediment, dissolved oxygen, Escherichia ( E.coli) , flocculant masses, lead in sediment, odor, oil and grease, PCBs in fish tissue, total phosphorus, scum/foam, sediment bioassay (chronic toxicity freshwater) and transparency/clarity. TMDLs 94 , 95 have been developed for phosphorus management and bacteria. Table 10: Summary of Designated Uses and Listing Status for Segment MA71-04, Alewife Brook 96 , 97 Designated Use Status Aquatic Life Impaired – Causes: Sediment bioassays – chronic toxicity freshwater, low DO Sources: CSOs, contaminated sediments, unspecified urban stormwater Fish Consumption Not Assessed 91 Kathleen M. Baskin, MassDEP, August 30, 2019, Final Determination to Adopt a Variance for Combined Sewer Overflow Discharges to Alewife Brook/Upper Mystic River Basin. 92 LETTER. Ken Moraff, EPA to Martin Suuberg, MassDEP, May 29, 2020. 93 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 94 Eastern Research Group, Inc. for EPA, Region 1, January 2020, Mystic River Watershed Alternative TMDL Development for Phosphorus Management – Final Report, https://www.epa.gov/sites/production/files/2020- 06/documents/mystic-river-tmdl-report.pdf 95 MassDEP, EPA Region 1, & ENSR International, October 2018, Final Pathogen TMDL for the Boston Harbor, Weymouth-Weir, and Mystic Watersheds, (Control Number CN 157.1), https://www.mass.gov/doc/final-pathogen- tmdl-report-for-the-boston-harbor-weymouth-weir-and-mystic-watersheds/download 96 MassDEP, March 2010, Mystic River Watershed and Coastal Drainage Area, 2004-2008 Water Quality Assessment Report, https://www.mass.gov/doc/mystic-river-watershed-2004-2008-water-quality-assessment-report- 0/download 97 MassDEP, 2021, Final Massachusetts Integrated List of Waters for the Clean Water Act 2018/2020 Reporting Cycle, https://www.epa.gov/tmdl/massachusetts-2018-2020-303d-list-report-and-related-documents 2023 Fact Sheet NPDES Permit No. MA0103284 Page 42 of 195 Designated Use Status Primary Contact Recreation Impaired – Causes: E. coli , secchi disk transparency; Sources: CSOs, sediments, unspecified urban stormwater Secondary Contact Recreation Impaired – Causes: E. coli , secchi disk transparency; Sources: CSOs, sediments, unspecified urban stormwater Aesthetics Impaired – Causes: secchi disk transparency; Sources: CSOs, sediments, unspecified urban stormwater 4.2 Ambient Data A summary of the ambient data collected in the receiving water in the vicinity of the Outfall T01 that is referenced in this Fact Sheet can be found in Appendix E of this Fact Sheet. 4.3 Available Dilution To ensure that discharges do not cause or contribute to violations of WQSs under all expected conditions, WQBELs are derived assuming critical conditions for the receiving water. 98 Massachusetts water quality regulations state that the MassDEP “will establish extreme hydrologic conditions at which aquatic life criteria must be applied on a case-by-case basis.” 314 CMR 4.03(3)(c). The MWRA DITP discharge is located approximately 8 miles offshore at a depth of 110 feet below the surface. The last 1.25 miles of the outfall is a multiport diffuser with 55 riser pipes that are oriented perpendicular to the outfall. Each riser pipe is capped with an 8-port diffuser head (although, on average, only 5 ports were opened in each port head). 99 Certain water quality-based effluent limits in the 2000 Permit were established with the use of a mixing zone. Mixing zones are regulated at 314 CMR 4.03(2) and are defined as “a limited area or volume of a waterbody as a mixing zone for the initial dilution of the discharge.” The MA WQS allow waters within a mixing zone to fail to meet specific water quality criteria provided specific conditions are met: • Mixing zones shall be limited to an area or volume as small as feasible. There shall be no lethality to organisms passing through the mixing zone as determined by the Department. The location, design and operation of the discharge shall minimize impacts on aquatic life and other existing and designated uses within and beyond the mixing zone. • Mixing zones shall not interfere with the migration or free movement of fish and other aquatic life. There shall be safe and adequate passage for swimming and drifting organisms with no deleterious effects on their populations. 98 EPA Permit Writer’s Manual, Section 6.2.4. 99 Carlton D. Hunt, Alex D. Mansfield, Michael J. Mickelson, Carl S. Albro, W. Rockwell Geyer and Philip J.W. Roberts, Plume Track and Dilution of Effluent From the Boston Sewage Outfall, Marine Environmental Research , 2010, 70, pp. 150-161. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 43 of 195 • Mixing zones shall not create nuisance conditions, accumulate pollutants in the sediments or biota in toxic amounts or otherwise interfere with the current or designated uses of the surface waters. 314 CMR 4.03(2) The dilution ratio established for Outfall T01 in the 2000 Permit, 70:1, was predicted in the physical hydraulic modeling study 100 which was conducted to determine the most effective diffuser design for the outfall. Post-discharge plume tracking surveys were required by the 2000 Permit to evaluate whether the actual dilution was less than the dilution predicted by the modeling study. The surveys (i.e., dye studies) were conducted in April and July 2001 and are detailed in reports submitted by MWRA in June 101 and July 2002, 102 respectively. The July 2001 study and results were also published in a peer-reviewed journal. 103 MassDEP and EPA confirmed by letter 104 “that the field studies verified the minimum initial dilution (70 to 1) assumed in the NPDES Permit.” This dilution is used for the evaluation of reasonable potential and the calculation of water quality-based effluent limits for Outfall T01 in the Draft Permit. The dye studies were conducted by adding dye to the effluent prior to discharge to the outfall tunnel and diffuser. The July 2001 survey is considered by EPA to be the worst case scenario survey even though the ambient test conditions were not ideal as plant flows were lower than “typical” summertime flows due to drought conditions, and the stratification in Massachusetts Bay was moderate; therefore, conditions did not represent the critical conditions as recommended in EPA’s Technical Support Document for Water Quality-based Toxics Control (TSD), 105 which advises that critical design periods for ocean mixing zone analyses must include maximum thermal or density stratification. Initial dilution determined by the July 2001 dye study ranged between 94 and 102, which is higher than the estimates from the earlier model study. It does appear that the diffuser is performing as predicted. However, given the less than critical conditions during the dye study, EPA has maintained the dilution of 70:1. In 2022, Deltares, an MWRA contractor, evaluated the effluent plume behavior using the Cornell Mixing Zone Expert System (CORMIX). The model simulation was not designed to determine 100 Phillip J.W. Roberts, and William H. Snyder, Hydraulic Model Study for Boston Outfall. II: Environmental Performance, Journal of Hydraulic Engineering , 1993, Vol. 119, No. 9, pp. 988-1002. 101 Hunt, C.D., Steinhauer, W.S., Mansfield, A.D., Albro, C.A., Roberts, P.J.W., Geyer, W.R. ad Michelson, M.J. 2002. Massachusetts Water Resources Authority, Effluent Outfall Dilution: April 2001, June 2002, Report No. 2002-06. https://www.mwra.com/harbor/enquad/pdf/2002-06.pdf 102 Hunt, C.D., Mansfield, A.D., Roberts, P.J.W., Albro, C.A., Geyer, W.R., Steinhauer, W.S. and Mickelson, M.J., 2002. Massachusetts Water Resources Authority, Effluent Outfall Dilution: July 2001, July 2002. Report No. 2002- 07. https://www.mwra.com/harbor/enquad/pdf/2002-07.pdf 103 Carlton D. Hunt, Alex D. Mansfield, Michael J. Mickelson, Carl S. Albro, W. Rockwell Geyer, and Philip J.W. Roberts, Plume Tracking and Dilution of Effluent from Boston Sewage Outfall, Marine Environmental Research 104 LETTER. Steve G. Lipman, MassDEP to Michael J. Hornbrook, MWRA. October 28, 2002. Re: Massachusetts Water Resources Authority, NPDES Permit Number MA0103284, Part I.18e – Outfall and Diffusers: Predicted Minimum Dilution. 105 USEPA, Technical Support Document for Water Quality-based Toxics Control, 1991, EPA/505/2-90-001, p. 74. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 44 of 195 the dilution factor for regulatory purposes but the “results are consistent with past observational and model studies (e.g., Hunt et al., 2010, Roberts et al., 2011).” 106 EPA has kept the more conservative initial dilution of 70:1 in the Draft Permit to assure that water quality standards are met during critical conditions (i.e., “typical” effluent flows, maximum ambient stratification and slack tide). 5.0 Proposed Effluent Limitations and Conditions The proposed effluent limitations and conditions derived under the CWA and State WQSs are described below. These proposed effluent limitations and conditions, the basis of which are discussed throughout this Fact Sheet, may be found in Part I of the Draft Permit. In addition to the requirements described below, the Draft Permit includes a narrative condition prohibiting pollutants introduced into POTWs by non-domestic sources from passing through the POTW or interfering with the operation of the treatment works. 5.1 Effluent Limitations and Monitoring Requirements In addition to the State and Federal regulations described in Section 2 of this Fact Sheet, EPA used data submitted by the MWRA in its 2005 permit application and subsequent permit application updates, monthly discharge monitoring reports (DMRs), WET test reports from January 2018 through December 2022, and additional data supplied by MWRA, at EPA’s request, to identify pollutants of concern. The data was used to evaluate the discharge during the effluent limitation development process (See Appendices C, E & F ) . The reasonable potential analysis to determine the need for effluent limits in the Draft Permit is in Appendix G and the results are discussed in the sections below. 5.1.1 Effluent Flow The effluent flow limit in the 2000 Permit is 436 MGD, as a dry day, 365 calendar day running average flow. This flow is based on an early facility plan. For the purpose of the 2000 Permit, a dry day is defined as a day with 0.09 inches of precipitation or less and no snow melt, provided that the precipitation on the previous day is less than 0.3 inch, and the precipitation on the day two days prior to the day in question is less than 1.0 inch, and the precipitation on the day three days prior to the day in question is less than 2.0 inches. A day with snow melt is defined as a day when there is snow on the ground and the air temperature rises above 32 degrees Fahrenheit. Flows from the CSO storage facilities are not included in the dry day calculation. In the 2000 Permit, compliance with the flow limit is determined each month by calculating the average dry day flow over the previous 365 calendar days. The once-a-month calculation includes all dry day flows that occurred during the reporting month. 106 Deltares. 2022. Massachusetts Bay Outfall Treated Effluent Discharge Plume Characteristics from the EPA- Supported Near-Field Mixing Model, Boston: Massachusetts Water Resources Authority. Report 2022-03. p. 15. https://www.mwra.com/harbor/enquad/pdf/2022-03.pdf 2023 Fact Sheet NPDES Permit No. MA0103284 Page 45 of 195 The DMR data during the review period shows that there have been no violations of the flow limit. The Draft Permit includes an effluent flow limit of 361 MGD, which is the annual average design flow of the re-sized secondary treatment facilities. 107 , 108 , 109 Because of the extent of the collection system, compliance with the flow limit is determined each month by calculating the average dry day flow over the previous 365 calendar days, (total dry day flow/total number of dry days). The once-a-month calculation shall include all dry day flows that occurred during the reporting month. This limit will apply to dry weather flows only. The definition of dry day is the same as in the 2000 Permit and is defined above. 5.1.2 Carbonaceous Biochemical Oxygen Demand (CBOD5) The CBOD5 limits in the 2000 Permit are based on secondary treatment standards pursuant to 40 CFR § 133.102(a)(4); the average monthly limit is 25 mg/L, and the average weekly limit is 40 mg/L. The 2000 Permit includes a maximum daily reporting requirement. The DMR data during the review period shows that there have been no violations of the CBOD5 concentration limits. The Draft Permit proposes the same CBOD5 concentration limits as in the 2000 Permit as there have been no changes to the secondary treatment standards. The monitoring frequency remains once per day. 5.1.3 Total Suspended Solids (TSS) The TSS limits in the 2000 Permit are based on the secondary treatment standards pursuant to 40 CFR § 133.102(b); the average monthly limit is 30 mg/L, and the weekly limit is 45 mg/L. The 2000 Permit includes a maximum daily reporting requirement. The DMR data from the review period shows that there have been no violations of TSS concentration-based limits. The Draft Permit proposes the same TSS concentration limits as in the 2000 Permit as there have been no changes to the secondary treatment standards. The monitoring frequency remains once per day. 107 Camp Dresser & McKee, Massachusetts Water Resources Authority, DP-29 Secondary Treatment Facilities, Recommended Plan for Completion of the Deer Island Facilities, 1995, pp.2-21 and 2-23. 108 LETTER. Michael J. Hornbrook, MWRA to Michele Barden, EPA. July 7, 2006. RE: Massachusetts Water Resources Authority NPDES Permit Number MA0103284, Renewal of NPDES Permit MA0103284, Design flow of Deer Island Wastewater Treatment Plant. 109 In accordance with 314 CMR 3.11(2)(a)11, in any given calendar year where the average annual flow of a permitted facility exceeds 80% of the facility’s average design flow, that facility shall submit a report to the Department describing what steps the permittee will take in order to remain in compliance with the limitations and conditions in its permit, including in particular, limitations on the amount of flow authorized to be discharged under the permit. https://www.mass.gov/doc/314-cmr-300-surface-water-discharge-permits 2023 Fact Sheet NPDES Permit No. MA0103284 Page 46 of 195 5.1.4 Eighty-Five Percent (85%) CBOD5 and TSS Removal Requirement Federal regulations at 40 CFR § 133.103(a) ( Combined Sewers ) state: “]t]reatment works subject to this part may not be capable of meeting the percent removal requirements established under 133.102(a)(3) and 133.102(b)(3), or 133.105(a) and 133.105(b)(3) during wet weather where the treatment works receive flows from combined sewers (i.e., sewers which are designed to transport both storm water and sanitary sewage). For such treatment works, the decision must be made on a case-by-case basis as to whether any attainable percentage removal level can be defined, and if so, what the level should be.” The 2000 Permit required the reporting of the influent CBOD5 and TSS in addition to the effluent on CBOD5 and TSS. After reviewing the DMR record for both influent and effluent CBOD5 and TSS, EPA has determined that the treatment plant is capable of meeting the 85 percent removal requirement for both parameters during dry weather conditions; and in fact, has been consistently achieving greater than 85% removal in all conditions. The DMR data during the review period shows that the median CBOD5 and TSS removal percentages are 95% and 95%, respectively. Thus, EPA is including this requirement in the Draft Permit to ensure that extraneous flows to the collection system are adequately controlled. The monitoring frequency is once per month. EPA similarly has included this condition in permits issued to other Massachusetts POTWs with combined sewer systems, such as Springfield, Haverhill, Lowell, Greater Lawrence, New Bedford and Lynn. The 85% removal requirement is not required during wet weather because a portion of the collection system is a combined system. Due to the inclusion of storm water from the combined portion of the collection system, influent CBOD5 loads are lower (i.e., more dilute) than those in a separate collection system. Because the influent is more dilute, it requires more highly treated effluent to get 85% reduction in load. For the purposes of this requirement, a dry day is defined as a day with 0.09 inches of precipitation or less and no snow melt, provided that the precipitation on the previous day is less than 0.3 inch, and the precipitation on the day two days prior to the day in question is less than 1.0 inch, and the precipitation on the day three days prior to the day in question is less than 2.0 inches. A day with snow melt is defined as a day when there is snow on the ground and the air temperature rises above 32 degrees Fahrenheit. Flow from the CSO storage facilities is not included in the dry day calculation. 5.1.5 pH The pH limits in the 2000 Permit are a range of 6.0 to 9.0 standard units and reflect the requirements in 40 CFR § 133.102(c). These limits are less stringent than the State WQSs for a Class SA water at 314 CMR 4.05(4)(a)(3) and were based on the potential buffering effect of the effluent in the receiving water at the time the 2000 Permit was issued. The DMR data during the review period show that there have been no violations of the pH limitations. Current State WQS for Class SA waters at 314 CMR 4.05(4)(a)3 have not changed for pH and require pH be in a range of 6.5 or greater than 8.5 standard units and not more than 0.2 standard 2023 Fact Sheet NPDES Permit No. MA0103284 Page 47 of 195 units outside the natural background range. MassDEP has developed a procedure for conducting a pH Adjustment Demonstration Project for Permittees that request an alternative pH limit in its NPDES permit. 110 For marine discharges, the demonstration project must be completed only once during a 1% occurrence spring tide, which is a tide with a maximum range of depths between high and low tides. When the requested pH limit is low (down to 6.0 S.U.), the study must be conducted when runoff conditions are greatest (during March/April or October/November) and during the last 2 hours of ebb tide (just before slack low tide). MWRA conducted a pH demonstration project on April 20, 2022, following a study plan submitted to MassDEP on March 29, 2022. After completion of the demonstration project, MWRA stated in a letter to EPA and MassDEP dated May 31, 2022, that: “[b]oth grab and composite DITP effluent samples adjusted down to a pH of 6.0 did not change the pH when mixed with receiving water samples at the established 70:1 near-field dilution factor. Even at 60% of this dilution factor, this study showed the pH of Massachusetts Bay receiving water did not change more than 0.2 standard units and would be well within the pH range of 6.5 – 8.5 for Class SA waters as prescribed in 314 CMR 4.00.” MassDEP approved this study by letter on June 17, 2022. 111 The Draft Permit includes pH effluent limit range of 6.0-8.5 standard units. Sampling frequency is once per day. Consistent with MassDEP’s approval: • MWRA shall provide ambient pH monitoring both outside the area of discharge influence and within the area of discharge influence to confirm compliance with SWQS. • Minimum sampling frequency and duration shall be monthly for a period of six month immediately following the pH limit approval or as otherwise approved by MassDEP. • Measurements of pH shall be taken using probes calibrated just prior to each use and at documented and representative locations. • Whenever feasible, sampling should be conducted during dry weather conditions (little or no antecedent precipitation). Data shall be submitted to MassDEP’s email portal on a monthly basis ( wqdata.submit@state.ma.us ). • Any and all exceedances of SWQS for pH shall be immediately reported to MassDEP via that same email portal. • Following the six-month period, MassDEP shall evaluate the submitted data to determine the need for additional monitoring and/or follow up. 5.1.6 Bacteria The fecal coliform limits in the 2000 Permit are: (1) An average weekly limit of 14,000 colonies/100 mL that is reported as a geometric mean. 110 MassDEP, undated, Procedures for a pH Demonstration Project for NPDES Permits. 111 LETTER. Lealdon Langley, MassDEP to Betsy Reilley, MWRA. June 17, 2002. RE: Massachusetts Water Resources Authority (MWRA), Deer Island Treatment Plant (DITP), NPDES Permit No. MA0103284, pH Adjustment Demonstration Project Approval. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 48 of 195 (2) A maximum daily limit of not more than 10% of individual sample collected in a given month exceeds 14,000 colonies/100ml, and not more than three (3) consecutive samples shall exceed 14,000/100 mL The effluent limits in the 2000 Permit were established using a mixing zone and compliance is required at the edge of the zone of initial dilution (ZID). The mixing zone for this discharge has an initial dilution of 70:1. Using the dilution of 70 times the applicable water quality criteria at the time of permit issuance of 200 colony forming units/100 mL; the effluent limit is 14,000 colonies/100 mL. The DMR data for the review period shows there have been no exceedances of the current fecal coliform bacteria limitations and fecal coliform counts are significantly below the limits in the 2000 Permit (See Appendix C). As previously stated, Massachusetts Bay in the vicinity of the outfall is classified as a Class SA water and designated for shellfishing in the MA WQS in accordance with 314 CMR 4.06(4). 112 The WQS at 314 CMR 4.05(4)(a) state that Class SA are “those coastal and marine waters so designated pursuant to 314 CMR 4.06; including without limitation, 314 CMR 4.06(2) and, (5), and certain qualified waters designated in 314 CMR4.06(6)(b). These waters are designated as an excellent habitat for fish, other aquatic life and wildlife, including for their reproduction, migration, growth and other critical functions, and for primary and secondary contact recreation. In certain waters, excellent habitat for fish, other aquatic life and wildlife may include, but is not limited to, seagrass. Where designated for shellfishing in at 314 CMR 4.06(6)(b), these waters shall be suitable for shellfish harvesting without depuration (Approved and Conditionally Approved Shellfish Areas). These waters shall have excellent aesthetic value.” Massachusetts Bay is listed in 314 CMR 4.06(b) Table 19 as designated for shellfishing and Massachusetts Bay in the vicinity of the DITP discharge is also designated for shellfishing as confirmed by MassDEP. 113 The receiving waters are currently classified as shellfishing waters although they are classified as “prohibited” for shellfishing by the Massachusetts Division of Marine Fisheries (MA Marine Fisheries) due to the existence of the DITP outfall. MassDEP does not consider the receiving waters as bathing beach waters as they are 9.5 miles offshore. The MA WQS at 314 CMR 4.05(4)(a)4 require: a. Waters designated for shellfishing: fecal coliform shall not exceed a geometric mean Most Probable Number (MPN) of 14 organisms per 100 ml, nor shall more than 10% of the samples exceed an MPN of 28 per 100 ml, or other values of equivalent protections based on sampling and analytical methods used by the Massachusetts Division of Marine Fisheries and approved by the National Shellfish Sanitation Program in the latest revision of the Guide For The Control of Molluscan Shellfish (more stringent regulations may apply, see 314 CMR 4.06(1)(d)(5)); 112 EMAIL. Claire Golden, MassDEP to Michele Barden, EPA. November 3, 2022. Subject: Request for Segment Number. 113 EMAIL. Claire Golden, MassDEP to Michele Barden, EPA. November 3, 2022. Subject: Request for Segment Number. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 49 of 195 b. For protection of primary contact recreation, surface waters shall meet the minimum criteria for bacteria set forth in 314 CMR 4.05(5)(f) 2. and 3. The MA WQS at 314 CMR 4.05(5)(f) require: 2. Coastal and Marine Waters. Concentrations of bacteria in Coastal and Marine Waters, subject to the reduced interval requirements set forth in 314 CMR 4.05(5)(f)3. as applicable, and except as otherwise provided in the seasonal exception set forth in 314 CMR 4.05(5)(f)4. as applicable, shall, on a year-round basis, satisfy 314 CMR 4.05(5)(f)2.a.: a. for enterococci: i. concentrations shall not exceed 35 cfu per 100 mL, calculated as the geometric mean of all samples collected within any 90-day or smaller interval; and ii. no more than 10% of all such samples shall exceed 130 cfu per 100 mL (the statistical threshold value). b. The preceding requirements are summarized in the following table: Bacterial Indicator Bacterial Criteria for Coastal and Marine Waters (cfu/100 mL)* Geometric Mean* Statistical Threshold Value* enterococci ≤35 ≤130 *The geometric mean for this indicator shall not be exceeded in any 90-day or smaller interval. No more than 10% of all samples collected within that interval shall exceed the statistical threshold value for this indicator. 3. Reduced Interval Requirements. The geometric mean and statistical threshold value used for calculating the minimum criteria for bacteria set forth in 314 CMR 4.05(5)(f)1. and 2., shall be calculated and assessed, respectively, over a 30-day or smaller interval in lieu of any otherwise applicable longer interval, if either of the conditions set forth in 314 CMR 4.05(5)(f)3.a.i. or ii. is met. a. Conditions which require a reduced interval: i. criteria are being applied to waters adjacent to any public or semi-public beach, at a location used for bathing and swimming purposes, and for the dates of operation of any such beach as posted or as otherwise established by the operator pursuant to 105 CMR 445.020: Operation; or ii. criteria are being applied to segments impacted by CSO-, B(CSO)-, SB(CSO)-, or POTW-discharges. b. Massachusetts Department of Public Health definitions: the terms "public bathing beach", "semi-public bathing beach" and "operator" as used in paragraph 314 CMR 4.05(5)(f)3.a.i. shall have the meanings as defined in 105 CMR 445.010: Public Bathing Beach; Semi-Public Bathing Beach; and Operator. (Standards and procedures for bathing water closures have been established by the Massachusetts Department of Public Health, at 2023 Fact Sheet NPDES Permit No. MA0103284 Page 50 of 195 105 CMR 445.000: Minimum Standards for Bathing Beaches (State Sanitary Code, Chapter VII).) 4. Seasonal Exception. The year-round minimum criteria for bacteria set forth in 314 CMR 4.05(5)(f)1. and 2., as subject to the reduced interval requirements set forth in 314 CMR 4.05(5)(f)3., as applicable, may be applied on a seasonal basis in lieu of a year- round basis upon MassDEP's determination that, because of a reduction in primary contact recreation during a specified period of time, such criteria are not needed to be protective. Bases for such determinations may include identification of periods when frequency of use is reduced due to cold weather (typically, from November through March); and/or consideration of other relevant and appropriate factors. Any such determinations shall be documented in writing (e.g., by the relevant provisions of surface water discharge permits issued pursuant to 314 CMR 3.00: Surface Water Discharge Permit Program) and made publicly available for review (e.g., through MassDEP's Surface Water Discharge Permit webpage). 5. Additional Bacteria Requirements. For additional bacteria requirements other than for primary contact recreation, see 314 CMR 4.05(3) and (4). The design of the Facility’s disinfection system and dechlorination system is unique to the DITP Facility. A portion of the 9.5 mile outfall tunnel is designed to be used as a chlorine contact chamber so that the Facility is able to maintain the minimum chlorine contact time of 15 minutes during peak plant flows of 1270 MGD. “The total disinfection time includes the time it takes for wastewater to flow through the two disinfection contact basins, the effluent launders, the outfall raceway, the outfall drop shaft and the first 850 feet of the 22.5 foot diameter outfall tunnel.” 114 In order to collect a representative sample of disinfected effluent, samples for fecal coliform (and Enterococcus, although not required by the 2000 Permit) analysis are collected at the end of the chlorine disinfection basin. The samples are then held for the amount of time that the effluent takes to reach the dechlorination point. The hold time is calculated using PI Process Book 115 (OSIsoft, LLC; San Leandro, CA) software available to both plant and laboratory staff or can also be calculated manually using the plant effluent flow rate. After that time has elapsed, the sample is manually dechlorinated. At that point in time, the sample has undergone the same amount of contact time with the disinfectant as the actual effluent. 114 EMAIL. Betsy Reilley, MWRA to Michele Barden, EPA. January 28, 2022. RE: Effluent Bacteria Sampling Attachment: 20220128_sampleloop.docx. 115 https://techsupport.osisoft.com/Products/Visualization/PI-ProcessBook/Overview 2023 Fact Sheet NPDES Permit No. MA0103284 Page 51 of 195 MWRA has also collected a long-term record of ambient bacteria monitoring data and data continues to be collected at 11 stations in Massachusetts Bay 116 , 117 , 118 (See Figure 13 ) to observe the presence, if any, of pathogen indicator bacteria in the waters around the outfall. MWRA has monitored fecal coliform and Enterococcus bacteria in Massachusetts Bay since 1999 (includes pre-discharge baseline data). The current ambient bacteria monitoring program was formalized under a Memorandum of Understanding between MWRA, the Massachusetts Division of Marine Fisheries (MA Marine Fisheries) and the US Food and Drug Administration (FDA) 119 and implementation of the MOU is required by the 2000 Permit. 120 The monitoring program consists of routine monthly surveys and adverse condition surveys which occur as needed. The adverse condition surveys are conducted in response to events at the treatment facility such as a chlorination system failure or a bypass of the secondary treatment that could result in an increased discharge of bacteria. MWRA has reported that “the vast majority of samples are non- detects, having bacteria levels below detectability by the methods used. Annual averages are much lower than water quality standards for shellfishing (fecal coliform) and swimming ( Enterococcus ).” 121 MWRA sampling stations N20 and N16 are located at the ends of the outfall diffuser. Station N21 is located immediately above the diffuser, but sampling at this location did not begin until 2018. Stations N02, N04, N09 and N07 are in the outfall nearfield. Stations F18, F24, F25, F14 and F13 are near the coastline and between the outfall and the shoreward active shellfishing beds. At all stations, samples are collected at a depth of 1 meter below the surface during all surveys. When the water column is stratified (typically May-October), a sample is also collected below the pycnocline, at 2 meters above the seafloor. 122 EPA reviewed ambient fecal coliform and Enterococci data collected between January 2018- December 2022, the review period for this permit reissuance. 123 These samples include both routine and adverse conditions sampling events and surface and sub-pycnocline samples. All the 116 Rex, Andrea, MWRA. 2011. Ambient water quality monitoring of the Massachusetts Water Resources Authority effluent outfall: indicator bacteria in Massachusetts Bay 1999-2011, https://www.mwra.com/harbor/enquad/pdf/2011-20.pdf 117 Codiga, Daniel L., Andrea C. Rex and Kelly Coughlin, MWRA. 2016. Indicator Bacteria in Massachusetts Bay 1999-2014: Water quality monitoring in receiving waters of the Massachusetts Water Resources Authority outfall, https://www.mwra.com/harbor/enquad/pdf/2016-01.pdf 118 Wu, David, MWRA. 2016. Seasonality of Enterococcus levels in Deer Island effluent https://www.mwra.com/harbor/enquad/pdf/2016-07.pdf 119 See Appendix of Rex, Andrea, MWRA. 2011. Ambient water quality monitoring of the Massachusetts Water Resources Authority effluent outfall: indicator bacteria in Massachusetts Bay 1999-2011, https://www.mwra.com/harbor/enquad/pdf/2011-20.pdf 120 EPA Region 1. 2000. NPDES Permit Number MA0103284, Footnote 15. 121 Codiga, Daniel L., Andrea C. Rex and Kelly Coughlin, MWRA. 2016. Indicator Bacteria in Massachusetts Bay 1999-2014: Water quality monitoring in receiving waters of the Massachusetts Water Resources Authority outfall, p. 1 122 Codiga, Daniel L., Andrea C. Rex and Kelly Coughlin, MWRA. 2016. Indicator Bacteria in Massachusetts Bay 1999-2014: Water quality monitoring in receiving waters of the Massachusetts Water Resources Authority outfall, p. 7 123 For a review of prior data, please see MWRA reports: Andrea Rex. 2011. Ambient water quality monitoring of the Massachusetts Water Resources Authority outfall: indicator bacteria in Massachusetts Bay 1999-2011 and the updated report, Codiga et al. 2016. Indicator bacteria in Massachusetts Bay 1999-2014: Water quality monitoring in receiving waters of the Massachusetts Water Resources Authority outfall. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 52 of 195 ambient fecal coliform samples collected during the review period meet the applicable WQS. The highest values were found at farfield stations, F18 and F14. These stations are more likely to be influenced by coastal sources (i.e., CSO outfalls and stormwater) rather than the DITP outfall. The high value at F18 was 122 Enterococci per 100 mL and was a surface sample collected 10/8/2019. The other high value was 108 Enterococci per 100 mL and was a sub-pycnocline sample collected on 7/5/2017. The surface sample collected at the same time and station was non-detect. If evaluated as a geometric mean of all samples taken within the six months prior to and including the high value, the WQS would still be met in both instances. EPA finds that inclusion of effluent limits for fecal coliform bacteria and Enterococcus, that account for the treatment occuring in the outfall tunnel and the continuation of the ambient bacteria monitoring program, will ensure that WQSs in Massachusetts Bay continue to be met. Compared to other Massachusetts facilities, the DITP outfall, T01, is unique. First, the diffuser is located 8-9.5 miles offshore from the Deer Island Treatment Plant and at a depth of 110 feet so that incidental contact with the mixing effluent is unanticipated. Second, the diffuser was designed to cause rapid and thorough mixing with the ambient waters. The initial dilution for the discharge is estimated to be 70:1 in the worst-case scenario, though it appears, from the ambient monitoring data, that criteria are being consistently met within very close proximity of the diffuser. Finally, the continuation of the ambient bacteria monitoring, will provide an additional layer of accountability to ensure that the disinfection system continues to operate as intended. The Enterococcus limits are based on recreational criteria and are applicable on a seasonal basis from April 1 through October 31. 124 Fecal coliform limits apply year-round. In addition to the effluent limits for bacteria, MWRA is required to update the existing Memorandum of Understanding (MOU) between the MWRA, the Massachusetts Division of Marine Fisheries (MA Marine Fisheries) and the US Food and Drug Administration (FDA) 125 and implementation of the MOU and the attached monitoring plan is required by the Draft Permit (See Footnote 11). The updated Plan shall follow the same procedures and locations as documented in Attachments A & B of the MOU with the addition of station N21, which is located over the mid-point of the diffuser. The updated MOU and monitoring plan shall be submitted to the MA Marine Fisheries and the FDA for review and signature. The signed MOU and attached updated monitoring plan shall be submitted to EPA and MassDEP within 12 months of the effective permit. Enterococcus should also continue to be monitored seasonally (April 1 through October 31) along with fecal coliform to ensure that MA WQS for bacteria are met. The Permittee shall report the results of the monthly ambient fecal coliform and Enterococcus monitoring at station N21 on their monthly DMRs. If the Bay is stratified at the time of sampling, the Permittee shall sample at the surface and below the pycnocline. If the Bay is not stratified at the time of sampling, the Permittee should enter a NODI code = 9 for the below pycnocline DMR report line. The ambient fecal coliform bacteria and Enterococcus monitoring 124 LETTER. Lealdon Langley, MassDEP to Lynne Jennings, EPA. May 23, 2023. RE: Massachusetts Water Resources Authority Deer Island Treatment Plant, NPDES No. MA0103284, Concurrence with EPA Approach to Determination of Bacteria Limits in Draft Permit. 125 See Appendix of Rex, Andrea, MWRA. 2011. Ambient water quality monitoring of the Massachusetts Water Resources Authority effluent outfall: indicator bacteria in Massachusetts Bay 1999-2011, https://www.mwra.com/harbor/enquad/pdf/2011-20.pdf 2023 Fact Sheet NPDES Permit No. MA0103284 Page 53 of 195 results at the other sampling locations shall be submitted as an attachment to the monthly DMR. If an adverse-conditions monitoring event occurs, MWRA shall provide a letter summarizing the event and the sampling data collected as an attachment to the monthly DMR. Any updates or changes in the Ambient Bacteria Monitoring Plan shall be submitted to MA Marine Fisheries and the FDA for review. The signed MOU and plan shall be submitted to EPA in the monthly DMR following signing by Marine Fisheries and the FDA. The MWRA reports and ambient data support the conclusion that water quality even in the immediate vicinity of the outfall exhibits bacteria levels that meet WQSs for existing and designated uses. As calculated below, the proposed effluent limitations for fecal coliform are a monthly geometric mean, Most Probable Number (MPN) of 980 organisms/100 mL and a maximum daily limit of 1960 organisms/100 mL. This is more stringent than the fecal coliform bacteria limits in the 2000 Permit. The proposed effluent limitations for Enterococcus are a monthly geometric mean of 2450 cfu/100 mL and a maximum daily limit of 9100 cfu/100 mL and applicable on a seasonal basis, April 1 through October 31. The sampling frequency for fecal coliform and Enterococcus is three (3) times per day, which is the same as the 2000 Permit. Fecal Coliform Bacteria: 14 organisms/100 mL * 70 (multiplying factor) = 980 organisms/100 mL 28 organisms/100 mL * 70 (multiplying factor) = 1960 organisms/100 mL Enterococcus: 35 cfu/100 mL * 70 (multiplying factor) = 2450 cfu/100 mL 130 cfu/100 mL * 70 (multiplying factor) = 9100 cfu/100 mL Effluent bacteria samples shall be collected at the end of the disinfection basin at the DITP. The holding time shall be calculated using MWRA’s current procedure using PI Process Book or an accepted manual method. The holding time and supporting calculations shall be submitted as an attachment to the monthly DMRs (See Footnote 8 of the Draft Permit). The Draft Permit also maintains the requirement that if the Massachusetts Division of Marine Fisheries and/or the U.S. Food and Drug Administration determine in writing that the fecal coliform bacteria limits are inadequate to ensure protection of shellfish resources, and EPA concurs in writing, then the Permittee shall meet the applicable Water Quality Standards at end- of-pipe (See Footnote 11 of the Draft Permit): 2023 Fact Sheet NPDES Permit No. MA0103284 Page 54 of 195 Table 11: Alternate effluent bacteria limits if MA Marine Fisheries and/or USFDA deem necessary. Effluent Limitation Monitoring Requirements Effluent Characteristic Average monthly Average Weekly Maximum Daily Measurement Frequency Sample Type Fecal Coliform Bacteria, (organisms/100 mL) 14 --- 28 3/Day Grab 5.1.7 Total Residual Chlorine The Permittee uses chlorine for disinfection of the effluent. The 2000 Permit includes effluent limitations for total residual chlorine (TRC) of 456 μg/L (monthly average) and 631 μg/L (maximum daily). There have been no violations of the TRC limitations during the review period. The applicable total residual chlorine criteria are found in the MA WQS at 314 CMR 4.06, Table 29. The saltwater instream criteria for chlorine are 7.5 μg/L (chronic) and 13 μg/L (acute). The Draft Permit maintains the TRC limitations from the 2000 Permit. Because it is impossible to collect a sample at the end of the outfall tunnel where the diffuser discharges into Massachusetts Bay, MWRA constructed a simulation loop that simulates the plant’s chlorination and dechlorination process. “In order to simulate the disinfectant contact time from the sample point to the point of dechlorination 850 feet within the outfall tunnel, a portion of the chlorinated wastewater from the plant’s disinfection contact basins is continuously pumped, using a variable speed hose pump paced with the total plant flow, through the pipe loop sampling system, consisting of 1550 feet of 2” diameter PVC pipe. The flow is then dechlorinated with sodium bisulfite, just as occurs for the main plant effluent, at a rate that is paced with the concurrent total plant and sodium bisulfite chemical feed flows. This mimics the dechlorination process in the main plant. Samples collected downstream from this simulated dechlorination process are representative of the effluent released in the bay and are expected to contain negligible chlorine residual. Sampler(s) designed to collect flow proportional composite samples and instantaneous grab samples are positioned at the end of this pipe loop sampling system. Total chlorine residual tests are collected at this location and analyzed in the field immediately.” 126 Total Residual Chlorine Limitations were calculated as follows: Chronic criteria * dilution factor = Chronic limit 7.5 μg/L * 70 = 525 μg/L (average monthly) Acute criteria * dilution factor = Acute limit 126 EMAIL. Betsy Reilley, MWRA to Michele Barden, EPA. January 28, 2022. RE: Effluent Bacteria Sampling Attachment: 20220128_sampleloop.docx. 2023 Fact Sheet Page 55 of 195 NPDES Permit No. MA0103284 11 μg/L * 70 = 770 μg/L (maximum daily) Based on anti-backsliding requirements described in Section 2.6 of this Fact Sheet, EPA has maintained the water quality based effluent limits from the previous permit of 456 μg/L as a monthly average limit and 631 μg/L as a maximum daily limit. The monitoring frequency is 3 times per day. For any pollutant with an existing WQBEL, EPA notes that the analysis described in 40 CFR § 122.44(d)(l)(i) has already been conducted in a previous permitting action demonstrating that there is reasonable potential to cause or contribute to an excursion of WQSs. Given that the permit already contains a WQBEL based on the prior analysis and the pollutant continues to be discharged from the Facility, EPA has determined that there is still reasonable potential for the discharge of this pollutant to cause or contribute to an excursion of WQSs. Therefore, the WQBEL will be carried forward unless specific conditions exist to justify relaxation in accordance with CWA §§ 402(o) or 303(d)(4). 5.1.8 Oil and Grease The 2000 Permit includes narrative language that “the effluent shall not cause or contribute to an exceedance of the water quality standard which requires that the receiving water shall be free from oil and grease and petrochemicals.” EPA interprets this narrative language to represent the absence of oil and grease in Massachusetts Bay. In this situation, EPA is establishing the oil and grease effluent limit as non-detect to reflect the absence of oil and grease in the receiving waters and to comply with the state’s water quality standards. Because the limit is below the analytical detection limit for this pollutant, the Region is following guidance set forth in Technical Support Document for Water Quality-based Toxics Control, March 1991, EPA/505/2-90-001, pages 111- 112 which recommends, "... that the compliance level be defined in the permit as the minimum level (ML).” Data submitted by MWRA at EPA’s request indicates a maximum effluent value of 39 mg/L for oil and grease (See Appendix F) using EPA method 1664B. The oil and grease ML is 5 mg/L using EPA Method 1664 (Revisions A and B) where the ML is the lowest point on the curve used to calibrate the test equipment for the pollutant of concern. If EPA approves a method under 40 CFR Part 136 for either, oil and/or grease that has a ML lower than 5 mg/l, the Permittee shall be required to use the improved method. The Draft Permit includes an effluent limit of non-detect as the narrative criteria is “free from oil and grease and petrochemicals” at 314 CMR 4.05(4)(a)7. The monitoring frequency is once per day. 5.1.9 Ammonia The 2000 Permit does not include ammonia limits but does require monthly monitoring and reporting of effluent ammonia concentrations. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 56 of 195 Ambient data, taken outside the zone of influence of the MWRA outfall in the Massachusetts Bay near site N18, is presented in Appendix E. The median concentration for the warm weather period (April 1 through October 31) is 0.026 mg/L and for the cold weather period (November 1 through March 31) is 0.028 mg/L. The ammonia criteria in EPA’s National Recommended Water Quality Criteria, 2002 (EPA 822- R-02-047) document are included by reference in the Massachusetts WQS ( See 314 CMR 4.05(5)(e)). The marine water quality criteria are dependent on pH and temperature. In determining whether the discharge has the reasonable potential to cause or contribute to excursions above the instream water quality criteria for ammonia, EPA used the mass balance equation presented in Appendix G for both warm and cold weather conditions to project the ammonia concentration in the vicinity of the discharge near N18. When there is reasonable potential, this mass balance equation is also used to determine the effluent limit(s) that would be required in the Draft Permit. To determine the applicable ammonia criteria, EPA used the 95 th percentile temperature data from the MWRA in the vicinity of the discharge to calculate a warm weather maximum temperature of 19.95° C and a cold weather maximum temperature of 12.75° C. EPA took the 95 th percentile due to the extensive data record available. EPA used the ambient pH monitoring shown in Appendix E, which indicates that the median pH is 8.2 S.U. Based on the information and assumptions described above, Appendix G presents the applicable ammonia criteria, the details of the mass balance equation, the reasonable potential determination, and, if necessary, the limits required in the Draft Permit. As shown, there is no reasonable potential; therefore, the Draft Permit does not require ammonia limits. However, effluent ammonia shall be reported on monthly DMRs. Ambient monitoring for ammonia shall also be required as part of the quarterly WET tests and reported on the DMRs. 5.1.10 Nutrients Nutrients are compounds containing nitrogen and phosphorus. Although nitrogen and phosphorus are essential for plant growth, high concentrations of these nutrients can cause eutrophication, a condition in which aquatic plant and algal growth is excessive. Plant and algae respiration and decomposition reduces dissolved oxygen in the water, creating poor habitat for fish and other aquatic animals. Recent studies provide evidence that both phosphorus and nitrogen can play a role in the eutrophication of certain ecosystems. However, typically phosphorus is the limiting nutrient triggering eutrophication in freshwater ecosystems and nitrogen is the limiting nutrient in marine or estuarine ecosystems. Thus, for this receiving water, and this permit, nitrogen is the nutrient of concern evaluated for effluent limitations in the discussion below. 5.1.10.1 Background The DITP discharges into Massachusetts Bay which is an embayment in the western Gulf of Maine. At the time of the last permit issuance, there were conflicting thoughts about how the 2023 Fact Sheet NPDES Permit No. MA0103284 Page 57 of 195 relocation of the discharge might affect the Bay. One theory was that relocating the outfall would result in cleaning up Boston Harbor at the expense of polluting Massachusetts Bay. The other theory was that moving the discharge from Boston Harbor to Massachusetts Bay would not have a significant effect on Massachusetts Bay as nitrogen from the existing discharge to Boston Harbor was already rapidly flushed into Massachusetts Bay. 127 To address the uncertainties and assure that WQSs are met, the 2000 Permit requires monthly monitoring and reporting of the effluent concentrations for total Kjeldahl nitrogen (TKN), total nitrate, and total nitrite (See Appendix C) and additional requirements. The additional requirements were based on the conservation recommendations included in the 1993 Biological Opinion (BO) 128 authored by National Marine Fisheries Service (NMFS) for the Section 7 Consultation under the Endangered Species Act. In response, the 2000 Permit requires the Permittee to develop and implement an ambient monitoring plan 129 and contingency plan. 130 Additionally, the Permittee is required to quantify ambient nitrogen, maintain a comprehensive technical survey of effective treatment technologies for nitrogen removal, and implement the Contingency Plan which includes caution and warning levels for total nitrogen, dissolved oxygen (DO), chlorophyll, and nuisance/noxious algae (See Table 12 ) among other parameters. The Contingency Plan and its thresholds were developed to identify any adverse impacts and determine if environmental conditions are changing or may in the future. The thresholds were established with consideration of MA WQSs, applicable at the time, baseline/background levels and expert opinion from the Outfall Monitoring Task Force (OMTF) 131 and later the Outfall Monitoring Science Advisory Panel (OMSAP). 132 Table 12: Contingency Plan Thresholds related to nitrogen and its potential impacts Parameter Type/Location Parameter Caution Level Warning Level Baseline/ Background Effluent Total Nitrogen 12,500 metric tons/year 133 14,000 metric tons/year Water Column nearfield bottom; Stellwagen, bottom Dissolved Oxygen, concentration 6.5 mg/L for any survey during stratification (Jun- Oct) unless background 6.0 mg/L for any survey during stratification (Jun-Oct) Nearfield: 6.05 mg/L 127 EPA, 1998, MWRA Fact Sheet, p. 20. 128 NMFS, 1993, Endangered Species Act – Section 7 Consultation, Biological Opinion on the Boston Harbor Project: Issuance of a National Pollutant Discharge Elimination System (NPDES) Permit for the Massachusetts Water Resources Authority (MWRA) Outfall, Northeast Region Office, NMFS, September 8, 1993. 129 MWRA, 1997, Massachusetts Water Resources Authority effluent outfall monitoring plan: Phase II Post- discharge monitoring. https://www3.epa.gov/region1/npdes/mwra/pdf/n.pdf 130 MWRA, 2001, Massachusetts Water Resources Authority Contingency Plan, Revision 1. https://www.mwra.com/harbor/enquad/pdf/2001-ms-71.pdf 131 The OMTF was established by the Massachusetts Executive Office of Environmental Affairs to oversee the development and implementation of the Outfall Monitoring Plan which was a predecessor to the Ambient Monitoring Plan required by the 2000 Permit. 132 The OMSAP is a scientific and technical advisory panel to advise EPA and MassDEP on all scientific and technical matters related to the DITP outfall and the impacts of the discharge on the receiving waters. 133 Based on prediction in EPA. 1988. Boston Harbor Wastewater Conveyance System: Final Supplemental Environmental Impact Statement. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 58 of 195 Parameter Type/Location Parameter Caution Level Warning Level Baseline/ Background conditions are lower 134 unless background conditions are lower Stellwagen Basin: 6.23 mg/L Water Column nearfield bottom; Stellwagen, bottom Dissolved Oxygen saturation <80% saturation for any survey during stratification unless background conditions are lower <75% saturation for any survey during stratification unless background conditions are lower Nearfield: 65.3% Stellwagen Basin: 67.2% Water Column nearfield bottom Oxygen Depletion Rate 1.5 x baseline (>0.037) 2 x baseline (>0.049) 0.024 Water Column nearfield Chlorophyll (nearfield mean, mg m -2 ) 1.5 x baseline annual mean 2 x baseline annual mean Annual: >108 mg m -2 Annual: >144 mg m -2 72 mg m -2 Chlorophyll-a 95 th percentile of baseline seasonal mean Winter/Spring: >199 --- 50 Summer: >89 --- 51 Autumn: >239 --- 90 Water Column nearfield Nuisance algae (except Alexandrium ) 95 th percentile of baseline seasonal mean Pseudo-nitzschia pungens (nearfield mean, cells L -1 ) Winter/Spring: >17,900 cells L -1 --- 6,735 cells L -1 Summer: >43,100 cells L -1 --- 14,635 cells L - 1 Autumn: >27,500 cells L -1 --- 10,500 cells L - 1 Phaeocyctis pouchetti Winter/spring: >2,860,000 cells L -1 --- 622,000 cells L -1 Summer: >357 cells L -1 --- 79 cells L -1 Autumn: >2,960 cells L -1 --- 370 cells L -1 Water Column nearfield Alexandrium tamarense, later changed . 100 cells L 135 Alexandrium catenella Any nearfield sample >100 cells L -1 --- 163 cells L -1 (Baseline max) 134 LETTER. Michael J. Hornbrook, MWRA to Glenn Haas, MassDEP and Linda Murphy, EPA Region 1, November 15, 2001. Re: Massachusetts Water Resources Authority, Permit Number MA0103284, Proposed Changes to Contingency Plan: Dissolved Oxygen and Alexandrium thresholds. https://www.mwra.com/harbor/pdf/20011115_cpmod.pdf 135 LETTER. Michael J. Hornbrook, MWRA to Glenn Haas, MassDEP and Linda Murphy, EPA Region 1, November 15, 2001. Re: Massachusetts Water Resources Authority, Permit Number MA0103284, Proposed Changes to Contingency Plan: Dissolved Oxygen and Alexandrium thresholds. https://www.mwra.com/harbor/pdf/20011115_cpmod.pdf 2023 Fact Sheet NPDES Permit No. MA0103284 Page 59 of 195 Parameter Type/Location Parameter Caution Level Warning Level Baseline/ Background (nearfield mean, cells L -1 ) Water Column nearfield Zooplankton Water Column farfield PSP extent 4 New incidence Sediments, nearfield Redox potential discontinuity 0.5 x baseline Ecological Setting: Massachusetts Bay Massachusetts Bay is a partially enclosed embayment that flows into the Gulf of Maine to the east. It is a coastal water as it lies between the mean highwater mark of the coastal baseline and the shelf break, as defined in EPA’s Nutrient Criteria-Estuarine and Coastal Waters. 136 The Bay is approximately 62 miles long and 31 miles wide and has an average water depth of 115 feet. 137 The physical, chemical, and biological properties of Massachusetts Bay vary due to seasonal cycling. Stellwagen Bank is an underwater plateau that borders the Bay to the east and is only 65 feet below the water surface therefore partially enclosing the Bay. 138 Stellwagen Bank is a designated National Marine Sanctuary established on November 4, 1992. 139 There is a weak but persistent current that flows counterclockwise through the Massachusetts and Cape Cod Bays (See Figure 14). This current flows southwesterly past Cape Ann, and then flows south along the eastern coast of Massachusetts, flowing out of the Bay north of Race Point on Cape Cod. 140 In the late spring and summer, Cape Cod Bay can become isolated from this larger circulation. 141 The larger scale current is responsible for the far-field movement of the diluted effluent. Massachusetts Bay experiences a seasonal cycle of stratification. Stratification is driven in early spring (typically April) by salinity variations caused by freshwater inputs from the rivers of the Gulf of Maine including the Merrimack, Androscoggin, Kennebec, and Penobscot Rivers. 142 136 EPA. 2001. Nutrient Criteria Technical Guidance Manual-Estuarine and Coastal Marine Waters. [EPA-822-B- 01-003], p. 1-5. https://www.epa.gov/sites/default/files/2018-10/documents/nutrient-criteria-manual-estuarine- coastal.pdf 137 Signell, R. P., Jenter, H. L., & Blumberg, A. F. (1996). Circulation and effluent dilution modeling in Massachusetts Bay: Model Implementation, verification and results. Open-File Report . https://doi.org/10.3133/ofr9615 138 Signell, R. P., Jenter, H. L., & Blumberg, A. F. (1996). Circulation and effluent dilution modeling in Massachusetts Bay: Model Implementation, verification and results. Open-File Report . https://doi.org/10.3133/ofr9615 139 https://stellwagen.noaa.gov/about/ 140 Rockwell Geyer, W., Gardner, G. B., Brown, W. S., Irish, J., Butman, B., Loder, T., & Signall, R. 1992. Physical Oceanographic Investigation of Massachusetts and Cape Cod Bays. Massachusetts Bays Program. p. 1. https://archives.lib.state.ma.us/bitstream/handle/2452/49977/ocm36241802.pdf?sequence=1&isAllowed=y 141 MWRA. 2003. Briefing for OMSAP Workshop on Ambient Monitoring Revisions, June 18-19, 2003. Boston: Massachusetts Water Resources Authority. Report 2003-ms-085. p.4.2 https://www.mwra.com/harbor/enquad/pdf/2003-ms-85.pdf 142 W.R. Geyer, R.P. Signell , D.A. Fong , J. Wang , D.M. Anderson , B.A. Keafer. 2004. The Freshwater Transport 2023 Fact Sheet NPDES Permit No. MA0103284 Page 60 of 195 Discharges from the Charles River as well as the MWRA outfall make up only a small percent of the total freshwater inputs to the Bay. 143 As surface water temperatures warm in May and June, the stratification of the Bay intensifies and becomes driven by the temperature differences between the warmer surface waters and colder bottom waters. Typically, Massachusetts Bay remains stratified until October/November when surface water temperatures begin to cool, and winds increase causing the water column to mix. The water column is well mixed in the winter months. Tides in the Bay are semidiurnal (every 12.4 hours). Because they are semidiurnal, they play a negligible role in the horizontal transport of materials as there is no net transport (i.e., they move back and forth). The tidal oscillations, however, can have an impact on vertical mixing which is an important factor in the diffusion of material. 144 Southwesterly winds in the summer can cause upwelling of cold, dense water while northeasterly winds in the fall and winter can cause strong downwelling and assist in the vertical mixing of stratified layers. 145 Stronger and short-lived currents are driven by weather and tidal activity. 146 Residence time for surface water in the Bay is on average 20 to 45 days; however, residence time for water below the pycnocline can be upwards of 300 days. 147 In general, the nutrient loading in the Bay follows the same seasonal patterns as the stratification cycle with surface level nutrients increasing in the spring due to nutrient-laden, freshwater inputs and again in the fall as nutrient levels increase as stratification ends and nutrients become re- mixed throughout the water column. These increases in nutrients contribute to phytoplankton blooms that primarily occur in early spring and again in the fall. During April through October, when the Bay is stratified, nutrient levels in surface waters are diminished as phytoplankton deplete available nutrients and dissolved oxygen. 148 In the fall, mixing events (such as increasing winds and northeasterly storms) end the stratification and the water column is replenished with and Dynamics of the Western Maine Coastal Current. Continental Shelf Research ; 24 (2004) 1339-1357. https://www.whoi.edu/fileserver.do?id=36085&pt=2&p=28251 143 Rockwell Geyer, W., Gardner, G. B., Brown, W. S., Irish, J., Butman, B., Loder, T., & Signall, R. 1992. Physical Oceanographic Investigation of Massachusetts and Cape Cod Bays. Massachusetts Bays Program. p. 2. https://archives.lib.state.ma.us/bitstream/handle/2452/49977/ocm36241802.pdf?sequence=1&isAllowed=y 144 J.D. Irish, & R.P. Signell. 1992. Tides of Massachusetts and Cape Cod Bays. p. 44 https://doi.org/10.1575/1912/857 145 Rockwell Geyer, W., Gardner, G. B., Brown, W. S., Irish, J., Butman, B., Loder, T., & Signall, R. 1992. Physical Oceanographic Investigation of Massachusetts and Cape Cod Bays. Massachusetts Bays Program. p. 3. https://archives.lib.state.ma.us/bitstream/handle/2452/49977/ocm36241802.pdf?sequence=1&isAllowed=y 146 MWRA. 2019. Ambient Monitoring Plan and Contingency Plan for the Massachusetts Bay Outfall: Monitoring Questions Status and 2000-2018 Threshold Test Results. p. 7. 147 Signell, R. P., Jenter, H. L., & Blumberg, A. F. (1996). Circulation and effluent dilution modeling in Massachusetts Bay: Model Implementation, verification and results. Open-File Report . https://doi.org/10.3133/ofr9615 148 Rockwell Geyer, W., Gardner, G. B., Brown, W. S., Irish, J., Butman, B., Loder, T., & Signall, R. 1992. Physical Oceanographic Investigation of Massachusetts and Cape Cod Bays. Massachusetts Bays Program. p. 1. https://archives.lib.state.ma.us/bitstream/handle/2452/49977/ocm36241802.pdf?sequence=1&isAllowed=y MWRA. 2003. Briefing for OMSAP workshop on ambient monitoring revisions, June 18-19, 2003. Boston: Massachusetts Water Resources Authority. Report 2003-ms-085. P.4.2 https://www.mwra.com/harbor/enquad/pdf/2003-ms-85.pdf 2023 Fact Sheet NPDES Permit No. MA0103284 Page 61 of 195 nutrients previously trapped below the pycnocline which can then trigger fall blooms. Zooplankton blooms tend to follow within several weeks of a phytoplankton bloom. Pre-discharge modeling estimated that oceanic inputs from the Gulf of Maine contribute 92% of the total nitrogen entering the Bay, with MWRA effluent contributing 3% and other sources (mostly atmospheric and riverine) contributing 5%. 149 Modeling was most recently updated in 2020 using the overall mass balance of nitrogen for 2016. The percentages have changed slightly with 93% of inflows from the Gulf of Maine and 7% from the DITP and negligible contributions from rivers; however, this updated model did not include inputs from CSOs or non-point sources. 150 Coastal Waters Generally; Effect of Nutrients on Coastal Water Quality The basic cause of nutrient problems in coastal waters is the enrichment of freshwater with nitrogen (N) and phosphorus (P) on its way to the sea and by direct inputs within tidal systems. EPA defines nutrient over-enrichment as the anthropogenic addition of nutrients, in addition to any natural processes, causing adverse effects or impairments to beneficial uses of a waterbody. 151 Eutrophication is an aspect of nutrient overenrichment and is defined as an increase in the rate of supply of organic matter to a waterbody. Increased nutrient inputs promote a progression of symptoms beginning with excessive growth of phytoplankton and macroalgae to the point where grazers cannot control growth. Phytoplankton are microscopic algae growing in the water column and their biomass is measured by chlorophyll-a concentrations. Macroalgae are large algae, commonly referred to as “seaweed.” The primary symptoms of nutrient overenrichment include an increase in the rate of organic matter supply, changes in algal dominance, and loss of water clarity which are followed by one or more secondary symptoms such as loss of submerged aquatic vegetation, nuisance/toxic algal blooms and low dissolved oxygen. In U.S. coastal waters, nutrient overenrichment is a common thread that ties together a diverse suite of coastal problems such as harmful algal blooms, fish kills, some marine mammal deaths, outbreaks of shellfish poisonings, loss of seagrass and bottom shellfish habitats, coral reef destruction, and hypoxia and anoxia. 152 Figure 15 shows the characteristic progression of nutrient impacts on a waterbody. 149 HydroQual. 2000. Bays Eutrophication Model (BEM): modeling analysis for the period 1992-1994. Boston: Massachusetts Water Resources Authority. Report ENQUAD 2000-02. S. 6-2 https://www.mwra.com/harbor/enquad/pdf/2000-02.pdf 150 Required by the 2000 Permit, the Bay Eutrophication Model is a three-dimensional hydrodynamic water quality model developed in 1995 by HydroQual and the USGS and most recently updated in 2020 for the purpose of predicting conditions caused by nutrient loading and in order to support decisions about the need for nutrient limits and the appropriate level of any such limit for the discharge. An overview of the model can be found here: https://www.mwra.com/harbor/enquad/pdf/2021-02.pdf 151 Bricker, S., B. Longstaff, W. Dennison, A. Jones, K. Boicourt, C. Wicks, and J. Woerner. 2007. Effects of Nutrient Enrichment In the Nation’s Estuaries: A Decade of Change. NOAA Technical Memorandum NOS NCCOS Coastal Ocean Program Decision Analysis Series 26. Silver Spring, MD. 328 pp. https://repository.library.noaa.gov/view/noaa/25526 152 Bricker, S., B. Longstaff, W. Dennison, A. Jones, K. Boicourt, C. Wicks, and J. Woerner. 2007. Effects of Nutrient Enrichment In the Nation’s Estuaries: A Decade of Change. NOAA Technical Memorandum NOS NCCOS 2023 Fact Sheet NPDES Permit No. MA0103284 Page 62 of 195 Nutrient dynamics are complex and are influenced by flushing time, freshwater inflow and stratification, and water depth. The deleterious physical, chemical, and biological responses in surface waters resulting from excessive plant growth impair designated uses in the receiving water. Excessive plant growth can result in a loss of diversity and other changes in the aquatic plant, invertebrate, and fish community structure and habitat. Nutrient-driven impacts on aquatic life and habitat are felt throughout the eutrophic cycle of plant growth and decomposition. Nutrient-laden plant detritus can settle to the bottom of a water body. In addition to physically altering the benthic environment and aquatic habitat, organic materials (i.e., nutrients) in the sediments can become available for future uptake by aquatic plant growth, further perpetuating and potentially intensifying the eutrophic cycle. The excessive growth of aquatic plants and algae within marine water ecosystems negatively impacts water quality and can interfere with the attainment of designated uses by: 1) increasing oxygen demand within the water body to support an increase in both plant respiration and the biological breakdown of dead organic (plant) matter; 153 2) causing an unpleasant appearance and odor; 3) interfering with navigation and recreation, for instance, by fouling engines and propellers, making waters unappealing to swimmers, and interfering with fishing lures and equipment; 4) reducing water clarity; 5) reducing the quality and availability of suitable habitat for aquatic life; and 6) producing toxins during certain harmful algal blooms. Cultural (or accelerated) eutrophication is the term used to describe dense and excessive plant growth in a water body that results from nutrients entering the system as a result of human activities. Discharges from municipal and industrial wastewater treatment plants, agriculture runoff, and stormwater are examples of human-derived ( i.e. , anthropogenic) sources of nutrients in surface waters. See generally, Nutrient Criteria Technical Guidance Manual – Estuarine and Coastal Marine Waters , EPA October 2001 [EPA-822-B-01-003], Chapters 1 and 3. Water Quality Standards Applicable to Massachusetts Bay The MA WQS under 314 CMR 4.05(5)(c) require that: … unless naturally occurring, all surface waters shall be free from nutrients in concentrations that would cause or contribute to impairment of existing or designated uses and shall not exceed the site-specific criteria developed in a TMDL or as otherwise established by the Department pursuant to 314 CMR 4.00 including, but not limited to, those established in 314 CMR 4.06(6)(c): Table 28: Site-specific Criteria. Coastal Ocean Program Decision Analysis Series 26. Silver Spring, MD. 328 pp. https://repository.library.noaa.gov/view/noaa/25526 153 “Algae” includes phytoplankton (microscopic algae measured by levels of chlorophyll a), macroalgae (commonly referred to as seaweed), and other plants stimulated by nutrient over-enrichment. Excessive algal growth contributes to low levels of dissolved oxygen through increased plant respiration and decomposition of dead plant matter. Notably, during the day, algae provide oxygen to the water as a by-product of photosynthesis. At night, however, when photosynthesis ceases but plant respiration continues, dissolved oxygen levels decline. Additionally, as these algae die, they are decomposed by bacteria that consume yet more oxygen. When dissolved oxygen levels are low, aquatic organisms become stressed and die, and overall aquatic health is degraded. 2023 Fact Sheet NPDES Permit No. MA0103284 Page 63 of 195 Nutrients are also prohibited in concentrations that would cause or contribute to cultural eutrophication. Cultural eutrophication may also result in exceedances of other nutrient-related water quality standards such as low dissolved oxygen, decreased water clarity, objectionable odors, and surface scum. The MA WQS at 314 CMR 4.05(4)(a)(1) requires that dissolved oxygen not be less than 6.0 mg/L Further, the MA WQS at 4.05(4)(a)(5), (6) and (8) state that waters must be free from “floating, suspended, and settleable solids,” free from “color and turbidity in concentrations or combinations that are aesthetically objectionable…”, and have no taste and odor other than of natural origin. To prevent cultural eutrophication, the MA WQS at 4.05(5)(c) states that, any existing point source discharge containing nutrients in concentrations that would cause or contribute to cultural eutrophication, including the excessive growth of aquatic plants or algae, in any surface water shall be provided with the most appropriate treatment as determined by the Department, including, where necessary, highest and best practical treatment (HBPT) for POTWs and BAT for non-POTWs, to remove such nutrients to ensure protection of existing and designated uses. Human activities that result in the nonpoint source discharge of nutrients to any surface water may be required to be provided with cost effective and reasonable best management practices for nonpoint source control . Also see Part 2.2.2 of this Fact Sheet above regarding antidegradation and existing uses which may be impacted by nutrient over-enrichment. Nitrogen and Endangered Species Act Concerns for Massachusetts Bay In its 1993 Biological Opinion for Endangered Species Act consultation Environmental Impact Statement and ultimately the 2000 Permit, the National Oceanic and Atmospheric Administration (NOAA), National Marine Fisheries Service (NMFS) found that the “outfall may affect, but is not likely to jeopardize, the continued existence of any listed or proposed species under NMFS jurisdiction.” 154 NOAA identified nutrient impacts as a primary concern for the relocation of the MWRA’s outfall to Massachusetts Bay. Specifically, the Biological Opinion addressed the possibility that nitrogen in the outfall’s effluent might cause or contribute to: (1) changes in prey availability and feeding patterns, (2) increased frequency and distribution of toxic phytoplankton blooms, and (3) increased biological oxygen demand. In response to these concerns, the 2000 Permit required effluent nitrogen monitoring (total Kjeldahl nitrogen (TKN), total nitrate and total nitrite). Additionally, the Ambient Monitoring Plan 155 and Contingency Plan 156 included in the 2000 Permit required MWRA to collect ambient data for total nitrogen (nitrite, nitrate, and TKN), dissolved oxygen concentrations, dissolved oxygen respiration rate, chlorophyll, nuisance and noxious algae, zooplankton, and sediment oxygen. MWRA has collected over 30 years of ambient monitoring data including over eight years of baseline monitoring and over 20 years of monitoring since the diversion of the outfall discharge to Massachusetts Bay (post-diversion monitoring). 154 NOAA, NMFS. 1993. NOAA Fisheries Endangered Species Act, Section 7 Consultation – Biological Opinion, Boston Harbor Project: Issuance of a National Pollutant Discharge Elimination System (NPDES) Permit for the Massachusetts Water Resources Authority (MWRA) Outfall. 9/8/1993. 155 MWRA. 1997. Massachusetts Water Resources Authority effluent outfall monitoring plan: Phase II Post- discharge monitoring. https://www3.epa.gov/region1/npdes/mwra/pdf/n.pdf 156 MWRA. 2001. Contingency Plan, Revision 1. https://www.mwra.com/harbor/enquad/pdf/2001-ms-71.pdf 2023 Fact Sheet NPDES Permit No. MA0103284 Page 64 of 195 5.1.10.2 Effluent Nitrogen Data The 2000 Permit required the Permittee to monitor effluent TKN, total nitrite and total nitrate once per month. Effluent data submitted in DMRs between January 2018 and December 2022 shows the following characterization of nitrogen in the DITP effluent: total Kjeldahl nitrogen (median=26.8 mg/L, n=60), total nitrite (median=0.25 mg/L, n=60) and total nitrate (median=0.165 mg/L, n=60) (See Appendix C). Using this data, calculated Total Nitrogen (=TKN+NO2+NO3) has a median concentration of 27.2 mg/L. Although the median concentration of total nitrogen is high, there appears to be no significant ambient impacts due to the discharge of nitrogen. EPA’s Office of Research and Development (ORD) concluded that “the discharge does not cause a broadly eutrophic condition in Massachusetts Bay…although local effects of the discharge on nutrient conditions have been noted.” 157 Thus, the Draft Permit maintains the requirements for the Permittee to monitor total Kjeldahl nitrogen, total nitrate, total nitrite and calculate and report total nitrogen. This information is important as the Permittee continues to study the potential impacts of the discharge and any relationship to other ambient changes. 5.1.10.3 Ambient Nitrogen Data Due to concern that nitrogen could cause excessive algal blooms, the Ambient Monitoring Plan requires the monitoring of nitrogen in Massachusetts and Cape Cod Bays. Data show that
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