CC 25-0966 CSO LTCP Progress 2025May22 — File 25-0966

Combined Sewer Overflow Updated Long Term Control Plan Progress & Related Efforts File ID 25-0966 Officer’s Communication to City Council Infrastructure & Asset Management 22 May 2025

Presenter's Preamble • This presentation contains numerous slides, most borrowed from other presentations, and any one of which could be a topic of prolonged discussion • It is the presenter’s intention to move very quickly through the slides and only provide the highest-level overview on each topic • The presentation includes pause points to answer questions and/or provide additional detail on any concept of interest (slides are numbered for reference) 2

Presentation Overview • Part One – Combined Sewer Overflow (CSO) Long Term Control Plan (LTCP) Update • What is a CSO & what is the MWRA? • Original LTCP • Updated LTCP • Example alternatives • Overall Capital Investment Plan • Financial Capability Analysis • Next steps / schedule • Part Two – Billing for Stormwater • Why should we do it? • How will it work? • What are the benefits? 3

Combined Sewer Overflows 4

What is a Separate Sewer System? 5 Two dedicated networks of pipes: one for sanitary flows, and one for stormwater flows. Residential sewage and industrial wastewater is conveyed to the Deer Island facility for treatment. All stormwater runoff is discharged to the Alewife, Charles and Mystic Rivers.

What is a Combined Sewer System? 6 One network of pipes for both sanitary and stormwater flow. All sanitary flow and stormwater from most storms is moved to the Deer Island Wastewater Treatment Facility. Occasionally, excess flow during heavy rain can cause a combined sewer overflow (CSO) into rivers.

MWRA Regional System Timeline 1889 – Regional sewer construction begins under Metropolitan Sewerage District 1952 – First regional sewage treatment plant 1972 – Clean Water Act 1985 – MWRA assumes control of sewer system 1995 – New Deer Island Treatment Facility begins operation 1988-1992 – Early upgrades 1994-2015 – Capital Improvement Projects completed as part of original Long Term Control Plan 2022 – Planning for updated CSO Control Plans 1876 – Boston sewer interceptor construction begins 7

Combined Sewer Overflow Long Term Control Plan “1992” or “1994” or “1997” 8

25 Years of Major Investment in sewer and stormwater infrastructure and maintenance overall resulting in: • CSO volume reduction of 2.9 billion gallons / year 87% reduction in overall CSO volume 93% of remaining CSO volume is treated • Closure of 40 / 86 CSO outfall points (5 effectively closed along South Boston beaches) • $911 million spent on 35 projects to reduce CSOs • Boston’s beaches are now considered the cleanest urban beaches in the country • CSOs now only contribute to bacterial water quality standard being exceeded a very small percentage of an average year (8hrs and 35hrs, in the Charles and Alewife/Mystic respectively). 9 Original MWRA System Wide CSO Long Term Control Plan Near Completion

System Wide CSO Reduction Since the 1980s Prior Long Term Control Plan • System wide improvements including the Charles, Alewife, Mystic resulted in significant reductions in CSO discharge since 1980s. *Annual discharge volume based on the prior Typical Year * System Wide CSO Reduction Since the Start of the CSO Program in the 1980s 10

11 Alewife Brook Somerville Closed: SOM001, SOM002A, SOM003 & SOM004 Remain: SOM001A Cambridge Closed: CAM0004, CAM400 Remain: CAM001 CAM002 MWR003 CAM401A CAM401B Upper Mystic Closed: SOM006, SOM007 Remain: SOM007A (100% Treated by MWRA Somerville Marginal Facility) Alewife & Upper Mystic Projects Over $215M spent Additional Project underway design to further reduce SOM007A Alewife Brook & Upper Mystic Projects

Charles & Mystic Variance 12 2016 – 2021: Monitor water quality 2022: Start Updated LTCP City of Cambridge Massachusetts Water Resources Authority (MWRA) City of Somerville Charles River Watershed Mystic River Watershed Cambridge Somerville MWRA Sewer Area Updated LTCP 12

Updated Combined Sewer Overflow Process and Regional Effort 13

• Cambridge, Somerville, and MWRA are developing Updated CSO Control Plans with the overall goal to reduce or eliminate CSOs. • The new plans focus on the Charles River, Alewife Brook, and Upper Mystic River (the variance waters). • New plans incorporate the impacts of climate change. What Are We Doing Now About CSOs? 14

Updated CSO Control Plan Steps: 1) 2050 Typical Year & 2050 Design Storms 2) Unify Hydrologic & Hydraulic models 3) Create alternatives: a) Identify scenarios to evaluate CSOs • 2050 Typical Year • 2050 5-yr • 2050 25-yr b) Combine CSO tools to develop various alternatives c) Optimize regionally for each variance water Step 3b Zoom In: CSO Reduction Tools 15

Future Baseline Condition Model Results Receiving Water CSO Discharge Volume (MG) Activation Frequency 2050 25- year Storm (7.8 inches) 2050 5-year Storm (5.3 inches) 2050 Largest Storm in the Typical Year (3.3 inches) 2050 Typical Year Prior Typical Year 2050 Typical Year Prior Typical Year 120.6 65.5 16.6 38.4 7.9 6 3 Charles River 40.1 20.9 4.84 20.9 9.9 13 8 Alewife Brook 27.2 17.4 10.5 29.3 1.3 8 2 Mystic River 2050 Design Storm CSO Activations and Discharge Volumes by Receiving Water 2050 Typical Year Reflective of Climate Change Conditions o A full year of rain data that best represents rain over time o A representative "average" year for planning, as rain changes from year to year Design Storms Reflective of Climate Change Conditions o 2050 5-Year 24-hour and 25-year 24-hour design storms 16

Pause for questions • Part One – Combined Sewer Overflow (CSO) Long Term Control Plan (LTCP) Update • What is a CSO & what is the MWRA? • Original LTCP • Updated LTCP • Example alternatives • Overall Capital Investment Plan • Financial Capability Analysis • Next steps / schedule • Part Two – Billing for Stormwater • Why should we do it? • How will it work? • What are the benefits? 17

Alternatives Under Consideration to Reduce or Eliminate CSO 18

Mystic River Sewer Separation City of Somerville - 2050 Typical Year CSO Control • 560 acres of localized sewer separation • 2 Storm drain outfalls • Large trunk storm drains • 5.5MG storage tank • 0.5 MG storage tank • Prelim. Estimated Cost: ~$700 million * Prelim. Timeline: ~40 yrs Potential Mystic River Projects 19 *Costs include sewer separation of some areas tributary to both Alewife Brook and Mystic River. Costs estimated using 2024-dollar amounts and not escalated to construction period. Costs subject to refinement.

SOM007A/ MWR205A: 3.7 MG storage SOM007A/MWR205A: 366 acres sewer separation SOM007A/MWR205A: new drain & stormwater outfall SOM007A/ MWR205A: 5.5 MG storage SOM007A/MWR205A: • 366 acres sewer separation • 1 new outfall & large storm drain • 5.5 MG stormwater storage • 3.7 MG treated CSO storage Prelim. Estimated Cost: ~$550 million Somerville Marginal Facility 20 Mystic Integrated Alternative: 2050 Typical Year CSO Control

Alewife Brook Sewer Separation City of Somerville - 2050 Typical Year CSO Control • 560 acres of localized sewer separation • New stormwater outfall on Alewife Brook • Large trunk storm drain • 3 constructed wetlands and land acquisition Prelim. Estimated Cost: ~$850 million * Prelim. Timeline: ~50 yrs Potential Alewife Brook Projects 21 *Costs include sewer separation of some areas tributary to both Alewife Brook and Mystic River. Costs estimated using 2024-dollar amounts and not escalated to construction period. Costs subject to refinement.

Alewife Integrated Alternative: 2050 Typical Year CSO Control MWR003: 0.5 MG storage CAM401B: 0.5 MG storage SOM001A: 264 acres sewer separation CAM401A: 2.1 MG storage SOM001A: new drain & stormwater outfall • CAM401A: 2.1 MG storage • CAM401B: 0.4 MG storage • MWR003: 0.5 MG storage • SOM001A: 264 acres separated + inline storage with throttles Prelim. Estimated Cost: ~$600 million 22

Legend: Potential Tunnel Alignment CSO Outfall Location where CSO drops into tunnel Pump station to pump stored flow to interceptor after storm Odor control/Ventilation Building Large Collection System Pipes Note: Facility locations are approximate Alewife Brook Potential CSO Storage Tunnel Alternatives (Tunnel Length: 1.4 Miles) Diameter (feet) Storage Volume (MG) Level of CSO Control 11 4.9 2050 Typical Year 22 20.6 2050 5 Year 32 41.6 2050 25 Year Preliminary Estimated Capital Costs Range from ~$700M to ~$1.7B* North Dorchester Bay Dewatering Pump Station North Dorchester Bay Odor Control/ Ventilation Facility *2024 dollars unescalated to construction period. Costs do not include land acquisition and may be further refined. MWR003 CAM401B CAM002 CAM001 SOM001A CSO from CAM401A Storage Tunnel to Control CSO Outfalls Tributary to Alewife Brook

Pause for questions • Part One – Combined Sewer Overflow (CSO) Long Term Control Plan (LTCP) Update • What is a CSO & what is the MWRA? • Original LTCP • Updated LTCP • Example alternatives • Overall Capital Investment Plan • Financial Capability Analysis • Next steps / schedule • Part Two – Billing for Stormwater • Why should we do it? • How will it work? • What are the benefits? 24

Updated CSO Control Plan Steps: 4) Develop conceptual layouts and preliminary cost estimates 5) Compare alternatives using weighted criteria 6) Assess Initially Preferred Alternative(s) for: • Financial Capability Assessment • Impact to rate payers • Implementation schedule • Compliance with Water Quality standards • What is the highest attainable use without a widespread economic or social impact? 7) Develop Draft Updated CSO Control Plan(s) Reduce/eliminate combined sewer overflows Reduce flooding and flooding impacts Reduce sanitary sewer overflows Improve water quality Rehabilitate old infrastructure (pipes, facilities) Improve resilience of our infrastructure to future climate conditions Improve service to low income and minority communities Offers community co-benefits (e.g., green space, gathering space, heat reduction) Minimize neighborhood disruption during construction Minimize costs to ratepayers / taxpayers Other criteria based on public feedback Step 5 Zoom In: Alternatives Evaluation Preliminary Criteria 25

Overall Capital Investment Plan Integrating priorities 26

27 $0 $5,000,000 $10,000,000 $15,000,000 $20,000,000 $25,000,000 $30,000,000 $35,000,000 $40,000,000 - 5,000 10,000 15,000 20,000 25,000 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 Water & Sewer Construction Metrics Large Diameter Sewer/Drain >24" (LF) Small Diameter Sewer/Drain <12"-24" (LF) Sewer/Drain Lining (LF) Pump Station Projects (Productivity) Water Main Replacement (LF) Water Main Lining (LF) Water Service Replacement (LF) Total Enterprise Fund Construction Costs ($)

Guiding principles for CIP project selection • Fulfill Regulatory Requirements • Comply with Administrative Orders and Permits • Mitigate CSOs • Improve Level of Service • Increase capacity to deliver water • Decrease sewer system backups • Mitigate Flooding • Add capacity and storage to reduce surface flooding • Reduce Risk • Rehabilitate or replace pipes before they fail • Prioritize pipes with greatest impact • Add water valves and sewer manholes to improve operations & maintenance 28

Morrison Ave & MROSS Projects • Preliminary designs complete • Final design initiation awaiting W&S rate approval 29

Financial Capability Assessment Process 30

What is and what is not a Financial Capability Assessment (FCA)? Helps communities understand their ability to implement CSO long- term control plans as mandated by the Clean Water Act (CWA) Helps in developing the schedule for implementing CSO control plans and economic impact analysis for water quality standards decisions Shows the financial impacts of CSO controls Does not evaluate affordability for individual customers Does not consider other financial needs or priorities 31

Financial Capability Assessment (FCA) Process EPA guidance prescribes methods to measure financial impact (low, medium, and high) associated with current and future sewer services within community using critical metrics such as: o Residential Indicator o Financial Capability Indicators o Lowest Quintile Poverty Indicator Score o Financial and Rate Models Evaluate the financial impact of alternative CSO controls and schedule 32

Residential Indicator Defined as a community's average cost per household for wastewater treatment and Clean Water Act controls needed to meet the requirements of the Clean Water Act. Cost per household Median Household Income (MHI) = Residential Indicator (%) Financial Impact Residential Indicator Low Impact < 1.0% Mid-Range Impact 1.0% - 2.0% High Impact > 2.0% 33

S O M E R V I L L E F C A A N A L Y S I S Calculation of Cost per Household for Somerville Service Area BASELINE ITEM $ 50,268,027 Total Current and Projected Costs per Year (FY2030) $ 41,410,940 Residential Share of Total Costs 35,035 Total Number of Households in Somerville Service Area $ 1,182 COST PER HOUSEHOLD 34

S O M E R V I L L E F C A A N A L Y S I S Income Levels 2018- 2022 Median Household Income (1) MHI per US Census Data (2018 - 2022 ACS 5 Year Estimates). $91,168 $97,328 $102,311 $108,896 $120,778 $77,278 $81,215 $84,385 $89,026 $96,505 $60,293 $62,843 $64,944 $69,021 $75,149 $- $20,000 $40,000 $60,000 $80,000 $100,000 $120,000 $140,000 2018 2019 2020 2021 2022 Median Household Income Somerville Massachusetts National 35

Residential Indicator (2024 Data) 2018- 2022 Median Household Income BASELINE ITEM $ 120,778 Median Household Income in 2022 (1) 1.081 CPI Adjustment Factor (2) $ 130,561 Adjusted Median Household Income for 2024 $ 1,182 Annual Cost per Household 0.91% RESIDENTIAL INDICATOR Low Impact (1) MHI per US Census Data (2022 ACS 5 Year Estimate). Where jurisdictions bound more than one census tract, the average MHI (weighted by household count) is presented. (2) MHI was adjusted using the 5 Year average CPI as outlined in EPA guidance. 36 S O M E R V I L L E F C A A N A L Y S I S

Each indicator is given a ranking of compared to other communities. Financial Capability Indicators 37 Debt Indicators • Bond Rating • Net Debt/Property Value Socioeconomic Indicators • Unemployment Rate • Median Household Income Financial Management Indicators • Property Tax/Property Value • Property Tax Collection Rate Weak Mid-Range Strong

Next Steps 38

Updated CSO Control Plan Schedule 39 Updated 1/02/2025

Pause for questions • Part One – Combined Sewer Overflow (CSO) Long Term Control Plan (LTCP) Update • What is a CSO & what is the MWRA? • Original LTCP • Updated LTCP • Example alternatives • Overall Capital Investment Plan • Financial Capability Analysis • Next steps / schedule • Part Two – Billing for Stormwater • Why should we do it? • How will it work? • What are the benefits? 40

Part 2: Billing for Stormwater Runoff A fair and logical solution to Somerville’s sewer problems Infrastructure & Asset Management 22 May 2025

Somerville has a twofold stormwater runoff problem 42

Flooding Constituent desire for system improvements especially in wet years 43

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Combined Sewer Overflows (CSO) Regulatory driver for system improvements 45

CSOs on Alewife combine with flood water • The Alewife Greenway Path is a heavily trafficked multi-use path on DCR land. It links Medford, Somerville, Arlington and Cambridge residents to the Alewife Red Line T stop. 46 Photo by David Stoff / Save the Alewife Brook Photo by Ann McDonald/ Save the Alewife Brook

The bigger the storm, the bigger the problem 47

Flooding Evident in the neighborhoods 48

Flood depth 1-Year, 24-Hour, 2050 Storm 49

Flood depth 5-Year, 24-Hour, 2050 Storm 50

Flood depth 25-Year, 24-Hour, 2050 Storm 51

Pipes & CSOs Underground & in the rivers 52

Limitations in both local and regional systems 53

54 0.0 50.0 100.0 150.0 200.0 250.0 300.0 Average Dry Weather Day Largest Storm 2050 TY 2050 5-Year Storm 2050 25-Year Storm Daily Volume (million gallons) Somerville surface flood volume Somerville- related CSO volume Somerville flow to MWRA system

Revenue generation & expense problem Currently, all operations & capital improvements to manage stormwater are paid from the Sewer Enterprise 55

Bills are based on water use 56 Majority of CIP & portion of CEB devoted to stormwater 0.0 50.0 100.0 150.0 200.0 250.0 300.0 Average Dry Weather Day Largest Storm 2050 TY 2050 5-Year Storm 2050 25-Year Storm Daily Volume (million gallons) Somerville surface flood volume Somerville- related CSO volume Somerville flow to MWRA system Sewer Enterprise

Stormwater not related to water use • Target water use • ~ five 2-family homes • Targe impervious area • ~ 20 times that of those 5 properties combined 57

Related to area, particularly impervious • Properties with more area contribute to the problem • Property owners can control how much impervious surface they have and/or how the runoff from those areas are managed 58 Increasing Impervious Surface = Increasing Runoff Generated

Proposal: Create 3rd enterprise fund & bill for impervious area in addition to water use Water, Sewer & Stormwater Enterprises & bills 59

Impervious area by parcel Detailed analysis 60

61 Detailed Impervious Area Development 61 S O M E R V I L L E – S T O R M W A T E R U T I L I T Y O V E R V I E W

62 Measured Impervious Area* 62 S O M E R V I L L E – S T O R M W A T E R U T I L I T Y O V E R V I E W 57M Square Feet of Impervious Area* Impervious Area (Sq. Ft.) Parcel Count Parcel Type 13,345,298 4,931 Two Family 4,856,230 2,310 Single Family 6,432,709 2,231 Three Family 6,366,855 1,698 Condo 2,125,127 529 Apartments 4-8 17,377,805 1,083 Non-Residential 2,503,693 117 City-Owned 3,109,853 51 MTBA 766,604 25 Commonwealth of Mass * Impervious area on streets and right-of-ways is equal to 28M Citywide

63 63 S O M E R V I L L E – S T O R M W A T E R U T I L I T Y O V E R V I E W Residential: 58% Non-Residential: 31% Other: 11% Residential 58% Non- residential 31% Other 11% Residential 90% Non- residential 8.3% Other 1.5% Parcel distribution Impervious area distribution

How will bills work? Balance of accuracy and simplicity 64

65 How to Structure the Stormwater Fee 65 S O M E R V I L L E – S T O R M W A T E R U T I L I T Y O V E R V I E W 65 • Recommend fee be based on impervious area contained on parcel • Impervious area tiers used to simplify administration 0 100 200 300 400 500 600 700 - 300 600 900 1,200 1,500 1,800 2,100 2,400 2,700 3,000 3,300 3,600 3,900 4,200 4,500 4,800 5,100 5,400 5,700 6,000 6,300 6,600 6,900 7,200 7,500 7,800 8,100 8,400 8,700 9,000 9,300 9,600 9,900 10,200 10,500 10,800 11,100 11,400 11,700 12,000 12,300 12,600 12,900 13,200 13,500 13,800 14,100 14,400 14,700 15,000 # of Parcels Impervious Area Tier 1 Tier 2 Tier 3 Tier 4 Tier 5 Measured 1,000 sq. ft.

66 Stormwater Fees 0 100 200 300 400 500 600 700 - 300 600 900 1,200 1,500 1,800 2,100 2,400 2,700 3,000 3,300 3,600 3,900 4,200 4,500 4,800 5,100 5,400 5,700 6,000 6,300 6,600 6,900 7,200 7,500 7,800 8,100 8,400 8,700 9,000 9,300 9,600 9,900 10,200 10,500 10,800 11,100 11,400 11,700 12,000 12,300 12,600 12,900 13,200 13,500 13,800 14,100 14,400 14,700 15,000 # of Parcels Impervious Area Tier 1 Tier 2 Tier 3 Tri-Annual Fee: Fee Dependent on Measured Area ($70 per 1,000 square feet of impervious) $34 $111 $173 $236 $304 Fees based on FY25 stormwater revenue requirements S O M E R V I L L E – S T O R M W A T E R U T I L I T Y O V E R V I E W Monthly Fee: $9 $28 $43 $59 $76

67 Geospatial Tiers Tier 1 (100 - 1000 sq ft) $34 Tier 2 (1,001 - 2,000 sq ft) $111 Tier 3 (2,001 - 3,000 sq ft) $173 Tier 4 (3,001 - 4,000 sq ft) $236 Tier 5 (4,001 - 5,000 sq ft) $304 Measured Over 5,000 sq ft Tri-Annual Stormwater Fee

Credit program will promote on-site control of stormwater Billing fairness is only half of the intent. Private property comprises 90-percent of total area and 70-percent of impervious area in the City. 68

69 Stormwater Fee Credits Stormwater fee credit is an ongoing reduction in the fee charged to a qualifying property in return qualifying stormwater management Credit is recognition that onsite/offsite stormwater management reduces the City’s stormwater expenditures Credits encourage property owners to proactively manage their stormwater impact S O M E R V I L L E – S T O R M W A T E R U T I L I T Y O V E R V I E W

We know on-site management works • Engineering Driveway & Paving Permit • https://s3.amazonaws.com/somervillema-live/s3fs-public/driveway- paving-permits-brochure.pdf • Engineering Site Plan Permit • Infiltrate/detain first ¾-inch runoff • Reduce peak rate from 10-year storm to mimic 2-year storm • https://s3.amazonaws.com/somervillema-live/s3fs-public/engineering- site-permit-rules-regs.pdf • Green Stormwater Infiltration Guidance • https://s3.amazonaws.com/somervillema-live/s3fs-public/gsi-planning- guidance.pdf 70

There are limits. It won’t solve flooding or CSOs But if we each do a little, we’ll all do a lot. 71

CSO reduction from on-site management 72 0 5 10 15 20 25 30 35 0% 25% 50% 75% 100% Million Gallons CSO per Year Percent of Private Properties Capturing the First 3/4 inches of Rain 2050 Typical Year CSO Discharge Volume SOM001A SOM007A

Implementation • Finalize FY2026 Water, Sewer & Stormwater Rate Proposal • City Council authorization of change to City Ordinance to create Stormwater Enterprise and fee • Public hearing on rates • City Council approval of rates, budget • Creation of FAQ’s for 311 and Water Billing Department 73

Pause for questions • Part One – Combined Sewer Overflow (CSO) Long Term Control Plan (LTCP) Update • What is a CSO & what is the MWRA? • Original LTCP • Updated LTCP • Example alternatives • Overall Capital Investment Plan • Financial Capability Analysis • Next steps / schedule • Part Two – Billing for Stormwater • Why should we do it? • How will it work? • What are the benefits? 74

Combined Sewer Overflow Updated Long Term Control Plan Progress & Related Efforts File ID 25-0966 Officer’s Communication to City Council Infrastructure & Asset Management 22 May 2025