2025_WSSC_LTWQT_MP_Final_Report_redacted.pdf

July 2025

Long Term Water Quality and Treatment Master Plan

Final Report

Contents – Full Report

Final Report Executive Summary …………………………………………………………………..…. 3

P1 TM1: Water Treatment Plant Capacity ……………………………………………………..…. 38

P1 TM2: Salinity .…………………………………………………………………………………..……… 60

P1 TM3: Water Quality ………………………………………………………………………………… 105

P1 TM4: PFAS ROM Cost Estimated for Potomac WFP ……………………………………… 181

P1 TM5: Regulatory Review ……………………………………………………………………….… 191

P1 TM6: Source Water Quality Risk and Resilience ………………………………….……… 283

P2 TM1: Treatment Alternatives Evaluation ….……………………………..………………… 340

P2 TM2: PFAS Treatability Tests …………………………………………………………………… 360

P2 TM3: Disinfection Byproduct Formation Tests ………………………………………….… 476

P2 TM4: Algae-Related Treatment Enhancement Through NF Tests ………………..… 528

P2 TM5: Salinity Impact on Water Corrosivity …………………………….……………….… 570

P2 TM6: Treatment and Hydraulic Capacity Phase 1 Testing ………….………………… 600

P2 TM7: Risk of Source Water Contamination and Resilience …………..…………….… 661

P2 TM8: Permanganate System Alternative Evaluation ………………………...………… 786

P2 TM9: Reclaiming Backwash Water and Gravity Thickener Overflow

(Potomac WFP) and Assessing Waste Rates (Patuxent WFP) ………………………..… 818

P2 TM10: Pilot Testing Recommendations ……………………………………………………… 847

2025 WSSC Long Term Water Quality and Treatment Master Plan 2

Executive Summary Page 1 of 35

2025 WSSC WATER

LONG TERM WATER QUALITY

AND TREATMENT MASTER PLAN

EXECUTIVE SUMMARY

Project name Long Term Water Quality and Treatment Master Plan

Project no. 23303125A

Client WSSC Water

Memo no. Executive Summary

Version 3 – Final

To Steve Mills, WSSC

From Narayan Venkatesan

Copy to George Rest

Prepared by Naomi Souza, George Rest, Narayan Venkatesan

Checked by Narayan Venkatesan, George Rest

Approved by George Rest

2025 WSSC Long Term Water Quality and Treatment Master Plan 3

Executive Summary Page 2 of 35

Contents

1 Introduction

1.1 Background and Purpose

1.2 Overview

2 Water Resource Management

3 Source Water Quality

3.1 Historical trends

3.2 Salinity

3.2.1 Salinity and Corrosivity

3.3 Cyanotoxins, Algal Blooms and Tastes and Odors

4 Risk of Source Water Contamination and Resilience

4.1 Overview

4.2 Primary Contamination Risks

4.3 Summary of Current and Recommended Resilience Measures

5 Water Quality Regulation Review

5.1 PFAS Rule

5.1.1 Potential Cost Impact of PFAS

5.2 Microbial and Disinfection Byproduct Rule

5.3 Lead and Copper Rule

6 Reliable Treatment Capacity

6.1 Potomac WFP

6.2 Patuxent WFP

6.3 Ability to Meet Projected Demands

7 Bench Scale Treatability Testing

7.1 PFAS Bench Testing

7.2 Disinfection Byproduct Bench Testing

7.3 Algae-related Treatment Enhancement

7.4 Technology Summary

8 Water Treatment Alternatives

8.1 Potomac WFP Treatment Alternatives and Pilot Testing

Recommendations

8.2 Reclaiming Backwash Water and Gravity Thickener Overflow (Potomac

WFP) and Assessing Waste Rates (Patuxent WFP)

8.2.1 Reclaiming Backwash Water and Gravity Thickener Overflow (Potomac

WFP) ………………………………………………………………………………………………………………32

8.2.2 Assessing Waste Rates at Patuxent WFP

8.3 Permanganate System Alternatives

9 Next Steps

2025 WSSC Long Term Water Quality and Treatment Master Plan 4

Executive Summary Page 3 of 35

1 Introduction

WSSC Water’s Long Term Water Quality and Treatment Master Plan is a collaborative effort, with engagement of WSSC Water internal stakeholders representing the Divisions of Production, Operational Reliability and Resilience, Engineering and Construction and Utility Services, and external stakeholders like the other major water utilities in the Washington, DC region, supported by WSSC

Water’s engineering consultant, Ramboll.

The findings from the Long Term Water Quality and Treatment Master Plan are presented in the Technical Memoranda. This Final Report provides a “executive level” summary and serves as a roadmap to assist the reader in finding information in the

Technical Memoranda.

1.1 Background and Purpose

WSSC Water developed this Long Term Water Quality and Treatment Master

Plan (Master Plan) to position WSSC Water (also referred to as WSSC) with a sustainable strategy for meeting its water supply and water quality objectives for the next 30 years. The Master Plan holistically addresses:

• Water supply reliability, considering the impact of climate change on

WSSC’s surface water sources, increasing demands for water and the potential for source water contamination.

• Source water quality, including long-term water quality trends in the

Potomac River and Patuxent reservoirs, such as increasing salinity and algal blooms.

• Recent and future drinking water quality regulations that established limits on per- and polyfluoroalkyl substances (PFAS) and are expected to establish more stringent limits on disinfection byproducts, algal toxins and manganese.

• Reliable treatment capacity and resilience of WSSC Water’s Potomac and

Patuxent Water Filtration Plants (WFPs), to meet water demands even during extreme weather events and unusual water quality conditions.

• Resilience of WSSC Water’s Potomac and Patuxent Water Filtration

Plants (WFPs), with focus on source water quality.

• Water resource management, including the maintenance of operations during low flows in the Potomac River and potential conversion of a nearby quarry into a regional water storage reservoir.

• Treatment Alternatives: based upon the desktop analysis and bench scale testing, the Master Plan identifies a range of treatment process alternatives that merit further consideration for pilot testing.

The Long Term Water Quality and Treatment Master Plan was developed in two parts. The Part 1 Report, issued in December 2023, was comprised of six technical memoranda that reported on a comprehensive range of investigations into water quality, regulations, and the resilience and reliability of WSSC Water’s water supply and treatment facilities. Part 2 results were documented in ten task reports (aka

2025 WSSC Long Term Water Quality and Treatment Master Plan 5

Executive Summary Page 4 of 35 technical memoranda), reporting on a mix of desktop evaluations, bench scale testing and full-scale demonstrations, all informed by the foundational work in Part

1. Throughout Part 1 and Part 2 of the Water Quality and Treatment Master Plan, WSSC Water staff engaged in 33 workshops and numerous other meetings and interviews to gather institutional knowledge, review findings, assess operational constraints and collect stakeholder feedback. This Final Report integrates the findings and recommendations from both Part 1 and Part 2.

This Master Plan and its technical memoranda are intended to provide technical information that WSSC Water can use, along with other relevant factors such as regulatory insights, governmental mandates, level of service and affordability in their decisions regarding future investments, practices and policies. The priorities and recommendations are based on conditions that exist and are known as of the date of the report and should be revisited as conditions and regulations change.

1.2 Overview

Part 1 of the Master Plan included a desktop evaluation of future water quality regulations and a preliminary assessment of water quality trends and operational data. Workshops and interviews were conducted with WSSC Water staff to review prior investigations, assess operational constraints, gather institutional knowledge, and collect stakeholder feedback.

Figure 1-1: WSSC Long Term Water Quality and Treatment Plan workflow diagram.

Part 2 of the Master Plan included a mix of desktop evaluations, bench scale testing and full-scale testing to assess treatment options, risk mitigation strategies and

2025 WSSC Long Term Water Quality and Treatment Master Plan 6

Executive Summary Page 5 of 35 demonstrate hydraulic and process loading capacities at the Potomac and Patuxent

WFP. Workshops and/or interviews were conducted with WSSC Water as needed to gather institutional knowledge and collect stakeholder feedback. The findings from

Part 2 study efforts were used to:

• Develop holistic treatment options and/or management strategies for various water quality parameters of concern identified in Part 1

• Identify potential risk and mitigation strategies associated with PFAS

• Evaluate treatment capacities of the water filtration plants

• Develop risk mitigation strategies during various “resilience’ related events

(i.e., spills, detrimental water quality; supply chain related issues etc.) as identified in Part 1.

• Develop a pilot study recommendation.

The findings from Part 1 and Part 2 study efforts were documented in detailed

Technical Memoranda; links to each document are provided below and throughout the text.

P2 TM1 – Treatment Alternatives Evaluation

P2 TM2 – PFAS Treatability Tests

P2 TM3 – DBP Formation Tests

P2 TM4 – Algae-Related Treatment Through NF Tests

P2 TM5 - Salinity Impact on Water Corrosivity

P2 TM6 - Treatment and Hydraulic Capacity Testing Phase 1

P2 TM7 - Risk of Source Water Contamination and Resilience

P2 TM8 - Permanganate System Alternative Evaluation

P2 TM9 - Reclaiming BW and GTO (Potomac WFP) and Assessing Wastage (Patuxent WFP)

P1 TM1 – Water Treatment Plant Capacity P1 TM2 – Salinity

P1 TM3 – Water Quality P1 TM4 – PFAS Treatment

ROM

P1 TM5 – Regulatory Review P1 TM6 – Source Water Quality Risk and Resilience

TM 10 – Pilot Testing Recommendations

Part 1 Technical Memoranda

Part 2 Technical Memoranda

2025 WSSC Long Term Water Quality and Treatment Master Plan 7

Executive Summary Page 6 of 35

2 Water Resource Management

As part of the Long Term Water Quality and Treatment Master Plan Ramboll reviewed information on source water risk assessment, immediate mitigations strategies, and climate resilience. Part 1 Technical Memorandum No. 6 P1 TM6

Source Water Quality Risk and Resilience provides a comprehensive summary of WSSC’s Water Resource Management practices and plans for the future. The aspects of P1 TM6 that are dedicated to source water quality as addressed in Section

4 of this Water Quality and Treatment Master Plan Report.

P1 TM6 also summarizes the available reports previously prepared for WSSC regarding water resources, in particular the Potomac River and Watershed, as well as Potomac and Patuxent Water Filtration Plant treatment capabilities. For aspects of

P1 TM 6 dedicated to water resource management, the reader is directed to Section

7 of the referenced tech memo. Highlights from several studies are repeated below, along with a brief summary of ongoing activities by WSSC Water that illustrate ongoing efforts to effectively manage its water supply resources.

Potomac Comprehensive River Basin Water Resources Plan (ICPRB, 2018) – This study characterized the Potomac River Basin, identified the main areas of concern, and listed recommended actions relevant to a sustainable water resource management plan that can be carried out by different stakeholders over a 15-year period. The Study’s recommendations could be considered “best practices” aligned with goals for: ensuring sustainable water uses, protecting and improving water quality, managing land use for sustainability, and protecting ecological health.

WSSC collaborates extensively with regional water utilities to protect water resources and improve water quality. In addition, WSSC works with ICPRB and the

Metropolitan Washington Council of Governments (MWCOG) to promote sustainable land use. The regional planning agencies work with entities such as local governments and conservation districts, to promote innovative land use solutions.

WSSC also collaborates with regional water utilities to protect ecological health. One effort involves standardizing sampling and analytical methods to build a regional consensus on what constitutes high ecological value and coordinating limits such as total maximum daily load (TMDLs). Other activities include: constructing stormwater retention systems; managing invasive species; preserving and protecting forests, wetlands, and stream buffer lands; and allocating water resources to meet aquatic life needs. For example, WSSC can work through ICPRB to identify water chemistry conditions that increase the likelihood of nuisance filamentous algal blooms forming in streams and the negative impacts of algal blooms on aquatic life. ICPRB also provides a regional coordinating function for various challenges such as floods and droughts that affect both communities and ecosystems, especially those impacting vulnerable coastal populations.

2025 WSSC Long Term Water Quality and Treatment Master Plan 8

Executive Summary Page 7 of 35

2020 Washington Metropolitan Area Water Supply Study (ICPRB, 2020) - This

ICPRB Study is updated every 5 years, most recently in 2020. The following is summarized from that report:

• Prior studies have found that Travilah Quarry would be the most effective in mitigating risk to WMA water supply from a contaminant spill in Potomac River. It was also found to be highly effective in providing the additional water supply storage required to mitigate the impacts of future severe drought incidents.

• The study considers nine scenarios and four potential system configurations (operational alternatives) to evaluate future conditions with and without climate change impacts. Climate change conditions include analyzing impacts due to an average precipitation increase of 8 to 10%, and an average temperature increase by 2.16 to 2.5 °C, with more intense droughts and rain events.

• Without considering the impact of climate change on future demands and stream flows, the report concludes that the current water supply system is reliable for 2040 demands but requires operational alternatives for 2050 demands.

• With climate change impacts, Travilah Quarry, one of the structural alternatives, in conjunction with the recommended operational improvements noted in the report, is required under all 2040 low flow scenarios to avoid system failure in severe drought, as well as under

2050 scenarios, considering additional cooperative use.

ICPRB’s 2025 update is scheduled for completion around the end of the year. In initial discussions between ICPRB and WSSC Water staff, ICPRB indicated they do not anticipate significant changes to the findings reported in the 2020 Water Supply

Study.

Climate Change Vulnerability Assessment, Adaptation, and Mitigation Plan (Jacobs

Engineering, 2020), The Climate Change Vulnerability Assessment, Adaptation, and

Mitigation Plan Project (CCVAAMP) was developed over the course of 5 years (2016-

2020) and encompassed four primary tasks:

1. Climate Analysis and Projections

2. Vulnerability Assessment and Adaptation Analysis

3. Adaptation Recommendations and Climate Change Design Guide

Development

4. Mitigation Planning

Climate hazards evaluated in this CCVAAMP include flooding, loss of power, damage to electrical equipment, and operational difficulties. The study focused on estimating future impacts of riverine (precipitation-driven) and sea level rise (coastal) consequences of climate change-driven flooding. The findings included the following regarding climate change-driven flooding of key water system assets:

• The Potomac and Patuxent WFPs are not at risk of flooding for current or future scenarios flooding o Thus, mitigation strategies were determined to not be needed for the

Potomac and Patuxent WFPs.

2025 WSSC Long Term Water Quality and Treatment Master Plan 9

Executive Summary Page 8 of 35

• Rocky Gorge RWPS is at risk of flooding for the 100 and 500-year flood scenarios.

• While Potomac RWPSs 1 and 2 were not included this study, WSSC staff informed that RWPS 2 is at risk of flooding due to its lower elevation and hydraulic connection to the river/intake through the wet wells.

3 Source Water Quality

3.1 Historical trends

The Water Quality and Treatment Master Plan involved review for trends in raw water quality (P1 TM3 Water Quality) of WSSC’s source waters over the past 40 years, whether due to climate change or other factors.

Some water quality parameters, such as pH, turbidity, and total organic content

(TOC) appear stable, with little if any trends in the source waters of the Potomac and Patuxent WFPs. Other parameters, such as alkalinity and hardness show gradual upward trends in the source waters, but these trends do not suggest significant adverse impacts on treatment or finished water quality.

Increasing trends were observed for temperature and salinity. To date, the impact of increasing temperature does not appear to be significant, but a continuing increase in raw water temperatures could cause an increase in disinfection byproduct (DBP) formation, for which implications are discussed in the Technical Memorandum P1

TM5 Regulatory Review. Additionally, water temperatures near 0°C still occur;

further review of the potential for frazil ice and ice blockage at the Potomac River intake is recommended.

3.2 Salinity

The increase of salinity in natural environments is a global phenomenon. The

Potomac River water quality report prepared by the Interstate Commission on the

Potomac River Basin (ICPRB) indicates that river water salinity (i.e., sodium and chloride) in winter months has increased nearly 10-fold over the past 70 years, apparently due to road and sidewalk deicing (P1 TM2 Salinity).

While USEPA does not enforce a drinking water standard for sodium, state and federal health agencies recommend sodium levels in drinking water not exceed

20 mg/L for people on very low sodium diets. Further, WSSC has observed that elevated salinity may be linked to other regulated drinking water quality parameters, such as manganese, chlorine demand/dosage and disinfection by products.

At Potomac WFP, the average sodium level is at or near 20 mg/L, and concentrations have been recorded up to 180 mg/L.

At Patuxent WFP, the average sodium level is approaching 20 mg/L, with concentrations up to

32 mg/L.

2025 WSSC Long Term Water Quality and Treatment Master Plan 10

Executive Summary Page 9 of 35

3.2.1 Salinity and Corrosivity

In Part 2, under Task 5, Ramboll used a water quality modeling tool to evaluate the changes in water corrosivity based on historical average conditions and extreme events of salinity in the Potomac River (P2 TM5 Salinity Impact on Water

Corrosivity). The evaluation indicates that water treatment infrastructure, in particular metal lines and solders, could be negatively impacted due to water corrosivity when concentrations of chlorides are around the average that WSSC has experienced in the past (38 mg/L) and be significantly affected above 100 mg/L.

Based on the model results and literature review, the main findings and recommendations from the Task 5 evaluation include:

• If salinity and particularly chlorides in the source water continues to rise, water corrosivity in the distribution system will increase as well.

• WSSC should continue to collaborate with regional agencies, industrial dischargers, and advocacy groups in promoting best practices for road and sidewalk deicing and identifying measures to limit the release of salt into the watersheds sourcing the Potomac WFP and Patuxent WFP.

• WSSC should continue to add orthophosphate to address water corrosion potential and maintain its lead service line replacement program initiative.

• If WSSC considers a chemical treatment change that would alter the finished water chemistry, WSSC should test progressive changes through small scale bench tests, before full implementation.

• If WSSC considers implementing a water treatment process that can significantly impact alkalinity, hardness or ionic composition such as by ion exchange resin or nanofiltration, water corrosivity changes should be reevaluated.

3.3 Cyanotoxins, Algal Blooms and Tastes and Odors

While significant levels of cyanotoxins have not been detected, WSSC has experienced operational impacts due to algal blooms, including taste and odors at the Potomac WFP and the presence of diatoms, at the Patuxent WFP, which have impacted reduced filter run times and plant capacity. As noted in Section 6, Reliable

Treatment Capacity, WSSC Water staff developed strategies that mitigate the impact of diatoms under typical operating conditions. Additional testing is proposed to assess operation at high production rates, i.e., greater than 72 MGD, during diatom events.

While no algal toxins have been detected to date in the Potomac or Patuxent WFP sources, there is potential for algal blooms to increase in frequency with changing climate. The P2 TM4 Algae-Related Treatment Enhancement through NF reported on the favorable ability of nanofiltration to remove algal toxins. Section 8

Water Treatment Alternatives includes recommendations for further consideration of technologies with potential to mitigate the impacts of harmful algal blooms.

2025 WSSC Long Term Water Quality and Treatment Master Plan 11

Executive Summary Page 10 of 35

4 Risk of Source Water Contamination and Resilience

4.1 Overview

Part 1 Technical Memorandum P1 TM6 Source Water Quality Risk and

Resilience serves as a comprehensive and well-resourced summary of prior research into source water contamination risks for the watersheds supplying the

Potomac and Patuxent WFPs. The TM also describes the current capabilities at each

WFP to address these risks, which include but are not limited to:

• Coagulation, sedimentation and filtration to remove particulate and some organics

• Oxidants including chlorine and potassium permanganate for disinfection and partial control of algae including diatoms

• Powdered activated carbon to remove taste, odors and some algal toxins

• Ultraviolet disinfection for enhanced disinfection of pathogens including cryptosporidium as could be released by animal feed operations

Part 1 recommendations were related to:

• Previously recognized source water quality risks, with focus on biological

(pathogens and algae), chemical (chemical spills), and climate vulnerability aspects,

• Current sampling and treatment strategies for algal blooms, in particular harmful algal blooms producing cyanotoxins and those related to diatoms,

• Climate change projections and adaptation strategies.

Note that some of the prior risk and resilience related studies were prepared to satisfy the requirements of the America’s Water Infrastructure Act (AWIA) of 2018.

The AWIA requires WSSC to update and recertify its Risk and Resilience Assessment and Emergency Response Plan every five years. WSSC Water certified the required update for the Risk and Resilience Assessment on March 27, 2025, in advance of the EPA deadline and Emergency Response Plan update is on schedule to be completed and certified to EPA by the September 2025 deadline.

4.2 Primary Contamination Risks

From the Part 1 risk assessment, the primary risk concerns for the WSSC Water source watersheds are petroleum, chemical or biochemical releases. Growing threats include increase in both temperature and salinity in the water, which should be monitored in the future. It was recommended that WSSC Water implement a formalized mitigation plan for WSSC Water that follows the AWWA

G300 standard. WSSC Water, in collaboration with its regional partners, is pursuing initiatives that would enhance plans to create resilience and redundancy of its water sources and water system and has identified opportunities to reduce risk.

Part 2, Task 7 of the Master Plan (P2 TM7 Risk of Source Water Contamination and Resilience) utilized readily available tools with current information and data to further assess the potential releases of contaminants and resulting risks at the

Potomac and Patuxent WFPs. These tools and additional research revealed the following risks, their potential impact to WSSC, and current and potential future resilience measures.

2025 WSSC Long Term Water Quality and Treatment Master Plan 12

Executive Summary Page 11 of 35

• Petroleum, oils, and transportation potential releases: WSSC’s source waters are vulnerable to potential petroleum and other chemical releases that may occur from a pipeline or transportation incidents involving road or rail accidents. Several roads and rail lines cross tributaries directly upstream of the plants. One CSX rail follows the Potomac River on the Maryland side from Harpers Ferry south to the Monocacy River (adjacent and up to 1000 ft away). In terms of major highways, Interstate 270 crosses the Watts Branch

Sub-watershed, and Interstate 70 crosses the Headwaters Patuxent River

Watershed, upstream of Potomac and Patuxent WFPs, respectively. The

Colonial petroleum pipeline is upstream of both WFPs; historical releases include a pipe rupture in 1993 that resulted in about 40,000 gal of No. 2 fuel into Sugarland Run. Fairfax Water, a neighboring utility withdrawing from the western side of Potomac River, shut their intake for 11 days. WSSC and the Washington Aqueduct intakes on the eastern side of the river were not impacted. In 2016, lubricating oil from a pump in the NRG Dickerson Power

Plant (MD) was released into the Potomac River, and for about 3 weeks booms were put in place to protect the intakes of the plants. In 2019, after a derailment accident at the Harpers Ferry Bridge two empty grain freight cars fell into the Potomac River, without impacts to water utilities.

Primary Resilience Measures:

o WSSC is an active member of the Potomac Drinking Water Source

Protection Partnership (DWSPP) and participates in the Early

Warning and Emergency Response Workgroup and listserv which allows for efficient communication in the event of a spill in the

Potomac River Basin.

o WSSC is actively supporting the Travilah Quarry Reservoir Regional

Water Supply project, which would provide a back-up to the Potomac

River in the event of a petroleum release or other known contamination event. WSSC projected that a practical volume for water storage for Travilah Quarry is 7.8 BG, which would provide approximately 20 days of storage for WSSC and the Washington

Aqueduct at a 400 MGD withdraw rate.

o WSSC can also mitigate petroleum contamination at both WFPs by deploying deflection booms and by feeding powdered activated carbon (PAC) and where PAC is not sufficient protection, WSSC can close their intakes until spill contaminants have adequately dispersed or travelled past the intake.

• PFAS releases: Recent efforts to monitor and assess PFAS occurrence in the Potomac River Basin have improved the understanding of potential contamination risks. State and federal databases and publicly available reports indicate a few occurrences of PFAS detections in community water systems above the PFAS NPDWR and environmental detections in military bases (Fort Detrick, MD, and Shepherd Field Air Base, WV) upstream of the

WFPs. More data will help WSSC assess the risk that PFAS concentrations could reach compliance limits in the NPDWR.

2025 WSSC Long Term Water Quality and Treatment Master Plan 13

Executive Summary Page 12 of 35

Primary Resilience Measures:

o WSSC is currently participating in a PFAS Source Assessment in the

Potomac River funded by the Water Research Foundation in cooperation with other water utilities and agencies from all neighboring states.

o WSSC is evaluating potential treatment options for PFAS and other contaminants through bench testing in the Water Quality and

Treatment Master Plan, and future pilot testing.

• AFOs and CAFOs potential releases: there are approximately 10 large

CAFOs upstream of the WFPs, along with several smaller AFOs and CAFOS identified in Maryland and Virginia that are potential contributors to biological contaminants such as Cryptosporidium or E. coli.

Primary Resilience Measures: WSSC has installed robust disinfection systems using both chlorine and ultra-violet (UV) light, to provide a high level of protection against biological contamination that could result from potential

AFO and CAFO releases.

• Other chemical and non-petroleum releases from nearby facilities:

industrial facilities or sites pose a contamination risk due to accidental and/or unintentional discharges of regulated contaminants, and potential discharges of unregulated and/or non-monitored contaminants despite their compliance status. The occurrence of such facilities was evaluated through

USEPA’s Drinking Water Mapping Applications to Protect Source Waters

(DWMAPS). Within the 20 facilities identified directly upstream of WSSC’s intakes (Watts Branch Sub-watershed, and Headwaters Patuxent River

Watershed) only one had a violation for total suspended solids. Two historical releases from industrial facilities were identified in tributaries of the

Potomac River since 2015, none which directly impacted WSSC.

Primary Resilience Measures:

o WSSC currently monitors raw water for all Safe Drinking Water Act

(SDWA) regulated constituents, and several unregulated constituents such as some PFAS that not included in the National

Primary Drinking Water Regulations (NPDWR).

o WSSC participates in the DWSPP Early Warning and Emergency

Response Workgroup to help prepare for spills, monitor, and respond to unexpected events that may impact water supply.

o WSSC is evaluating new treatment technologies that may also mitigate other contaminants not directly tested in the current bench test studies, or future pilot tests.

2025 WSSC Long Term Water Quality and Treatment Master Plan 14

Executive Summary Page 13 of 35

4.3 Summary of Current and Recommended Resilience Measures

Table E-4-1 provides a summary of resilience measures and the water quality risks they are intended to address. The table presents operational practices, early warning and detection technologies and capital improvements including recommendations in prior resilience studies. Table E-1 also includes recommendations for continued investigation into treatment process improvements that are being considered under this Water Quality and Treatment Master Plan to mitigate the impacts of contaminants of concern.

Table E-4-1 Summary of recommended resilience measures and water quality risks addressed in this memo.

Water Quality Risks Addressed by Each Resilience Measure

Resilience Measure

Upstream chemical and/or petroleum releases and accidental spills

PFAS

Releases (Also addressed in other TMs)

E. coli and Cryptosporidiu m contamination from AFOs and CAFOs

Non-contamination risks - Source Water Quality (Addressed in other TMs)

Operational Practices

Maintain Existing UV Disinfection Systems X X

Maintain strong relationships, collaboration, and communication with ICPRB, other water utilities, and other stakeholders/agencies. This includes involvement with the spill notification networks and the ICPRB Emergency River Spill Model.

X X X X

Perform a more detailed assessment of potential contamination sources for emerging contaminants

X

Shut down intakes when necessary X (larger quantities)

Maintain use of powdered activated carbon (PAC) and/or deflection booms when possible1

X (small quantities)

Taste and odor-

T&O

Continue to update and practice emergency response plans for major releases, contamination, and water quality issues. This includes the January 2025 Consequence Management Plan for Chemical and Petroleum Contamination (Hazen and Sawyer, 2025)

X X X X

Conduct additional distribution system modeling of impacts from the loss of the Potomac supply in the event of a spill (Hazen and Sawyer, January 2015)

X

Explore options for high-capacity connection with neighboring water utilities and establish a regional agreement to improve resilience to a Potomac River contamination event (Hazen and Sawyer, January 2015)

X X

Explore treatment standards and maximum allowable contaminant concentrations for spills with Maryland Department of the Environment (MDE) and United States Environmental Protection Agency (USEPA) (Hazen and Sawyer, January 2015)

X

Conduct additional jar tests under a wider range of conditions to gain a better understanding of the effectiveness of PAC treatment of a spill and impact of PAC addition on downstream processes and determine optimum coagulant dosages and belt filter press settings when dosing high concentrations of PAC (Hazen and Sawyer, January 2015)

X

Discuss protocols for disposing of contaminated materials2 with MDE and USEPA to understand regulatory flexibility and limits (Hazen and Sawyer, January 2015)

X X

2025 WSSC Long Term Water Quality and Treatment Master Plan 15

Executive Summary Page 14 of 35

Water Quality Risks Addressed by Each Resilience Measure

Resilience Measure

Upstream chemical and/or petroleum releases and accidental spills

PFAS

Releases (Also addressed in other TMs)

E. coli and Cryptosporidiu m contamination from AFOs and CAFOs

Non-contamination risks - Source Water Quality (Addressed in other TMs)

Capital Improvements

Supply redundancy through alternative water supplies such as Travilah Quarry

X X

High turbidity, algal toxins, T&O, manganese, salinity, disinfection byproducts (DBP)

Continue to investigate new treatment processes

- Chlorine Dioxide Manganese, DBP

- Ozone X Manganese, DBP/T&O/algal toxins

- Granular Activated Carbon - GAC3 X4 X DBP/T&O/algal toxins

- Ultrafiltration/Ceramic Membranes X High turbidity

- Ionic Exchange X DBP/T&O/algal toxins

- Novel Adsorbents X4 X DBP/T&O/algal toxins4

- Nanofiltration X4 X X DBP/T&O/algal toxins

- Chloramines X DBP

Implement early warning and detection technologies such as additional sensors in existing locations as well as upstream of the intakes and/or oil booms for spills in the river. Potential to collaborate with others to share lab resources (Hazen and Sawyer, 2015 and 2020).

X

1. The general operations strategy for a contamination event would be to deploy the deflection boom, monitor the concentration of the contaminant plume, treat water at a lower flow rate to ensure PAC dosages are sufficient to remove contamination, and shut down the Plant when concentrations exceed the threshold for effective PAC treatment

2. Includes treatment plant residuals, backwash, decontamination wash water and solid wastes, flushing water, etc.

3. Use a combination of PAC and GAC for spills since GAC/PAC would offer advantages over PAC alone in terms of continuous readiness and more adsorptive capacity.

4. Indicates that the treatment effectiveness depends on the chemical/type of spill and/or the type of novel adsorbent.

2025 WSSC Long Term Water Quality and Treatment Master Plan 16

Executive Summary Page 15 of 35

5 Water Quality Regulation Review

The memorandum P1 TM5

Regulatory Review enumerated the most relevant current and upcoming drinking water regulations, particularly in reference to the Safe Drinking Water

Act (SDWA). Since then, USEPA finalized the PFAS National Primary

Drinking Water Regulation (NPDWR), issued the Lead and Copper Rule

Revisions (LCRR) and Lead and Copper

Rule Improvements (LCRI), and continues to assess changes to the

Microbial and Disinfection Byproduct

Rule (M-DBP).

USEPA Regulations Recently Issued or

Under Review:

PFAS National Primary Drinking Water

Regulations (NPDWR)

Microbial and Disinfection Byproduct Rule

(M-DBP)

Lead and Copper Rule Revisions (LCRR) and

Lead and Copper Rule Improvements

(LCRI)

5.1 PFAS Rule

USEPA issued a final National Primary Drinking Water Regulation (NPDWR) for six Per- and Polyfluoroalkyl Substances (PFAS) on April 10, 2024. WSSC Water has been monitoring PFAS levels in the finished water at their Potomac River WFP and

Patuxent WFP since January 2020. Trace levels of PFAS have been detected in

WSSC’s finished water, and in one sample at Potomac WFP, the PFAS concentration was above the proposed maximum contaminant level (MCL) for PFOS and

PFOA. This one result would not create a violation under the proposed rule, which compares the running annual average of PFAS to the proposed MCLs. Nonetheless, the PFAS Rule presents a compliance risk because:

• The PFAS MCL’s are at low, part per trillion concentrations, which are at or near detection limits,

• WSSC Water cannot control the presence of PFAS in its source waters, and

• Current treatment processes at the Potomac WFP and Patuxent WFP are not designed for PFAS removal.

While the PFAS Rule was finalized in 2024, there are ongoing legal and regulatory actions that would revise the Rule. The American Water Works Association (AWWA) and the Association of Metropolitan Water Agencies (AMWA) filed a petition for judicial review, indicating concern “…that EPA did not use the best available data and appropriate processes in developing the PFAS regulation.” As of May 2025, there has not been any decision on the AWWA/AMWA petition. However, on May 14, 2025, EPA announced it plans to rescind the PFAS NPDWR and issue new rulemaking in Fall

2025 and finalize it in Spring 2026. The announcement indicated EPA would extend the enforcement date from 2029 to 2031 and reconsider the regulatory determinations for PFHxS, PFNA, HFPO-DA (Gen X) and the Hazard Index of these three plus PFBS. The MCLs for PFOA and PFOS would remain unchanged, based on current reporting. The most impactful of these potential changes to the PFAS

NPDWR would be the time extension, which would allow more time for WSSC Water to continue monitoring its source waters for the presence of PFAS, explore the potential benefits of source control, and conduct pilot testing before determining its

PFAS treatment strategy.

2025 WSSC Long Term Water Quality and Treatment Master Plan 17

Executive Summary Page 16 of 35

5.1.1 Potential Cost Impact of PFAS

Ramboll prepared a supplemental memorandum P1 TM4 Rough Order of

Magnitude (ROM) Cost Estimates for PFAS Treatment at Potomac WFP to assist WSSC Water in assessing the potential cost of implementing treatment technologies that would reduce PFAS to concentrations below the proposed MCLs.

Ramboll’s independent ROM cost estimate for addition of granular activated carbon

(GAC) treatment for PFAS at Potomac WFP results in a capital cost of approximately

$700 million to $1.4 billion, for half to full rated plant capacity respectively, which when O&M is added to the estimated debt service, results in total annual cost of approximately $73 million to $109 million/year. Additional investigations in Part 2 identified an innovative alternative treatment strategy with potential to reduce the capital cost by up to roughly 50%. See also Section 7 Bench Scale Treatability

Testing for information on bench testing for GAC, anion exchange, nanofiltration and two novel adsorbents, and Section 8 Water Treatment Alternatives for additional information on the potential approaches to address the PFAS Rule.

5.2 Microbial and Disinfection Byproduct Rule

USEPA determined that multiple Microbial and Disinfection Byproduct (M-DBP) focused rules are candidates for revision, including the rules governing haloacetic acids (HAAs) and total trihalomethanes (TTHMs). USEPA anticipates issuing proposed rule revisions in Summer 2025, according to its most recent update in

February 2025. These revisions may require changes to treatment processes and/or operation, which could carry significant cost impacts to WSSC Water.

5.3 Lead and Copper Rule

Since the Part 1 Report was issued in 2023, USEPA issued the Lead and Copper

Rule Revisions (LCRR) and the Lead and Copper Rule Improvements (LCRI).

WSSC Water submitted its service line inventory prior to the compliance deadline of

October 16, 2024, and is actively engaged in complying with the various reporting and notification requirements of the LCRI. WSSC Water has undertaken a lead service line replacement program with a goal of replacing all lead service lines by the

EPA requirement date of 2037.

2025 WSSC Long Term Water Quality and Treatment Master Plan 18

Executive Summary Page 17 of 35

6 Reliable Treatment Capacity

The Water Quality and Treatment Master Plan assessed the reliable treatment capacities at WSSC Water’s Potomac and Patuxent WFPs; details of the desktop assessment prepared in Part 1, Task 1 are reported in P1 TM1 Water Treatment

Plant Capacity and the field tests performed at each plant during Part 2, Task 6 are discussed in the memo P2 TM6 Treatment and Hydraulic Capacity Phase 1.

6.1 Potomac WFP

Field testing in Part 2 supported the commonly attributed net rated capacity of approximately 285 MGD at Potomac WFP when operating with typical raw water quality. For context, maximum output since 2010 was approximately 234 MGD.

Under terms of a Consent Decree, Potomac WFP production could be limited to 100

MGD (net 90 MGD) when extremely high amounts of solids (turbidity) are present in the raw water. The 100 MGD constraint reflects the solids handling capacity at

Potomac WFP during an extremely high turbidity event.

6.2 Patuxent WFP

The Patuxent WFP has a nominal rated capacity of 72 MGD and was designed with gross hydraulic capacity of 120 MGD for flocculation, sedimentation and filtration processes with the intent that the added capacity could be utilized in an emergency.

The purpose of Part 2 tests at Patuxent WFP was to assess the facility’s ability to maintain target turbidity in the filtered water while operating at unit loading rates in excess of 72 MGD equivalent. The tests demonstrated that Patuxent WFP was able to maintain the target turbidity while the sedimentation basins and filters operated at gross capacity of up to 120 MGD, and at WFP net capacity of between 90 MGD and 105 MGD, depending on the number of filters in operation and the frequency of backwashing.

While the high-rate testing to date at Patuxent WFP is encouraging, additional testing and evaluations are recommended:

• Filter performance efficiency as measured using the Unit Filter Run Volume

(UFRV) metric was relatively low during the high-rate tests at Patuxent WFP.

Additional field testing is proposed to assess the impacts of sustained operations at the higher treatment rates and over a range of water temperatures. The additional testing would provide a better basis for estimating the net production capacity for Patuxent WFP when operating at peak hydraulic unit loading rates.

• In the recent past, diatom events have limited the net capacity at Patuxent to as low as 40 MGD, but WSSC Water staff developed strategies that mitigate the impact of diatoms under typical operating conditions. Additional testing is proposed to assess the reliability of high production rates, i.e.

greater than 72 MGD, during diatom events.

• WSSC Water recently completed construction of a fourth raw water pipeline, enabling the conveyance of up to approximately 110-120 MGD to Patuxent

WFP. As a result, it is now possible to conduct “whole plant” tests, to better

2025 WSSC Long Term Water Quality and Treatment Master Plan 19

Executive Summary Page 18 of 35 define Patuxent WFP’s overall capacity, including hydraulic capacities of the plant’s pretreatment and raw water flow measurement, backwash recycle capacity and finished water (gravity and pumping) delivery.

6.3 Ability to Meet Projected Demands

The Capacity Technical Memorandum compared the combined plant capacities with

WSSC Water’s projected 2045 water demands. Under most conditions, treatment capacity is projected to be adequate, but two unlikely conditions present scenarios in which WSSC’s production capacity may not be sufficient:

1) Peak turbidity event in Potomac River concurrent with 2045 projected demands: The 2045 average day “high demand” projection for WSSC system-wide is 197 MGD. Allowing for a 110% peaking factor during a high turbidity event would require 217 MGD of total production capacity. If

Potomac WFP is limited to 100 MGD production (90 MGD net) concurrent with this 2045 projection, WSSC would not have sufficient capacity even if

Patuxent WFP operates at its estimated peak hydraulic capacity (90 to 105

MGD net). This future concurrence of peak turbidity at Potomac WFP with relatively high demand is considered possible but unlikely.

2) Peak turbidity event in Potomac River concurrent with 2045 projected demands and a diatom event at Patuxent WFP: Pending additional testing at

Patuxent WFP during diatom events, it is anticipated Patuxent WFP may be limited to its rated capacity of 72 MGD (65 MGD net) during a diatom event, resulting in a more significant deficit than above. This future concurrence of events is considered possible but highly unlikely.

Note: The conversion of Travilah quarry into a regional water storage reservoir would significantly enhance WSSC Water’s reliable treatment capacity by mitigating the risks presented above by allowing the Potomac WFP to switch from river water to reservoir water during periods of peak turbidity, as well as during periods of chemical and biological contamination, algal blooms, wintertime “frazil ice” and salinity spikes related to road salting.

Please see Table E-8-1 for a summary of each WFP production capacities.

Table E-8-1: Potomac and Patuxent WFPs water production capacity summary.

WFP

Nominal Gross

Capacity

(MGD)

Net Nominal Capacity (MGD)

Net Peak Capacity

(MGD

Peak Net Capacity during Potomac River High Solids

Events (MGD)

Peak Net Capacity during Potomac River High Solids and Diatoms

(MGD)

Range of Estimated

Reliable Net Capacity (MGD)

Potomac 300 234 234 90 90 90 to 234

Patuxent 72 65 90 to 105 90 to 105 40 to 65 40 to 105

Totals 372 299 324 to 339 180 to 195 130 to 155 130 to 339

2025 WSSC Long Term Water Quality and Treatment Master Plan 20

Executive Summary Page 19 of 35

7 Bench Scale Treatability Testing

As a result of recommendations from Part 1 of the Master Plan, a series of bench scale studies were proposed and later discussed with WSSC during workshops at the beginning of Part 2. An overall treatment alternatives table (also described as a prioritization matrix) detailing treatment options, challenges, and contaminants of interest was prepared as a part of Task 1 (P2 TM1 Treatment Alternatives

Evaluation). To assess certain aspects of the proposed treatment enhancements or alternatives, three main groups of bench tests were conducted: PFAS treatability, DBP formation, and removal of algal toxins and taste and odor compounds, as described in the following sections.

7.1 PFAS Bench Testing

Despite the lack of PFAS detections in the Patuxent WFP sources and with only trace levels of PFAS being detected in the Potomac River source water, WSSC could face compliance risks with the new NPDWR due to its low MCLs and the uncontrollable nature of some PFAS sources. The Potomac WFP was selected for treatment studies and considered for potential future implementation because of previous detections of

PFAS, higher production capacity, and the river’s large watershed with higher risk of source water contamination. Treatment options were selected based on current practices, literature review, regulatory requirements, and commercial availability.

Two well-established PFAS removal methods were considered: exclusion by a membrane and adsorption by a sorptive media. NF and reverse osmosis (RO) membranes are both recognized as Best Available Treatment technology (BAT) by

EPA. NF was selected for evaluation based on its significantly lower reject volume and lower cost than RO. As for the sorbents, the six media selected included one granular activated carbon (GAC), four ionic exchange resins (IX), and a novel adsorbent (cyclodextrin). These sorbents were tested for their sorption capacity via isotherms and five were further evaluated through rapid small scale column tests (RSSCTs). A secondary novel adsorbent (modified clay) was evaluated along with GAC as an option to treat the concentrated NF reject due to its reported tolerance to co-contaminants by testing its PFAS sorption capacity. All experiments were conducted with Potomac WFP post-filtration samples spiked with

10 PFAS, including all 6 compounds listed in the NPDWR. Experimental methods and results are further described in P2 TM2 PFAS Treatability Tests

Because any new treatment method is expected to impact other water quality parameters and potentially improve the removal of other contaminants of concern such as TOC, this task was coupled with Task 3 related to DBP formation. The treatment effluent of five adsorbents were subjected to DBP formation potential tests as described in P2 TM3 Disinfection Byproduct Formation Tests. NF was also tested for concomitant removal of algal compounds as described in P2 TM4

Algae-Related Treatment Enhancement Through NF Tests.

Selected findings of this study are presented below, see P2 TM2 PFAS Treatability

Tests for additional details.

2025 WSSC Long Term Water Quality and Treatment Master Plan 21

Executive Summary Page 20 of 35

Isotherm Tests:

• Six adsorbents were screened for their PFAS sorption capacity via isotherm tests:

o GAC - Calgon FILTRA-SORB® 400-01 (F400) o IX – Calgon CalRes 2301 (CalRes 2301), o IX – Dupont™ AmberLite™ PSR2 Plus (PSR2+), o IX – Purofine™ PFA694E (PFA694), o IX – LEWATIT® TP 108 (TP 108) o Cyclodextrin – Cyclopure DEXSORB® (Dexsorb)

• One ionic resin was discarded due to lower sorption capacity (TP

108), and the others proceeded into Rapid Small Scale Column

Testing.

Rapid Small Scale Column Test (RSSCT):

• RSSCTs confirmed expectations that the tested adsorbents are more effective at removing certain PFAS, such as long chained PFAS and sulfonic acids, while less effective at removing short-chain PFAS and carboxylic acids.

o The PFAS Rule which EPA announced they will reestablish in

2026, is expected to include MCLs only for PFOA and PFOS, both long chain compounds that are effectively removed by the tested adsorbents.

• The resin PSR2+ outperformed the other adsorptive media tested with respect to breakthrough time and adsorption capacity.

• The resin CalRes 2301 had the lowest removal efficiency of all ionic resins.

• GAC performed less effectively than expected in the RSSCT;

however, GAC should be included with subsequent on-site piloting to confirm the findings in this study since it offers some operational advantages, and it may perform better in a long-term pilot and full-scale application.

o GAC resilience to oxidation by chlorine makes it a good candidate for PFAS treatment at the site.

o GAC offers potential advantages in its ability to be reactivated, mitigating disposal issues.

o GAC catalytically quenches chlorine and could serve as a lead vessel to subsequent resin vessels is a tandem GAC/IX treatment scenario.

o Particularly rapid break through observed with PFOS was surprising and may indicate testing anomalies.

•…