Trihalomethanes Removal Evaluation June 26 2019 Introduction Purpose

Trihalomethanes Removal Evaluation June 26, 2019

Introduction & Purpose S Background With the onset of EPA’s Stage 2 Disinfectants and Disinfection Byproducts Rule, the Town was proactive in investigating and implementing process modifications to enhance treatment efficiency and effectively reduce regulated DBPs. S Motivation Although the system is in compliance with the Stage 2 rule, the potential for exceedance still exists particularly of total trihalomethanes (TTHMs) during the summer. S Purpose The purpose of this work was to assist the Town to develop and evaluate alternative DBP control strategies and provide recommendations for an effective DBP control strategy. TETRA TECH 2

How Do DBPs Form? An unintended consequence of chemical disinfection is the formation of DBPs. Free Chlorine Dissolved Organics (TOC) (Cl 2) Tem p Disinfection Byproducts (DBP’s) Br Tim e Factors Contributing to Higher TETRA TECH 3

Types of DBPs Trihalomethanes (TTHMs) Haloacetic Acids (HAA 5) Types of TTHMs: Chloroform Dichlorobromomethane Dibromochloromethane Bromoform Types of HAAs: Dichloroacetic Acid Trichloroacetic Acid Chloroacetic Acid Bromoacetic Acid Dibromoacetic Acid Maximum Contaminant Level: 80 μg/L Maximum Contaminant Level: 60 μg/L Regulatory compliance is based on a locational running annual average (LRAA). TETRA TECH 4

DBP Control Strategies S Flushing S Modified Disinfection DBP s ‒ Move Cl 2 location ‒ Reduce Cl 2 dose and/or time ‒ Use an alternative disinfectant S Remove DBP precursors (aka TOC) ‒ ‒ ‒ Coagulation Optimization GAC Adsorption Biological Active Carbon (BAC) Ozone-BAC MIEX / Ion Exchange Membranes S Remove DBP after formation ‒ Aeration ‒ Biofiltration TETRA TECH 5

Water Quality and Treatment Goals Constituent Goal Basis Concentration Goal Achieved? Treatment Requirement TTHM 80% of MCL 64 µg/L No 40% to 50% HAA 5 80% of MCL 48 µg/L Yes Goal Met Meet DBP Goals ≤ 2. 0 mg/L No 50% to 65% TOC TETRA TECH 6

Technologies Identified & Evaluated Spray Aeration GAC/BAC Ozone BAC Ion Exchange TETRA TECH 7

Spray Aeration Treatment Integration TETRA TECH 8

Spray Aeration Treatment Overview 1 Two Key Considerations: TTHM Speciation 2 TTHM Re-Formation TETRA TECH 9

TTHM Speciation [VALUE] 27% Chloroform Dibromochloromethane 60% Bromodichloromethane Bromoform TETRA TECH 10

TOTAL REGULATED DBPS (µg/L) Spray Aeration Treatment Example 80 µg/L THM Limit TTHM Formation WTP SITE BOUNDAR Y CONTACT TIME (DAYS) DISINFECTI ON CUSTOMERS TETRA TECH 11

TOTAL REGULATED DBPS (µg/L) Spray Aeration Treatment Example 80 µg/L THM Limit TTHM Removal WTP SITE BOUNDAR Y CONTACT TIME (DAYS) DISINFECTI AERATIO ON N CUSTOMERS TETRA TECH 12

TOTAL REGULATED DBPS (µg/L) Spray Aeration Treatment Example 80 µg/L THM Limit WTP SITE BOUNDAR Y CONTACT TIME (DAYS) DISINFECTI AERATIO ON N CUSTOMERS AERATIO N TETRA TECH 13

GAC/BAC Treatment Integration TETRA TECH 14

GAC/BAC Treatment Overview Two Key Considerations: 1 Empty Bed Contact Time 2 Carbon Change Out Frequency TETRA TECH 15

Biologically Active Carbon (BAC) Biological Removal Absorption F E C D B A TETRA TECH 16

Ozone-BAC Treatment Integration TETRA TECH 17

Ozone-BAC Treatment Overview Two Key Considerations: 1 Empty Bed Contact Time 2 Biodegradable TOC Fraction TETRA TECH 18

Ion Exchange Treatment Integration TETRA TECH 19

Fixed Bed Ion Exchange Overview Two Key Considerations: 1 Effectiveness 2 How Frequently Does it Have to be Regenerated TETRA TECH 20

Treatment Performance DBP Precursor (i. e. TOC) Removal TTHM Reduction Goal Achieved? Does not Remove TOC 20% to 40% Mostly 30% to 70% Yes BAC 25% Typical (5% to 60% Range) 8% to 50% Possibly Ozone-BAC 25% Typical (5% to 60% Range) 15% to 50% Possibly 30% to 60% Yes Water Quality/ Treatment Spray Aeration GAC Adsorption Ion Exchange ≈ ≈ TETRA TECH 21

Conceptual Cost Opinions Construction Cost Opinion ($) Unit Construction Cost Opinion ($/gal) Spray Aeration System within Clearwell $770, 000 $0. 40/gal Spray Aeration System within Bear Hill and Scituate Hill Tanks $1, 600, 000 $0. 80/gal GAC/BAC Filtration $2, 000 $1. 00/gal Ion Exchange $3, 900, 000 $1. 95/gal Ozone-BAC $5, 800, 000 $2. 90/gal Alternative at 2 MGD Capacity Relative Operating cost Minimal $$$$ Moderate/High $$$$ TETRA TECH 22

Recommendations Phase I: Spray Aeration ‒ Perform bench-top evaluation of spray aeration. ‒ Installation of spray aeration within the clearwell. ‒ Installation of additional spray aeration at the Bear Hill and Scituate Hill tanks or proceed with Phase II: Organic Removal ‒ Installation of organic removal technology capable of removing 50%to 65% of the combined filtered water TOC levels. ‒ Install a 1. 5 to 2. 0 MGD expandable to 3. 0 MGD GAC or ion exchange technology. ‒ GAC could be allowed to convert into biological mode during the higher quality winter/spring months. ‒ If GAC/BAC is selected, the design could be phased to allow the subsequent installation of ozonation, if required at a later TETRA TECH phase. 23

Q&A June 26, 2019