Balancing DBP Formation with Corrosion Control Concerns for a Blended Water Supply on Maui

County of Maui Department of Water Supply

PNWS-AWWA Annual Conference Kennewick, WA May 5, 2017

Bill Persich, P.E. Joanie Stultz, E.I.T.

• Background and Project Objectives • Description of Existing System and Operations • Water Quality Assessment • Recommended Chemical Feed Systems

Presentation Summary

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Background and Project Objectives

Four Water Supply Sources

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• Customer Notification Required When Upper Kula Customers Cycle to Free Chlorine Disinfection

• Increases Disinfection Byproduct Formation of Upper Kula Water Due to Excess Free Chlorine

• Biofilm Sloughing • Possible Taste and Odor Problems

Problems of Mismatched Disinfectants

Brown and Caldwell 5 https://www.kwrwater.nl/en/onderzoek/health-en/biological-activity/

• Pre-design for a New Chloramination Station at the Omaopio Tank

• Understand Additional Chemical Feed Systems Based on Water Chemistry

Project Objectives

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Description of Existing System

Existing Water Treatment

Description Water system

Lower Kula/Makawao Upper Kula

Water System Kamole Weir WTP Pookela well Piiholo WTP Olinda WTP

Treatment process Membrane Filtration Disinfection Only Direct filtration Membrane Filtration

Primary disinfection Chlorine Chlorine Chlorine Chloramines

Residual disinfection Chlorine Chlorine Chlorine Chloramines

Corrosion control Soda ash Not used Soda ash Food-grade lime

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Piiholo WTP Dual Media Filter Wailoa Ditch Outlet to Kamole WTP Olinda WTP Pookela Well Discharge Head

• Pump Station • 3 Submersible pumps, one as standby • 2,400 GPM Firm Capacity

Upper Kimo Tank Booster Pumps

New Upper Kimo Pump Station

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Water Quality Assessment UCF Blending Study

• Study Performed by University of Central Florida • Water Quality Blending Concerns After Chloramination

• Total Chlorine Residual Stability • DBP Formation (TTHM/HAA5)

• Tested Various Composite Blends in June 2016 • UKT: Blends of Lower Kula Water Only (Upper Kimo Tank) • UKS: Blends of Upper and Lower Kula Water (Upper Kula System)

Blending and Disinfectant By-products (DBP) Study

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Results of Total Chlorine Residual Stability

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• Lower(UKT) and Upper Kula(UKS) Blends were comparable

• Less decay and longer retention time for UKS

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200

Tota

l Cl 2,

or F

ree

Cl2

,mg/

L

Time, hours

Disinfectant Residual Decay Curves Summary

UKS1 (total)

UKS2 (total)

UKS3 (total)

UKT (free)

96 hours (0.7 mg/L)

168 hours (0.4 mg/L)

Results of TTHM/HAA5 Testing

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0102030405060708090

0 48 96

TTH

M, µ

g/L

Holding Time, hours

UKT1

UKT2

UKT3

MCL

MCLG

010203040506070

96

HAA

5, µ

g/L

Holding Time, hours

UKT1

UKT2

UKT3

MCL

MCLG

0102030405060708090

0 6 48 96 168

TTH

M, µ

g/L

Holding Time, hours

UKS1

UKS2

UKS3

MCL

MCLG

010203040506070

168

HAA

5, µ

g/L

Holding Time, hours

UKS1

UKS2

UKS3

MCL

MCLG

MCL

MCLG

MCL

MCLG

MCL

MCLG

MCL

MCLG

• Results Can be Impacted by Excessive Water Age in UKT Blends • Pre-formed DBP’s from Lower Kula Not Considered

Chloramination Recommendations

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• New Chloramination Station at the Omaopio Tank • Total Chlorine Residual Target: 2.5 mg/L • Chemicals

• Sodium Hypochlorite Solution (12.5% by wt.) • Anhydrous Ammonia

Water Quality Assessment RTW Modeling for Corrosion Control Chemical Dosing

Corrosivity Indices of Water Sources

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Water quality constituent

Finished water

Olinda WTP

Finished water

Kamole WTP

Finished water

Piiholo WTP Finished water Pookela Well

Desired corrosivity values

TDS, mg/L 26.2 46.0 45.0 86.0

Temperature, °C 21.2 23.6 22.9 20.0

pH 9.00 9.20 9.30 8.64

Alkalinity, mg/L as CaCO3 5.6 14.6 25.8 40.0

Ca, mg/L as CaCO3 9.70 4.25 2.75 17.00

Cl-, mg/L 5.2 9.1 5.1 4.0

SO4-2, mg/L 0.6 1.1 0.5 2.1

Calculated Langelier index -0.92 -0.64 -0.49 -0.24 => 0 (minimize

corrosion risk)

Calculated alkalinity/(Cl- + SO4

-2) 1.0 1.4 4.6 6.6 >5

Calculated Ryznar index 10.84 10.49 10.29 9.12 <6–7

Calculated aggressiveness index 10.73 10.99 11.15 11.47

>12 (not corrosive) 10–12 (mildly corrosive) <10 (corrosive)

• Chloramination Will Slightly Reduce Corrosivity of Blended Water

• Sodium Hypochlorite Adds Non-Carbonate Alkalinity • Raises pH > 9.0

• Evaluation Conditions: Most Conservative • Assume Potentially Most Corrosive Lower Kula Water

100% Kamole WTP • Assume All Lower Kula Free Chlorine Residual Gone • Assume Total Chlorine Residual 2.5 mg/L required

Evaluate Supplemental Corrosion Control Measures for New Facilities

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1. Make No Further Corrosion Control or pH Adjustments • Valid if No Current Lead/Copper Rule Violations • Valid if Current State of Piping Corrosion is Acceptable • pH Will Increase Slightly

2. Reduce pH to Target 9.0 • Add CO2 at the New Chloramination Station

3. Provide Additional Corrosion Control and Adjust pH • Select Target LI = 0.0 (Theoretical “Ideal” Water) • Add Soda Ash • Control pH to 9.0 with CO2

Three Possible Corrosion Control Options

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Feature Existing Upper Kula Water

Option 1a Option 2a Option 3a

Description Existing Only Chloraminate Only Adjust pH Adjust LI and pH

Total Chlorine Residual, mg/L

2.5 2.5 2.5 2.5

Soda Ash Dose, mg/Lb

0 0 0 92

CO2 Dose, mg/L 0.0 0.0 1.3 36

pH 9.0 9.4 9.0 9.0

LI -0.92 -0.43 -0.82 0.0

Three Options for Supplemental Corrosion Control Measures

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a. Calculation based on 100% Kamole WTP Water for Blending b. To be dosed at existing WTPs

Results

Ideal Water

3. Add Soda Ash and CO2 if “Ideal” Water is Desired

1. Corrosion Potential Reduced for All Options 2. Add CO2 if pH Adjustment is Desired

Recommended Chloramination Facilities

Recommended Disinfection Feed System for New Chloramination Station

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• 12.5% Liquid Sodium Hypochlorite • Design Dose: 0.5 to 5.0 mg/L Cl2 /L • Design Flow: 1,100 – 2,400 gpm • Four(4) 275 gallon totes for 30-day supply • 3 diaphragm metering pumps (60 gpd)

Recommended Ammonia Feed System for New Chloramination Station

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• Anhydrous Ammonia (Liquefied gas) • 5:1 Mass ratio to Cl2 (Mass Cl2/Mass N) • Design Dose: 0.1 to 0.5 mg/L NH3-N/L • Design Flow: 1,100 – 2,400 gpm • Four(4) 150 lb Cylinders for 30-day supply • 2 Ammoniators (18 ppd NH3)

Optional CO2 Feed System for New Chloramination Station

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• Carbon Dioxide (liquefied gas) • Design Dose: 0 to 36 mg/L NH3-N/L • Design Flow: 1,100 – 2,400 gpm • Seven (7) tons CO2 for 30-day supply • 1 Carbonic Acid Generator (1,033

ppd CO2)

Sodium Hypochlorite Feed Schematic

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Ammonia Feed Schematic

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Recommended Chloramination Station Plan View

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Bulk Delivered Hypochlorite

Proposed Site Layout

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Construction Cost Estimate

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Cost Item Total Cost

Base Construction Cost $799,000

Supplemental Constructiona $440,000

Allied Construction Costsb $985,000

Subtotal $2,220,000

Sales tax (4.166%) $92,700

Total Construction Cost $2,310,000

a. Supplemental: Demolition/Abandonment, Civil site work, Electrical, I&C b. Allied Construction Costs: Escalation, Startup, Contingency (30%), Earthquake insurance, Liability, Bonds, change orders

• Bulk Hypochlorite Delivery • No CO2 System

Thank you. Questions?

Chloramination

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HOCl H+ + OCl-

Cl2 + NH3 NH2Cl + H2O

Free Chlorine Disinfection Monochloramine Disinfection

Cl2 + H20 HOCl + HCl Cl2 + H20 HOCl + HCl

HOCl + NH3 NH2Cl + H2O

5:1 Mass ratio to Cl2 (Mass Cl2/Mass N) https://commons.wikimedia.org/wiki/File:Chloramination_breakpoint_curve_(theoretical).jpg