WATER QUALITY – FROM SOURCE TO TAPKEVIN T. LAPTOS, REGIONAL PLANNING LEADER

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• Co-Authors

• Scott Huneycutt, Union County Public Works

• Ben Cownie, Black & Veatch

• Jeff Coggins, Black & Veatch

ACKNOWLEDGEMENT

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• Introduction

• Case Study - Union County, NC

• Background/Objective

• Water quality data analysis

• Hydraulic modeling

• Summary & Conclusions

PRESENTATION OVERVIEW

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INTRODUCTION

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Goal

DELIVERING HIGH QUALITY WATER –THE FOCUS IS SHIFTING

• Water Treatment Plants

• Produce high quality drinking water

• Meet water quality regulation

standards

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Deliver high quality water

to the customer tap

• Water Distribution Systems

• Degrade treated water quality

• Meet water quality regulation standards???

DISTRIBUTION SYSTEM ADVERSE IMPACTS

• Increases water travel time from WTP to customer

• Pipeline network

• Storage facilities

• Additional time for reactions and processes to occur

• Reduction in Cl2 residual

• Formation of DBPs

• Nitrification (in Chloramine systems)

• Sedimentation

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DISTRIBUTION SYSTEM SOLUTIONS

• Potential exists for significant water quality problems

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Elevated

Standpipe

Ground

Reservoir

• Potential problems can be avoided through proper system planning, design, and operation

• Storage facility solutions

• Pipeline network solutions

• Operational solutions

CASE STUDY -UNION COUNTY, NC

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BACKGROUND

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• Union County Water System

• Southeast of Charlotte

• Two (2) sources of supply (Chloramines)

• Catawba river - CRWTP

• Yadkin river – Wholesale purchase from Anson County

• Five (5) pressure zones

• Average daily demand of 10.5 mgd

• Changes in the Distribution System (2010)

• Expansion of water supply agreement with Anson County

• Pressure Zone realignments

• New WQ and operational challenges

• Very low chlorine residual in 853 East Zone

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OBJECTIVES

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• Develop understanding of water age, chlorine residual, and other water quality parameter profiles in 853 East Zone

• Identify capital and/or system operational solutions to increase chlorine residuals in 853 East Zone

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PRELIMINARY WQ DATA ANALYSIS

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• Biological Nitrification

• Potential exists in systems that add ammonia to form chloramines

• Microbial activity prevalent in locations of system with low chloramine residuals

• Free (unreacted) ammonia combined with lower residuals can trigger growth of nitrifying bacteria

• Two steps

• Step 1 – Conversion of Ammonia to Nitrite

• Step 2 – Conversion of Nitrite to Nitrate

NH3 + O2 NO2- + 3H+

NO2- + H2O NO3

- + 2H+

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PRELIMINARY WQ DATA ANALYSIS

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• Analyze WQ sampling data

• From Oct 2011 to Feb 2013

• 7 Locations

• Profile key parameters related to chloramines application and WQ

Primarily focused on potential biological nitrification

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PRELIMINARY WQ DATA ANALYSIS

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• Total Chlorine

• Tallwood and Hargette significantly lower

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

S O N D J F M A M J J A S O N D J F M

To

tal

Ch

lori

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, m

g/

L

Entry Point

Presson Road

Marshville Tank

Tallwood

Hargette

New Salem

2011 2012 2013

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PRELIMINARY WQ DATA ANALYSIS

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• Free (unreacted) ammonia

• Tallwood and Hargette significantly lower

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

S O N D J F M A M J J A S O N D J F M

Fre

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mm

on

ia,

mg

/L

Entry Point

Presson Road

Marshville Tank

Tallwood

Hargette

New Salem

2011 2012 2013

Nitrites, pH and dissolved oxygen values at Tallwoodand Hargette also different from other sites

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PRELIMINARY WQ DATA ANALYSIS

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WATER QUALITY

SAMPLING POINT

ESTIMATED WATER AGE

(DAYS)

Entry Point 3

Presson Road 9

Marshville Tank 4

Tallwood 17

Hargette 14

New Salem 7

• Utilize model to determine average water age at each sampling point

Highest water ages at Tallwood and Hargette

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PRELIMINARY WQ DATA ANALYSIS

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• Tallwood and Hargette WQ sampling points indicate biological nitrification

• Model-predicted water ages high (14 to 17 days)

• Remaining five WQ sampling points do not indicate biological nitrification

• Model-predicted water ages lower (3 to 9 days)

Water age of 12 days established as “threshold” to avoid biological nitrification

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MODEL CALIBRATION

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• Existing hydraulic model updated

• All-pipes

• Water demand allocation

• Calibration

• Confirm model accurately simulates SCADA readings at tanks, pump stations, pressure monitoring locations

• Increase confidence that the model can accurately predict water ages

• High water ages simulated at Hargette and Tallwoodsample locations

• Hargette: long dead-end main

• Tallwood: NW Tank impacts

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WQ MODELING – BASE SCENARIO

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High Water AgesHigh Water Ages

853 East

853 West

• Shift 853 West/East Zone Boundary to the West

• Added more demand in vicinity of NW Tank

• Increased tank turnover and decreased water age to < 12 days

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WQ MODELING – SCENARIO 1

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853 East

853 West

• Eliminate 853 West/East Zone Boundary

• Increased NW Tank turnover similar to Scenario 1

• Decreased water ages to < 12 days

• Provided supply flexibility from Anson County

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WQ MODELING – SCENARIO 2

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Eastern Flow Maximized Eastern Flow Maximized

853 East

853 West

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FINAL RECOMMENDATIONS

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• Eliminate 853 West/East Zone Boundary (Scenario 2)

• Reduces water ages below 12 days at all locations (except some isolated dead-ends)

• Decreases potential for biological nitrification

• Increases chlorine residual

• Previously recommended by Master Plan

• Free Chlorine Burn-Out

• Temporarily discontinue ammonia feed

• Allow free chlorine to kill any nitrifying bacteria in pipes

• Resume ammonia feed after measurable free chlorine is established throughout system

SUMMARY & CONCLUSIONS

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• Many water quality challenges still exist in distribution systems

• Possible to establish correlation between water quality sampling results and simulated water age

• Water age is a useful surrogate parameter to assess water quality

• Complex constituent (i.e. chlorine, DBPs) modeling not necessarily needed

SUMMARY & CONCLUSIONS

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SU

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NC

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• Manage water age in distribution systems by proper system planning, design, and operations

• Increase chlorine residual

• Reduce Nitrification (chloramine systems)

• Reduce DBPs (free chlorine systems)

• System operational changes

• Effective at reducing water age

• Much less cost to implement than capital improvements

• System modeling is an effective system assessment approach

• System-wide water quality results

• Ability to compare relative benefit of system improvement scenarios

SUMMARY & CONCLUSIONS (CON’T)

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COMMENTS OR QUESTIONS?

KEVIN T. LAPTOS, REGIONAL PLANNING LEADER

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