water quality –from...•system operational changes •effective at reducing water age •much...
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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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PR
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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
ne
, 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
e A
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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SU
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CO
NC
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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
MM
AR
Y &
CO
NC
LU
SIO
NS
• 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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