Wall Decay Coefficients - Ohiowater.org

Determination of Chlorine Bulk and Wall Decay
Coefficients for Calibration of the GCWW All-Pipes
Distribution System Model
Haishan Piao
Yeongho Lee
David Hartman
Cheryl Bush
OAWWA Annual Conference
September 22 , 2010
Columbus, Ohio

Presentation Overview
• GCWW System Overview
• Chlorine Monitoring Field Test
• Chlorine Bulk/Wall Decay Coefficients
• Calibration Goals and Results
• Conclusions

Greater Cincinnati Water Works:
System Overview
• 2 Treatment plants:
• Miller: Surface
• Bolton: Ground
• Avg. day pumpage:
140 MGD
• 3100 miles of Water main
• 20 Pumping stations
• 27 Storage tanks
• 11 Pressure zones
• Customers
• Retail
• Wholesale
• Population: 1.1 millions

Distribution System Model:
All Pipes Model
• Built from System-
Wide GIS Data
• Includes all pipes
≥2” in diameter
• Pipes: 200,000
• Hydraulic Calibration
• Chlorine Calibration
• Master Planning,
WQ Analyses, and
Operational
Modeling

Model Calibration Flow Chart
All Pipes Model Construction
Flow/Pressure/Head Loss
Field Testing
Chlorine Monitoring
Hydraulic Calibration
Max Day Calibration
Min Day Calibration
Hydraulic
Verification
Chlorine Calibration
Bulk/Wall Decay
Coefficients Options
Chlorine Calibration
Model Scenarios

Friction Coefficient (C-Value)
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
Model Hydraulic Calibration
• Detailed Analysis and Assignment of C Factors
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
All Mains Constructed
Since 1947 (New Mains)
1947 to Present Before 1947
Mains Constructed before
1947 (Old Mains) as shown
> =42"
24" to 36"
12" to 20"

Field Testing to Monitor Chlorine
Residuals
• Conducted during summer and fall of
2007.
• 5 monitoring zones
• 38 temporary
monitors per zone
• Free chlorine
• pH
• Total – 190 locations
• Calibration day for
each zone

Field Testing to Monitor Chlorine
Residuals (cont’d)
• Monitoring Equipments
• Free chlorine and pH:
• ATi Q45H/62
• Data Logger:
• Hobo H08-005-4
Chlorine/pH
Controller
Chlorine
Probe
Pressure
Regulator
pH
Probe

Water Surface Elevation (ft)
Model Hydraulic Verification
685
680
675
670
665
660
655
650
645
640
7/23/07 7/30/07 8/6/07 8/13/07
SCADA Data
Model Data

• Bulk Decay
• Nature of source water
• Type of water treatment
• Wall Decay
• Pipe material
• Pipe condition
Chlorine Decay

Chlorine Bulk Decay Coefficients
• Bulk decay coefficients were developed
based on simulated distribution system
(SDS) test conducted during field testing
program
• Four samples collected for SDS tests at
10-day intervals
• August 9
• August 20
• August 30
• September 10
• 1 st order curves were developed based on
water age and source

Miller Plant First Order Bulk Decay Curves
Miller Plant

Bolton Plant First Order Bulk Decay Curves
Bolton Plant

Chlorine Wall Decay Coefficients
• Approaches to develop wall decay
coefficients:
• Standard global coefficients: Software built-in
“F” curves based on C factor
Wall Decay Coefficient = F/C
• Multiple curves based on C factor, pipe
diameter, and water source
• Single customized curves based on C factor

Wall Decay Coefficients:
Software Built-in “F” curves

Wall Decay Coefficients:
Multiple Curves Based on C-Factor and Diameters –
Wall Option 1 (W1)

Wall Decay Coefficients:
Multiple Curves Based on C-Factor & Source –
W4 & W5

Wall Decay Coefficients :
Single Custom Curve Based on C-Factor –
W2, W3 & W6

Wall Decay Coefficients:
Overview
W1 Lined
W1 Unlined - Small Diam
W1 Unlined - Large Diam
W2 - Single Curve
W3 - Single Curve
W4 - Single Curve - Miller
W4 - Single Curve - Bolton
W5 - Single Curve - Miller
W5 - Single Curve - Bolton
W6 - Single Curve

Model Inputs for Water Quality Runs
• Bulk and wall decay coefficients
• Chlorine concentration at clearwells
• Hydraulic time step – 60 min
• Water quality time step – 2 min
• Simulation time – 21 days

Chlorine Calibration Goals
• Age ↑ - Chlorine↓
• Older water – further out
in the system
• 0-12 hrs → 0.1
• 12-24 hrs → 0.15
• >24 hrs → 0.2

Miller Plant First Order Bulk Decay Curves
Miller Plant

Calibration Results:
Bulk Decay Options Comparison
Summary of B1 and B2 Results with Comparative Wall Decay Options
Number of Locations Calibrated
Water Age 0-12 hrs 12 - 24 hrs > 24 hrs
Calibration
Goals 0.1 mg/L 0.15 mg/L 0.2 mg/L
Total
Locations
%
Calibrated
Number of
Locations
3 7 25 35
B1W1 0 4 16 20 57
B1F-7 0 4 22 26 74
B1F-10 0 4 23 27 77
B2W1 1 6 24 31 89
B2F-10 1 6 22 29 83
B2W2 1 6 25 32 91

Calibration Results:
Wall Decay Options Comparison
• Software Built-in Wall Decay “F”
Curves
• Decay coefficients depend only on
C factor
Wall decay Coefficient = F/C
• Less accurate results

Wall Decay Coeficient, Kw
Wall Decay Coefficients:
0.00
Wall Decay Coefficients
Hazen Williams C Value
0 20 40 60 80 100 120 140
-0.05
-0.10
-0.15
-0.20
-0.25
-0.30
W1 Lined
W1 Unlined - Small Diam
W1 Unlined - Large Diam
W2 - Single Curve
W3 - Single Curve
W4 - Single Curve - Miller
W4 - Single Curve - Bolton
W5 - Single Curve - Miller
W5 - Single Curve - Bolton
W6 - Single Curve
-0.35

Calibration Results:
Wall Decay Comparison (cont’d)
170 Points of Calibration
(After Eliminating Bad and Questionable Data)
Number of Locations Calibrated
Water Age < 12 hrs 12 - 24 hrs > 24 hrs
Calibration
Goals
Number of
Locations
0.1 mg/L 0.15 mg/L 0.2 mg/L
Total
Locations
25 29 116 170
%
Calibrated
B2W1 13 24 106 143 84.1
B2W2 14 24 106 144 84.7
B2W3 13 25 109 147 86.5
B2W4 14 24 108 146 85.9
B2W5 14 25 108 147 86.5
B2W6 14 25 107 146 85.9

Calibration Results:
Wall Decay Comparison (cont’d)
Test
Zone
Modeled Concentration vs. Observed Concentration (170 Points of Calibration)
Option
B2W1
Deviation in Chlorine Concentration (mg/L)
Option
B2W2
Option
B2W3
Option
B2W4
Option
B2W5
Option
B2W6
Zone 1 0.116 0.103 0.113 0.121 0.113 0.109
Zone 2 0.098 0.137 0.102 0.094 0.102 0.110
Zone 3 0.125 0.095 0.115 0.117 0.111 0.109
Zone 4 0.059 0.054 0.053 0.057 0.053 0.052
Zone 5 0.110 0.086 0.096 0.088 0.090 0.093
System 0.102 0.095 0.096 0.095 0.094 0.095

Conclusions
• Field testing data were used for chlorine
calibration of GCWW all pipes distribution
system model.
• Chlorine Bulk Decay Coefficients:
• Bulk decay coefficients can be variable.
Especially for Miller water.
• Higher decay rate for younger water than older
water.
• Multiple 1 st order decay curves had to be
developed based on water age for each water
source to obtain the best results.

Conclusions (cont’d)
• Chlorine Wall Decay Coefficients
• Aggressive decay for older pipes compared to
younger pipes.
• Software Built-in “F” curves did not yield
desirable results.
• Highest degree of calibration achieved by using
curve based on pipe roughness, pipe diameter,
and water source.
• Wall decay coefficients simplified by a single
custom curve based on C-factor without
sacrificing calibration accuracy.

Acknowledgement
• Black & Veatch
• Eva Sinha, P.E.
• Jeff Stillman, P.E.
• Marissa Albright, P.E.
• Kevin Laptos, P.E.
• Larry Gaddis, P.E.
• ID Modeling
• Jerry Edwards, P.E.

Questions???
Haishan.Piao@
GCWW.Cincinnati-Oh.gov