Sustainability of water supply: a risk-based approach for distribution networks
Rehan SadiqAssociate Professor
Okanagan School of Engineering
University of British Columbia
Canada-Mexico Industry-Science Workshop forCanada-Mexico Industry-Science Workshop for
Innovation in Water Sustainability TechnologiesInnovation in Water Sustainability Technologies
March 29–30, 2010March 29–30, 2010
Chihuahua, MexicoChihuahua, Mexico
Sustainability
Sustainable development refers to the development that meets the needs of the present without compromising the ability of future generations to meet their own needs
Sustainability Matrices
DPSIR
Driving Force
Population growth
Economic development
Technology
Pressure
Water quantity
Water quality
Continuity
State
Condition of infrastructure
System reliability
Contamination
Exposure
Water quality failure
Hydraulic failure
Structural failure
Effect
Well-being
Morbidity
Mortality
Action
Proactive PreventiveHazard
ManagementProtective Corrective
DPSEEA
Waheed et al. (2009)
Water distribution networks
ToxicityAssessment
Risk Characterization
Exposure Assessment
Hazard Identification
Human Health Risk
Assessment Framework
Risk Assessment Risk Management
Risk Acceptance
RiskControl
RiskCommunication
Estimated value of Sustainability index
Acceptable value of Sustainability index
Decision actions
Control strategies
Interventions
1.0
0.0
Estimated value of Risk index
Acceptable value of Risk index
1.0
0.0
Sustainability Assessment
Risk Assessment
– Multiple barrier approach – Precautionary principle
– Total water quality management (TWQM)
– Hazard analysis critical control points (HACCP)
Source water protection
Water treatment
Disinfection
O&M of water distribution
MonitoringPublic
awareness
Physical barriers Virtual barrier
Water Quality Management
Public Utilities
Safety SafetyFree of excess chlorine residual Maintaining chlorine residual
Taste and odour Taste and odour
Good appearance Corrosion control
Uniform water quality DBP formation
Ranking of major water quality issues
• WRF-NRC joint study (FYs 2003-2009)
• Identify the multiple sources, pathways and causes of water quality failure (WQF) in distribution networks
• Develop a framework for integrating effects of various contributory factors to quantify risk of WQF as a function of aging water mains
water quality can be a decision driver for renewal of distribution mains
WRF-NRC Project
• Deteriorated pipes – increased breakage frequency
– leaks, softening
– leaching, internal corrosion
– tuberculation
‘Aging’ Water Distribution Systems
Europe
Disastrous Consequences
• Direct• Indirect and social
InspectionCondition rating
Failure risk
Corrosion initiation
• Size of corrosion pit• # broken wires, damaged• Coating• Delamination• Tuberculation …
Distress Indicators
• Failure modes• Current factor of safety …
Interpretation and Condition Assessment
Failure consequence
(cost of failure)
• Material properties• Pipe dimensions• Internal pressure• Temperature changes• Loss of bedding
support…
Physical model
1
Fac
tor
of s
afe
ty
Time (years)
• probability of failure• time to failure
Deterioration model
Decision-making:risk vs. renewal or
inspection
Failure of System Integrity and Decision-making
Water Main Renewal:Failure Criteria
Water Main Renewal:Failure Criteria
Permeation
Contaminant intrusion
Leaching
Biofilm formation
Water treatment deficiency
Disinfectant loss &THMs formation
Internal corrosion
Water Quality Deterioration Mechanisms
Water Quality Modelling
• Hydraulic simulators (e.g. EPANET)– Residual chlorine, Disinfection byproducts (DBPs)– Organics– Water age
• Regression & kinetics-based models– Residual chlorine, DBPs– Biofilm– Corrosion
• GIS-based display models
Risk map
Attributes layers
Age Pipe materialBreakage frequencySoil propertiesPressureResidual chlorine…
Risk inferencing through scoring methods or MCDA
Water Quality Modelling
Water quality indicators
Site-specific factors (Environs)
Operational and hydraulic factors
Mitigative decision actions
Pipe attributes
Potential for WQF Potential for WQF
Pipe deterioration mechanisms
Water quality deterioration mechanisms
Water m
ain
Risk-based Conceptual Framework
Complexity in Evaluating Impacts of Pipes on Water Quality
• Pipes of different ages, materials, sizes under varying environmental conditions
• Variations in operational and hydraulic conditions
• Difficult and expensive to collect data on performance and deterioration
• Some factors/ processes affecting pipe performance are not fully understood
Complexity in Evaluating …
• causes and effects are not well understood…
• highly non-linear in behavior…
• requires methods that combine human knowledge, experience, expert judgment …
• low probability & high consequences…
Fuzzy Cognitive Maps (FCMs)
Fuzzy Cognitive Maps (FCMs)
CiCj
wij
Ci
Ci + 1
Cn
Cj
C1
C2
C3C5
C6
C4
w14
w54
w12
w56 w36
w23w32
w42
w24 w52
w43
w16
w61
w46
w35
GWT fluctuation
Condition of appurtenances
Potential for cross-connection
Pressure
Contamination distance
Leakage from pipes
M7
S1
Type of soil Burial depth
Load level Breakage rate
Pipe age
Pipe diameter
Pipe material
M5External corrosion
M9
M2
Contaminant intrusion
M3
Time to responsePotential for leaks
M1
Leakage from appurtenancesM6
M8
M4
Potential for Contaminant Intrusion
Predicting Water Quality Failures (WQF)
Potential for contaminant intrusionPotential for contaminant intrusion
Pot
entia
l for
wat
er q
ualit
yde
terio
ratio
n m
echa
nism
s
Potential for Internal corrosionPotential for Internal corrosion
Potential for leachingPotential for leaching
Potential for Biofilm formationPotential for Biofilm formation
Potential for disinfectant loss andTHMs formationPotential for disinfectant loss andTHMs formation
Potential for permeationPotential for permeation
Modular FCMs
Physico-chemicalWQF
Physico-chemicalWQF
MicrobiologicalWQF
MicrobiologicalWQF
AestheticWQF
AestheticWQF
Supervisory FCM
Potential for WQFPotential for WQF
MediumMedium
Low
Low
Low
Low
V. low
Medium
High
Medium
Medium
Low
V. high
Medium
Low
Medium
Medium
Low
Medium
Medium
V. low
V. low
V. lowV. low
V. low
V. lowV. low
V. low
V. low
V. low
V. low
V. lowLow
V. low
V. low
V. low
Predicting WQF…
Decision Support Tool Q-WARP
Pipe attributes EnvironsOperational/
Hydraulic factorsWater quality
indicators
Pipe age
Pipe diameter
Pipe material
…
Pipe age
Pipe diameter
Pipe material
…
pH
Res. disinfectant
Organic content
…
pH
Res. disinfectant
Organic content
…
Soil type
GWT fluctuations
Contaminant source…
Soil type
GWT fluctuations
Contaminant source…
Pressure
Water age
Velocity
…
Pressure
Water age
Velocity
…
Inputs
Potential for water quality deterioration mechanisms
Potential forwater quality failures
Outputs
• Predict risk of WQF in a given segment of pipe under given set of conditions
• Use qualitative/ quantitative input data
• Accommodate missing input data
• Generate multiple scenarios for different decision actions to facilitate decision-making
Basic information about the user and the pipe under investigation is provided.
Analysis for the existing condition of water quality in a pipe under investigation.
Analysis to identify the key input factors under given conditions.
Final report to print and document the results of a scenario.
The input data provided in this sheet facilitates subsequent analyses.
Water quality analysis for the proposed decision actions for the pipe under investigation.
Summary of results
Baseline analysis
Decision analysis Sensitivity analysis
Stanley Street - Philadelphia
• A comprehensive study was conducted on the deterioration of water quality in a 540-feet 6" unlined cast iron main in Philadelphia
• The pipe was installed in 1874 on Stanley Street. Stagnant conditions of the main’s dead-end configuration caused water quality deterioration
• Pipe flushing resulted only in short-term improvement. Though the water main replacement in 1987 has produced acceptable turbidity levels and higher disinfectant residuals, the dead-end configuration still caused poor water quality
Dead end
Bell fuel oil
12”
12”
20”
Firehydrant
6” Unlined cast iron pipe
1874 to April 1987
Fire station# 2703
12
3
Dead end
Bell fuel oil
12”
12”
20”
Firehydrant
6” Unlined cast iron pipe
1874 to April 1987
Fire station# 2703
12
3
Fire station# 2703
Dead end
Bell fuel oil
12”
12”
20”
Firehydrant
4” Ductile iron pipe(cement lining)
8” Ductile iron pipe(cement lining)
New fire hydrant
3
2 1
April 1987 to 2005
Fire station# 2703
Dead end
Bell fuel oil
12”
12”
20”
Firehydrant
4” Ductile iron pipe(cement lining)
8” Ductile iron pipe(cement lining)
New fire hydrant
3
2 1
April 1987 to 2005
Fire station# 2703
Dead end
Bell fuel oil
12”
12”
20”
Firehydrant
4” Ductile iron pipe(cement lining)
8” Ductile iron pipe(cement lining)
New fire hydrant
3
2 1
April 1987 to 2005
Stanley Street - Philadelphia
Stanley Street…
• Scenario 1 (before pipe replacement ~ 1983-1987)
• Scenario 2 (after pipe replacement ~ 1987-1988)
• Scenario 3 (~ 2002-2005)
Scenario 1 – Location 2 Baseline analysis
Scenario 1 – Location 2 Decision analysis
Scenario 1 – Location 3 Baseline analysis
Scenario 1 – Location 3 Decision Analysis
Stanley Street - Summary
• The water quality is deteriorated due to stagnant conditions at location 3
• Flushing can improve water quality on temporary basis but does not provide a long-term solution. Though the water main replacement has in general improved the water quality at location 2, it had no significant impact on location 3 (especially related to potential for biofilm formation and disinfectant loss)
• The looping of water main is an ideal solution to permanently achieve an acceptable water quality in the Stanley Street
Stanley Street - Summary
Additional measures may include:
• More frequent water quality sampling at location 3• Installation of smaller diameter pipes – to reduce residence
time (water age) • Extension of the dead end well beyond the last point of
consumption and installation of a fire hydrant at the very end of the line
• Installation of an automatic bleed valve at the end of the dead end to reduce residence time.
Summary & Conclusions
• Sustainability and risk assessment frameworks can be jointly developed for water supply systems
• Proposed approach can be extended to develop a decision support tool for integrated water resource management
• Water quality can be used as a main decision driver for rehabilitation/ maintenance/ replacement of water mains, treatment plants, storage reservoirs etc.
• Soft computing methods (e.g., FCM) can be used for robust decision-making for complex sustainability problems
Thanks for listeningYou always got to be prepared, but you never know for what -
Paradox of risk management
Financial supports from Water Research Foundation (US) and the Institute for Research in Financial supports from Water Research Foundation (US) and the Institute for Research in Construction (NRC-IRC) of the National Research Council of Canada are acknowledged. Construction (NRC-IRC) of the National Research Council of Canada are acknowledged.
