Modeling Water Quality In Drinking Modeling Water Quality In Drinking Water Distribution Systems: Its Water Distribution Systems: Its Potential for Enhancing Water Potential for Enhancing Water

SecuritySecurity

By: Robert Clark

Will DiscussWill Discuss

Concern over the vulnerability of water Concern over the vulnerability of water distribution systems to security threats distribution systems to security threats

Basics of water quality modeling and its Basics of water quality modeling and its application in drinking water networksapplication in drinking water networks

Two examples of water quality modeling Two examples of water quality modeling for water security for water security

The future use of water quality modeling The future use of water quality modeling as part of a decision support framework as part of a decision support framework

9/11 Raised Concerns About Critical 9/11 Raised Concerns About Critical Infrastructure in the USInfrastructure in the US

Water supply was identified as critical Water supply was identified as critical infrastructureinfrastructure

It is now general consensus that the It is now general consensus that the vulnerability of drinking water networks vulnerability of drinking water networks systems to security threats is a major systems to security threats is a major concernconcern

Utility industry has also recognized the Utility industry has also recognized the importance of environmental monitoring in importance of environmental monitoring in maintaining water securitymaintaining water security

Drinking Water Systems In The U.S.Drinking Water Systems In The U.S.

There are 54,000 community water There are 54,000 community water systems in US serving 264 million peoplesystems in US serving 264 million people

79% of the population receives drinking 79% of the population receives drinking water from large utilities (serving 10,000 or water from large utilities (serving 10,000 or more), representing 14% of the systemsmore), representing 14% of the systems

21% of the population receives water from 21% of the population receives water from small utilities (serving less than 10,000 small utilities (serving less than 10,000 people) representing 86% of the systemspeople) representing 86% of the systems

U. S. Water Supplies Have Common U. S. Water Supplies Have Common CharacteristicsCharacteristics

Water source Water source A lake, reservoir, river or ground water from an aquiferA lake, reservoir, river or ground water from an aquifer Surface supplies generally have conventional Surface supplies generally have conventional

treatment facilities and disinfectiontreatment facilities and disinfectionGround water systems Ground water systems May have full range of treatment technology but some May have full range of treatment technology but some

practice chlorination only or do not disinfect at allpractice chlorination only or do not disinfect at allTransmission systems Transmission systems Tunnels; reservoirs and/or pumping facilities; and Tunnels; reservoirs and/or pumping facilities; and

storage facilitiesstorage facilitiesDistribution system Distribution system Carrying finished water pipes to consumerCarrying finished water pipes to consumer

Distribution System is Most Distribution System is Most Vulnerable Part of Water SystemVulnerable Part of Water System

Community water supplies designed to deliver water Community water supplies designed to deliver water under pressure and most of the system capacity is under pressure and most of the system capacity is reserved for fire fighting purposesreserved for fire fighting purposes

Could damage or destroy a tank or reservoirCould damage or destroy a tank or reservoir Potential for the deliberate introduction of Potential for the deliberate introduction of

contaminants into a distribution system (back flow, contaminants into a distribution system (back flow, cross connections)cross connections)

Need to be able to predict contaminant transport Need to be able to predict contaminant transport pathways and to measure concentration of pathways and to measure concentration of contaminants in networks contaminants in networks

Cyber attack could also provide a serious threat to an Cyber attack could also provide a serious threat to an utilities operations. However many SCADA systems are utilities operations. However many SCADA systems are not connected to the Internetnot connected to the Internet

Predicting Contaminant Movement In Predicting Contaminant Movement In Drinking Water Distribution SystemsDrinking Water Distribution Systems

Movement of water in distribution systems is Movement of water in distribution systems is complexcomplex

The ability to predict movement is still relatively The ability to predict movement is still relatively crudecrude

Also need to be able to predict changes in Also need to be able to predict changes in concentration of contaminants concentration of contaminants

Few attempts to integrate monitoring and modelingFew attempts to integrate monitoring and modeling

Contaminants May Be Conservative, or Contaminants May Be Conservative, or May Experience Decay or Growth May Experience Decay or Growth

Changes may take place in the bulk phase Changes may take place in the bulk phase or at the pipe wallor at the pipe wall

Quality may be influenced by:Quality may be influenced by: Cross ConnectionsCross Connections Failures at the Treatment BarrierFailures at the Treatment Barrier Transformations in the bulk phaseTransformations in the bulk phase

Schematic of Chemical and Microbiological Transformations at the Pipe Wall

Schematic of Chemical and Microbiological Transformations in Drinking Water

Water Quality Modeling PrinciplesWater Quality Modeling Principles

Conservation of mass within differential lengths of pipeConservation of mass within differential lengths of pipe

Complete and instantaneous mixing of the water enteringComplete and instantaneous mixing of the water enteringpipe junctionspipe junctions

Appropriate kinetic expressions for the growth or decay of theAppropriate kinetic expressions for the growth or decay of thesubstance as it flows through pipes and storage facilitiessubstance as it flows through pipes and storage facilities

This change in concentration can be expressed by a differentialThis change in concentration can be expressed by a differentialequation of the form:equation of the form:

ijijij

ijij Ck

dx

dCv

dt

dC

Where: – Cji is the substance concentration mass/ft3) at position x and time t in the link between nodes i and j

– vij is the flow velocity in the link (equal to the link’s flow divided by its cross-sectional area in ft/sec

– kij is the rate at which the substance reacts within the link (mass/ft3/sec)

Storage tanks can be modeled as completely mixed,Storage tanks can be modeled as completely mixed,variable volume reactors where the change in volumevariable volume reactors where the change in volumeand concentration over time are:and concentration over time are:

Where:Where:- V- Vss is the volume (ft is the volume (ft33) of the tank) of the tank- C- Css is the concentration in tank s is the concentration in tank s

)()(

silj ssjLkksksss

k jkjks

s

CkCQCQdt

CVd

QQdt

dV

The following equation represents the concentration of materialThe following equation represents the concentration of materialleaving the junction and entering a pipe:leaving the junction and entering a pipe:

kj

Lxkjkj

xij Q

CQC

00xij

C

WhereWhere::

linktheofendtheationconcentrattheisC

and

linktheofbeginningtheationconcentrattheisC

Lxkj

xij

0

Model InteractionWater quality models are generally piggy backed on hydraulic models.

Water Quality Model

Hydraulic Model

Flows and velocities

Water quality results

Will Use EPANET To Illustrate the Need Will Use EPANET To Illustrate the Need For Integrating Modeling and For Integrating Modeling and

MonitoringMonitoring First example will be the application of First example will be the application of

EPANET to North Marin Water District in EPANET to North Marin Water District in California California • Illustrates the linkage between monitoring Illustrates the linkage between monitoring

and modelingand modeling Second example is the waterborne outbreak Second example is the waterborne outbreak

in Cabool Missouri in 1990in Cabool Missouri in 1990• Forensic application of modelingForensic application of modeling

Modeling of ContaminantsModeling of Contaminants

First field study using EPANET in First field study using EPANET in North Marin CaliforniaNorth Marin California

Modeled chlorine residual Modeled chlorine residual propagation and THM formationpropagation and THM formation

Applied to two source systemApplied to two source system

North Marin Water SystemNorth Marin Water System

Located near Novato , CaliforniaLocated near Novato , California Serves over 50,000 peopleServes over 50,000 people Virtually no rainfall during warm summer Virtually no rainfall during warm summer

monthsmonths Uses two sources of dramatically different Uses two sources of dramatically different

quality quality

LAKE

RIVER

Node 105

Node 120

NORTH MARIN NETWORK

Trace Lake

20.00

40.00

60.00

80.00

percent

Day 1, 5:00 AM

TTHM Formation for Stafford Lake and North Marin Aquaduct

020406080

100120140160180

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45

Time in Hours

ug/L

iter Stafford Lake

North Marin

Predicted Stafford Lake

Predicted Aquaduct

TTHMs at Node 12O versus time in hours

0

20

40

60

80

100

120

140

160

180

0 10 20 30 40 50

Time in Hours

TT

HM

s i

n u

g/L

TTHMs at node 120

Actual vesus predicited TTHMs at node 120

0

20

40

60

80

100

120

140

160

180

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49

Time in hours

TT

HM

S in

ug/

L

Actual TTHMs

Predicted TTHMs

Actual TTHMS vesus time at node 105

0

20

40

60

80

100

120

140

160

180

0 10 20 30 40 50 60

Time in hours

TTH

Ms

in u

g/L

Actual TTHMS

TTHMs versus time in hrs for Node 105

0

20

40

60

80

100

120

140

160

180

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48

Time in hrs

TTH

Ms

in u

g/L

TTHMs

Predicted TTHMs

Salmonella contamination occurred in Salmonella contamination occurred in municipal tank due to failure of hatches municipal tank due to failure of hatches and ventsand vents

Taste and odor complaints caused water Taste and odor complaints caused water officials to start flushing programofficials to start flushing program

Out of population of approximately 1000 Out of population of approximately 1000 people, 440 became ill and 7 people diedpeople, 440 became ill and 7 people died

Used model to track outbreak and identify Used model to track outbreak and identify sourcesource

EPANET Applied to Waterborne EPANET Applied to Waterborne Outbreak in Gideon Missouri in 1993Outbreak in Gideon Missouri in 1993

Municipal Water System in Gideon Municipal Water System in Gideon Was Old and in DisrepairWas Old and in Disrepair

Tuburculation and corrosion in the Tuburculation and corrosion in the distribution pipes was a major problemdistribution pipes was a major problem

Two municipal tanksTwo municipal tanks Another tank was located on the Another tank was located on the

property of the Cotton Compress which property of the Cotton Compress which was the major employer in the areawas the major employer in the area

Waterborne OutbreakWaterborne Outbreak

On November 29, 1993 Communicable On November 29, 1993 Communicable Disease Coordinator for the Missouri DOH Disease Coordinator for the Missouri DOH became aware of two high school students became aware of two high school students with culture confirmed with culture confirmed SalmonellosisSalmonellosis

Within two days five additional patients were Within two days five additional patients were hospitalized with confirmed hospitalized with confirmed salmonellosissalmonellosis

Missouri Department of National Resources Missouri Department of National Resources was informed that DOH suspected a water was informed that DOH suspected a water supply link to outbreaksupply link to outbreak

DNR samples were positive for fecal coliformDNR samples were positive for fecal coliform City of Gideon was required to issue a boil City of Gideon was required to issue a boil

water orderwater order

Number of Absentees in Gideon Schools

Homes with Cases Between 11/23 – 11/28 and 11/29 – 12/10 1994 in Gideon, Missouri

Comparison of Early Confirmed Comparison of Early Confirmed Cases and Salmonella Positive Cases and Salmonella Positive Sample Versus Penetration of Sample Versus Penetration of Tank Water During First Six Tank Water During First Six Hours of Flushing ProgramHours of Flushing Program

Current Status of Water Quality/Hydraulic Current Status of Water Quality/Hydraulic ModelsModels

Increasingly sophisticatedIncreasingly sophisticated Applied to exposure studiesApplied to exposure studies

• ATSDR study on contaminated ground ATSDR study on contaminated ground waterwater

Much research into modeling changes in Much research into modeling changes in water qualitywater quality• Formation of DBPs and Chlorine ResidualsFormation of DBPs and Chlorine Residuals

Tank Mixing ModelsTank Mixing Models

EPA Research in Real Time Monitoring EPA Research in Real Time Monitoring SystemsSystems

First EPA effort was development of sensors for First EPA effort was development of sensors for temperature, chlorine residual, fluoride and nitrate temperature, chlorine residual, fluoride and nitrate data with Battelledata with Battelle

Asked to assist during MCL violation in Asked to assist during MCL violation in Washington DCWashington DC

Initiated research on development of sensors and Initiated research on development of sensors and probes for chlorine residual, pH and temperature probes for chlorine residual, pH and temperature using pipe loopsusing pipe loops

Applied to DC water systemApplied to DC water system Future efforts should focus on integrating modeling Future efforts should focus on integrating modeling

and monitoringand monitoring

Summary and ConclusionsSummary and Conclusions

Water systems have been classified Water systems have been classified as critical infrastructureas critical infrastructure

Identified as potentially vulnerableIdentified as potentially vulnerable Contaminant Propagation Can be Contaminant Propagation Can be

Modeled and there are various Modeled and there are various models availablemodels available

EPANET is a public sector model EPANET is a public sector model that has become widely usedthat has become widely used

Summary and ConclusionsSummary and Conclusions

EPA has been conducting research into EPA has been conducting research into sensor development sensor development

Applied to operation of small package Applied to operation of small package plantsplants

Extended to chlorine residual monitoring Extended to chlorine residual monitoring in Washington DC systemin Washington DC system

Future research will focus on integrating Future research will focus on integrating remote sensing and water quality remote sensing and water quality modelingmodeling