vaawwa-susceptibility of pws to negative pressure ... of pws to negative pressure transients kala...

Susceptibility of PWS to Susceptibility of PWS to Negative Pressure TransientsNegative Pressure Transients

Kala Fleming, PhD

VA AWWA Research Committee Seminar

Monday, October 22, 2007

2

Pump Station 5-min Pressure Recording

0

10

20

30

40

50

6/22/2004 6/23/2004 6/24/2004 6/25/2004 6/26/2004 6/27/2004 6/28/2004

Time

Pres

sure

(psi

)

3

DS Monitoring at 1 Reading per sec

pump start-up

pump shutdown

4

Negative for > 16 sec;as low as –10.1 psi (-69 kPa)

Gullick et al. 2005. J. Water Supply & Technol. – AQUA 54(2): 65-81.

Closer Look at Negative Pressure Profile

5

Why Do Pressure Transients Matter?

222 333

sewer mainsewer main

leaking pipe

leaking pipe

111

External Pathogens

Leaking Pipes

Transient Low Pressure

Microbial Risk?

6

Presentation Overview

Overview of Transient Pressure:– How do negative transients occur?

– Evolution of a transient pressure wave

Findings of AWWARF Project #3008

IL Case Study:

– What locations are impacted when the largest pump station looses power?

– Which mitigation approach works best?

Microbial Risk Assessment

7

Sudden change in demand – Flushing operations– Opening and closing a fire hydrant

Sources of Transient Pressures

Service interruptions– Power failure– Main breaks

Routine distribution system operation– Pump startup and shut down– Valve operation: open/close– Any sudden changes in flow

routineoperations

routineoperations

service interruptions

service interruptions

demandchange

demandchange

8

Transients influenced by fluid properties

Fluid Density

– water is heavy, large forces required to change flow

Fluid Compressibility

– water not easily compressed, small mass imbalances cause large forces

9

Transient Pressures from Unsteady Flow

power loss at pump velocity change pressure wave

ΔH = (c / g) ΔV

ΔH = instantaneous pressure head changedownstream of pump

c = wave speedg = acceleration

ΔV = change in velocity

http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html

Note: a wave is a disturbance that transmits energy and momentum from one point to another through a medium without significant displacement of matter between the two points

** only applicable for simple pipeline **

10

Pressure Wave in Single Pipeline

HGL-steady state

Adapted from Thorley 2006. Fluid Transients in Pipelines .

9 sec after failure

DISTANCE (mile)50 10

12 sec after failure

Reflection increases

pressure after ~ 14 sec

450 ft

HGL 7 sec after power failure

4.6 miles in 7 seconds

Wave front 7 sec after power failure

ΔH

hL

232 ft minimum head envelope during power failure

HGL-pumping

pump runs down in 7 seconds

Wave speed is 3,500 ft/s or ~0.66 mile/sec

g = 32.174 ft/s2 & V = 2 ft/s

ΔH = (c / g) ΔV

11

Pressure Wave in Single Pipeline

TIME (seconds)

100

200

300

400

500

4020

600

60 800

pump run down in 7 seconds

additional headloss until reflected wave

approaches

PRES

SUR

E H

EAD

(fee

t)

12

Negative for > 16 sec;as low as –10.1 psi (-69 kPa)

Gullick et al. 2005. J. Water Supply & Technol. – AQUA 54(2): 65-81.

Negative Pressure Profile

In more complex systems, reflections occur with changes in

diameter, changes in pipe material and at dead ends or other

discontinuities

13

Transient Analysis

Pressure pulses are generated when flow conditions change from one steady state to another

Pipeline plays a relative passive role, primarily transmitting disturbances from point to point

Boundary conditions (devices and connections at the end of each line) play the crucial role in determining the character and nature of system response and propagation

Hydraulic Modeling

Used to track pressure wave initiation, propagation, reflection…

15

Modeling is Important !

If you can model a system, i.e. describe its behavior using mathematical equations, then you can predict future behavior.

Key Benefits:– Identify Problems

– Optimize System Operation

– Make Informed Decisions

16

Model power loss at a pump station

negative pressure

0 to 20 psi

pressure > 20 psi

Pressure KeyPressure Key

Flow KeyFlow Key

Flow < 100 gpm

Flow > 100 gpm

use model to understand how

pressure and flow vary in the system

model is desktop representation of

real system

model is desktop representation of

real system

The term transient describes unsteady flow.

continuity and momentum equations used to solve unsteady flow problems

start with steady state or EPS model

Findings from AwwaRF Project # 3008

18

Project # 3008 Overview

16 participating systems

system size: 0.1 – 39 mgd

number of pumped sources ( 1 to 29)

pressure zones (1 to 24)

topography/elevation (flat, moderate, hilly)

distribution storage facilities (0 – 18 floating tanks)

Surge relief features

Variables:

19

Project # 3008 Significant Findings

Systems with steady state or EPS models already have the basics to assess potential for transient pressures!

In the absence of surge mitigation at pump stations, alldistribution systems were susceptible to low/negative pressure fluctuations

System susceptibilities ranged from 1% to 98%

– water velocity, number of floating storage facilities, number of source inputs and system configuration influence system vulnerability

– Velocities greater that 3 ft/s downstream of pump stations increase the risk of low/negative transient pressures

20

Storage Reduces Susceptibility

R2 = 0.9

0%

10%

20%

30%

40%

50%

60%

0 20 40 60 80 100 120

Miles of Main per Floating Storage

Perc

ent N

odes

with

Neg

ativ

e Pr

essu

re

at time of max flow to storage

at time of max flow from storage

21

System SizeSystem Size

Other factors…

Smaller systems showed increased susceptibility

5 of 6 systems with < 10 mgd system delivery drew negative pressure in greater than 35% of the system with complete loss of pumping power

Surface vsGround

Surface vsGround

System Config.System Config.

Hilly distribution systems (> 150 ft elevation difference) were less susceptible

Systems with more floating storage facilities were less susceptible to negative pressures

Locations at or near dead ends were more susceptible to negative pressures

Groundwater systems may have an increased susceptibility to low/negative pressure transients

A few systems showed

IL Case Study

Using modeling to prevent low/negative pressures after a power outage

23

IL Pressure Regulations

State is currently enforcing the maintenance of pressure greater than 20 psi under all flow conditions.

If pressure is less than 20 psi for even one second, a Boil Water Notice must be issued.

24

IL Water System Impacted By Regs

System fed by surface water and has a relatively flat topology

Primary pump station has a capacity of 30 MGD

Under 2006 max day conditions, HGL at plant varied between 899 ft and 906 ft (corresponding to 64 to 72 psi)

Primary pump station has unstable power supply.

Currently no floating storage in system

25

More Storage = Less Transient Pressure

R2 = 0.9

0%

10%

20%

30%

40%

50%

60%

0 20 40 60 80 100 120

Miles of Main per Floating Storage

Perc

ent N

odes

with

Neg

ativ

e Pr

essu

re

at time of max flow to storage

at time of max flow from storage

26

Pressure Monitoring Required

27

Rationale for Selecting Monitoring Locations?

28

Low Pressure Measured

29

How to Proceed?

Quick Fix

– Lease a generator that operates 24/7

Long Term

– Use model to assess extent of transient low pressures and examine range of solutions

30

Determine Susceptible Locations

31

What type of surge mitigation ?

24/7 generator

One 30,000 gal hydro tank & one 1MG elevated tank at Location B

One 30,000 gal hydro tank & one 1MG elevated tank at Location A

UPS sized to support 9 pumps

Two 20,000 gal hydropneumatic tanks

$ 30,000 per monthDo nothing

$ 1.5 millionOption 4




32

Hydropneumatic Tanks

air

water

pipeline under steady-state conditions

compressor

air

water

pipeline experiencing downsurge

compressor

water leaves tank to maintain pipeline pressure

33

Hydropneumatic tanks as a surge mitigation option

hydropneumatic tanks installed on

4/5/05

34

Transients in Distribution Systems

Is occurrencein smaller

piping significant ?

Is occurrencein smaller

piping significant ?

study of

unsteady flow

of liquids begins in

mid-19th century

study of

unsteady flow

of liquids begins in

mid-19th century

What is impactof transients

on water quality ?

What is impactof transients

on water quality ?

33

AW research demonstrated brief periods (20-50 sec) of low & negative pressure in several systems

Characteristics that increase vulnerability to negative pressures investigated

Pre-2000Pre-200033

2211

2000 - 20062000 - 20062211

What are typical intrusion volumes?

What is final concentration near nodes?

Assess Microbial Risk

2006 future2006 future

Focus on transients intransmission

mains

Focus on transients intransmission

mains


NNecessary. Provides logical approach to determine if transients can cause sufficient intrusion to impact the health of water consumers.

36


222 333

sewer mainsewer main

leaking pipe

leaking pipe

111

External Pathogens

Leaking Pipes

Transient Low Pressure

Microbial Risk?

37

We have Leaks…

2 4

< 10,00010,000 – 50,000

Source: AWWA 2005 –Benchmarking Performance Indicators for Water and WasteWater Utilities

*121 Participants*

14 1612106 80

50,001 – 100,000

100,001 – 500,000

> 500,000

WestSouth

MidwestNortheast

Distribution System Water Loss(Median Range, 25th – 75th Percentile)

Distribution System Water Loss(Median Range, 25th – 75th Percentile)

⎥⎦⎤

⎢⎣⎡ +

ddistribute volume)authorizedbut unbilled volume billed (volume - ddistribute volume100distribution

water loss (%) =

Percent

38

We have pathogens near pipe…

0

20

40

60

80

100

% O

ccur

renc

e

Total C

olifor

mFe

cal C

olifor

m

Clostrid

ium

Bacillu

s

Virus

RT-PCR

Phage

Water

Soil

Overall 63% (20/32) of samples were positive for viruses: enteroviruses (Sabin strain), Norwalk, and Hepatitis A virus

39


microbes outside distribution system piping

microbes outside distribution system piping

frequency of power outagesfrequency of

power outages

pathogen concentrations at intrusion nodes

after a power outage

pathogen concentrations at intrusion nodes

after a power outage

microbial risk forcustomer

microbial risk forcustomer

theoretical probability distribution

pipe flows; consumption patterns

intrusion volumesintrusion volumes

U.S.EPA annual acceptable microbial risk level is 10-4

There is quite a bit of uncertainty in

determining risk posed by intrusion

There is quite a bit of uncertainty in

determining risk posed by intrusion

40

Sustained Power Loss (>3 min)

Total Intrusion Volume = 7.4 gal (28.0 L)

22 nodes (41%) have intrusion volumes of 0.1 gal (0.4 L) or greater

Highest intrusion volume near customers was 0.74 gal (2.8 L)

J-45 0.7 gal

intrusion

Intrusion occurs at 54 demand nodes

41

J-45 0.26 gal

intrusion

Total Intrusion Volume = 3.8 gal (14.4 L)

15 junctions (28%) have intrusion volumes of 0.1 gal (0.4 L) or greater

Highest intrusion volume was 0.26 gal (1.0 L)

Power restored 2 seconds after power loss

Intrusion occurs at 53 demand nodes

Intrusion Volumes

42

Estimate Dilution Factors

38 L38 LIntrusion @ Node J-45

– Duration = 16s

– avg flow before transient period = 36 gpm

VoCo = VfCf

– Vo = 1L

– Vf = 38 L

Dilution factor @ J-45 = 2.6 X 10-2

0.26 gal intrusion

1L

43

Estimate Dilution Factors

0.01 gal intrusion

10 gal10 gal

0.04 L

Intrusion @ Node J-181

– Duration = 2 s

– avg flow before transient period = 79 gpm

VoCo = VfCf

– Vo = 0.04 L

– Vf = 10 L

Dilution factor @ J-181 = 4.0 X 10-3

44

Intrusion could be responsible for coliform positive samples…

For intruded volume, assume total coliforms = 1.6 x 103

MPN/100mL & fecal coliforms = 5 x 102 MPN/100mL

J-45 0.26 gal

intrusion

J-613, J-682 & J-683

> 1000 MPN/100 mL

~ .04 gal (1.5 L) intrusion

30 MPN/100 mL

106 MPN/100 mL

45

New AwwaRF Project

1. Assess microbial intrusion risk

• Determine daily exposure

• Use dose response model to determine risk of infection

2. Conduct utility survey to gauge how utility managers use pressure management to protect water quality

3. Monitor pressure & water quality continuously for two months, in six locations, in four different water systems

4. Develop Best Practices for Managing Distribution System Pressures

• Pressure monitoring

• Disinfectant residual maintenance

• Hydraulic modeling

“Managing Distribution System Pressures to Protect Water Quality”““Managing Distribution System Pressures to Protect Water QualityManaging Distribution System Pressures to Protect Water Quality””

Risk Management

Through

Pressure Management …

47

Pressure Management Approach

Distribution System Evaluation

Distribution System Evaluation

peak hour of max day hydraulic modeling assessments

peak hour of max day hydraulic modeling assessments

Are pressures less than 20 psiat any customer

locations?

Are pressures less than 20 psiat any customer

locations?

Can system producerequired fire flows

while maintaining pressuregreater than 20 psi?

Can system producerequired fire flows

while maintaining pressuregreater than 20 psi?

customer demandscustomer demands

power loss at all pump stations

power loss at all pump stations

Do any locationstemporarily

draw pressureless than 0 psi?

Do any locationstemporarily

draw pressureless than 0 psi?

fire flows

measurepressure and disinfectant

residual levels at low pressure locations



Review Surge MitigationOptions: system:

hydropneumatic tankelevated storageuninterruptible powerpump operation

Review Surge MitigationOptions: system:

hydropneumatic tankelevated storageuninterruptible powerpump operation





**surge model required**

48

Recap of Key Ideas

Transient pressures occur in water systems

Hydraulic modeling and

pressure monitoring are

important assessments that

should be conducted to

determine if low/negative

transient pressures occur in

your system

Important research questions need to be addressed:

– What are the health risks posed by intruded water ?

– How effective are disinfectant residuals?

– Do chlorine and chloramine provide the same level of protection from transitory contamination?

49

Intrusion References

Fleming K.K. and M.W. LeChevallier. 2007. Susceptibility of Distribution Systems to Transitory Contamination. Drinking Water Research. Vol 17, No 2. AwwaRF, Denver, CO.

Fleming K.K., R.W. Gullick, J. P. Dugandzic and M.W. LeChevallier. 2006. Susceptibility of Distribution Systems to Negative Pressure Transients. American Water Works Association Research Foundation, Denver, CO.

Friedman, M., L. Radder, S. Harrison, D. Howie, M. Britton, G. Boyd, H. Wang, R. Gullick, M. LeChevallier, D. Wood. And J. Funk. 2004. Verification and Control of Low Pressure Transients in Distribution Systems. AWWA Research Foundation. Denver, CO.

Gullick, R.W., M.W. LeChevallier, J. Case, D.J. Wood, J.E. Funk, and M.J. Friedman. 2005. Application of pressure monitoring and modeling to detect and minimize low pressure events in distribution systems. J. Water Supply & Technol. – AQUA 54(2): 65-81.

Gullick, R. W., M. W. LeChevallier, R.S. Svinland, and M. J. Friedman. 2004. Occurrence of Transient Low and Negative Pressures in Distribution Systems. J. Amer. Water Works Assoc. 96(11):52–66

Karim, M, M. Abbaszadegan, and M.W. LeChevallier. 2003. Potential for Pathogen Intrusion During Pressure Transients. Journal AWWA, Vol. 95, No. 5, pp. 134-146.

Kirmeyer, G. J., M. Friedman, K. Martel, D. Howie, M. LeChevallier, M. Abbaszadegan, M. Karim, J. Funk, and J. Harbour. 2001. Pathogen Intrusion into the Distribution System.AWWA Research Foundation and American Water Works Association. Denver, CO.

Walski, T.M. and T.L. Lutes. 1994. Hydraulic Transients Cause Low-Pressure Problems. Journal AWWA, 86(12):24-32.

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Contact InformationKala K. Fleming, PhDEnvironmental EngineerAmerican Water1025 Laurel Oak RoadVoorhees, NJ 08043 USAphone: (856) 309-4556fax: (856) 782-3603e-mail: [email protected]

AcknowledgementsProject funding provided by AwwaRF and by the

utility subsidiaries of American Water.

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