Presentation - AL/MS Section of AWWA

Harry D. Gong, Jr., P.E.
AL/MS AWWA Section Newsletter
Editor/Communications Chair
Environmental Engineer
Mississippi State Department of Health
Developing and Implementing
Distribution System
Flushing Program
From July 2002 AWWA Journal
(Journal AWWA 94:7; Melinda
Friedman, Gregory J. Kirmeyer, &
Edward Antoun)
Why do you flush?
• A corrective measure in response to
customer complaints
• To expel contaminants inadvertently
introduced into the system
Four Steps to a flushing program
1. Determining the appropriateness of
flushing as part of a maintenance program
2. Planning and managing the flushing
3. Implementing a flushing program and data
4. Evaluating and revising the program
• Although magnitude and frequency of
flushing programs will vary from system to
system, its probably one the many tools that
should be considered a good practice for
maintaining water quality in distribution
• It is also an important part of a good
distribution maintenance program
Step 1: Determining the
appropriateness ...
Should a utility consider a routine flushing program?
• Do you utilize an undisinfected groundwater supply?
• Do you use a water source w/ elevated Fe or Mn?
• Do you experience positive coliform results?
• Do you plan a treatment change?
• Do you experience frequent customer complaints
related to WQ?
• Do you have difficulty maintaining a disinfectant
Step 1: Determining the
appropriateness ...
• Is the system lacking an aggressive valve,
hydrant, tank exercising program?
• Is the water considered corrosive?
How many apply to your system?
• If any of those questions apply to your utility, it is
probable that WQ improvements would be realized
from a flushing program.
• If you had a yes to more than one, you should not
only consider it, but the utility could benefit from
more frequent flushing.
• Answering No, can you document the WQ issues
are not occurring
• You can’t assume residuals are maintained
• Monitoring should be conducted to document …
Questions needing an answer
• Are there hydraulic constraints in achieving
flushing velocities
• Is there enough water available to flush at
desired velocities
• Requirements for disposing of the water?
• What’s the estimated cost for conducting
• Is flushing the solution or only part of the
Questions needing an answer
• What other operational/maintenance practices
should be considered?
• Entire system or only a part
Other issues
• Effort high/benefit low = flushing may not benefit
• Other approaches - treatment, disinfection, may
address WQ issues
• Combo - cost effective
Step 2: Planning and Program
• Most important step to obtaining water
quality while minimizing unnecessary costs
and undesirable secondary effects
• What are your objectives
– Should include both WQ and
hydraulic/maintenance consideration
– Will depend on specific WQ goals
Uni-directional Flushing
• Isolating particular pipes or loops by creating single
directional flow
• Should be “engineered” with considerations
Crew size
Flushing duration
Equipment availability
Source location
• Comprehensive or spot base use
• Velocity usually  5 fps
• Can lead to both WQ and hydraulic improvements
Uni-directional Flushing
– Reducing time
– Allows for simultaneous implementation of
preventive maintenance activities
– Use less water than conventional flushing
– Standardizing procedures
– Reduces trouble shooting efforts
Conventional Flushing
• Little or no preplanning
• Involves opening hydrant, valve, etc. until WQ
issues are met
• Detectable disinfectant residual
• Reduction/elimination of color
• Reduces turbidity
• No valve isolation is involved, velocity not at max
• Low velocities & non-maximized cleaning
efficiency thereby transporting contaminants from
one main to another
Conventional Flushing
• Disadvantages to WQ
Increased complaints before and after
Waste of water
Short lived WQ benefits
Potential for increase coliform occurances
Continuous blowoff
• For systems w/ numerous dead ends and severe
water circulation problems
• Done to force a low velocity flow through small
• Velocity < 1 fps, adequate velocity may not be
• Can help restore disinfection residuals & water age
• Large quantity of water that may not provide a
Implementation of flushing
• Comprehensive systemwide basis
• Spot base - implemented more frequently
especially in chronic WQ areas
• Will depend
– System configuration
– WQ goals
Preliminary Program
• Will vary by planning and development
• Uni-directional flushing program produces
greatest long term effects
• Greatest level of planning involved
Obtain maps and review
hydraulic models
• Major step
• Maps
Flushing loops
Booster Station
Tanks, etc.
• Discharge locations
Preliminary Program
• List of stakeholders (customers/other water
– Who will be affected?
– Review with them to avoid problems
• Combining flushing program with
preventive maintenance
– Not stand alone program
– Coordination of other programs
Notify Public
Explanation of waste and complaints
Public appreciation
Educate and inform - both public and employees
Use media
Sensitive users flushing would be imperative
Step 3: Program Implementation
and Data Collection
Dividing the system into loops
Section starting with a source, manageable sections
Crew size, equipment, duration of flushing
Set desired flushing velocities > 5 fps
Outline step-by-step procedures w/ precise
• Maps for individual loops
• Assign worse case scenarios
• Program implementation
Step 3: Program Implementation
and Data Collection
• Program implementation flushing techniques
From well/plant to water line ends
Larger to smaller mains
 5 fps velocities
Exercising valves and hydrants
Trained and equipped crews
Best time - late night, early morning 11 pm - 5 am
Safety for crew and property
Data collection for program
• Helps determine if objectives are met
• Baseline
Helps locate problem areas
Make one system change at a time
Cost data tracked
• During flushing
– Data collected on specific WQ parameter
During flushing
Data collected on specific WQ parameter
Collect beginning, middle, end
Time to reach goal should be recorded
Pressure and flow data should be recorded
Upstream pressure checked, Why?
Update maps during procedure
Water disposal?
After flushing
• Short term
– Positive and negative results of flushing
– Check WQ parameters upstream of flushed area
– Can “stir it up”
• Long term
Take the time to manage data
• Use to justify costs
• Use to refine program
• Comparison of short-term and long-term to
determine if flushing has led to improvements
• If “clearing time” is not decreasing, no benefits
• Other approach may be necessary (treatment)
Step 4: Evaluate program and
refine it as necessary
• Justify need or no need for it
• Benefits may not be realized instantly
• Experimentation may be necessary
Step 4: Refining and Evaluating
a Flushing Program
• Were water quality objectives met?
• What were the estimated costs/savings
associated with the program?
• Were there positive secondary effects
because of the flushing program?
• Were there negative secondary effects from
the flushing program?
Additional Safety Considerations
• Ensure crews are properly equipped with
personal protective equipment and the
correct tools
• Use appropriate size crew
• Operation of valves within paved portions
of active streets
• Diversion of traffic
• Wear brightly colored vests
Additional Safety Considerations
• Keep the public away especially children
• Use written procedures and help coordinate
• Open hydrant valves completely
• Open and close hydrants and valves slowly
• Use well-restrained energy dissipators
• Discharge flushing water directly to a
sanitary or storm sewer whenever possible
• Four Steps in Developing a Flushing
Determine the appropriateness
Develop a plan to manage the program
Implement the plan and collect data
Evaluate the results and revise as necessary
Additional Information
Stay in touch
Linked In:
601-576-7518 or (cell) 601-573-0002
Copy of this presentation is available for download in the
Education/Training Section of the Section Website
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Article that this flushing presentation is from at the following link:
Non-members may purchase a copy of the article for $30
That’s It