Hydrant flushing programs

HYDRANT FLUSHING PROGRAMS

Brian GongolDJ Gongol & Associates, Inc.

September 16, 2015

Iowa AWWA Fall Short CourseDMACC / Ankeny, Iowa

Important note

This presentation borrows heavily from an AWWA learning module for small systems entitled "Distribution System Operations and the Impact of a Flushing Program on Water Quality"

The AWWA module was funded by the EPA Much of the text and a limited number of illustrations are

taken from that presentation The layout/organization of the content and most of the

illustrations are original and are intended to improve upon the original

What's the purpose of flushing?

Flushing is usually considered a corrective measure

Flushing is better seen as a tool to maintain water quality

Why flush?

Flush to address customer complaints

Flush to remove sediment and loose deposits

Flush to expel contaminants after a backflow incident

Flush to scour distribution lines

Flush to decrease water age in dead-end mains

Flush to restore chlorine residuals

Flush to prevent nitrification

Flush to respond to nitrification

A look at flushing programs

Who here has an active flushing program?

What triggers a round of flushing in your system?

A four-step flushing program

1: Determine if flushing is appropriate

2: Plan and manage flushing

3: Collect data

4: Evaluate and revise the program

Flushing isn't always appropriate

Ask these questions first

Do you use unfiltered surface water?

Do you use undisinfected ground water?

Do you have high iron and/or manganese?

Do you have positive results for coliform?

Do you have elevated heterotrophic plate counts?

Is your water chloraminated?

Has treatment changed in a way that could affect water quality?

Do your customers complain a lot?

Do parts of your system have low disinfectant residuals?

Are you aggressive about exercising valves, hydrants, and tanks?

Is your source water corrosive?

Does sediment accumulate in your storage facilities?

If you answered "Yes", flushing can help

To recap: Flushing helps in these cases

Unfiltered surface water Undisinfected ground water High iron High manganese Coliform HPCs Chloramines Treatment changes Valve exercise Corrosive source water Sediment

If none of those apply, try something else

Five alternative options

Alternative 1: Source treatment

Alternative 2: Booster disinfection

Alternative 3: Valve exercise

Alternative 4: Pipe lining

Alternative 5: Storage tank elevation adjustment

But let's suppose flushing is appropriate

If you're going to flush, you need a plan

Plan your flushing with clear objectives

Objectives for water quality

What are you trying to achieve? What has to improve? How much improvement is enough?

Objectives for cost

It may not have reached the customers, but the water still has value

So does your time and labor

Plan for water quality

Flush with clean water behind you

Plan for hydraulic consequences

Plan for mechanical consequences

Determine flushing approach

Approach 1: Conventional

Approach 2: Unidirectional

Approach 3: Continuous blow-off

Three approaches in detail

Approach 1: Conventional flushing

Most common method

Requires minimal pre-design

Just keep opening hydrants

Open hydrants in the distribution systemuntil criteria are met

Criteria

Disinfectant residual Discoloration Turbidity

Think ahead

Don't draw poor-quality water into high-quality areas Most important for nitrification remediation

No isolation means low velocity

What can you expect from conventional flushing?

Restoration of disinfectant residual

Expulsion of some poor-quality water in some areas

But conventional flushing has shortfalls

Shortfall 1: Customer complaints

Shortfall 2: Wasted water

Shortfall 3: Improvements are minimal

Shortfall 4: Improvements are short-term

Shortfall 5: Risk of increased coliform incidents

Shortfall 6: Chlorinated water discharge

Is there a better way than conventional flushing?

Approach 2: Unidirectional flushing

Unidirectional flushing can be isolated in the distribution system

System-wide or as-needed

Velocity matters

Velocities 3 fps or greater

Remove silt and sediment Reduce disinfectant demand


Promote scouring Remove biofilm Loosen deposits Reduce disinfectant demand


Remove sand from inverted siphons

Pipe size, flow, and velocity

Size FPS GPM 400 gpm hydrants 1000 gpm hydrants

4" 6 250 1

6" 6 550 1

8" 6 950 2

12" 6 2,100 5 2

24" 6 8,300 8

36" 6 20,000 20

Other benefits of unidirectional flushing

Valves get operated

Simultaneously flush and complete preventative maintenance

Wastes less water than conventional flushing

Establishes baseline for future comparisons

Reduces troubleshooting

Unidirectional flushing illustrated








Think: Flush from the inside out

Guidelines for unidirectional flushing

Tell customers in advance

Reach out to high-need customers

High-need customers: Hospitals

High-need customers: Dialysis patients

High-need customers: Restaurants

High-need customers: Hotels and pools

Unidirectional flushing is for night owls

Avoids service disruptions

Start from the source and work outward

Use diffusers and hoses to avoid property damage

Water should move from flushed into un-flushed areas

That's what makes it uni-directional

Flush from larger into smaller mains

Think: Flushing from clean to dirty

Smaller mains shouldn't flush larger mains

Not enough flow Not enough velocity

Keep pipe lengths short

Use valves where appropriate Maximize velocity over short runs

Maintain pressure above 20 psi

Warning: Gate valves trap slugs of water

If isolating with gate valves, re-open the valve before closing the hydrant

Removes slugs of water trapped behind valves

Get the most from unidirectional flushing

Plan ahead Collect data Analyze the data Improve the next plan

Approach 3: Continuous blow-off

Used if you can't escape stagnation or circulation problems

Continuous blow-off is slow

Usually 1 fps or slower

Good for restoring and maintaining disinfectant residuals

Reduces water age

Usually results in significant water loss

Doesn't fix the problem at the source

Continuous blow-off illustrated

Mainly useful at small dead ends

Recap: Three options for flushing

Conventional Unidirectional Continuous blow-off

If (appropriate) flushing has been planned and executed...

...then for the love of Neptune, collect some data

Data key 1: Identify loops

Flush from large to small

Flush from source to periphery

Flush in loops that can be completed in one shift

Data key 2: Check your speed

Aim for 6 fps pipe velocities

Data key 3: Develop and document a sequence

Get specific

Detailed instructions for the order ofopening and closing valves and hydrants

Conduct a trial run

Be ready for the unforeseen, especially on a trial run

Flush during off-peak hours

Have a safety protocol in place

Collect data in action

Collect baseline data

Collect data during the flush

Collect data after the flush

So you've determined that flushing is appropriate...

...and you've planned the flushing program...

...and you've collected data on a trial run...

...now, evaluate and revise

Did you meet the water-quality objectives?

How much did the flushing program cost?

How much did the flushing program save?

Did any bonus benefits result?

Did you encounter any unforeseen problems during or after?

Make it a habit

As with any good health practice,do it again and again and again

Establish a baseline

A few nitty-gritty details

Do your training before you're in the field

How to flush a hydrant

Open and close slowly to prevent surges

A 1 fps velocity change can comewith a 50 to 60 psi pressure rise

Open hydrant valves completely

Prevents water from discharging through the barrel drain Protects the hydrant support Preserves water quality if sampling from a partially-open

hydrant

Restrain your flow dissipators

Limits property damage Protects workers

Discharge directly to sewers when possible

When sewers aren't available, redirect traffic

And use signage!

When is dechlorination appropriate?

Flushing time depends on the objective

Sample water frequently until objective is met

Common objectives

Reduction in turbidity Reduction in color Increase in chlorine residual

The point of quality objectives

What's "good enough" determineshow much flushing is enough

Record flushing time to estimate water use

Hydrant safety

Use caution!

Flushing water has a lot of force

Water could contain rocks, bolts, and other objects

Check all attachments for tightness

Warn motorists and watch for traffic

Be cross-connection aware

When using hoses to discharge to sewers,watch for cross-connection

Expect water hammer

Other people will notice

Coordinate with the fire department

Promotes teamwork Kills two birds with one stone Offers a buffer with the public Fire departments are almost bulletproof in the public eye

Notify the public

They will think you're just wasting water

You are flushing to improve water quality

You are flushing to maintain the system

You are flushing to reduce chemical treatment

You are flushing to reduce chemical use in distribution

You are flushing to promote system hydraulics

You are flushing so they don't get sick

You are flushing to maintain fire protection

Resources

AWWA Video – Unidirectional Flushing http://www.awwa.org/store/productdetail.aspx?

productid=7076

AWWA Water Distribution Operator Training Handbook http://www.awwa.org/store/productdetail.aspx?

productid=36142344

AWWA Water Distribution Systems Handbook http://www.awwa.org/store/productdetail.aspx?

productid=6435

WRF Report: Guidance Manual for Maintaining Distribution System Water Quality

http://www.waterrf.org/Pages/Projects.aspx?PID=357

Questions?

Questions?

Thank you for coming!

Thank you for your attention!

Contact us anytime with questions

Brian Gongol DJ Gongol & Associates 515-223-4144 [email protected]

References

Primary text supplied by AWWA Flushing diagrams supplied by AWWA All other photos are original work by and copyright reserved

to Brian Gongol

Hydrant flushing programs

Engineering