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Table of Contents Unidirectional Flushing (UDF) Guide for Water Distribution Systems i W192BV-10-D-2006, Task Order 003

Table of Contents Preface Introduction Flushing a Distribution System UDF Plan UDF Sequences Frequency of Conducting a UDF

Step-by-Step Guide for Unidirectional Flushing of a Water Distribution System

Appendix A UDF Forms

Appendix B References and Additional Information

Appendix C Example Notification of Distribution System Flushing

Preface Unidirectional Flushing (UDF) Guide for Water Distribution Systems 1

Preface Introduction The purpose of this guide is to provide water practitioners a methodology to implement an effective Unidirectional Flushing (UDF) plan. A UDF plan, as opposed to routine water main flushing, is a process of closing valves and opening hydrants to direct clean water down a single water main, thus creating a velocity that can scour the pipe and remove sediments from the bottom of the pipe. A UDF process can:

• Improve water quality

• Improve carrying capacity of pipes

• Benefit the operation of the water system

A UDF plan identifies the general sequence of pipes to be flushed, the specific sequence of valve operations, and the estimated duration of each flushing sequence.

This document is aimed primarily at base Water Shop personnel who are responsible for the hands-on maintenance of the water distribution system.

This preface includes a general description of a UDF plan and the reasons for conducting it. Following this preface is a step-by-step guide for conducting a UDF plan at Air Force bases. Following the step-by-step guide are appendices that include references and additional information and an example notification of distribution system flushing.

A Microsoft Excel file associated with this UDF guide can be found at:

https://cs.eis.af.mil/a7cportal/eDASH/Web% 20Part%20Pages%20%20Programs/Water %20Quality.aspx. Go to Documents, Resource Type: Tools

Flushing a Distribution System A variety of water quality problems that occur in a distribution system can be, at least partially, addressed by distribution system flushing. For example, the American Water Works Association Research Foundation (AwwaRF) maintained that once taste and odor problems are encountered, the only reasonable action is to bring better quality water into the area by extensive flushing.

AwwaRF also noted the importance of records to assist in identifying problem areas, documenting effectiveness of operations, and promoting good customer relations (AwwaRF 1992).

Water main maintenance should include flushing distribution mains for many reasons, including:

• Corrosion control

• Sediment and debris removal

• Taste and odor control

• Colored water

• High turbidity

• Low disinfectant residuals

• Bacteriological growth

• Customer complaints

The general objective of flushing is to assist in preserving and/or improving water quality and service.

Preface Unidirectional Flushing (UDF) Guide for Water Distribution Systems 2

Traditionally, distribution system flushing included opening hydrants without closing valves to isolate specific water mains for flushing. This traditional approach is referred to in this document as “conventional flushing.” Conventional flushing procedures involve flushing mains in areas where water quality complaints have occurred - a reactionary approach.

Conventional flushing procedures can also be system-wide, but no effort is made to assure that clean water is entering the pipe being flushed or that adequate velocities are being reached to scour the pipes.

Conventional flushing typically does not result in enough velocity to remove biofilm or to remove all sediment from the pipes.

Improvements in distribution system water quality may be marginal and short-lived.

Unidirectional flushing consists of isolating particular pipe sections, typically through closing appropriate valves and opening hydrants in an organized, sequential manner. Unlike conventional flushing, unidirectional flushing targets individual pipe segments to maximize flushing effectiveness. By isolating individual pipe segments, it is possible to consistently achieve scouring velocities of five feet per second (fps) or more that can effectively remove sediments and biofilm, which can accumulate in the water distribution system.

In addition, a UDF plan is organized such that each target pipe segment is flushed from a “clean” source. Complete unidirectional flushing of a water system ensures that every pipe segment is effectively cleaned.

UDF Plan A UDF plan should be developed for all Air Force water systems to maintain the cleanliness and efficiency of the piping network.

The most effective way to develop a UDF plan is to use a hydraulic computer model of the distribution system. Modeling software has provisions for developing flushing sequences and for calculating the volume of water and time needed for adequate flushing. The model can also calculate whether problems in the distribution system, such as low or negative pressure, may occur elsewhere in the system when a pipe is flushed.

A UDF plan can also be developed without a hydraulic computer model. This UDF guide is intended for bases that do not have a hydraulic model of the distribution system.

Developing a UDF plan will require a map of the system showing:

• Pipe locations

• Pipe diameters

• Valve and hydrant locations (with identification or numbering)

• Connections to flushing water sources, such as elevated storage tanks, pump stations, and connections to community water systems providing water for the base.

Advantages of a UDF Plan over Conventional Flushing:

• Improved flushing and scouring velocities

• Removes biofilm and sediment

• Flushes with clean water

• Overall cleaner distribution system

Preface Unidirectional Flushing (UDF) Guide for Water Distribution Systems 3

A strategy for flowing fresh water (from a well, water treatment plant, or city connection) through the system at adequate scouring velocities should be developed.

The methods outlined in this step-by-step guide can help expedite a manual process to find the most effective UDF plan.

The UDF plan will require trial and error to optimize the plan in the field.

UDF Sequences A UDF plan requires opening and closing certain valves, and opening flushing hydrants for each specific segment of main.

These segments are referred to as “flushing sequences.” The plan requires operating water system fixtures consistently according to the plan to ensure minimum flow velocities can be achieved and that no contamination of previously cleaned lines occurs (i.e., the plan must be followed in the order of the pre-defined steps).

The UDF plan consists of flushing logs, which are data tables describing the sequence (one flushing log for each sequence) and a map or maps showing the location of the sequence, valves to be closed and opened, and hydrant(s) to be flushed. To build a UDF plan, drawings are developed showing a system of flushing sequences to flush all pipes in the distribution system. The flushing logs also describe actions and guidelines for the flushing sequence, and outline the information to be collected by crews conducting the UDF plan.

The flushing logs have two purposes. First they provide UDF plan information. Second, they serve as a form to record field data.

The flushing sequences are grouped together into sequence groups. The sequence groups are created as a guideline for organizing and planning the UDF plan. It is estimated that each sequence group can be completed within approximately one day.

Frequency of Conducting a UDF The Unified Facilities Criteria (UFC), Operation and Maintenance: Water Supply System UFC 3-230-02 recommends conducting a flushing plan annually. The recommendation is based on a conventional flushing plan.

After a UDF plan has been successfully conducted for a few years, it may be possible to reduce the frequency to every two years or more because unidirectional flushing is more effective than conventional flushing.

Indicators could also be used to determine when the next UDF should be conducted.

Water system indicators could include:

• Low chlorine residuals

• Increase in THM or other disinfection byproduct concentrations

• Increase in the number of water quality complaints, such as discoloration, taste or odor.

• Increase in measured turbidity

• Increase in heterotrophic plate count

(HPC) concentrations

Step-by-Step Guide for Unidirectional Flushing of a Water Distribution System

Table of Contents Unidirectional Flushing (UDF) Guide for Water Distribution Systems

Table of Contents

Planning Step 1 Obtain Water Maps Step 2 Pre-Flush Turbidity Measurements Step 3 Inspect Valves and Hydrants Step 4 Prepare Flushing Sequence Plan Step 5 Locate and Operationally Test Flushing Valves and Hydrants .. 7 Step 6 Revise Flushing Sequence Plan Step 7 Prepare Flushing Forms Step 8 Pre-Flushing Notifications Step 9 Gather Tools and Supplies Step 10 Prepare Repair Contingency Plan

Field Work Flushing Step 11 Field Team Meeting Step 12 Flushing – Pre-Position Workers and Equipment Step 13 Set Up Dechlorination Equipment, If Needed Step 14 Verify Radio Communications Step 15 Verify Tank Water Depths and Pump Status Step 16 Sequence 1 – Isolate Appropriate Valves Step 17 Sequence 1 – Begin Flushing Step 18 Sequence 1 - Measure Color/Turbidity

Field Work Post-Flushing Step 19 Sequence 1 – Record Flushing Data Step 20 Sequence 1 – Remove Flushing Diffuser and Fasten Hydrant

Caps Step 21 Inspect for Landscape Damage and Debris Step 22 Sequence 2 – Open Previously Closed Valves Step 23 Repeat Steps 12 through 23 for Sequence 2

Post-Flushing Step 24 End of Day - Mark, Clean/Dirty Boundary Closed Valves with Orange Cones Step 25 End of Day - Provide Fire Department and Night Operator with Map of Temporary Closed Valves Step 26 End of Day - Notify Shop Supervisor and Customer Service .. 21 Step 27 End of Project Flush Dead end Mains and Unflushed Hydrant

Leads Step 28 End of Project - Review Lessons Learned

Figures Figure 1 Unidirectional Flushing Plan Flushing Plan Sequence Groups . 5 Figure 2 Unidirectional Flushing Plan Sequence 1-4

Tables Table 1 Flow Rate and Number of Hydrant Outlets Required to Flush Water Mains with 40 PSI of Pressure Table 2 Flushing Metrics for Pipes Table 3 Unidirectional Flushing Field Log Table 4 Estimating Volume of Water Needed for Flushing Sequence .. 10

Unidirectional Flushing (UDF) Guide for Water Distribution Systems

Steps for Flushing Program

Step 1 Obtain Water Maps pg 1

Step 2 Pre-Flush Turbidity

Measurements pg 2

Step 4 Prepare Flushing Sequence

Plan pg 4 pg 7

Step 5 Locate & Operationally Test Flushing Valves & Hydrants

Step 6 Revise Flushing Sequence

Plan pg 7

Step 7 Prepare Flushing Forms pg 8

Step 8 Pre-Flushing Notifications pg 11 pg 12

Step 9 Gather Tools & Supplies

Step 10 Prepare Repair

Contingency Plan pg 13

Step 3 Inspect Valves & Hydrants pg 3

Field Work Flushing

Step 12 Flushing – Preposition

Workers and Equipment pg 15

Step 14 Verify Radio

Communications pg 16 pg 16

Step 15 Verify Tank Water Depths and Pump Status

Step 17 Sequence 1 – Begin

Flushing pg 17

Step 18 Sequence 1 – Measure

Color/Turbidity pg 18

Step 13 Set Up Dechlorination Equipment, if Needed pg 16

Step 11 Field Team Meeting to discuss protocols, radio protocols, safety, & emergency procedures pg 14

Step 16 Sequence 1-Isolate

Appropriate Valves and Place Orange Cones to

Mark Closed Valve pg 16

Field Work Post-Flushing

Step 23 Repeat Steps 12 through

23 for Sequence 2 pg 20

Step 21 Inspect for Landscape Damage and Debris pg 20

Step 19 Sequence 1–Record

Flushing Data (i.e., flow rate, total gallons flushed, final turbidity, etc.)

pg 19

Step 22 Sequence 2-Open

Previously Closed Valves, Which Need to be Opened for Next Sequence pg 20

Step 20 Sequence 1-Remove Flushing Diffuser &

Fasten Hydrant Caps pg 20

Post-Flushing

Step 28 End of Project – Review

Lessons Learned pg 22

Step 26 End of Day – Notify Shop Supervisor and Customer

Service pg 21

Step 24 End of Day – Mark, Clean/Dirty Boundary Closed Valves with Orange

Cones pg 21

Step 25 End of Day – Provide Fire

Department and Night Operator with Map of

Temporarily Closed Valves pg 21

Step 27 End of Project – Flush Dead

End Mains and Hydrant Leads pg 21

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1. Measure turbidity at key locations in the distribution system with portable turbidity meters or visual methods using pre-prepared standards. Turbidity measurements should be done a week or two before flushing to represent pre-flushing conditions.

2. If possible, use turbidimeters to obtain the most accurate field data. However, visual methods, as described on this page, can also be effective.

3. Note locations where higher turbidities may be expected, such as dead end mains and in-line locations where lower turbidities may be expected.

4. The data will be useful in identifying problem areas where more extensive flushing may be necessary.

Visual Turbidity Measurements

Turbidity can be measured by visual observations and using pre-prepared standards. The methods and standards used are not as important as consistency.

Visual turbidity kits allow viewing of a sample in a clear jar and comparing turbidity to other jars with known turbidity. Another technique calls for the user to fill a beaker incrementally until an object on the bottom of the beaker is not legible. The amount of water in the beaker is directly related to the turbidity.

It is best to choose a standard that reports the turbidity measurement in standard units, such as nephelometric turbidity units (NTUs), which allows different standards to be used in the future.

Turbidity standards and testing tools for visual measurements are commercially available. Several examples are shown below:

http://www.benmeadows.com/refinfo/techfacts/tec hpdf/turbidity-1247.pdf http://www.hach.com/stablcal-turbidity-standards-calibration-kit-2100p-portable-turbidimeter-sealed-vials/product?id=7640202625&callback=qs http://www.dynamicaqua.com/turbidity.html#tube

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Field Work Flushing

Step 18

Sequence 1 – Measure Color/Turbidity

1. Using a portable turbidity meter or visual method described in Step 2, measure turbidity at 1-minute intervals while the hydrant is being flushed.

2. Use the turbidity data to determine when to stop the flushing sequence. Make sure to note if flushing must go longer than planned to achieve clear water.

3. At completion of the test, slowly close the flushing hydrant to minimize surges/water hammer in the distribution system.

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for

Field Work Post-

Step 20

Sequence 1 - Remove Flushing Diffuser and Fasten Hydrant Caps

• If needed, grease cap threads using food grade grease.

Step 21

Inspect for Landscape Damage and Debris

• Make necessary repairs, if possible, or record the damage and make arrangements for repairs at a later date.

Step 22

Sequence 2 – Open Previously Closed Valves

• Open previously closed valves, which need to be opened for the next sequence. Make sure to move orange cones, indicating that the valve is closed.

• Close valves necessary for the next sequence.

Step 23

Repeat Steps 12 through 23 for Sequence 2

Post-Flushing

Step 24

End of Day – Mark, Clean/Dirty Boundary Closed Valves with Orange Cones

• Identify which valves can and should remain closed overnight.

Step 25

End of Day - Provide Fire Department and Night Operator with Map of Temporarily Closed Valves

• Closed Valves affect available fire flow.

Step 26

End of Day – Notify Shop Supervisor and Customer Service

• Notify that work was completed and notify of work to be completed the following day.

• Notify of damage that needs to be repaired.

Step 27

End of Project – Flush dead end mains and unflushed hydrant leads to remove stagnant water from the system.

• Flushing unflushed hydrant leads allows all hydrants to be operated and confirms that all hydrants are working.

• In general, 6-inch hydrant leads should be flushed at a flow rate of 450 gpm for a minimum of 10 seconds for every 25 feet of hydrant lead. Each lead should be flushed at least 30 seconds.

Post-Flushing

Step 28

Review Lessons Learned

Conduct a meeting with the UDF planning and field team to discuss:

1. What went well and what did not go well.

2. Ways to improve the UDF plan.

3. How will the completed UDF plan’s effectiveness be evaluated? (Fewer water quality complaints, improved chlorine residuals, lower turbidity, lower heterotrophic plate counts.)

4. How will the system be monitored to determine when unidirectional flushing should be performed again?

5. Decide how to track information that will be useful for improving UDF plans in future years. (Store printed data? Store electronically?)

UDF Forms

Appendix A Unidirectional Flushing (UDF) Guide for Water Distribution Systems

This Appendix includes forms to aid with performing a UDF. Both hard copy ane electronic forms are provided.

1. Unidirectional Flushing Field Log - A blank form of Table 3 in the step-by-step guide. It can be copied and manually filled out or it is available electronically as an Excel spreadsheet.

2. Estimating Volume of Water Needed for Flushing Sequence. – This is a copy of Table 4 from the step-by-step guide. It can be copied and manually filled out or it is available as an Excel spreadsheet. If used electronically data should be entered in the white cells. The shaded cells contain formulas that will perform the calculations.

3. Velocity Conversion Table – This is a useful document for estimating the velocity in a pipe when flow rate and pipe size are known.

References and

Additional Information

Appendix B Unidirectional Flushing (UDF) Guide for Water Distribution Systems

References and Additional Information The following is a list of documents that were reviewed during this project, which provide sources for additional information. Additional information about unidirectional flushing can be found in the following documents.

1. Akridge, Angela; Anderson, Jerry; Gaus, Lisa; Niemann, Ted; A Partnership Crafts a Best Management Practice for Water Main Flushing and Disposal; 2002 AWWA Annuual Conference Procedings

2. AWWA Unidirectional Flushing DVD, 2002 (available for purchase from AWWA)

3. AWWA, Water Quality in the Distribution System, 2005

4. AWWA, Water Transmission and Distribution, Fourth Edition, Principles and Practices of Water Supply Operations, 2010

5. AWWARF, Cost and Benefit Analysis of Flushing, 2004

6. AWWARF, Guidance Manual for Maintaining Distribution System Water Quality, 2004

7. AWWARF, Implementation and Optimization of Distribution System Flushing Program,

8. Friedman, Melinda; Sherwin, Chris;

Hiltebrand, David; Establishing Contaminant Specific Flushing Velocities; AWWARF Study 2606, 2000 AWWA Water Quality Technical Conference Procedings

9. Barbeau, Benoit; Julienne, Karine; Gauthier, Vincent; Millette, Robert; Prevost, Michele;

Dead-End Flushing of a Distribution System:

Short and Long-term Impacts on Water Quality, 1999 AWWA Water Quality Technical Conference Procedings

10. Carriere, Annie; Barbeau, Benoit; Gauthier, Vincent; Morissette, Chantal; Millette, Robert;

Lalumiere, Alain; Unidirectional Flushing:

Loose Deposits Charactisation in the Test Zones of Four Canadian Distribution Systems; 2002 AWWA Water Quality Techincal Conference

11. Cossins, Fay; Hartman, David J.; Smith, Gardell; Merz, Rick; DeMarco, Jack;

Cincinnati Water Works, Cinncinnati, OH, The Cincinnati Water Works’ Unidirectional Flushing Pilot Program Results and Alternative Approaches for Full-Scale Implementation, AWWA, 2000

12. Friedman,P.E., Melinda; Hill, Andrew; Smith, Ph.D., Sian; Ta Ph.D., Tuan; Hinedi Ph.D., Zeina; Establishing Site-Specific Flushing Velocities; 2002 AWWA Water Quality Technical Conference

13. Hiltebrand, David J.; Theiss, Richard J.;

Distribution/Water Quality Control for Small Systems; 2002 AWWA Annual Conference Procedings

14. Jonus, Scott; Harbour, Joe; Murphy, Brian;

Distribution System Flushing Optimization to Reduce Environmental Impact, 2002 AWWA Water Quality Technical Conference

15. Reiss, C.Robert; Nantz, Harold; Schumi, Paul; Successful Completion of a Uni- Directional Flushing Program, Florida Water Resources Journal, December 2009

16. U.S. Army Corps of Engineers, Naval Facilities Engineering Command, and Air Force Civil Engineer Support Agency, Unified Facilities Criteria (UFC), Operation and Maintenance: Water Supply Systems, UFC 3-230-02, 2001

17. Williams, SM; Mains Flushing and Sediment Measurements in Water Main, 2002 AWWA Water Quality Techincal Conference

Example Notification of Distribution System

Appendix C Unidirectional Flushing (UDF) Guide for Water Distribution Systems

Example Notification of Distribution System Flushing The Base Civil Engineering Water Shop will be flushing water mains from ____________ to _____________, between ____ a.m. to ____ p.m.

The Water Shop will be monitoring water quality during that time. Area water users are asked to run their water for 10 minutes if they notice discoloration of the water.

Although water will be safe to drink, customers may chose to temporarily avoid or minimize using water if they notice hydrants being flushed nearby. (Cook and laundry – See Page 11)

The Water Shop can be reached at ____________.