Unidirectional Flushing Thomas F Clark Monroe County Water

Unidirectional Flushing Thomas F. Clark Monroe County Water Authority 11/21/2020 AWWA Seminar 1

Introduction n Why bother to flush ? What is unidirectional flushing? What are the benefits of unidirectional flushing? 11/21/2020 AWWA Seminar 2

Flushing…. why bother? n n n Customer complaints on “stale” water. Low chlorine residuals. Dead ends. Distribution system chemistry changes. Loss of “C” factor. Sediments/corrosion products. 11/21/2020 AWWA Seminar 3

Where do sediments come from? n Everything from microscopic debris from the finished water leaving the plant, to material brought into the system from main repair and tank outflows to the corrosion of cast iron pipe. 11/21/2020 AWWA Seminar 4

What are some of the other factors which cause water to degrade? n n n Age Poorly managed storage facilities Biofilm/microbial growth Nitrification Cross-connections/backflow Permeation/leaching 11/21/2020 AWWA Seminar 5

Flushing…. why bother? n n High flow events or main breaks within the system will eventually cause problems with turbidity. Low flow mains will eventually lead to taste and odor problems, iron and sediment accumulation, etc. 11/21/2020 AWWA Seminar 6

Flushing…. why bother? n n Periodically remove biofilm. Maintain/increase disinfectant residual. A chance to exercise valves and hydrants. Respond to consumer complaints. 11/21/2020 AWWA Seminar 7

Flushing…… n n n n There a number of reasons NOT to flush…. . Water availability Time and people Cost of water Property damage Complaints from consumers CAUSED by flushing. Other job tasks that are waiting to be done. 11/21/2020 AWWA Seminar 8

Spot Flushing n n n Historically, spot flushing has been done. Generally, flushing velocities of < 5 fps are used. Often this is done in conjunction with other maintenance tasks associated with hydrants and valves. Random opening of hydrants – often not in an organized manner. Does not have a lasting beneficial effect. BUT it is quick and easy !!!! 11/21/2020 AWWA Seminar 9

Procedures…. . n n n Normally, one opens a hydrant and hopes for a sufficient pipeline velocity. Or, a sufficient number of hydrants are opened to raise pipeline flow. Discharge water until it runs clear. Inspect the hydrant. Maybe conduct water quality checks such as turbidity, chlorine residual, clarity. 11/21/2020 AWWA Seminar 10

Unidirectional Flushing n n n Water flows in one direction only. Method is systematic and pre-planned. Produces more effective scouring. Use less water in general. Improved quality is longer lasting. 11/21/2020 AWWA Seminar 11

Principles of Unidirectional Flushing n n n Work outwards from a clean source of water. Use a prearranged pattern. Work from a large diameter main to a small diameter main. Close valves where necessary to ensure that flow is from a clean source on a one way path and to isolate pipe sections. Flush until water reaches your target water quality. 11/21/2020 AWWA Seminar 12

Principles of Unidirectional Flushing n n Maintain 20 psi system pressure everywhere. Ensure that a sufficient flow rate is achieved to produce a pipeline flow velocity of 4 - 5 ft/second. 11/21/2020 AWWA Seminar 13

Pipeline Velocities at Various Flushing rates GPM 6 inch 8 inch 12 inch 16 inch 250 2. 8 fps 1. 6 fps 0. 7 fps 0. 4 fps 500 5. 6 fps 3. 2 fps 1. 4 fps 0. 8 fps 750 8. 4 fps 4. 8 fps 2. 1 fps 1. 2 fps 1000 11 fps 6. 4 fps 2. 8 fps 1. 6 fps 1250 14 fps 8. 0 fps 3. 6 fps 2. 0 fps 11/21/2020 AWWA Seminar 14

Conventional Flushing 11/21/2020 AWWA Seminar 15

Unidirectional Flushing 11/21/2020 AWWA Seminar 16

Field Parameters for Flushing Disinfectant Residual Depends on level entering the system Free chlorine of 0. 5 mg/l – 1. 0 mg/l Turbidity less than 2 ntu 11/21/2020 AWWA Seminar 17

Field Parameters for Flushing Volume turnover Try to turn over 3 x the pipe diameter Evaluate each flushing effort as conditions dictate. 11/21/2020 AWWA Seminar 18

Pipeline Volume Info n Pipe Size Inches Volume per 1000 ft Gallons 4 6 8 10 12 16 18 24 653 1, 470 2, 610 4, 080 5, 875 10, 444 13, 218 23, 500 11/21/2020 AWWA Seminar 19

Calculate Pipeline Residence Time n n Calculate residence time (flow through) of 1, 000 LF of 12 inch pipe when the main is delivering 820 gpm. Since we have 1000 ft of 12 inch pipe, we’re talking about 5, 875 gallons of water that needs to be displaced. 5, 875 gallons/flow rate = residence time 5, 875 gallons/820 gallons/min = 7. 2 minutes 11/21/2020 AWWA Seminar 20

Impact of unidirectional flushing 11/21/2020 AWWA Seminar 21

Impacts on the Environment From Flushing n Watch for free/total chlorine levels n n n Neutralize chlorine by use of sodium sulfite, sodium bisulfite, sodium thiosulfate, etc. Don’t use excessive sulfite chemical as it will create an oxygen demand in receiving waters. Watch for TSS levels n 11/21/2020 Impound sediment laden water to allow for settling prior to discharge. Catch basin sumps, lagoons, sand bagging on a road, etc are options. AWWA Seminar 22

General Considerations in Flushing/Flowing Water n Ten States Standards n n 11/21/2020 8. 1. 1 - Pressure - The system shall be designed to maintain a minimum pressure of 20 psi at ground level at all points in the distribution system under all conditions of flow. Hydrants should be spaced from 350 ft – 600 ft depending on the nature of the area. AWWA Seminar 23

Needed Fire Flow for a System n n For one and 2 family dwellings not exceeding two stories, we use the following flows: Distance between Buildings Over 100 ft 31 ft – 100 ft 11 ft – 30 ft less than 10 ft n Needed Fire Flow 500 gpm 750 gpm 1, 000 gpm 1, 500 gpm Ref: AWWA Manual M-31 11/21/2020 AWWA Seminar 24

A Cautionary Note…. . n n n Flushing will result in increased flow velocities…. . Increased flow velocities in the water mains result in reduced system pressures…. that means You need to be aware of the concept of the hydraulic grade line. 11/21/2020 AWWA Seminar 25

Hydraulic Grade Line n n What is it? It’s the level that water would rise in a thin glass column were you to tap such a glass tube into your main. 11/21/2020 AWWA Seminar 26

Hydraulic Grade Line Friction loss Pump head added 50 psi PRV 85 psi 11/21/2020 60 psi AWWA Seminar 27

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55 psi n 7 psi 35 psi (20 psi in main)

Elevation + (Pressure x 2. 31) = HGL 11/21/2020 AWWA Seminar 31

Elevation + (Pressure x 2. 31) = HGL 11/21/2020 AWWA Seminar 32

Fire Flow Test Residual Hydrant Flow Hydrant 70 psi Static 50 psi Residual 11/21/2020 19 psi Pitot AWWA Seminar 33

69. 3 feet = V 2 / 64. 4 30 psi = 69. 3 feet V = 66. 8 fps Pitot Pressure P = 30 psi (- 10 % ) V=0 P = 0 psi V = 60 fps Q=Vx. A Q = 920 gpm 11/21/2020 AWWA Seminar 34

Fire Flow Calculation n n Conduct Flow Test Extrapolate flow at desired residual pressure 11/21/2020 AWWA Seminar 35

Example 70 psi 50 psi Resid. 20 psi Press. n Static pressure = Residual Pressure = Pitot Pressure = Actual Flow Rate n Fire Flow at 20 psi n n n 70 psi 50 psi 19 psi 0 gpm 750 gpm Hydrant Flow 1230 gpm

Where to Get More Information n Other training sessions List books, articles, electronic sources Consulting services, other sources 11/21/2020 AWWA Seminar 37