Harry D. Gong, Jr., P.E. AL/MS AWWA Section Newsletter Editor/Communications Chair AND Environmental Engineer Mississippi State Department of Health Developing and Implementing a 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 program 3. Implementing a flushing program and data collection 4. Evaluating and revising the program Background • 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 systems. • 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 residual? 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? Applicable? • 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 flushing? • Is flushing the solution or only part of the solution? 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 Management • 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 Benefits – 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 lines • Velocity < 1 fps, adequate velocity may not be achieved • Can help restore disinfection residuals & water age • Large quantity of water that may not provide a solution Implementation of flushing techniques • Comprehensive systemwide basis • Spot base - implemented more frequently especially in chronic WQ areas • Will depend – System configuration – WQ goals Preliminary Program Development • 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 Valves PRVs Booster Station Tanks, etc. • Discharge locations Preliminary Program Development • List of stakeholders (customers/other water departments) – 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 Feedback 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 instruction. • 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 assessment • Helps determine if objectives are met • Baseline – – – – Monitoring 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 activities • 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 Summary • Four Steps in Developing a Flushing Program 1. 2. 3. 4. 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: www.linkedin.com/in/hgongjrpe18005 Email: Harry.Gong@msdh.ms.gov email@example.com Phone: 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 (www.almsawwa.org) AWWA Members can download a free copy of the AWWA Journal Article that this flushing presentation is from at the following link: http://www.awwa.org/publications/journalawwa/abstract/articleid/14615.aspx?ct=f475955b1dd24e2eb00a3c0 e64a2905cde73a40629aa8cef3dd0e1dac7d6f58e1e8e45a662aeae3 bf6f0ef12069f340b2e14de05aa7284ec556ba5c2d2af4d57 Non-members may purchase a copy of the article for $30 That’s It Questions?