Uni-Directional Flushing in Reidsville, NC - A Team Effort

Authors:

  • Jeff Cruickshank, PE - Hazen and Sawyer
  • Kevin Eason, PE - City of Reidsville
  • Stephen Coleman - Mueller Service Company

Uni-directional flushing (UDF) is getting increased attention from water utilities because of the Stage 2 Disinfectants and Disinfection Byproducts (DBP) Rule. This rule focuses on water quality in distribution systems, where DBPs form when chlorine reacts with organic material in drinking water and bio-films on pipe walls.

UDF expels sediment from water mains and scours bio-films. In distribution systems that use chloramines as the residual disinfectant, UDF helps control nitrification in areas with excessive water age. UDF induces high velocities by closing valves so water reaches flowing hydrants from only one direction through a single pipe.

UDF is labor intensive because it requires hundreds of valve operations. Careful planning is required so water is routed to flowing hydrants only through pipes that have been flushed previously. Specialized software helps plan UDF using hydraulic models.

The City of Reidsville decided on UDF as part of its compliance strategy for the Stage 2 DBP Rule. However, city crews did not have sufficient manpower to conduct UDF in a timely manner. In addition, parts of Reidsville’s distribution system are more than 75 years old, and the City’s GIS did not include sufficient information about the old valves and hydrants to effectively plan and implement a UDF program. The City decided that outsourcing was the best method of getting the job done.

This presentation describes a team effort that successfully implemented UDF in Reidsville, covering the entire distribution system comprising about 100 miles of pipe. The team consisted of utility staff, an environmental engineering consultant that planned the UDF sequencing, and a municipal infrastructure assessment company that initially collected information on the valves and hydrants and subsequently executed the UDF program.

Lessons learned from this project are discussed from the perspective of the City, the consultant and the infrastructure assessment company. The emphasis is on practical knowledge concerning both planning and execution of a UDF program. In addition, the discussion explains a number of indirect benefits to the City.

This presentation will help other water utilities understand UDF, recognize potential problems and work around them.

For more information, please contact the author at jcruickshank@hazenandsawyer.com.

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