Unidirectional flushing can help ensure that water is delivered to the consumer's tap with minimum degradation in quality. Distribution system deficiencies continue to be responsible for more than 25 percent of waterborne disease outbreaks in the United States each year, a statistic that underscores the need for water suppliers to effectively control water quality within the distribution system. Flushing is one of the most powerful tools available to a water utility for maintaining this control. Unidirectional flushing (UDF) is a refinement designed to bring water through the system in a controlled fashion at velocities sufficient to provide a scouring action within the distribution piping. First developed in the early 1990s, UDF is being utilized by a growing number of utilities as a cost‐effective way of improving and preserving water quality in the distribution system. In this overview of UDF, the authors summarize the technique's key components and potential benefits and explore how UDF fits into overall efforts to control distribution system water quality.
Water utilities throughout the United States will be affected by the 1986 amendments to the Safe Drinking Water Act. The authors describe these effects along with suggesting preparations that can be undertaken to meet the requirements of the new law when it is fully implemented. Water utilities must deal with new contaminant standards, including installation of new treatment technologies that may be needed to meet these new standards. Wellhead protection programs and required disinfection of groundwater and surface water supplies will change the way in which many systems now operate. The far‐reaching effects of more stringent regulation of the by‐products of disinfection, coupled with disinfection adequate to contend with viruses and Giardia, will cause an exquisite balancing of potentially conflicting goals in water treatment.
The Surface Water Treatment Rule (SWTR) requires that all community and noncommunity water supply wells, springs, and infiltration galleries be evaluated to determine whether they are under the direct influence of a surface water. Those groundwater supplies that are found to be under the direct influence of a surface water will be subject to the requirements of the SWTR. This determination will have a significant impact on many existing water utilities and on the development of new supplies. The guidance manual for the SWTR provides a general outline of a procedure that can be used to make the determination of direct influence. This procedure was applied to two groundwater supplies.
This article discusses the benefits of a flushing program to the water quality in a distribution system and compares and contrasts conventional flushing with unidirectional flushing. Also, several additional issues are discussed relating to water quality that include: coordinating unaffiliated groups when they perform activities affecting the distribution system such as the fire department and public works department; deteriorating water quality and biological growth in tanks or reservoirs where the level remains constant; maintaining water quality in systems with extensive uncoated iron pipe with effective corrosion control; and, reducing the number of artificial dead‐ends and minimizing the problems associated with broken valves during a flushing campaign with a regular valve exercise program.
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