The Changing Face of Distribution System Management
Possible effects of new regulations on distribution system management
It now seems likely that sometime within the next few years, the U.S. Environmental Protection Agency will enact new regulations for the management of drinking water distribution systems. Although new rules have not yet been promulgated, there will be much debate about their efficacy and appropriateness when and if they are.
However, there is general agreement that should this type of regulation go forward, it may be the most costly regulatory program in the history of the Safe Drinking Water Act.
The EPA has been actively seeking comment from utilities and other stakeholders on a variety of distribution system topics, and has held a series of well-publicized workshops to lay out current issues and seek consensus.
These regulations could affect the allowable water age within the distribution system; create a federal cross-connection program; set up standards for acceptable repair and maintenance procedures; and mandate enforcement penalties. Perhaps the most controversial aspect is the possibility that the agency could require all distribution systems to install and maintain backflow preventors at every connection, including residential connections. This aspect alone represents a national cost that could exceed billions of dollars.
Replace or repair?
Main breaks are very expensive. Loss of water during a break can be significant, especially if the break empties tanks. Service disruptions result in lost revenue and may be utterly unacceptable to customers that depend on reliable water service (hospitals, restaurants and other commercial properties). Traffic disruptions can also result in lost wages and diminished productivity for a broad swath of the community. Main breaks invariably result in a loss of system pressure, which can cause line contamination and degradation of water quality, and the liabilities associated with main breaks can be more expensive than the cost of replacing the entire main.
Not only are main breaks expensive, repeated breaks generate substantial ill will toward the offending utility. The questions are, How much is too much? How often is too often? At what point does it make sense to replace the main rather than wait for the next unexpected break?
The cost of installing a new distribution main is nothing short of mind numbing – the national average is in the range of $15 to 20 per in.-ft. Based on that alone, utilities find it difficult to justify replacing lines still in service. And when the cost of pavement cutting, service-connection repair, and relocation of other utilities is factored in, especially for replacement of old, crumbling mains in urban areas, the costs can be several-fold higher. The conventional wisdom is that only when the breakage rate is exceptionally high, or the labor costs very low, will it be more cost- effective to replace the line in its entirety than to repair individual breaks.
This outlook is proving to be shortsighted. Assessments of the direct costs for a repair do not represent the full impact to the utility. Recent studies suggest that the indirect costs usually exceed 40% of the total repair costs. Just the clean-up and waste disposal costs can be as high as break-repair costs.
At any given moment, it is easier to justify the economics of break repair versus main replacement, but it is important to recognize that the direct cost of a repair rarely represents the full cost. A conscientious distribution system management program must take the long view by considering the direct and indirect costs, weighing the impact on stakeholders, and recognizing that system integrity and reliability are at the heart of the service contract between the utility and its customers.
Response to water quality degradation
As a corollary to the repair/replacement discussion above, distribution managers now recognize that pipeline rehabilitation, especially non-structural lining techniques, are a viable and competitive option to main replacement. Rehabilitation technologies have merit and should be considered in any decision process on line replacement, particularly when the issue at hand is management of water quality. In the past two decades, well over a dozen different technologies have entered the market, and the cost of line rehabilitation has dropped substantially.
Rehabilitation technologies consist of structural lining techniques including slip lining, close-fit slip lining and cured-in-place pipe lining. These techniques can restore both the structural and hydraulic integrity of the pipeline. Non-structural lining techniques, which are appropriate only for structurally sound, unlined cast or ductile-iron mains that have developed serious tuberculation, result in a smooth, protective coating on the interior of the pipe. This coating restores hydraulic capacity of the line, ensuring corrosion protection. The most popular of the non-structural techniques is epoxy-resin lining. Almost a thousand miles of distribution main is rehabilitated each year using this technique, and the costs have dropped as low as $1 per in.-ft.
Whether the EPA enacts new regulations for the management of drinking water distribution systems, this issue will undoubtedly remain in the spotlight.
The EPA has put together a series of white papers on a broad range of distribution system topics, including aging infrastructure, corrosion control, biofilms, regrowth, permeation and leaching, cross-connections, and others.