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Renewing water distribution systems
An old problem with new possibilities
Neil S. Grigg, Ph.D.
Professor, Department of Civil Engineering
Colorado State University
Fort Collins, Colorado
Member, APWA Engineering and Technology Committee
As water utilities seek to deliver high-quality water through their distribution systems, they face increasing infrastructure challenges from breaks, corrosive deterioration, and other forces. Their aging and invisible water distribution networks are spread over large areas with many connections, and they require large capital expenditures for renewal. In addition to reliability issues, utilities also must comply with water quality requirements, such as the Lead and Copper Rule.
Fortunately, utilities have available a wide array of emerging tools to manage their distribution system assets. To review these tools, the American Water Works Association Research Foundation (AwwaRF) sponsored a project (No. 2772) about three aspects of system renewal—how to assess condition, how to set priorities, and how to perform renewal tasks. The report, entitled "Assessment and Renewal of Water Distribution Systems," will be available from AwwaRF in mid-2004.
Surprisingly, the some 1,000,000 miles of water mains in the United States could take 200 years or more to completely replace. For the most part, distribution pipes installed from the late 1800s to the late 1960s were of cast iron. While cement mortar lining improved resistance to corrosion and improved jointing reduced leaks, the inventory continues to wear out and cause problems. Pipe advancements included ductile iron pipe, asbestos cement (AC), pipe polyvinyl chloride (PVC), and high-density polyethylene pipe technologies. According to AWWA's latest survey of distribution systems, today's systems comprise a mixture of about 29% cast iron, 24% ductile iron, 17% PVC, 15% AC, and the remainder of steel, concrete, and other materials. Utilities have a hard time getting their boards excited about massive renewal projects, and replacement rates may be slowing to a rate of less than once in 200 years. Thus, utilities must find ways to manage an old inventory while meeting new challenges.
The report covers a broad swath of technologies—from technology-based assessment tools for operators to capital strategy planning methods. An "issue tree" illustrates the renewal problem and provides a structure for its analysis. It recognizes, for example, the constraint of different materials in the network and the lack of standard designs and configurations. It covers the requirements for success by answering the what, why, who, how, and when questions; that is, knowing what to do, being capable to do it, and being motivated to do it.
Slip lining project on Pico Boulevard in Los Angeles (courtesy of Los Angeles Department of Water and Power)
The first step in renewal is condition assessment, which is the "science" and engineering side of distribution system management. It includes locating assets, diagnosing failures, learning about deterioration mechanisms, and measuring condition. Ideally, condition assessment is to continually assess condition of the organization's assets so that return on investments can be maximized, but from a practical standpoint this is not fully realized because utilities practice varying degrees of maintenance and renewal strategies. Regardless of the philosophy about maintenance, research suggests that more advances will be made in condition assessment than in other arenas of distribution system capital management. The report offers a framework for condition assessment to provide a common ground to exchange information. It also links the parameters of condition assessment with the uses of the information for renewal work by operators, engineers, maintenance personnel, and by budget and finance staff.
Planning and prioritization is the "management" side, and requires the utility to find funding sources, relate to governing boards and the public, and provide management and financial accountability. Utility tasks in planning and prioritization range from problem assessment to making decisions about solutions, as embodied in the capital planning, programming, and budget process. In prioritization, utilities face the dual problem of identifying their highest priority pipe renewal projects and comparing them to other capital investments, which are often more visible and attractive. Techniques for decision analysis have received much attention in the research literature, and if the fragility of individual pipes is known, utilities are fully prepared to set priorities for renewal.
The third topic, or the "construction" side, comprises the physical work of maintenance, repair, and renewal. The general situation in repair, rehabilitation, and replacement is that practices among utilities vary greatly. All utilities repair broken pipes and leaks, but some utilities rehabilitate pipes regularly, and others focus on replacement without much rehabilitation activity. At the project workshop, participants observed that North American water utilities are reluctant to use newer technologies for pipe renewal. Reasons are lack of awareness, cost effectiveness, liability, and uncertainty about sustainability. Options mentioned to speed adoption of new technologies were cost reduction by assembling larger projects; providing training; providing education for management, politicians and customers about benefits of new technologies; and using the private sector for construction of renewals. The lines between "repair," "rehabilitation" and "replacement" can be blurred.
The report summarizes the tools available to utilities to plan and manage their distribution capital program. The basic toolkit available to utilities includes inventory as the core activity; condition assessment; a maintenance management system; system planning and needs assessment; system financial accounting; an asset management framework; a capital improvement plan and program; a capital budget; and an overall capital management strategy and framework. Each of these tools has a research base, which is explained in the report. In addition, AwwaRF has other reports, including a recent Capital Planning Strategy Manual, to describe these tasks.
Laying pipe (Source: American Water Works Association. All Rights Reserved)
A number of infrastructure-related issues still need attention to improve distribution system management. To begin, high levels of investment are needed, while the credibility of needs studies requires improvement. Utility management must also continue the development of its workforce to manage distribution systems. In planning, prioritization, and performance evaluation, improved methods are required, but uncertainty about expected service lives of water mains makes it impossible to estimate investment needs precisely. The need for research about pipe materials, structural characteristics, and construction practices is cited by workshops and projects and this need will continue, particularly to understand failure mechanics better. Condition assessment shows great promise for distribution systems management, but more practical methods for use by all utilities are required. While high-quality water is required to the tap, the shift in responsibility at service connections creates unknowns and uncertainties about quality control. Data management has emerged as one of the principal issues in distribution systems management.
Management technologies for managing distribution systems are improving. However, some utilities believe that the renewal problem is urgent, requiring more national investment. Others believe that the problem is not serious, and that pipes will last longer than projections show. Some utilities believe that they should rehabilitate or replace on the basis of observed failures, rather than try to "assess" condition of pipe inventory. Some use advanced methods for planning and prioritization; others are only beginning to think about implementing formal methods. "One size fits all" does not apply to all capital renewal methods.
In addition to being a member of APWA's Engineering and Technology Committee, Neil Grigg is a member of the International Affairs Committee and the Editorial Advisory Board for the APWA Reporter. He can be reached at (970) 491-3369 or at email@example.com.