United States Environmental Protection Agency Water Engineering Research Laboratory Cincinnati OH 45268 Research and Development EPA/600/S2-87/024 June 1987 SEPA Project Summary Water Main Evaluation for Rehabilitation/Replacement Robert M. Clark, Martin Allen, and D. Kelly O'Day This report describes a series of studies that identified factors contributing to water main failures and developed decision strategies on main rehabilitation, replacement, and preventive maintenance. The objective of this report is to provide the water utility industry with practical methods to assess long- term changes in the condition of distribution systems and to assist in rehabilitation/replacement planning decisions. Written as a guidance manual, the report discusses the following topics: 1. A comparison of utility repair recordkeeping practices with recommended procedures for analysis of leak and break trends. 2. Description of structural properties of water mains and the role external environmental conditions and corrosion processes play in water main deterioration. 3. Description of techniques to evaluate water main conditions with a recommended physical testing program that determines internal and external corrosion rates. 4. Presentation of economic models related to leakage control, main rehabilitation, and main replacement 5. Description of suggested water distribution system inventory procedures including geographic referencing systems, computer mapping, and hardware/software requirements. 6. Discussion of approaches to monitor distribution system conditions, to determine repair rates and patterns, and to coordinate the cost of monitoring with long-term benefits. 7. Presentation of independent planning steps that can be adopted by all utilities depending on system needs, budget, and personnel. The steps include standardized assessment programs, economic models for decision making, and computerized rehabilitation/re- placement This Project Summary was developed by EPA's Water Engineering Research Laboratory, Cincinnati, OH, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction In recent years, the condition of water distribution systems nationwide has attracted a great deal of media, political, and research attention. A number of divergent views have resulted regarding the magnitude of water distribution problems and the level of capital expenditures needed to address these problems. These conflicting viewpoints arise from the lack of extensive research undertaken in the past into the effectiveness of water distribution system planning and maintenance activities. Standard analytical procedures have not been developed by the water utility industry to assess distribution system conditions. For this reason, no benchmark or set of procedures has been established to compare distribution system conditions. ------- Recently, several institutions or organizations have surveyed water utilities nationwide to determine the type and magnitude of existing infrastructure problems. The surveys, conducted by the American Water Works Association (AWWA) and CH2M Hill Consultants, indicate that a significant variation exists within utility infrastructure improvement planning systems. Different sizes of systems tend to emphasize different types of program. The larger systems tend to be more sophisticated systems. Availability of useful information is indicative also of differing levels of planning and programming. Research efforts in recent years have focused primarily on methods to assess current conditions of water distribution systems, including realistic evaluations of the structural, hydraulic, and water quality problems encountered. These important research needs have not been addressed until recently by the industry. Results from the surveys as well as other sources of information have indicated a number of different types of research needs. Research Needs The development of a standard condition assessment terminology that can be utilized by all water utilities is a major research priority. The establishment of standardized nomenclature would enable water utilities to compare capital programming approaches and results. This standard should include an accepted set of terms and definitions as well as a consistent method to assess current and future performance levels of distribution systems. Variations in distribution system problems by region of the country should not hinder the development of such a standard. Although the type of distribution system affected ranges from older, established systems in the midwest and northern regions to younger, growing systems in the southern and western regions, water quality, hydraulic, and structural deterioration problems are not limited to any one region. Research must also address the need for an increased understanding of the structural deterioration process. There is a particularly critical need for more research into the causes of internal corrosion. Internal corrosion of water mains can lead to several problems, including the loss of hydraulic capacity, water discoloration, and a decrease in the effective main wall thickness. The impact of internal corrosion on water quality has taken a back seat in the research community compared with other drinking water quality research issues. Although most water quality research has focused on the use of various disinfection treatment processes to control and mitigate system-wide bacterial growth, the effect of a localized deterioration of the distribution grid on water quality must also be recognized. A research need is to draw correlations between internal corrosion levels and water quality deterioration. Future research must seek new techniques and materials for the replacement, rehabilitation, and repair of water mams. More economical approaches should be found to counter inflationary trends and to assist utilities in many sections of the country to increase their maintenance efforts. Research is needed to develop an objective framework for water utility managers to better compare and understand various strategies available to them for distribution system maintenance. This report primarily addresses this critical research need. In addition to defining the above mentioned research needs, the study reported in this project summary was conducted with five major objectives: analyze leak and break patterns from a selected set of utilities; examine the major causes of water main deterioration; survey analytical techniques used by utilities to evaluate water mam conditions; discuss the economies of leakage control, main rehabilitation, and replacement; develop a series of recommendations focusing on the types of information necessary in building a water distribution system inventory; provide a series of recommendations for monitoring distribution system conditions; and, present a series of planning steps for rehabilitation that may be adopted by all size utilities depending on their system needs, budget, and personnel. Analysis of Utility Leak and Break Patterns The study team analyzed records on broken water mains for six utilities: Denver Water Department, East Bay Municipal District (California), Kenosha Water Utility (Wisconsin), Louisville Water Company (Kentucky), New York City Water Supply Bureau, and Philadelphia Water Department. The utilities varied in size of service area, geological conditions, and geographic location. Comparative information on mam break patterns by age, diamete construction period, and material in th six utilities studied is presented in thi section. Each utility's recordkeepm system was examined. A recommende procedure is included for the analysis c leak and break repair data. Eight exhibit: including a sample repair form and series of data plots, are presented. It was concluded from this study th< water main leak and break patterns var widely among utilities and within a give utility. Variations in pipe materials, joir materials, design practices, constructio practices, soil conditions, corrosio conditions, external loadings, an weather conditions all contribute t variations in leak and break experience; Even with these variations across utilities there are similar patterns which must b recognized. Water Main Deterioration The causes of water mai deterioration are the focal point of thi section Structural properties of wate mains are discussed, including technical subsection describing thi interplay of external loads, beddmi conditions, and corrosion on thi deterioration process The genera principles of corrosion are described witl respect to both internal and external pipi conditions. A series of photographs c pipe samples that underwent variou types of corrosion is presented. Thesi samples were obtained under thi Philadelphia Water Department's materie testing program. A discussion of thi relationship between the age of wate mams and their rate of deteriorate encompasses changes in castmi techniques, construction practices, am materials over time. It was concluded that a water main wi fail when the forces exerted on the man exceed the main's effective strength This strength decreases from its origine design strength as a result of internal an< external corrosion, reducing the mam' ability to withstand various appliei forces. Many environmental factor should be investigated for their roles n this process. Assessing Water Main Conditions A survey of analytical techniques use< by utilities to evaluate water mail conditions is provided in this section Descriptive analysis techniques evaluati the frequency and patterns of mail breaks for several utilities, including Eas Bay Municipal Utility District (California] Philadelphia Water Department, am several utilities in Great Britain am ------- Canada. Three predictive model case studies from Des Moines, the USEPA, and the Massachusetts Institute of Technology are reviewed. Physical analysis to estimate water main conditions is outlined. Analyses from Vancouver, Philadelphia, and the Army Corps of Engineers Construction Engineering Research Laboratory are presented. The predictive model approach offers utilities an evaluation method for assessing the interplay of environmental and structural factors which lead to water main deterioration and failure. Utilities are cautioned that this approach will require continual enhancement to refine predictive capabilities as each utility collects information on the interplay of loads, environmental factors, and failures of its main. Economics of Distribution System Rehabilitation The economics of leakage control, main rehabilitation, and replacement are examined in this section. Economic trade-offs of alternative maintenance and capital programs are shown in models and discussed through sensitivity analyses. Simple work sheets are presented so that managers can examine and develop unit costs for their individual utilities. Water Distribution System Inventory This section presents recommen- dations focusing on information necessary in building a water distribution system inventory. Geographic reference system requirements, inventory procedures, computer mapping capabilities, and hardware/software requirements are discussed. The recommended inventory system includes a combination of coordinate, link node, and street address reference capabilities. Monitoring Distribution System Conditions By monitoring its distribution system, a water utility can obtain the important information needed to establish a cost- effective rehabilitation/replacement planning system. A series of recommendations that water utility managers can use to monitor distribution system conditions is presented. Trend analyses of both leak and break rates as well as hydrant, valve, and service repairs are suggested as means to assess system conditions. The need for annual assessment of distribution systems is examined. These annual assessments include analysis of current and anticipated future trends and identification of those portions of the system experiencing higher or lower failure rates. Developing a Rehabilitation Planning System Several water distribution planning system approaches developed by water utilities across the country are presented in this section. The series of planning steps presented may be adopted by all utilities depending on their system needs, budget, and personnel. These planning steps include a- standardized main repair recordkeeping system for the annual assessment of distribution network conditions, the analysis of repair patterns by geographic area, the establishment of repair pin maps, a main testing program, the development of economic models for maintenance decision making, the preparation of a computerized inventory of the water distribution system, and the development of both water main condition predictive models and computer-based rehabilitation/-replacement screening and selection systems. Reactive and predictive planning system approaches by four utilities are illustrated in this section as case studies. Various combinations of the planning system components described above are used by each utility. Summary and Conclusions Designing and implementing a water main decision planning system is an on-going evolutionary process. It begins with an assessment of the distribution system condition. From this assessment a reactive planning system may be designed and implemented. This, in turn, can lead to the development of a predictive planning system. Regardless of the level of sophistication and computerization involved, each utility should collect information concerning system conditions, implement preventive maintenance measures, identify chronically failing mains, and prioritize these mains for repair or replacement. The utility policy and replacement criteria may change from year to year, but the basic process remains the same. Case studies of live utility planning systems were presented to illustrate various approaches to these primary planning tasks. If a utility decides that a predictive planning method is desirable, the first step is the development of a comprehensive water main inventory and maintenance history database. This database should include the location of inventory, maintenance history, and environmental description for each record. A variety of options for inventorying water mains are available and span a wide cost range. The second step in the implementation of a predictive planning approach is the development of a physical condition assessment model. This model enables the utility to approximate the deterioration process based on engineering principles, and estimate the relative break and leak frequency for the main. This ability to better estimate the future condition of the main makes preventive maintenance and replacement activities more cost- effective due to more precise prioritization and scheduling capabilities. Additional criteria assessment models such as hazard assessment or economic evaluation models may also be developed. These criteria assessment models may be coupled with a physical condition assessment model to select and prioritize mains for replacement or other maintenance activities. Field data collection and testing should take place to verify critical model assumptions. Increased planning system sophistication will increase implementation cost, particularly the cost of building and updating a water main information database. These costs must be weighed against the benefits of more effective decision-making regarding repair, replacement, abandonment, and preventive maintenance activities. Improved budgetary planning can be a means of justifying additional funding for system improvements. Improved system reliability and water quality conditions are other important benefits which should be measured. These costs and benefits should be investigated thoroughly before a commitment is made to implement a predictive planning system. The full report was submitted in fulfillment of Cooperative Agreement No. CR810988 by American Water Works Association Research Foundation under the sponsorship of the U.S. Environmental Protection Agency. ------- The EPA author. R. M. Clark (also the EPA Project Officer, see below), is with Water Engineering Research Laboratory, Cincinnati. OH 45268; M. Allen is with American Water Works Research Foundation, Denver, CO 80235; and D. Kelly O'Day is with Peer Systems, Inc.. Philadelphia, PA. The complete report, entitled "Water Main Evaluation for Rehabilitation/ | Replacement, (OrderNo. PB87-175378/AS; Cost: $18.95. subjecttochange) \ '; will be available only from: ' National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Water Engineering Research Laboratory U.S. Environmental Protection Agency Cincinnati, OH 45268 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Official Business Penalty for Private Use $300 EPA/600/S2-87/024 ------- |