Effective Use of Infrastructure Funds: Prioritizing Pipe Rehabilitation Projects
Last Modified: Sep 28, 2010
- Crystal Broadbent, P.E. , Meg Roberts, P.E. - Hazen and Sawyer
As water distribution systems age, utilities are faced with the need to rehabilitate water mains to respond to increasing demand and to minimize leaks, pipe breaks, and loss of capacity from tuberculation. Due to high costs and limited funds, utilities are forced to prioritize rehabilitation projects to provide the best return on investment. Prioritizing pipe improvements can be done through desk-top evaluation or using specialized software packages. The end result for either method is a scoring system that allows the utility to optimize capital improvement or maintenance funds and properly schedule pipe rehabilitation to address the most critical needs first.
Several criteria should be considered to properly prioritize pipes for rehabilitation. The importance of each factor is subjective and varies among utilities. Input to the analysis may include: main break history, pipe age, pipe material, valve status, soil pH, pressure, flow velocity, water age, and proximity to critical facilities, such as hospitals. A scoring and weighing system is assigned for each input, and each pipe is then assigned a weighted sum. The higher the score, the more critical the pipe is to the system, and the higher the priority for rehabilitation.
For example, pipe material can have an impact on water quality. Unlined cast-iron pipes are known to become tuberculated and harbor biofilms that decrease disinfectant concentrations and may cause taste and odor problems and/or increase disinfection byproducts. Water quality is a high priority for all utilities, and, thus, pipe material may be weighted more heavily than another factor.
After prioritizing, the pipes can be tabulated and mapped, with rehabilitation costs estimated for each. Pipes can be grouped into annual projects that conform to budget constraints. The best methods of rehabilitation for each pipe (e.g., pipe replacement vs. pipe lining) can then be evaluated based on factors such as pipe type and site conditions.
This presentation will look at two case studies for which pipe project prioritization was completed: Roanoke Rapids, NC and Danville, VA. Different methods of prioritizing pipes, assigning scoring values, making repair or replacement decisions, and estimating costs will be discussed for each case.
Ultimately, by using a systematic approach to prioritize pipes for rehabilitation, a utility can make efficient use of its capital improvement or maintenance funds. By attending this presentation, attendees will learn through guidance and examples how best to approach prioritizing water pipeline rehabilitation projects.
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