Title
Asset Management Program Update - Water and Sewer Mains
Description
This report provides the Transportation, Infrastructure, and Planning Subcommittee with information on the Water Services Department’s Asset Management Program for Water and Sewer Mains.
THIS ITEM IS FOR INFORMATION AND DISCUSSION.
Report
Summary
Asset Management Program
The Water Services Department (WSD) is committed to an asset management program to support its mission of providing high quality, reliable, and cost-effective water services that meet the public needs and maintain public support. Asset management is an intentional, proactive approach to maximize the useful life of assets while minimizing life cycle cost. This means asset renewal is based on age, condition, criticality, and risk value. Within the WSD, each asset is identified and catalogued according to strict naming conventions in the asset database. The condition of the asset is also recorded in the asset database. Proper preventive maintenance procedures are identified and noted for each asset allowing work orders with proper maintenance activities to be assigned to employees. Standardizing work management processes using a modern computer maintenance management system ensures proactive maintenance on the right assets at the right time.
Risk analysis is also part of asset management. Risk is defined as the Probability of Failure times the Consequence of Failure. The Probability of Failure is dependent on the condition and reliability of the asset, the asset age and effective life, and redundancy of the asset. The Consequence of Failure factors the impact on service and duration of failure, higher replacement cost and repair difficulty, potential for staff and public injuries, and the importance of the asset.
Age, condition, criticality, and risk value are used to forecast the asset's end of life. The risk analysis is used in determining the replacement timeline of the asset, allowing for proper planning of the capital improvement program. The overall goal is to align maintenance and replacement programs so assets will have longer useful lives, resulting in longer replacement cycles. This alignment ensures that capital improvement programs for replacement and rehabilitation budgets are adequately funded and prioritized to replace the department’s critical assets at the end of their useful life. The right assets are replaced at the right time and cost.
Water Distribution System
The City’s water delivery system is composed of over 7,100 miles of pipelines. Reliable water delivery for our customers depends on a well-maintained transmission and distribution system. The distribution system delivers water directly to individual customers from 12-inch and smaller pipelines which account for 91 percent of the water delivery system. The transmission system, typically 16-inch and larger pipelines, moves water from water treatment plants and storage reservoirs into the distribution system. Continued pipeline rehabilitation and replacement investment is one of the largest infrastructure costs to the water utility second only to water treatment plant investments.
WSD crews continually repair, rehabilitate, and replace various pipelines throughout the distribution system. The Water Main Replacement Program is focused on replacement of substandard and under performing mains to maintain reliable delivery to our customers. This program has traditionally been focused on the distribution system’s smallest mains. The Transmission Main Inspection and Assessment Program, began in 2003, is focused on condition assessments of the City's largest mains to reduce the risk of transmission main failures that have potentially catastrophic consequences. The Medium-Diameter Transmission Main Inspection and Assessment program is a relatively new program that focuses on evaluating and prioritizing the remainder of the transmission system for rehabilitation and replacement. WSD staff have projected the cost of replacing or rehabilitating all pipelines based on an anticipated life expectancy, on average, of 75 years. For water pipelines, the estimated cost for replacement is $15.5 billion.
Risk profiles are different for distribution and for transmission mains. Distribution mains are more susceptible to corrosion and fatigue which makes them more likely to fail than transmission mains. Transmission pipelines normally carry a much higher volume of water and tend to be in or near major roadways, infrastructure, or environmentally sensitive areas, making their failure of greater consequence than distribution mains. Because of these different risk profiles, WSD has developed strategies for managing the two systems to avoid failure. Failure is defined differently depending on the type of main. For transmission mains, failure can be defined as any disruption in the pipeline's ability to deliver water because of the large impact on customers, streets, and private property. Avoiding failure for these mains requires detailed information about the condition of the main and a solid funding plan to install, renew, or relocate mains. Since 2003, the City has performed condition assessments and inspections on more than 128 miles of large-diameter transmission mains. These condition assessments are the basis for the current Transmission Main Rehabilitation and Replacement Program.
For distribution mains, failure is more difficult to define because a single main break has a short-term impact to the City's customers and the water system. Because of this, the end of a distribution main's useful life is the point at which the main becomes too costly to operate or when the potential impact to City customers becomes unacceptable. Determining the end of a pipeline's useful life requires development of service level goals, detailed analysis of pipe performance data, and economic analyses. These factors are used to develop the City’s water main replacement schedule.
Sewer System
The City’s sanitary sewer collection system is composed of more than 5,000 miles of sewer lines. The city collection system begins at the point where the residential line taps into the sewer main. The collection system is made up of small diameter lines which are those 15-inches and smaller and larger diameter lines which are those greater than 15-inches in diameter. Roughly 92 percent of the collection system is made up of small diameter lines. The remaining 8 percent of the collection system are large diameter gravity lines that go up to 90-inches in diameter. The small and large diameter lines collect wastewater and deliver it by gravity or through one of the 29 lift stations to one of the City of Phoenix wastewater treatment plants. Continued collection system rehabilitation and replacement investment is one of the largest infrastructure costs to the wastewater utility second only to wastewater treatment plant investments.
WSD crews continually repair, rehabilitate, and replace various collection system sewer lines, manholes and appurtenances. In addition to sewer lines, crews focus on manholes, lift stations, pumps, valves, force mains and odor control facilities. These items are all necessary to keep the system operational and to convey the sewage to the treatment facilities. There are three main programs that make up the sewer line collection system. They are the Small Diameter and Manhole Program, Large Diameter Program, and the Multi-City Program. The Small Diameter and Manhole Program focuses on the nearly 4,600 miles of sewer pipe 15-inches or less and the associated manholes. Rehabilitation in this program typically consists of using a cured-in-place-pipe lining product. Typically, this can be done during low flow conditions and bypass pumping is not needed. The process involves lining the sewer line with a new structural resin product and reinstating, or opening, the lateral lines that connect the property owners’ line with the newly lined sewer. The time needed to line the sewer is less than one day and does not require excavation or repaving. The associated manholes are assessed using the NASSCO grading standard. Manholes are graded on a scale from one (nearly new) to five (requiring immediate attention). Manholes rated as a grade five are addressed and rehabilitated using either a coating process or an insert. Manholes graded three or four are noted in the asset management system to be reassessed. The Large Diameter Program, and the Multi-City Program assess and rehabilitate sewer mains greater than 15-inches. The large diameter lines and associated manholes are assessed using the same 1-5 NASSCO grading scale. Large diameter lines are more complex to rehabilitate since bypass pumping is needed. All sewer lines and manholes are susceptible to hydrogen sulfide which cause odors and causes corrosion. The goal of the large and small diameter programs is to rehabilitate the infrastructure before failure occurs. WSD staff have projected the cost of replacing or rehabilitating all pipelines based on an anticipated life expectancy, on average, of 75 years. For wastewater pipelines, the estimated cost for rehabilitation is $5.4 billion.
Infrastructure Replacement
The water and sewer systems are aging, and approximately one quarter of the City's pipelines are nearing the end of their useful lives. This inventory of necessary pipeline rehabilitation and replacement requires continual investment to ensure reliable water delivery and collection of wastewater for our customers. The oldest mains in the City systems date from the late 1800s and early 1900s. A disproportionate number of pipes, 41 percent of the City's pipelines, were installed between 1950 and 1980 during the peak years of City population growth. These pipes will contribute to an increasing number of water main breaks as the mains age and begin to fail. To maintain current service levels, over the next 40 years, as the infrastructure dating from those peak years continues to age, investment in pipe replacement must increase correspondingly. Due to the high cost of pipeline rehabilitation and replacement, it is critical that pipeline rehabilitation and replacement be carefully prioritized with well-constructed financing plans to proactively plan these activities.
The standard industry range for water and sewer pipe life expectancy is 50 to 100 years, however pipe life expectancy is influenced by environmental conditions, pipe material, and various other factors. Anticipated life expectancy is not always the best method to manage pipeline assets because this approach tends to lead to renewal of older pipes that are in good condition and ignores younger pipes that are failing. Because of this, WSD has developed an asset management plan that evaluates the likelihood and consequence of failure for all water pipes to determine the pipeline's overall risk. This risk is then used to prioritize water main rehabilitation or replacement efforts to ensure dollars are spent wisely. For sewer mains, the NASSCO grading standard is used to assess and prioritize the sewer main rehab projects.
The Water and Sewer Mains Asset Management Program for rehabilitation and replacement is budgeted in the department's Capital Improvement Program. Continued pipeline rehabilitation and replacement investment is needed to ensure that these critical infrastructure assets continue to deliver water to and collect wastewater from our customers.
Department
Responsible Department
This item is submitted by Deputy City Manager Ginger Spencer and the Water Services Department.