By Alan Ambler
Most municipalities that have been maintaining aging infrastructure for decades simply absorb the effort and costs required to repair water main pipeline breaks when they occur. Seldom do many municipalities make the efforts required to track the costs and evaluate the cost benefit of proactively rehabilitating the existing pipe line versus continuing to repair emergency breaks. The overall costs of the emergency breaks on larger diameter pipeline systems can grow exponentially.
Additionally, social and environmental costs associated with water main pipeline failures are often borne by third parties, such as customers, residents, businesses and insurance companies. Social costs may include loss of business revenue due to increased traffic congestion or poor accessibility, worker productivity loss, loss of time due to traffic delays, accelerated deterioration of alternate roads that must be used during maintenance of traffic activities, damage to established landscaping and property values, and increased accident rates. Environmental costs can include increased greenhouse gas emissions, noise, impact to natural resources, dust and debris and any additional environmental impact due to uncontained fluid release.
This article will detail potential actual costs incurred to fix water main failures. For the purpose of relevant comparison, various cost scenarios for an escalating level of water main pipeline failure impacts are presented. Two lesser cost failure scenarios that many utilities often encounter were evaluated for their social, environmental and economic impacts and a third scenario was reviewed from available technical literature for the potential for a much more catastrophic failure. All three failure scenarios are presented here.
Failure Scenario 1
The first water main pipeline failure scenario is of a more routine nature. The failure of a small diameter (less than 6 in.) pipeline in question is more of a small section circumferential failure that is often detected as a growing leak from the distribution system. Initially, a small two-man crew would be dispatched to the site to evaluate the full extent of the required repair work. Evaluation of the failure indicated four workers were required to decommission the existing water main, excavate to the failed pipeline and install mechanical adapters and replace 4 ft of pipeline.
The crew that responded to the initial work order was able to isolate the section of water main pipeline relatively easily by locating existing valves that were still operational. The isolated section of water main pipeline only impacted four potable water customers so social impact was relatively minimal. Also, the water loss from the leak was also minimal so no efforts were made to quantify the water lost. No direct environmental damage was observed that was not easily restored by the crew. Therefore, the cost evaluation for the first scenario was primarily limited to man hour, equipment and material costs.
Economic analysis of the water main pipeline failure is provided in Table 1. It is useful to note that the actual replaced section of existing pipeline was limited to approximately 4 linear feet (lf) of small diameter pipe. The cost per lf of replacement was $525 per lf. Construction costs to replace potable water main pipelines for preplanned projects vary considerably over North America and for a litany of other items, such as project size, replacement method, pipe material, depth, soil conditions, risk, project location and many other variables. Comprehensive installation costs to complete a pre-planned project with minimal restoration costs can vary from $25 per lf to $175 per lf for a small diameter water main project. When the replaced length of pipeline during the emergency repair is compared to a proactive approach to replacing the existing pipeline, it is easily observed that emergency replacement is simply not cost effective when compared to a proactive replacement program.
Failure Scenario 2
The second water main pipeline failure scenario is of less routine nature. The failure of a medium diameter pipeline (greater than 6 in. but less than 12 in.) in question is a larger more substantial water main failure. A full section of the medium diameter pipeline failed and isolation valves were not as readily available to shut down the water during the failure. This water main pipeline failure scenario required 10 service workers, five service trucks, a backhoe, a vacuum truck and a loader. The second scenario had more significant environmental and social impact and efforts were made to quantify these impacts. Economic analysis of the water main pipeline failure is provided in Table 2 below.
It is useful to note that the actual replaced section of existing pipeline was limited to approximately 15 lf of medium diameter pipeline. The cost per linear foot of replacement was $3,635 per lf. As mentioned previously, comprehensive construction costs for potable water replacement projects can vary widely. Restoration costs in developed urban and sub-urban areas can be significantly higher than the cost of the actual potable water main pipe material. Construction costs for a pre-planned medium diameter potable water main replacement project can vary between $35 per lf and $1,000 per lf depending on many project variables. When the replaced amount is compared to a proactive approach to replacing the existing pipeline, it is easily observed that emergency replacement is simply not cost effective when compared to a proactive replacement program.
Literature review was conducted to analyze the social, environmental and economic costs of larger diameter water main pipeline failure to ascertain the potential outcome of large diameter failure within municipal systems. This was examined in the paper, “Empirical Analysis of Water-Main Failure Consequences,” presented at the International Conference on Sustainable Design, Engineering and Construction in 2015. The paper was authored by: Dr. Kalyan R. Piratla and Sreeganesh R. Yerri of Clemson University; Sepideh Yazdekhasti, now with Xylem; Dr. Jinsung Cho of California State Polytechnic University; Dr. Dan Koo of the Indiana University Purdue University-Indianapolis; and Dr. John C. Matthews of the Trenchless Technology Center at Louisiana Tech. Multiple catastrophic failure scenarios were evaluated but a recent failure of a 30-in. steel potable water main pipeline is presented here as a potential worst-case scenario for municipal water systems.
Failure Scenario 3
In this example, a 30-in. steel potable water main pipeline failure that was analyzed was a 2014 pipeline failure that occurred on the University of California–Los Angeles campus. This water main pipeline failure was a high-profile water main failure that attracted national news coverage and caused significant environmental, social and economic damage. The failed potable water main pipeline was 93 years old.
The crews that responded to the break required four hours to shut the water off to the section of pipeline due to inoperable and non-locatable valves. More than 160 firefighters responded to the water main break to search more than 200 cars in flooded subterranean parking garages, according to the Empirical Analysis paper. The social impact of the water main pipeline failure was enormous. A historical basketball court was flooded during the potable water main pipeline failure.
It was estimated that almost 75,000 gallons per minute of water loss occurred for a total of approximately 18 million gallons of treated water released during the break. Evaluation of the economics of this scenario for potable water main pipeline failure was provided for lost potable water, cost and time to repair and return to service, travel delay for the surrounding public, supply outage and substitution costs, potential health risk and property damage are included in Table 3 below.
Unfortunately, additional crew time, restoration and social and environmental costs were not available to directly present the third catastrophic failure scenario in the same format as the first two scenarios. However, it was assumed that only 75 lf of the existing 30-in. steel water main pipeline was replaced. Therefore, the cost of replacement was $481,333 per lf. Construction costs for large diameter potable water main pipelines vary considerably based on reasons previously mentioned for small and medium diameter pipelines. Construction for a large diameter pipeline can vary from $500 per lf to $2,500 per lf or more. When the replaced amount is compared to a proactive approach to replacing the existing pipeline, it is easily observed that emergency replacement is simply not cost effective when compared to a proactive replacement program.
Municipalities that own, operate and maintain potable water systems throughout the country should understand that reactive maintenance programs are costly and ineffective. These municipalities should consider incorporating proactive programs that provide capital investment into these pipeline inventories to replace the aging infrastructure. Often, municipalities maintain vast inventories of aging pipelines that make it difficult to determine where to begin replacing infrastructure. Comprehensive asset management programs that include pipeline condition assessment tools are useful for managing pipeline inventories but are also costly and time consuming to undertake. It will continue to be a challenge to try to predict where these pipeline inventories may fail in order to plan the most beneficial proactive replacement program. However, municipalities will greatly benefit from reduced maintenance costs from the proactive replacement program.
Edward Alan Ambler, P.E., is the owner of AM Trenchless, specializing in trenchless technologies, such as pipe bursting. He previously worked for the City of Casselberry, Florida, managing the municipal utility and developing its capital improvement program. He serves on the board of directors of the North American Society for Trenchless Technology (NASTT).
