Buying Time at a Discount – Prioritizing Capital Repairs through Wireless Active Monitoring

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Abstract:

Aging collection systems are a ticking time bomb. Older systems have pervasive inflow and infiltration (I and I), aging pipes can crack and leak, force mains reaching the end of their useful lifetime have higher risk of failure, and fractures or defects in pipes accumulate over time causing crumbling or collapse leading to overflows or backups. The conventional and somewhat reactive means of dealing with these problems is to embark on costly capital improvement projects (CIPs) with infrastructure replacement priorities based on extensive camera surveys and engineering flow studies, combined with documented problem areas or “trouble spots”. This approach can cost agencies millions of dollars and often take years to fully accomplish.

In the current harsh climate of economic stress, system operators are faced with the difficult choice of deferring or canceling projects in exchange for higher operating risks associated with spills, fines, and increased regulatory and public scrutiny. This dilemma is exacerbated by a lack of continuous real-time, system-wide data. Worse, for agencies that have a history of sewer spills related to capacity or aging problems, they may be facing onerous consent decrees and/or be forced into large scale CIPs as the only solution. These situations stretch staff resources, limit programmed equipment expenditures and ultimately lead to highly unpopular rate spikes or bond measures to pay for these improvements.

The advent of system-wide active wireless monitoring for wastewater collection systems over the past few years now offers a viable and highly attractive financial alternative to this traditional path of expensive CIPs, rate increases, and disgruntled ratepayers. Permanently installed sensors, costing only a few thousand dollars per site, deployed in a small but statistically representative percentage of an agencies' manholes, provide a continuous real-time picture of water levels. This comprehensive data, when trended, often refines and better targets the extent of system's problem areas and greatly decreases CIP expenditures. In addition, the data may provide a demonstrable basis to justify extensions to these assets' useful life, a primary driver of capital improvement plans. Further, by utilizing permanent real-time remote level trending at the locations of a proposed CIP, an agency can quantitatively determine which locations are the “worst offenders”, determine mean times to failure, and prioritize corrective projects more systematically. Even when it is established that a location has required exceptional or accelerated maintenance activity or has been designated as a “trouble spot” by the maintenance staff, it may not require immediate rehabilitation or replacement until the behavior of the asset has been more completely documented with empirical data. The rehabilitation project may be deferred to next budget cycle or further while the agency still maintains assurance that the risk is reduced at the problem locations by continuous monitoring and immediate high water level notification that these sensors provide directly to emergency response crews.

This paper will consider case studies where system-wide remote monitoring enabled collection agencies to defer or actually postpone indefinitely costly capital improvement projects. An example discussed in this paper is the Mt. Crested Butte (CO) Water and Sanitation District which faced a 10 million collection line replacement project mandated by the Colorado Department of Public Health and the Environment. The District was able to obtain relief from the state through the installation of a continuous level monitoring system costing less than 100,000, therefore realizing more than a 100:1 savings while reducing spill risk and obtaining additional service life from this existing infrastructure. This paper will also discuss the Fallbrook (CA) Public Utility District which was able to utilize a similar system-wide wireless level sensor array to delay and better prioritize various its capital projects, decreasing stress on unplanned replacement on budgets and making more intelligent planning decisions based on real data provided by these permanent installations.
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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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