An evaluation of leaks detected over the past 20 years indicates that the WCWD system experiences leaks of two distinct types. The first are small, chronic leaks that are difficult to detect or locate. In the aggregate, the small leaks result in substantial water loss but are typically not of sufficient size to directly affect water pressure within the system (thus have no observable impact on water delivery, further reducing the detectability). The second are leaks that become serious with little or no warning. Larger and even catastrophic leaks that directly affect water pressure must still be located by walking the line, because there is no way to determine exactly where the leak is occurring (barring obvious surface evidence). In the past, a percentage of these larger leaks have not been detected until substantial subsidence has occurred, resulting in the formation of sinkholes.
Although the WCWD water distribution system has been active along essentially the same alignment since the 1850s, no formal map of any of the system components currently exists. Knowledge of the system is largely anecdotal and experiential and is passed from OM to OM. The absence of any formal map greatly impedes the capacity of the District to engage in systematic capital improvement planning, organized leak detection, and documentation of emergency and ongoing maintenance of the system.
As originally conceived, work on this task would have focused on retaining a leak detection firm (specializing in the location of pipes and subsurface utilities) and, following its mapping effort, developing a systematic evaluation of the existing Downtown distribution system, with the intent of developing a phased strategy for leak detection and repair.
This task also included preparation of a GIS-based map for the entire water system. This initial mapping was to include the location of the main line distribution system, service junctions, service connections and lateral lines, as well as precise mapped locations and flagging of the sites for the installation of water meters.
Once the Downtown system had been mapped, the project engineer and the pipeline/utility location specialist were to collaborate to develop a preliminary leak detection methodology, approach, and needs assessment. Additionally, a needs assessment was to catalog leaks detected during the mapping effort to develop a zonal map of the Downtown area, and detail the extent and magnitude of leaks (in both main line and service/connection laterals) detected throughout the downtown area in this preliminary assessment.
The objective of the feasibility study was to develop a systematic leak repair methodology and approach for the WCWD to implement. Based on the results of the needs assessment, the project engineer, WCWD General Manger, and the pipeline/utility location specialist were to evaluate the feasibility of a downtown-wide leak repair program. This evaluation was to include both proactive (repair replacement) and reactive (repair) components.
Current Status (September 2016)
As the Project Team became more familiar with the infrastructure system and the extent of local knowledge as to facility location and placement, it became clear that the original strategy of hiring a firm to detect and map the leaks prior to meter installation was a costly approach that no longer aligned with the expanded project perspective of the team. Instead, it was determined that the work effort could be more efficiently accomplished by joining the meter installation (Project #12) with Project #13, and simply detecting leaks during meter installation using the monitoring of meter readings to determine the post-installation leak/water use profiles. In part, this was a feasible option because of the extensive infrastructure location efforts of the OM and WCWD staff over the prior year.
The efficacy of meter installation with respect to leak detection in the District became apparent on the first day of the installation. After discovering several leaks, the project team made the determination that detecting leaks as part of the meter installation – rather than as a separate and distinct work effort, was the most efficient and cost effective strategy for detecting and repairing leaks. This strategy also had the advantage of detecting and repairing leaks throughout the entire system, rather than only within the Downtown area. Additionally, as the installation of meters has allowed for a more systematic identification of leaks – the current strategy will be to read the meters at frequent intervals through the end of 2015 to determine where leaks are occurring, both in the distribution lines and on lateral lines within customer properties. In support of this decision, within one day of installing meters in the zone along Relief Hill Road a single leak was discovered that totaled 1,300 gpd.
As a result of this revised strategy, the Leak Detection and Repair project has been completed, as it was undertaken concurrently with the meter installation, completed in July 2015. However, any leaks detected through 2016 will be repaired by the district (if found on the main distribution or water treatment infrastructure), or steps will be taken to ensure repair (if the leaks are on the customer side of the installed meters).
The WCWD Board is developing a strategy and accompanying policies to direct the repair of leaks associated with metered readings. In the past, leak repair has been undertaken solely on the basis of observed leaks. The lack of a meter on the storage tank and the challenges of ‘walking the line’ along both Maybert and Relief Hill (due to topography and vegetation) had previously limited detection of significant leaks or to leaks that were so catastrophic that the ability of the tank to fill or water to be distributed was directly affected
City of Nevada City
Bryan McAlister, City Engineer, (530) 265-2496 x126, firstname.lastname@example.org
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