Assessment and Rate Case Evaluation of 45 Tanks

This study included the assessments, inspection, analysis, design upgrades,
and cost-estimates for 45 water storage facilities including 22 steel tanks and 23 concrete tanks. The inspection included interior ROV inspection, WHB Engineers operating company, self-performed. The analysis was performed using site-specific seismic values to satisfy the current Code as well as addressing upcoming seismic requirements. Analysis was performed considering the latest editions of AWWA, ACI, CBC, and ASCE 7 documents.

As is commonly the case in California, many steel tanks were constructed without anchorage and with insufficient freeboard. Careful analysis supported a measured reduction in water level to comply with current Code. Having a specialty in prestressed tanks, WHB Engineers leveraged an expertise to carefully review the circumferential and vertical prestressing in order to confirm the level of compression in the concrete corewall. This was used to determine the watertightness of the tank.

After careful assessment, each tank was assigned a grade, a priority, and a cost to upgrade. Upgrade options were estimated and prioritized. Connections to the tanks were also reviewed for resilience during earthquakes. Seismic-induced earth settlement would likely cause a differential displacement between the tank and its pipe connections. Historically, this has been a failure mechanism during strong ground motion. Special pipe fittings which can accommodate differential settlement were recommended and need to be carefully specified in order to function correctly.

Two final tables were produced for the deliverable; one for Los Angeles County and one for Ventura County. These tables with the supporting cost-estimates and calculations will be used to support Rate Case decisions for hundreds of thousands of customers. Customers of the California American Water can now have confidence in a road map for the reliable distribution of water.