Got a Lot of Wire Breaks, Now What? An Overview of the Santa Clara Valley Water District’s Emergency Repair of a 96-Inch PCCP and Changes in Program and Policies

A segment of a 96-inch diameter prestressed concrete cylinder pipe (PCCP) raw water transmission line operated by the Santa Clara Valley Water District (SCVWD) suddenly ruptured near Casa De Fruta in Santa Clara County, California on August 1, 2015. The failure resulted in the loss of over 20 million gallons of water and the shutdown of the San Felipe System impacted water supplies to both Santa Clara and San Benito Counties for over a month. The emergency repair involved the replacement of the failed pipe segment with a section of cement mortar lined steel pipe, and also included the repair of two distressed pipe segments using carbon fiber reinforced polymer (CFRP). The failed section of PCCP was installed by the U.S. Bureau of Reclamation (Reclamation) in the mid-1980s as part of the San Felipe system of the central valley project. SCVWD is responsible for the maintenance and operation of the system of about 40 miles of the San Felipe system, which consists of tunnels and pipelines ranging from 96-inches to 144 inches in diameter. A 2007 electromagnetic inspection of the Santa Clara Conduit conducted by Reclamation found 15 pipe sections with broken prestressing wires ranging from 5 to 30 wire breaks. Up to 30 wire breaks were found on the now ruptured segment of pipe. Plans made to re-inspect this area within 5 years of the 2007 inspection never materialized due to operational constraints as well as emerging concerns about the possible spread of Zebra Mussels that were present in the Hollister Conduit portion of the San Felipe system. The rapid degradation of this pipe section raised a lot of questions and concerns amongst SCVWD and reclamation staff, regarding the root cause of the failure and the long-term management strategy for PCCP. With assistance from engineering consultants and Reclamation staff, a thorough investigation ensued to determine the cause of the pipe failure. SCVWD is using information from this failure and experience managing PCCP to re-evaluate its current pipeline maintenance program strategies and policies as it pertains to PCCP. The intent of this paper is to provide the reader with an overview of failure and a discussion of the policy issues and changes needed to safely and effectively manage PCCP.