65B - PROPOSED WATER AND SEWER RATE ADJ

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City of Santa Ana, CA I SEWER RATE STUDY strengths of pipe have been made over the 150 years that clay has been used in the United States. (from www.ncyi.org/fags.asi3#faall). The installation method and backfill material also has a significant impact on its likelihood of failure. Any movement on the infrastructure or the surrounding sub -soil may also lead to stress fractures. An evaluation of the City's pipe data on materials, age, QSR ranks, etc. was performed to identify likely pipe cohorts. This evaluation included trends as observed in the source data (especially the QSR inspection ranks by materials) and also general past performance knowledge of similar materials in similar environments. Based on a review of the analysis results above, it was concluded that a significant factor influencing the likelihood of failure for the City's sewer mains is age (vintage); especially considering that almost 90 percent of the mains are made of Vitrified Clay Pipe (VCP). The following pipe cohorts were developed as logical grouping of pipes having similar deterioration rates. The associated Cohort Rank is also included. These ranks were then multiplied by two to create a range of 1 to 10 (for overall PoF calculation). • Cohort 5, High: All sewer pipelines installed before 1946 • Cohort 4, Med -High: All pipes with an unknown installation year • Cohort 3, Med: All pipes (except PVC and High Density Polyethylene) installed between 1946 and 1975 • Cohort 2, Med -Low: All pipes (except PVC and High Density Polyethylene) installed after 1975 • Cohort 1, Low: All PVC and High Density Polyethylene pipes installed after 1946 and any pipes which have been lined since their original installation As a precaution, all pipe materials with unknown installation year were assigned a rank of Medium High (4). The City is encouraged to investigate further to identify these missing dates. This might be accomplished by reviewing appropriate as -built drawings, or assuming install years based on neighborhood construction periods or adjacent pipe attributes. This effort was beyond the scope of this investigation. Once installation year data is identified, these pipe segments may likely acquire lower Cohort ranks. Lined pipe (including: Felt Liner, Fold Form PVC Liner, Fiber Glass Liner, and Spiral Wound Liner) data is stored in the pipe material field. Therefore, actual pipe material is unknown. Also, the timing of pipeline lining is often unclear. Therefore, it was assumed that any CCTV inspection data referred to the pipe conditions prior to lining. Once lined, the pipe was assumed to have been "fixed" and is currently in very good structure condition. Thus all lined pipe was assigned a Low (1) rating. Figure B 20 provides a graph of pipe cohort ranks (1 -5) and associated total pipe lengths (miles) for each rank. This distribution shows that the majority (68 %) of the sewer pipes fell into Cohort 3, as they were non - plastic pipes installed between 1946 and 1975. Figure B 21 provides a map of sewer mains color coded by Cohort Rank. BLACK & VEATCH I Appendix B: Sewer CIP Prioritization Process 65B -250