65B - PROPOSED WATER AND SEWER RATE ADJ

Home Browse Search

City of Santa Ana, CA I SFWER RATE STUDY Consequence of Failure Analysis (CoF) In a process similar to the PoF analysis, criteria for the Consequence of Failure (CoF) were also identified and evaluated. These criteria are described below. Pipe Diameter The assumption here is that larger pipes will be more costly to repair or replace. Likewise, should they fail the consequences will likely be more severe. For the purpose of this analysis, CoF grades were assigned to ranges of pipe sizes increasing in pipe diameter as shown in Figure B 25 below. Pipe records having an unknown diameter were assigned a value of 4. Figure B- 25: Sewer System Pipelines CoF Scores by Diameter Customer Impacts The concern here is for increased risk of service interruptions for customers upstream of a possible facility failure. Using GIS processes, the cumulative count of upstream laterals was calculated for each main segment. Upstream lateral counts of 0 to 36,994 were identified. Although this was generally an effective approach, the counting process was not 100 percent precise. Missing data and inconsistent network connectivity produced some errors. Since the errors did not appear to be significant and since the accuracy of the actual count values did not need to be precise, these errors were ignored. The lateral count ranges were assigned grades between 0 and 10. Figure B 26 displays the distribution of upstream lateral counts throughout the collection system and the assigned grade ranges. As shown, more than 60% of the sewer pipelines have fewer than 100 upstream laterals, corresponding to a CoF Grade of 0. However, approximately 15 percent of the sewer pipelines have more than 500 upstream laterals, which correspond to a high CoF Grade of 10. Pipe records having an unknown lateral count were assigned a Grade of 6. BLACK & VEATCH I Appendix 8: Sewer CIP Prioritization Process 65B -258