Laserfiche WebLink
96 <br />SEWER RATE STUDY I City of Santa Ana, CA <br />Overall QSR Segment Score <br />Using the Overall QSR Segment Score Method described previously, an overall QSR score was calculated <br />for each pipe segment. This method uses a formula of multiplying both rank scores times the number of <br />occurrences to identify a total risk factor for the pipe segment. Again, lined pipe was assigned a grade of <br />0. These scores ranged from 0 to 161. To convert to the desired scoring scale range, these raw values <br />were divided by 16.1 to get decimal values 0 to 10. As in the Raw QSR Grading Method, the Cohort rank <br />was used as a substitute for any missing QSR values. <br />Other PoF Considerations <br />Several other physical properties and environmental conditions were considered for inclusion in this <br />analysis. Some of them are addressed below. Although these factors were not actually used in the PoF <br />prioritization analysis, they may someday provide useful information. Therefore, the City is encouraged <br />to reevaluate these once their Asset Management system is more mature. <br />• Mains by Diameter: There does not appear to be any obvious correlation of sewer pipe failure <br />and pipe diameter. Therefore, this aspect was not considered for PoF calculations. <br />• QMR: As described previously, since this is mostly a maintenance indicator it was not <br />considered as a contributor to structural condition assessment. <br />• Repairs: City staff indicated that repair locations were primarily used to indicate planned work <br />activities based on the results of the CCTV inspections and that they do not indicate an <br />additional level of information about the pipeline condition. Therefore, repairs were not <br />included as a factor. <br />• Enhanced Maintenance Locations (EMLs): Again, since this is mostly a maintenance indicator it <br />was not considered as a contributor to structural condition assessment. <br />• Spills: Also not considered a structural factor. <br />• Soils: A high level review did not reveal any obvious correlation of high QSR scores or repair <br />concentrations for sewer pipe to key soil characteristics. This is to be expected as VCP is <br />normally not very impacted by most soil conditions such as corrositivity, pH, etc. Linear <br />extensibility can be a contributing factor, but appears to be low to moderate in most of the City; <br />being high only in the far southern area (where sewer pipeline issues are uncommon). The City <br />may want to further review these considerations in the future. <br />Overall PoF Calculation <br />To produce an overall PoF score for individual pipe segments, weighted scores for each of the <br />contributing PoF criteria were added together. The resulting PoF scores are, by design, within the range <br />of 0 to 10. For simplicity, the three PoF criteria were all assigned the same weighting (level of <br />importance). By adjusting these weights other assessment scenarios could be created. Table B 2 <br />provides a summary of the PoF criteria used in this analysis. <br />65B -255 <br />NOVEMBER 2014 <br />