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86 <br />SEVER RATE STUDY I City of Santa Ana, CA <br />Overall QSR Segment Score Method <br />Although the Raw QSR Grading Method is simple, it ignores the number of defects observed or any <br />lower grade defects. For a more complete evaluation and prioritization, NASSCO suggests using a <br />combined segment scoring method. This approach uses a formula of multiplying both rank scores times <br />the number of occurrences to identify a total risk factor for the pipe segment (i.e. considers the number <br />of defects — not just the grade of the worst defect): <br />Overall QSR Segment Score = Worst Defect x No. of Worst Defects plus <br />2nd Worst Defect x No. of 2 "d Worst Defects <br />For the QSR example of 5236 given above, this would result in QSR Segment Score of 28. <br />(5x2) +(3x6) =28 <br />This approach is very useful in prioritizing pipe segments into ranked lists based on overall structural <br />severity. It should be noted that pipe segments having numerous Grade 4 defects and only a couple <br />Grade 5 defects could actually receive a higher overall QSR Segment Score than a pipe having only Grade <br />5 defects. <br />An analysis of the City's QSR values determined that the Overall QSR Segment Scores ranged from 0 (no <br />defects observed) to a high score of 161. About 22 percent had no values (not rated) and 70 percent had <br />scores less the 10. These resulting scores were used in the prioritization process described later in this <br />document. Figure B 16 provides a map of sewer mains color coded by Overall QSR Segment Score. <br />[INTENTIONALLY LEFT BLANK] <br />65B -245 <br />NOVEMBER 20'. <br />