APPLICATION OF NEW SEWER CONDITION ASSESSMENT METHODOLOGY MEASURES THE RELATIVE CONVEYANCE PERFORMANCE AND RISK IMPACTS OF FOG AND OTHER PIPE DEFECTS

Collection system owners or operators are under increasing pressure to improve the reliability of their sewer conveyance system performance. However, this push comes at a time when municipal funding budgets are limited or cut. Therefore, the owner and operators are required to make better decisions about the operation and maintenance (O&M) of their systems. These pressures are well documented to have originated primarily from regulatory collection system emphasis and the general public's demand for improved service. As a result, O&M activity has gained significance and priority as a municipal activity. Condition assessment evaluations provide the baseline data and information to better prioritize both O&M and rehabilitation activities and expenditures to respond to these pressures.A utility wanted to revitalize its closed-circuit television (CCTV) inspection program, but was not satisfied with the current defect scoring and ranking systems. It was found that popular industry condition assessment defect ranking methods needed enhancements to address equipment and data improvements in defect detection technologies and to provide for more definitive defect ranking that asset management decisions require. Other enhancements needed were more accurate defect scores to reflect the relative significance of the defect to expected performance and improved methods for scoring multiple, reoccurring defects in the same pipe segment. To address these and other important needs, a new Sewer Condition Risk Evaluation Algorithm Model (SCREAM) was developed.This paper will describe how SCREAM was applied to the utility's existing condition assessment database and the comparative results. The paper presents the basis and provides examples of several key improvements that were included to address the needed enhancements. For instance, in developing specific defect scoring such as for fats, oils, and grease (FOG) and sediment, it was important to differentiate the hydraulic impacts of the different ways the material clings to the pipe and restricts sewer flow. This aspect was important for the defect scores to reflect the relative performance impact. A continuous blockage has approximately twelve and eight times the surcharge depth, compared to a spot or point blockage at 20 percent and 50 percent restriction, respectively (see Figure 2).