Sewer Inspection Methodology

The entire lined-concrete pipe system was assessed using a Closed Circuit Television (CCTV) for each manhole-to-manhole run. Each CCTV inspection was documented with a written field report and a viewable recording placed on electronic media. The inspection operations were normally completed during periods of relatively low system flow, which generally occurred during night time hours. As inspections were completed, the information was reviewed for entirety and clarity with additional field information requested as necessary. Each defect type found within a pipe run was quantified and assigned a rating based on the National Association of Sanitary Sewer Companies (NASSCO) Pipeline Assessment and Certification Program (PACP) standards and ratings to the resultant defect data. Table 1 presents the NASSCO grading system. It should be noted that the similar rating system used in Canada is through the North American Association of Pipeline Inspectors (NAAPI).

Table 1. NASSCO grading system



Defect Condition

Rate of Pipeline Deterioration


Immediate Attention

Pipe has failed or will fail within the next 5 years



Pipe will probably fail in 5 to 10 years



Pipe may fail in 10 to 20 years



Pipe is unlikely to fail in at least 20 years



Failure is unlikely in the foreseeable future

By applying standardized defect codes to this assessment project, each similar defect will have comparable ratings to help in generating the condition assessment results. The codes also help to standardize the condition assessment procedure and convert the inspector’s defect data into meaningful condition grading information.