Knowledge Acquisition and Validation of an Expert System for Prioritizing the Inspection of Sewers

The sewer infrastructure of the US is in a state of disrepair due to municipal budget constraints for utilities, a history of neglect and most importantly a lack of critical information about the aging and complex sewer networks that convey wastewater for 75% of the US population. This paper describes an expert system, Sewer Cataloging, Retrieval and Prioritization System (SCRAPS), that prioritizes sewer inspections that target the collection of information of critical areas sewer network. The knowledge base of this expert system was assembled with input from a national group of experts, drawn from both the public and private sectors. Input from the experts developed the system's logic, which assesses the overall need to inspect based on the line's consequence and likelihood of failure. The inference engine is based on Bayesian belief network theory, which allows the uncertainty in the experts' beliefs to be propagated through the system. The tool was developed with a rapid prototype application process. The validation of the tool shows that the tool assesses pipeline case studies similar to other sewer infrastructure experts. Introduction Wastewater collection and conveyance systems are extremely important, yet invisible components of our nation's urban infrastructure. In the US, approximately 19,000 wastewater collection systems provide service to 75% of the population (EPA 1999). Unfortunately, many wastewater collection systems in the US are in a state of disrepair and fail to convey sewage as intended. The failings of the degraded systems burden society with possible pathogen exposure, beach closures, water way pollution, road and building damage and the disruption of critical services and commerce. In a recent study the EPA reports that the “performance of a collection system is directly linked to the O[peration] and M[aintenance] program for the system” (Arbour 1998). Improvement of the operation and maintenance (O&M) strategy of a sewer system naturally improves the effectiveness of the system. Efficient and successful O&M programs must have detailed information with which to make informed decisions and strategic plans. Sewer system evaluation surveys (SSES) are the standard for gathering such operation and maintenance information. These surveys include activities such as closed caption television filming, flow monitoring, and manhole inspections.