Failure Analysis Helps SD1 of Northern Kentucky Improve Its Continuous Sewer Assessment Program


  • Bo Copeland - Hazen and Sawyer

Sanitation District No. 1 of Northern Kentucky (SD1) is the second-largest public sewer utility in Kentucky, serving more than 290,000 residents throughout Boone, Campbell, and Kenton counties and maintaining 1,600 miles of sanitary sewer line, 440 miles of storm sewer, 134 wastewater pumping stations, 15 flood pump stations, 8 package treatment plants, and 3 regional treatment plants.

During implementation of its CMOM Program, SD1 developed a Continuous Sewer Assessment Program (CSAP). The goal of the program was to develop a logical approach to prioritizing inspection, cleaning, and other maintenance of the system. This included the development of a decision tree that would determine the next action on a pipe after inspection. This next action could be re-inspection or cleaning in a certain period of time or placing the pipe on the rehabilitation list.

Sewer pipe structural and maintenance condition are each assessed and scored based on CCTV inspections, and next actions for pipes are determined based on each of these scores separately. The most conservative of these dictates the next action that is actually scheduled. The triggers for re-inspection and the return frequencies were made relatively conservative at the start of the program to get a better understanding of operation and maintenance (O&M) “hotspot” areas. Additionally, the original goal of the plan was to inspect the entire system, as it existed in 2008, within ten years.


The program has been effective in reducing O&M blockage-related overflows in the system. However, SD1 has been conducting a comprehensive review and analysis of the program with the goal to manage risks related to the CSAP more effectively and efficiently by utilizing historical data to better understand the historical behavior of its collection system and, thereby, to revise and improve internal CSAP processes.

This study is a comprehensive review and analysis of the CSAP that utilizes findings from analysis of the last eight years’ worth of data in order to prioritize the inspection and cleaning of gravity sewer assets based on the historical behavior of the sewer system. The goals of this analysis include:

• Reduce re-inspection and cleaning frequencies overall, while maintaining adequate frequency of re-inspection and cleaning for pipes with highest likelihood of failure.
• To the extent reasonably practicable, avoid preventable structural and blockage-related failures (especially overflows and building backups).
• Based on review of historical inspection and failure data: update scoring thresholds for determining next actions; optimize frequency of re-inspection and cleaning for each range of scores; improve use of other considerations (e.g., previous scores) in determining next actions, and refine criteria used to place pipes in the rehabilitation program.


As part of this program update, SD1 evaluated the historical sewer inspection and failure records since July 2008 to determine if re-inspection triggers could be further refined and return frequencies lengthened without significantly increasing risk of failure and to make further data-driven recommendations.

Extensive data, including pipe attributes, inspections, overflows, work requests, and work orders were exported from SD1’s CMMS software and analyzed with a data visualization software tool called Tableau®, which allows large data sets to be manipulated through custom calculations and filters and displayed in intuitive graphs and charts. Separate lists of pipe structural failures (overflows, basement backups, or sinkholes caused by structural-related pipe condition) and blockage failures (overflows or basement backups caused by non-structural pipe blockages) were developed from the data. Queries were used to join and filter the data that were presented in the Tableau® visualizations, which showed changes in individual pipes’ condition scores between inspections, trends in condition scores and failures for the sewer system as a whole, and correlations between pipes’ failures and their attributes and previous condition scores. Filters were created to “drill down” into these visualizations and look at different subsets of the data being displayed.

The results of this evaluation helped SD1 to better understand the historical behavior of the sanitary sewer system. SD1 intends to perform additional analysis of the historical data in early 2017 to further investigate questions that were identified during the study. The findings of this study and any subsequent analysis will be used to revise and improve CSAP processes with the ultimate goal to better assess infrastructure condition and life cycle, cost-effectively minimize O&M blockage-related spills, and implement system renewal and rehabilitation in a way that targets dollars where they have the highest benefit. This presentation will help the audience understand strategies for using knowledge-based tools to make informed decisions to ensure public health and to cost-effectively manage sewer rehabilitation and replacement.

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