Achieving sewer success
Buried infrastructure management (BIM) can help you improve your sewer system while managing costs. Here are the steps necessary to implementing an effective BIM program (see chart on page 34):
- Using GIS, create an up-to-date map of your sewer system, with detailed information on the physical characteristics of manholes and pipes.
- Inventory the system with a date-stamped record of the condition of each asset and link it to the GIS map.
- Identify immediate capital and O&M needs by assigning an overall O&M and structural condition grade to each manhole and pipeline.
- Prioritize activity through risk assessment of the probability and consequence of failure for each asset.
- Plan utility service level goals regarding financial abilities and goals. The outcome of the plan should be an optimized BIM program that leverages the utility's financial and human resources.
Aging infrastructure and changing operational conditions are deteriorating our nation's sewer collection systems. Limited availability of resources to address the problem also poses a monumental challenge. These dilemmas have driven utility managers to implement a “find and fix as you go” approach. This often directs resources and spending to repairs that may not improve system performance or improve the overall condition of the assets measured by the utility condition index (UCI).
Sewer utilities can improve performance and reverse the aging process by implementing buried infrastructure management (BIM), a systematic planning process that allows them to leverage resources to maximize the immediate and long-term benefits of every action. The outcome: improved performance and increased UCI.
The process leading to an optimized BIM program begins with accurate mapping and a current inventory of the service (i.e., maintenance requirements) and structural condition of each asset (such as manholes and pipelines). This identifies the location, physical characteristics (such as age, material, size, and function), and the service and structural condition of the assets, which in turn helps the utility identify segments that require immediate attention.
Then, assets can be ranked according to the probability and consequences of failure. Assets most critical to system operation will rate higher on the consequence scale; assets in poorer condition will have a higher probability of failure. Assets with both a high consequence score and a high probability of failure pose the greatest risk and should receive the most attention. Those with a high consequence score should be inspected more often as failure of these carries the greatest cost. This effort provides the basis for a prioritized list of maintenance and capital improvements that help achieve the desired level of service.
During planning, multiyear budget forecasting and assessment of how different levels of spending improve the UCI are performed to establish the scope of work and budget for each year. Maintenance activities are scheduled based on potential for blockage and the consequence of backups and overflows. The schedule of capital improvements considers factors such as how different budget scenarios affect the overall condition of the sewer system, and the overall capital needs of pipelines, structures, treatment, and pumping facilities. The outcome of this task is a focused maintenance management and capital program designed to achieve immediate benefits in performance and the UCI.
BIM IN ACTION
In 2002, the town of Marblehead, Mass., experienced sewer surcharging and basement backups in areas previously not identified as problematic. The Marblehead Water and Sewer Commission (MWSC) immediately sprang into action to establish a program to inspect, inventory, and assess the condition of its 87 miles of sewer pipe, 2000 manholes, and 29 pump stations.
Recognizing the need to document the location and condition of its buried assets, the MWSC hired a consultant to prepare a GIS map of its collection system. Developed from existing as-built drawings and records, the commission substantially completed its electronic mapping by 2004. With the completion of the initial mapping efforts, the MWSC then hired InfraMetrix LLC of Wakefield, Mass., to develop a buried infrastructure inventory and assessment program and to demonstrate the program on the 187 manholes and 6.5 miles of pipe that comprise the Shorewood Road Pumping Station District's gravity sewer system.
Using truck-mounted zoom cameras and condition-assessment software, InfraMetrix located each of the district's manholes and inspected each manhole and pipeline. The physical characteristics—along with the service and structural condition of all of the MWSC's assets—were recorded on CD and evaluated in accordance with WRc defect codes, a standard methodology for describing internal sewer pipe conditions. Once the condition assessment was completed, InfraMetrix expanded upon the commission's GIS to include the video inspections, defect photos, and the service and structural condition ratings determined by certified Pipeline Assessment Certification Program (PACP) specialists. Having determined the maintenance requirements and structural defects, the commission performed cleaning and repairs to reduce the risk of costly emergency repairs and customer settlements.