A Comprehensive Approach to Prioritizing Stormwater Capital Improvements

Authors:

  • Troy McPherson, PE, Alan Davis, PE - Hazen and Sawyer
  • Stephen McLaughlin, PE - City of Virginia Beach Public Works

Learn more about this project.

The approach used to develop and implement the methodology in this project.

Risk modifiers were utilized to recognize an asset's relative risk based upon its combination of geographic position, physical features and past performance. Based upon interviews with city operations and inspections staff, specific descriptors were identified representing considerations that suggest potential for greater consequence of cave-in related asset failure.

OBJECTIVE – The City of Virginia Beach, Virginia Public Works Operations (PWO) has taken a proactive approach to condition assessment, prioritization, and rehabilitation and/or replacement of their stormwater infrastructure assets. This approach has resulted in a methodology for condition assessment that considers specific stormwater system criteria and effectively prioritizes improvements for the evaluated assets.

METHODOLOGY – A stormwater infrastructure specific coding system was developed to supplement the standards of the Pipeline Assessment and Certification Program (PACP) as established by National Association of Sewer Service Companies (NASSCO). Supplemental defect codes for CCTV assessment and a unique above ground defect coding system were developed to analyze the relationship between buried stormwater infrastructure and above ground documented defects. The applied coding system and analysis were utilized to generate an asset grading system.

The asset grading system utilizes a quantitative risk assessment approach to identify the assets that represent the highest risk to the owner. Combining the probability of asset failure based upon the overall pipe rating and the magnitude of the loss related to the asset’s combination of relative geographic position, physical features, and past performance generates the asset’s improvement prioritization ranking.

Building upon the prioritization ranking, individual asset improvement costs are determined by defining specific construction methods and associated costs. The associated costs are arranged cumulatively and compared to the owner’s threshold for capital improvement expenditures in order to determine the specific assets to be rehabilitated or replaced.

BENEFITS OF PROJECT – This project offers significant benefit to the asset management community due to its unique risk based analysis approach, coding system, and resulting correlation between above ground and buried asset defect observations. The owner benefited by utilizing a defendable, analytical approach to infrastructure capital improvement prioritization and the efficient use of capital funding.

STATUS – To date, approximately 200,000 linear feet of stormwater infrastructure has been analyzed and prioritized with programmed cost savings associated with this methodology exceeding $2.5 million for the first year alone. The final prioritized construction documents were provided to the owner in October of 2014 with construction scheduled to be complete by April 2015.

For more information, please contact the author at tmcpherson@hazenandsawyer.com.

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