How does a utility approach evaluating their aging sanitary sewer infrastructure? After all, no two systems are alike. Wouldn’t it be convenient to have more universal standards to determine required, immediate replacement or repairs due to deteriorated conditions, or what may be unworthy of any repairs in the short term?

It absolutely is more convenient, and in fact, the National Association of Sewer Service Companies (NASSCO) has already established standards for collecting condition data on existing sanitary sewer pipes, manholes and laterals that can be used for sewer systems across the nation.

By using NASSCO’s standards for coding each identified defect, that defect is assigned a condition rating on a scale of 1-5:

NASSCO Rating System

  1. Minor defect grade
  2.  Minor to moderate defect grade
  3. Moderate defect grade
  4. Significant defect grade
  5. Most significant defect grade

NASSCO’s standard codes, which have been incorporated into many data collection software packages, provide a common database output for sewer inspection results. The advantage to using this standard is that it removes some of the subjectivity from determining what should get fixed now and what can wait until later.

This standardized approach provides results that when revisited years after the data is retrieved, can still be understood in terms of the condition of the asset at the time of the original inspection. The established condition ratings make it easier to take action at any point in time rather than trying to base decisions on antiquated field sketches or someone’s hand-written comments about found defects.

Deterioration Mechanisms

There are multiple factors that influence the deterioration of pipelines. The varying types of deterioration can be summarized into three categories: structural related, maintenance related, and construction/design related.

Supplemental Technologies

The primary means of pipeline assessment still uses standard CCTV methods. However, other technologies have been developed that are capable of providing a higher level of accuracy than CCTV can provide with a 2-dimension view. These technologies, such as Laser Profiling or Sonar, can be used in conjunction with CCTV.

Risk Management

It is not uncommon for utilities to have funding constraints. Some utilities are using a Risk Management Approach to assess both the condition – Likelihood of Failure (LoF), and criticality – Consequence of Failure, (CoF) to help prioritize where to focus efforts, and available dollars. NASSCO’s risk management tools can determine which assets should be considered high priority based on what the consequences are should that asset fail. CoF considers environmental, social, and economical factors such as:

  • Costs for repairs, legal fees and fines due to failure
  • Impacts on hospitals, schools, business and other critical services due to asset failure
  • Contamination of soil, groundwater or other waterways due to asset failure
  • Once the LoF and CoF are established, risk can be calculated and plotted. Utilities can then make timely, cost-effective decisions on infrastructure improvements based on risk calculations.

Wright-Pierce has extensive experience assisting communities develop and implement collection system management and assessment programs. For more information, contact us today.