Assets can remain functional longer than their original design life. They also may become functionally obsolete before that time. To avoid replacing them too soon, public agencies need a planning tool that shows if an asset is aging more or less rapidly than expected and calculates rehabilitation vs. replacement costs based on the factors they decide are most important.
The City of San Diego Public Utilities Department is one such agency. Two opposing forces — aging infrastructure and budget constraints — created the need to plan and manage water and sewer assets in a way that supports all three aspects of the department’s triple bottom line (social, economic, and environment) approach to doing business.
The department calculates remaining useful life (RUL) with the following formula: 10% x (50-T1) + 90% of (TL-T1) or (TS-T1).
Assume a concrete reservoir built in 1975 is assessed in 2015. Because the structure is 40 years old, remaining capacity is 60% and original design remaining life (50 - T1) is 10 years. Assessed condition remaining life (ACRL) is calculated as: