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Assessment of Whole Life Costs for Green Infrastructure

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Abstract:

Whole life costing (WLC) is about identifying future costs and referring them back to present day costs using standard accounting techniques such as Present Value (PV). It can be thought of as the sum of money that needs to be invested today to meet all future costs as they arise throughout the life cycle of a facility. The Water Environment Research Foundation (WERF) has funded two projects that developed tools to estimate WLC for a variety of gray and green stormwater infrastructure based on construction costs as well as operation and maintenance requirements.

Research on construction costs for various stormwater facilities has identified a variety of factors that affect the expected costs. These factors include project size, retrofit vs. new construction, site suitability, experience of contractors, and many others. Consequently, it is generally not wise to use a generic cost estimate for specific projects. However, there may be cases, such as evaluating various scenarios for watershed retrofit, where a generic construction cost estimate may be useful.

One might expect that maintenance costs would be relatively constant for a given type of stormwater control; however, this is not the case. Surveys of regulatory agencies across the US indicate that much of the maintenance cost is driven by aesthetic concerns, rather than the operational requirements of the stormwater controls. Green infrastructure (GI) placed in highly visible locations often receive far more maintenance (mainly related to vegetation management) than those located elsewhere. One caveat is that many GI type controls are located on private property, so that maintenance costs are effectively transferred to the site owner and are not borne by the regulatory agency itself.

The tools funded by WERF allow engineers, municipal officials and others to generate WLC estimates for a variety of stormwater controls. The tools allow estimates of construction cost based on itemized components as well as based on size of the watershed treated. The user can input local values for salaries of maintenance crews, equipment costs, and expected frequency of maintenance or use default values to develop an estimate of WLC. These WLCs for various facilities allow the user to select a stormwater treatment strategy that minimizes totalexpenditures while achieving the desired improvements in area receiving water quality.

Document Type: Research Article

DOI: http://dx.doi.org/10.2175/193864712811727148

Publication date: January 1, 2012

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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