Cost Estimating Tools for Low-Impact Development Best Management Practices

The stormwater community has a critical need for evaluating the life-cycle costs of Low-Impact Development (LID) Best Management Practices (BMPs) as part of encouraging communities to incorporate LID. Great effort has gone towards demonstrating that LID BMP techniques can mediate negative stormwater effects including increased discharge volume from impervious surfaces and pollution loading as water travels through urban settings. However, LID BMPs must be proven to be cost effective as well as technically functional. The current suite of cost tools available through the Water Environment Research Federation (WERF) is being expanded to include vegetative roofs, rainwater catchment systems, and bioretention facilities. These tools provide a detailed framework to facilitate cost estimation for capital costs, operation and maintenance costs, and life-cycle net present value. The tools can serve as a format for cost reporting for past, current and future projects, and also provide users with planning-level cost estimates. The cost tool includes both a parametric cost estimation to demonstrate approximate cost per drainage area, and a line-itemized engineer's cost estimation tool. The line-item engineer's estimate allows the user to customize their project, while exposing the user to an extensive list of potential costs and opportunities to maximize stormwater management value. The use of this cost tool will enable consistent reporting of cost data on LID BMPs, so that users will be able determine the cost of each component of the project, both in materials and in planning and design. The standard format will also improve the ease of preparing cost estimates, since the necessary line items are broken out for consideration. Creating an understanding of the life-cycle cost benefits of LID will lead to more use of LID and green infrastructure in development and redevelopment.