There is much literature that summarizes costs for various types of runoff management projects, although local social, economic, political, and other conditions will drive actual estimates. For example, CASQA’s Development BMP Handbook provides capital and operation and maintenance costs for many BMPs. Additionally, as part of the City of Los Angeles’ One Water Initiative, capital cost information was compiled and reported for many of the more commonly used SCMs in the Southern California region.
Most other cost resources are based on data throughout the United States and include regression equations, tools, and data sets based on literature reviews or surveys. The best resource may be local municipalities that are subject to NPDES permits and have likely implemented similar projects.
View BMP Cost Resources in North America (includes annotated descriptions of each resource).
In 2019, the Environmental Finance Center at Sacramento State (EFC) will begin hosting a stormwater cost estimating tool, developed using existing literature and data, along with statewide surveys of capital and O&M costs for green and grey infrastructure. The tool will also provide suggested methods for best practices in stormwater management accounting.
Tips for Estimating Costs
- A design engineer typically develops a cost estimate based on the quantities specified in the final plans and local pricing, so have the project design team on board early is helpful for cost planning.
- Resources such as costing books and on-line data centers can help estimate line-item cost estimates. Such materials are updated annually or every few years. Searching “construction cost estimate resources” through an internet browser will provide multiple such projects. Examples include RSMeans and Sierra West Group.
- Estimates will need to include a contingency amount intended to account for unknown occurrences, such as increased labor rates, material expenses, or unexpected field conditions requiring design alternations.
- Design with maintenance in mind to balance capitol and long-term maintenance costs. In many cases, incorporating features that lessen long-term maintenance efforts and costs may be well worth additional capital cost investments.