Since the mid-1990s, the EPA has entered into agreements with numerous municipalities and sewer authorities regarding long-term plans to control combined sewer overflows (CSOs). The centerpieces of many of these plans were locally-funded, and often staggeringly expensive, "gray" infrastructure. However, in response to public pressure and improvements in technology, the EPA began to accept CSO control plans utilizing less costly "green" infrastructure, such as green roofs, permeable pavements, and revitalization of vacant lots. And, the agency recognized that if it offered communities the opportunity to reduce project costs, it would create an incentive for communities to innovate and speed improvements. The impact of these policy changes became apparent in 2010 when the EPA agreed to amend the City of Indianapolis' multi-billion dollar consent agreement to allow for the use of more "green" infrastructure, saving the city $740 million.

In early March, to further facilitate the use of green infrastructure in control plans, the EPA released a publication entitled "Greening CSO Plans," which is intended to assist municipalities and sewer authorities with green infrastructure approaches for controlling CSOs.

"Greening CSO Plans" is the EPA's latest and most comprehensive guidance on green infrastructure. Although green infrastructure is unlikely in most instances to fully control CSOs, it can often reduce the size of more capital-intensive control measures.

The EPA's publication is designed to help municipal officials and sewer authorities quantify green infrastructure contributions to an overall CSO control plan. The document's tools include:

  • a general overview of the regulatory and policy context for incorporating green infrastructure into CSO control programs;
  • a description of how municipalities may develop and assess control alternatives that include green infrastructure; and
  • a demonstration of a modeling tool, the Storm Water Management Model v. 5.0 (SWMM5), that can help quantify green infrastructure contributions to CSO control.