Prioritization of Green Infrastructure for CSO Communities—Identifying Effective Implementation Opportunities

Combined sewer systems (CSS) are under regulatory mandate to reduce or treat combined sewer overflow (CSO) discharges in order to protect receiving waters. Under the requirements of the Clean Water Act, municipalities are responsible for developing comprehensive long-term control plans (LTCPs). These plans must identify a selected alternative, a level of control and a schedule for reducing discharges. Historically, CSO control methods included various approaches to manage the excess flows, including storage, remote treatment and conveyance to a centralized treatment plant or sewer separation. Many of the plans developed subsequent to 2007 include an approach which relies on green infrastructure and similar stormwater source controls. Green infrastructure includes practices and site-design techniques that store, infiltrate, evaporate, or detain stormwater runoff and in so doing, control the timing and volume of stormwater discharges from impervious surfaces (e.g., streets, building roofs, and parking lots) to the sewer system. In order to determine the most effective use of green infrastructure, municipalities are evaluating a number of strategies and approaches to its application. Implementation must consider site-specific issues in each community and the opportunities for cost effective implementation. An evaluation of 12 municipal programs that incorporate green infrastructure into their LTCP was performed in 2011. This paper summarizes the various approaches that municipalities used for evaluating green infrastructure. Those approaches included GIS evaluations, modeling and cost / benefit assessments.