Grey vs. Green Infrastructure Evaluation: What is the Most Cost Effective Solution?

Green infrastructure has become a buzzword in utility planning and design for cities across the country. Each community wants to jump on the green bandwagon, and for good reason. In certain areas of the country, green infrastructure can allow for additional funding opportunities and grants; studies have reported water quality benefits for various green infrastructure best management practices (BMPs); green infrastructure can reduce impervious areas in urban development and reduce stormwater runoff to local sewers; and green infrastructure can provide a host of other environmental and public development benefits. Unfortunately, green infrastructure solutions, to stormwater and combined sewer overflow (CSO) management issues, can come at a higher capital and life cycle cost when compared to the traditional grey alternatives.With strict government mandates and low budgets, some public utilities base their decisions on the lowest cost option. Other public utilities, in an effort to support sustainable solutions, have adopted green standards that require the use of green BMPs on all stormwater and CSO projects. Neither of these approaches truly evaluates all the benefits of both grey and green solutions and neither provides the needed data or guidance to select the most cost effective solution.As part of the City of Fort Wayne (Indiana) Combined Sewer Overflow (CSO) Long-Term Control Plan (LTCP) program, the Green Scorecard was developed to be used as a tool to aid planners in comparing grey infrastructure and green infrastructure alternatives. The Green Scorecard has been used on four preliminary engineering reports (PERs) to aid in the alternative analysis, and is continuing to be used for current evaluations. These PERs were planning level reports focused on reducing CSO volumes and activations, within the City. In the four completed reports, a total of 17 CSO reduction alternatives have been evaluated with the scorecard. Of those, 3 represented asset management only alternatives, 6 were grey only alternatives (partial separation), 2 were green only alternatives (green infrastructure), and 6 were a hybrid of grey and green alternatives. Those PERs resulted in the recommendation of 1 asset management, 1 green, and 2 hybrid alternatives. These results indicate a well rounded and truly unbiased approach for evaluating alternative solutions to stormwater and combined sewer overflow (CSO) management issues.