A Triple Bottom Line Assessment of Traditional and Green Infrastructure Options for Controlling CSO Events in Philadelphia's Watersheds

The Philadelphia Water Department (PWD) is currently evaluating the implementation of various combined sewer overflow (CSO) control alternatives. This includes traditional engineering approaches that rely on physical infrastructure (e.g., building large diameter tunnels), as well as more “natural” approaches that rely on “green infrastructure” techniques (e.g., vegetated bioswales, permeable pavement).This report provides a Triple Bottom Lineoriented benefit-cost assessment of the CSO control alternatives under consideration by PWD. The focus is on the benefits and external costs of the alternatives. The key finding of this report is that the green infrastructure approaches generate a broader and more valuable array of environmental, public health, and social benefits than do traditional CSO control strategies. Benefits of green infrastructure evaluated and monetized include: Improved recreation opportunities, increased property values, reduced heat-stress related fatalities, improved air and water quality, green jobs, reduced energy use, and reduced disruption due to construction and maintenance activities.