Mark Kim, CFO of DC Water, believed building green infrastructure in Washington, DC, was an innovative way to improve the performance of the city's aging sewer system and save money. In considering the options to fund a pilot program, Kim was especially intrigued by a new financing structure: social impact bonds (SIBs). Partnering with Eric Letsinger of Quantified Ventures, they built on SIBs to develop an Environmental Impact Bond. This case discusses the risks and potential rewards of financing the pilot through a new structure at the intersection of public policy, finance, and science, the costs and benefits of employing green infrastructure, and the potential investor base for the new financial product. It also challenges students to consider the use of private capital to finance social outcomes.