Philadelphia and the U.S. Environmental Protection Agency signed an agreement in April that paves the way for $2 billion in green infrastructure investment over the next 25 years for controlling combined-sewer overflows, or CSOs, and managing stormwater more sustainably. The agreement pledges EPA's endorsement of the "Green City, Clean Waters" plan, a long-range commitment to protect and enhance the city's watersheds by managing stormwater with bioretention, tree trenches, swales, green roofs, rain gardens and porous pavement.