The growing stormwater crisis
Stormwater runoff is a fast-growing source of freshwater pollution worldwide, and the largest source of water pollution in U.S. cities. During times of frequent or large storm events in many urban areas, sewer systems are often overwhelmed and allow run off from the streets—a combination of rainwater, oil, grease, heavy metals, pesticides and sometimes even raw sewage—to be discharged directly into our lakes, rivers and oceans.
It’s a problem without an easy answer, and hundreds of municipalities are struggling to meet regulatory-mandated water quality goals designed to address this pollution. This includes Washington D.C., which features one of the country’s oldest sewage systems and where runoff deluges local rivers that bring billions of gallons of water into the Chesapeake Bay estuary each year. This severely degrades aquatic habitat and impacts industries within the Chesapeake Bay, North America’s most productive estuary. Because of this threat to local waterways, the U.S. capital is among hundreds of cities required by Federal regulation to invest in new infrastructure to manage stormwater runoff.
Green infrastructure is the solution
While billions of dollars may be spent to engineer “gray” solutions (traditional pipes, pumps and tunnels), green infrastructure (GI)—rain gardens, bioswales and restored wetlands—not only offer cost savings but also generate co-benefits in the form of urban green space, improved air quality, reduction in urban heat islands, increased biodiversity and habitat, and community development.
Unlike gray infrastructure (such as treatment plants), which carries stormwater away from the source, green infrastructure relies on nature-based methods to retain stormwater directly at the point where it falls. This green infrastructure mimics natural water storage and filtration processes, which allows water to be treated naturally and slows its progress to sewers, thereby lessening the chance that those systems will be overwhelmed. Green infrastructure benefits people by reducing localized flooding and adding jobs to build and maintain green infrastructure sites.
The LEED Offsite Rainwater Management pilot
LEED’s Offsite Rainwater Management Pilot ACP (Alternative Compliance Path) is designed to reduce runoff volume through a stormwater credit market mechanism, with retention from off-site, low-impact development (LID) and green infrastructure systems providing equivalent or better stormwater capture benefits than those on-site.
This pilot credit is an alternative compliance path for LEED v4 and LEED v4.1 Building Design and Construction (BD+C) and Operations and Management (O+M) Rainwater Management credit, which allows projects to gain rainwater retention points through the purchase of off-site rainwater retention credits through a local Stormwater Retention Credit (SRC) market mechanism approved by USGBC. The ACP stems from the advent of the SRC market in Washington, D.C.