Keep Your Stormwater to Yourself!

On February 20, Urban Green Council hosted a salon about the new stormwater rules from the NYC Department of Environmental Protection (NYC DEP) and innovative design strategies for compliance.  NRDC’s Larry Levine recently wrote about the new rules on our blog, which reduce allowable stormwater flow by 90% in some cases.

Deep reductions certainly make sense. According to Riverkeeper "more than 27 billion gallons of raw sewage and polluted stormwater discharge out of 460 combined sewage overflows (CSOs) into New York Harbor alone each year.”

James Garin and Angela Licata (NYC DEP) provided background on the new rules and their goals.  In addition to reducing CSO, the DEP is trying to encourage co-beneficial strategies that increase biodiversity, reduce heat island effect, lower energy use, and add value to properties. One way to do this is by increasing green infrastructure (natural processes that filter water such as green roofs and bioswales) and decreasing grey infrastructure (traditional stormwater and waste water treatment like pipes and sewers).

A big topic at the event was how most compliance is being achieved through detention (holding the water back for a little while so the sewer system isn’t overwhelmed, but ultimately still sending it back to the treatment plant or river) as opposed to retention (holding it onsite and either using it or letting it evaporate, putting no strain on the sewer system). Some would argue that the greater benefits of retention mean we should be doing more to encourage it.

Michael Nilson (Langan Engineering) and Jeff Miles (Kiss + Cathcart Architects) shared recent projects on which they’ve of applied a mix of green and grey strategies. At Bushwick Inlet Park, rainwater is collected from paved surfaces on the hill to irrigate the green roof slope. All other rainwater infiltrates into the ground or passes through a tidal wetland landscape at the river’s edge; no stormwater is sent to the city’s combined stormwater system.

Solar 2a green energy arts and education center, meets the new stormwater requirements and features a high-tech grey strategy, a “smart tank.”  These tanks use internet-based predictive weather data, tank level sensors, and other controls to switch a rainwater harvest tank (retention) into a detention tank when needed to manage stormwater, saving both money and space on the site.

The increased cost of installing larger tanks has been one of the primary criticisms of the new stormwater rules. Architect Jeff Miles argues that the cost difference between green and grey strategies is spurring innovation like smart tanks and vegetative systems. “We’re constructing the future so we should be developing new ways to think about old problems like stormwater,” he says. According to Jeff, early collaboration between the client, architects, and engineers is crucial to a project’s success.

There is a lot of potential for these new rules to bring value but we need to hear more success stories where green infrastructure is used. A tax credit for green infrastructure retrofits available from DEP should also aid innovate owners.