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D.E.P. reports bioswales outperforming expectations

Mar 20, 2015

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A pilot program using sidewalk gardens to curb the flow of sewage into city waterways is producing surprisingly good results, according to a report issued by the Department of Environmental Protection.

The gardens, called "bioswales," consist of deep, wide vegetation pits cut into sidewalks and filled with soil and horticulture designed to absorb storm water. The city's antiquated combined sewer system is often overwhelmed by rains that dump billions of gallons of untreated sewage into the city's waterways every year. Swales in three targeted neighborhoods have exceeded diversion mandates set by the state, according to the D.E.P.

"It's really about a way to manage storm water as close to the site as possible," said Angela Licata, the department's deputy commissioner for sustainability. "We very much want to promote the greenest of technology."

The D.E.P., the state Department of Environmental Conservation and the federal Environmental Protection Agency form an often contentious triumvirate battling the flow of untreated sewage into the city's rivers and streams. While New York waters are cleaner than they have been in decades, more than 20 billion gallons of sewage flows, untreated, into the water each year.

Under a 2012 consent order, the D.E.P. is required to incorporate a certain amount of "green infrastructure" into its battle plan along with "gray infrastructure," or traditional sewage treatment plants. Green infrastructure can be anything from bioswales to rooftop gardens to permeable playgrounds.

The standard for effective bioswales is capturing the first inch of rain over 10 percent of the city's impermeable surface—the roads, roofs and concrete that account for about two-thirds of the city landscape.

The swales piloted by D.E.P. captured an inch of rain over 14 percent of the surfaces, the agency reports. Engineers and researchers at the D.E.P. say that when deployed over a wider swath of the city, the bioswales could have a noticeable impact.

"We went really high-tech," Licata said in an interview. Aside from sensors to measure water flow, the agency also installed infrared and time-lapse cameras to measure the ancillary benefits of the bioswales such as wildlife and plant interaction.

"By January 2016, we're going to try to develop a citywide metric for how this green infrastructure performs," Licata said.

The $4 million pilot program focused on three sections of the city: Bushwick, East New York and Edenwald. Aside from topography, those areas were chosen because sewers there drain into a single pipe, allowing the D.E.P. to measure flow before and after the bioswales.

Each swale held as much as 2,000 gallons of storm water, and helped divert roughly 20 percent of storm water, the agency said.

The full agency report on the bioswale program can be read here:

Reporter: David Diambusso

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