Cities

PlaNYC on Water Quality


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New York City's biggest water quality problem can be described with a three letter acronym: CSO. It stands for Combined Sewage Overflows. Combined overflows provide the much needed relief to our sewers when the city's treatment facilities become overwhelmed by a combined overload of wastewater from buildings and stormwater runoff from the streets: they divert this flow directly into our rivers, canals and bays instead.

Sewer overflows basically prevent raw sewage and polluted stormwater runoff from backing up into our homes, schools, offices, streets, and anywhere else a drain connects to the sewer -- but at a steep cost for the health of the waters in and around the city. According to Riverkeeper, New York City dumps "more than 27 billion gallons of raw sewage and polluted stormwater discharge" via sewer overflows into our surrounding waterways every year. So it's not surprising that the focus of PlaNYC's 10 initiatives devoted to restoring the health and quality of New York City's waterbodies (with the goal of making 90 percent of the waters safe for recreation by the year 2030) is primarily on sewage and stormwater management.

In the name of full disclosure, I've spent the last year working for a conservation agency whose primary concern was New York City's sewage and stormwater management. I've come away from this work with a unique perspective on the opportunities at hand, and a strong bias against traditional approaches to the problem.

The real culprit in this water quality disaster, which occurs nearly every time it rains, is our insatiable love for impermeable surfaces -- the hard skin of the typical city which fails to absorb rainfall. As you walk the streets and sidewalks (which are impermeable), catch the sunset from your roof (which is impermeable), or take in a game of soccer on one of the city's many artificial turf playing fields (which are impermeable), just imagine how much impermeable surface area there is in New York City.

Let's go back in time to New Amsterdam, circa the early 17th century. Much of the city's surface area still acts like natural ground cover. In an average rain, 40 percent of the precipitation is returned to the atmosphere through evapo-transpiration, 50 percent might enter the ground by means of infiltration, and a mere 10 percent becomes runoff. Fast-forward to today, when 75-100 percent of the city's surface area is impermeable, and the story of your average rainfall changes significantly. Evapo-transpiration (which also cools the city as water evaporates) is cut to less than 30 percent; infiltration to 15 percent. This leaves just over half of that rainfall to flow over roofs, sidewalks and streets, picking up pollutants along the way to entering the sewer system as stormwater runoff. This volume is so large that treatment facilities are overwhelmed -- leaving sewer overflows to compensate for what the system can't handle.

PlaNYC cuts right to the chase, identifying sewer overflows as one of two major problems requiring solutions. The second is the city's man-made canals, which the lack natural water flows that would otherwise flush out pollutants. These are contaminated by oil and toxins in addition to the sewage dumped into them during sewage overflow "events."

The first two of PlaNYC's ten water quality initiatives are important, but not worldchanging, at least not yet. Initiative 1, "Develop and implement Long-Term Control Plans", piggybacks a process long ago begun by the NYC Department of Environmental Protection (DEP). DEP is legally bound by the mandates of the federal Clean Water Act to eliminate 85 percent of sewer overflows before they become water quality issues. To date, the DEP has approached this primarily through end-of-pipe solutions: building massive sewage/stormwater storage facilities to contain the untreated water during storms, and slowly drain that water back into the sewer system as treatment capacity becomes available. The Long-Term Control Plans will determine how DEP moves forward in fulfilling its Clean Water Act obligations, but plans thus far have failed to integrate the most innovative and beneficial stormwater management practices, which involve dealing with stormwater before it enters the sewer.

Initiative 2 re-enforces the DEP's end-of-pipe approach by expanding the wet weather capacity at treatment plants.

Although these first two initiatives may not be what we hoped for, things get better further on. Other initiatives include retrofitting the combined sewer system by separating storm and sanitary pipes in new developments like the Bronx Terminal Market and Columbia University's expansion in Northern Manhattan. Street trees and "Greenstreets" parks will be redesigned to capture and retain stormwater. According to the NYC Department of Parks and Recreation, trees already capture an estimated 870 million gallons of the city's stormwater each year. And in addition to decreasing runoff, these trees absorb summer heat as that water transpires through their leaves and evaporates.

The city will expand on proven successes like the Staten Island Bluebelt, which leverages natural drainage corridors to convey, treat and detain stormwater. While replicating the Bluebelt's success will be limited by the city's density, plans are underway to expand the program into Queens and Brooklyn, which could go a long way in protecting strained aquatic ecosystems in Jamaica Bay and Long Island Sound.

Best Management Practices (BMP) are all the rage in Portland, Seattle, Minneapolis, Chicago, and New York City isn't going to miss out. PlaNYC calls for the formation of an interagency BMP Task Force. BMPs integrate ecological systems into the urban environment, enhancing them to provide valuable services like capturing stormwater, filtering pollutants from the air and water, and even mitigating the urban heat island effect. The city's Department of Design and Construction partnered with the Design Trust for Public Space to author a guidance document on "High Performance Infrastructure" in 2005, recommending BMPs for use in the public right of way. The interagency Task Force will expand on this work, looking at everything from vegetated swales that capture and filter stormwater along roadways to reintroducing mussel habitats, so that the shellfish can act as natural bio-filters by cleaning up the city’s devastated man-made canals. Pilot projects are already underway.

Aside from roads, perhaps two of the biggest contributors to New York City’s impermeable surface area are roofs and parking lots. PlaNYC addresses both of these directly by modifying zoning resolutions to require tree cover and perimeter landscaping around parking lots, and creating a property tax abatement to offset 35 percent of the installation costs of green roofs.

One of the best tools out there for managing stormwater and filtering pollutants is still nature’s own: wetlands. The city lost over 86 percent of its wetlands in the last century, but in 2005, Mayor Bloomberg signed Local Law 86 to form the Wetlands Transfer Task Force. By September of this year, the task force will submit recommendations on the feasibility of transferring all city owned properties containing wetlands to the Department of Parks and Recreation and other agencies that can protect them from further degradation. PlaNYC calls for supplemental studies to identify gaps in existing regulations and the development of a comprehensive policy to protect and manage the city’s wetlands.

PlaNYC’s water quality section closes by describing an 1860s effort to create 15 pools along Manhattan’s waterfront that were open to the flowing water. In spite of the their popularity, the pools closed shortly after opening due to the presence of raw sewage. Looking forward to 2030, New Yorkers are challenged once again to imagine swimmable shores:


With the city’s waters now cleaner than at any time in half a century, it’s time to revive ideas like these in a 21st century form. That means exploring possibilities such as creating permanent pools along our rivers which in turn could be designed as habitat for mollusks and other life forms, enriching the ecology of the waters and cleansing the. This balance between ecology, recreation, and water quality will underpin our efforts as we continue to reclaim our waterways for the next generation of New Yorkers.

Opening 90 percent of the city’s waters to recreation could mean water quality only high enough for "secondary contact" like boating or fishing, but PlaNYC has sparked New Yorker’s imaginations with visions of a healthy, swimmable estuary .

Image credit Solar One

Comments

It is still astonishing to me that this is the way we're dealing with our sewage. It may be the 21st century now, but New York is still a 17th century city in some ways...

Posted by: Emily Gertz on May 9, 2007 9:43 PM

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