The New York City (NYC) Department of Environmental Protection (DEP) has introduced a $1.5 billion plan for developing “green infrastructure” over the next two decades to capture and store rainwater before it overwhelms sewage treatment plants. If approved, the plan would reduce the total volume of storm runoff entering the city’s sewer systems by 3.8 billion gallons per year, cutting the current overflow problem by 40 percent, according to reports.

NYC’s sewer system currently processes more than 1.3 billion gallons of wastewater each day, routing it through more than 7,000 miles of sewer pipes and 14 treatment plants. On dry days, the plants easily handle the volume but, during downpours, storm water washes directly into sewers from streets and buildings and quickly overwhelms treatment systems.

As part of the plan, the city will convert 10 percent of its hard surface area into permeable zones and construct several “tree pits” of about 100 square feet as part of 30 separate green-infrastructure demonstration projects. The DEP is also testing the durability of permeable concrete for sidewalks and exploring construction of “blue roofs” designed to retain and slowly release rainwater that accumulates on top of buildings. DEP is currently seeking approval from the state Department of Environmental Protection for the 154-page plan. See Greenwire, October 4, 2010.