Blending Green and Grey: A Public Works Approach to Rainwater Harvesting

The average water consumption for New York City is approximately 4,146 ML/d (1,070 mgd) or about 505 L (133.5 gal) per person per day. The borough of Manhattan alone uses an estimated 776 ML/d (205 mgd) of this water. In 2008, Mayor Michael R. Bloomberg developed a Sustainable Stormwater Management Plan, which calls, in part, for the reduction of flow into the City's combined sewer system. In keeping with this vision for a more environmentally sustainable city, the New York City Department of Sanitation (DSNY or the Department) is incorporating environmentally sustainable design elements into their proposed 438,498 sq. ft. Manhattan 125 Maintenance Garage with the goal of attaining LEED Silver status. The facility will serve as a central location for DSNY vehicles and equipment to be parked, maintained, washed and refueled. As part of this sustainable design approach, the Garage will be equipped with a 75,700 L (20,000 gal) capacity rainwater and steam condensate harvesting system. The harvesting system is designed to provide the Garage with non-potable water for flushing toilets, truck washing, irrigation, and cooling tower make-up water. To meet local codes, the system was designed with treatment components to filter and disinfect the collected rainwater and condensate as well as coloring, temperature control, and recirculation elements. This paper provides a design overview for a large-scale rainwater and steam condensate harvesting system, quantifies system inflows and outflows, discusses the challenges of local codes, and how “green infrastructure” plays an important role in decreasing potable water demand as well as runoff and inflows into combined sewer systems. It also shows how solid waste management maintenance facilities can be incorporated into broader public works sustainable initiatives.