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The New York City Department of Environmental Protection's Pilot Phoshorus Offset Program: A Model forResponsible Development Within a Watershed.

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Kent Manor is a 303 unit affordable housing condominium project located in the Town of Kent, Putnam County, New York, and is located within the New York City watershed. Prior to the construction of the project, the New York City Department of Environmental Protection (NYCDEP) enacted their final watershed regulations prohibiting surface discharges from wastewater treatment plants. Subsequently, the NYCDEP stopped the Kent Manor project.

The watershed regulations had provisions for a pilot phosphorus offset program, whereby up to three projects within the watershed with surface discharges would be approved, provided that any increase in phosphorus loading would be offset somewhere else in the watershed.

Malcolm Pirnie prepared an application for inclusion in the pilot program, which included a design to route all storm water runoff and the wastewater treatment plant discharge through two extended detention ponds, a series of constructed wetland “modules”, and a wet pond with a wetland marsh fringe. Analytical modeling showed that the post-development phosphorus load was approximately 20 pounds per year. Because the pilot program required a three-to-one offset for the increased phosphorus load, a total of 60 pounds per year of phosphorus would need to be offset within the same watershed.

An existing off-site shopping center was selected as the most favorable location for the offset. The calculated loads from the shopping center met the 60 pounds criteria. A storm water treatment system that utilizes pelletized organic matter to remove nutrients and other pollutants was proposed. The treatment system is installed “in-line” into the existing storm water conveyance system, is below ground, and requires minimal earth disturbance and maintenance.

The pilot phosphorus offset program provides a mechanism, in conjunction with Total Maximum Daily Load (TMDL) calculations to a receiving water body, to allow economic growth to continue while maintaining and enhancing water quality.

Document Type: Research Article


Publication date: 2000-01-01

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