A Management Challenge: Living in a Phosphorus-Restricted Watershed

The Catskill-Delaware region in New York, including Delaware County, has renowned natural beauty and resources, with a valued heritage and culture. It is also includes the watershed area encompassing the major reservoirs of the New York City water supply system. The Cannonsville Reservoir in Delaware County is the third largest reservoir in the New York City Water supply system. Its water quality is determined by two factors: what flows into it each year from the watershed, and how the reservoir is operated. Total phosphorus loads from point and nonpoint sources in the watershed have been measured since 1991. Loads vary from an observed low of 21,000 kg to a peak of 174,000 kg. A typical annual load is likely to be in the range of 50,000–60,000 kg year. Unfortunately, this loading is sufficient to maintain concentrations of phosphorus in the reservoir at 20μg/L or above. In consequence, the Cannonsville reservoir basin is designated as phosphorus restricted. Under this designation, new or increased discharges of waste water to surface waters is prohibited. To protect the economic vitality of its communities and businesses, the County is now compelled to develop a rigorous management program to quantifiably reduce phosphorus loading to the reservoir. Principal sources of the phosphorus delivered to the reservoir include: waste water treatment plants (WWTP); failing septic systems; urban storm water runoff; and manure spreading in the Cannonsville basin. The actual total annual loading of phosphorus from WWTP is estimated to be 7000kg. The estimate of potential annual loading from the 200 septic systems known to be failing is about 2000kg, although the actual number of failing systems is believed to be substantially higher than 200. Total phosphorus in storm water from village drainage could also be as high as 2000kg, and the total phosphorus in animal manure is estimated to lie between 274,000kg/year and 410,000kg/year.