Background
The U.S. Geological Survey (USGS), in cooperation with the Village of Patchogue and the New York Department of State, collected water-quality samples from 10 shallow wells within the village to document the effects of onsite wastewater disposal on groundwater discharging into the Patchogue River. The onsite disposal of wastewater within the Patchogue River basin - a riverine estuary that discharges into Great South Bay, Suffolk County, Long Island, NY - has adversely affected water quality and aquatic habitats within both the tidal and non-tidal portions of the river. Of particular concern are increased loads of nutrients (nitrate, nitrite, ammonia, and phosphorus) to the shallow groundwater system which flows into the Patchogue River. Increased nutrient loads can lead to eutrophication in the receiving waters. Among the undesirable effects of eutrophication are an increase in plant and algae growth, which can result in increased water turbidity, odors at low tide, and a decrease in dissolved-oxygen concentration that can result in fish and shellfish mortality. In response to increased development within the approximately 14 square-mile basin, the Village of Patchogue has begun to develop a Local Waterfront Revitalization Plan that will guide efforts to improve the water quality of the Patchogue River and the adjacent Great South Bay estuary.
Approach
Groundwater samples were analyzed for physical properties, nutrients, organic carbon, major ions, trace elements, and stable isotope signatures of nitrogen (d15N). Results were compared with data from previous studies completed in nearby areas to reveal possible trends in the concentrations of groundwater parameters. The chemical signature of effluent plumes from onsite wastewater-disposal systems in sandy glacial aquifers has been studied in detail and has shown that elevated concentrations of major ions, nitrate, and phosphorous (depending on the age of the septic system) are common. Total nitrogen, sulfate, and potassium concentrations from this study were similar to results from medium - high density residential land-use areas in previous groundwater studies of Long Island. Measured calcium and chloride concentrations were greater in this study than in previous studies, but this may be attributed to the Village's proximity to the saltwater Great South Bay.(see attached image file (A6407-Fig1.jpg)
The stable isotope signature of nitrogen (d15N) can be used to identify potential sources of nitrate in the water-table aquifer. Previously reported nitrogen-isotope signature ranges for Long Island indicate septic waste has a typical d15N signature between 7 and 12 parts per thousand, whereas nitrate from chemical fertilizer has a range between 1 and 7 parts per thousand. Nitrate isotopes suggest that the groundwater in this study is influenced by several sources, including fertilizer, septic waste, and pets (see attached image file (LK00-A6407-Fig2.jpg).
Publications
Abbene, I.J., 2010, Shallow groundwater quality in the Village of Patchogue, Suffolk County, New York: U.S. Geological Survey Scientific Investigations Report 2010-5132, 19 p., at http://pubs.usgs.gov/sir/2010/5132/
Project
Location by County
Suffolk County, NY
