Long Island Water Suitability Case Studies

Science Center Objects

A collection of studies that focused on the quality of groundwater and surface water, are presented in this section. The reports associated with these areas of water quality concerns are linked as an online source for further reading.

Saltwater Occurrence and Intrusion in the Aquifers of Long Island, New York

Freshwater on the island discharges along most of the periphery of the island, which prevents saltwater from entering the aquifers. In western Long Island, however, saltwater wedges that are hydraulically connected to the sea are found in aquifers on the Atlantic Ocean side of the island. The saltwater wedge in the Lloyd aquifer extends seaward of the wedges in the overlying aquifers because of the relatively impermeable clays of the Raritan confining unit, and the high potentiometric head in the Lloyd Aquifer, which force freshwater in the Lloyd aquifer to extend seaward of the island (figure 29). The positions of the saltwater wedges have been attributed mainly to natural conditions that prevailed long before the start of groundwater development in western Long Island. Groundwater pumping, however, has caused a landward migration of the freshwater-saltwater interface in aquifers in western Long Island since the late 1890s (Lusczynski and Swarzenski, 1966; Buxton and Shernoff, 1999). Saline groundwater is also probably migrating downward into the Lloyd aquifer from the overlying Jameco and Magothy aquifers in areas of heavy pumping. In the Forks areas of eastern Long Island, saltwater underlies freshwater in lens-shaped reservoirs that resemble those that underlie outer areas of Cape Cod, Massachusetts (Nemickas and Koszalka, 1982).

graph of cross section on Long Island with estimated salty groundwater areas

Figure 29. Generalized cross section on Long Island with estimated salty groundwater areas (Barlow, 2003).(Public domain.)

Recent investigations which focused on saltwater concerns within public supply system are presented in Stumm (2001) and Stumm & others (2002).

Pesticide Occurrence

Pesticide-Related Chemicals Detected in Long Island Groundwater 1996-2010

Detailed water quality monitoring data, from monitoring conducted by Suffolk County and the U.S. Geological Survey, are available in a document titled “Water Quality Monitoring for Pesticides, Historical Monitoring Data for the Long Island Pesticide Pollution Prevention Strategy”. Datasets in that document indicate minimum, maximum and median concentration levels of pesticides and degradates detected from about 1997 to 2011.

Source: Link to Online Report

The U.S. Geological Survey (USGS) National Water Quality Assessment (NAWQA) program is designed to assess the status of the Nation's water quality, describe trends in water quality, and provide a sound scientific understanding of the primary natural and human factors that affect the quality of the Nation's water resources. One component of the NAWQA program is the study of pesticides to determine their occurrence, concentrations, and seasonal variability in surface and groundwater throughout the country. The study was conducted as part of the Long Island-New Jersey (LINJ) coastal drainages NAWQA project. The LINJ study area is one of 59 areas studied nationwide.

Source: Link to Online Report

The NAWQA Pesticide National Synthesis Project, which began in 1992, is a national-scale assessment of the occurrence and behavior of pesticides in streams and groundwater of the United States and the potential for pesticides to adversely affect drinking-water supplies or aquatic ecosystems.

Source: Nawqa report

Source: Nawqa fact sheet

    Nitrogen Loading

    Although nitrogen is abundant naturally in the environment, it is also introduced into aquifers through sewage and fertilizers. Chemical fertilizers or animal manure is commonly applied to crops to add nutrients. It may be difficult or expensive to retain on site all nitrogen brought on to farms for feed or fertilizer and generated by animal manure. Unless specialized structures have been built on the farms, heavy rains can generate runoff containing these materials into nearby streams and lakes. Wastewater-treatment facilities that do not specifically remove nitrogen can also lead to excess levels of nitrogen in surface or groundwater.

    Several USGS investigations have evaluated the nitrogen loads and trends entering Long Island's surrounding estuaries from groundwater and surface water. Trends in nitrogen concentration and nitrogen loads entering the South Shore Estuary Reserve (Monti and Scorca, 2003) were evaluated on 13 major south-shore streams in Nassau and Suffolk Counties, Long Island, New York with adequate long-term (1971-1997) water-quality records. Furthermore, 192 south-shore wells with sufficient water-quality data, were selected for analysis of geographic, seasonal, and long-term trends in nitrogen concentration. An example of the long-term trend in one of the 13 streams is shown in figure 30.

    graph of Annual mean nitrogen load calculated for Bellmore Creek, Nassau County, N.Y.

    Figure 30. Annual mean nitrogen load calculated for Bellmore Creek, Nassau County, N.Y. (Monti and Scorca, 2003)(Public domain.)

    Seasonal and long-term trends of nitrogen loads entering Long Island Sound from groundwater and streams on Long Island, New York were analyzed for four major streams on the north shore of Long Island that have long-term discharge and water-quality records for the period 1985-1996 (Scorca and Monti, 2001).

    Volatile Organic Compounds

    Volatile Organic Compounds (VOCs) "are organic compounds that can be isolated from the water phase of a sample by purging the water sample with inert gas, such as helium, and, subsequently, analyzed by gas chromatography. Many VOCs are human-made chemicals that are used and produced in the manufacture of paints, adhesives, petroleum products, pharmaceuticals, and refrigerants. They often are compounds of fuels, solvents, hydraulic fluids, paint thinners, and dry-cleaning agents commonly used in urban settings. VOC contamination of drinking water supplies is a human-health concern because many are toxic and are known or suspected human carcinogens — (U.S. Geological Survey, 2005).

    Source: Nawqa Reports on VOCs analysis.

      Pharmaceuticals Occurrence

      In 2002, the U.S. Geological Survey (USGS), in cooperation with the Suffolk County Water Authority (SCWA), began a 4-year study to document the occurrence of pharmaceutically active compounds in groundwater wells throughout Suffolk County. Benotti and others (2006) collected seventy (70) water samples from 61 wells in the upper glacial and Magothy aquifers (9 wells were sampled twice) during 2002–2005 and analyzed for 24 pharmaceuticals. Wells were selected for their proximity to known wastewater-treatment facilities that discharge to the shallow upper glacial aquifer. Of the 70 samples taken, pharmaceuticals were detected in 28, of which 19 contained one compound, and 9 contained two or more compounds. The report summarizes the results from the study and relates the concentrations and frequencies of detection to those reported from a 1998–2000 nationwide study of streams that receive wastewater (Kolpin and others, 2002).

      Perchlorate Occurrence

      Perchlorate (ClO4-) is a common groundwater constituent with both synthetic and natural sources. A potentially important source of ClO4- is past agricultural application of ClO4-3- fertilizer imported from the Atacama Desert, Chile, but evidence for this has been largely circumstantial. Bohlke and others (2009), reported perchlorate was present in all samples collected in the study, and some concentrations exceeded the New York drinking-water guidance level of 50 nmol/L (5 μg/L). The highest concentrations were from the areas where fireworks disposal and military activities were potential sources.


      Table of Contents

      State of the Aquifer, Long Island, New York - Introduction

      Location and Physical Setting


      1. Hydrolgeologic Units
      2. Fresh and Saltwater Relations/Interactions

      State of the Aquifer System

      1. Precipitation
      2. NWIS - the USGS Data Archive 
      3. Surface Water - Streamflow
      4. Groundwater Levels
      5. Water Table and Surface Maps
      6. Water Use
      7. Groundwater Budget
      8. Inflow to the Groundwater System
      9. Outflow from the Groundwater System
      1. Case Studies

      Interactive Content