Groundwater-Quality of Nassau County, Long Island, New York

There are over 1.3 million residents in Nassau County that rely on groundwater as their sole source of potable drinking water. The mixed land uses (residential, commercial, industrial, agricultural, and recreational) of Nassau County contribute point and non-point sources of aquifer contamination. Nassau County water purveyors currently operate supply wells screened in the upper glacial, Magothy, and Lloyd aquifers. The protection and long-term sustainability of all three aquifers are vital concerns for the Nassau County Department of Public Works (NCDPW). Monitoring of groundwater for contaminants of emerging concern (CEC) associated with mixed land uses within these aquifers is necessary for understanding the water-quality conditions of Nassau County’s drinking-water supply.

NCDPW has over 500 monitoring wells screened throughout the three aquifers. These monitoring wells have been sampled infrequently since 2010 for special projects, including regulatory and non-regulatory programs under the Environmental Protection Agency, New York State Department of Conservation, NAVY Grumman, water purveyors, and others. An analysis of the ambient quality of water from these wells is needed to provide additional insight to the current extent of groundwater contamination, and to identify potential new areas of concern in those areas lacking current monitoring.

Objectives and Scope

The primary objective is to analyze groundwater quality samples collected from selected-monitoring wells screened in the Nassau County aquifer system. The data will provide the NCDPW with the information needed to evaluate and manage groundwater resources in Nassau County. A secondary objective of the project is to provide these data to other stakeholders through a publicly-accessible database.

Relevance and Benefits

This project will benefit the NCDPW by providing groundwater-quality data from areas that have not been regularly monitored since 2010. Monitoring of ambient water quality is critical to Nassau County because groundwater is its sole source of drinking water. Up-to-date knowledge of groundwater quality will provide the NCDPW and water purveyors throughout Nassau County with the ability to evaluate and manage the resource.

An important part of the USGS mission is to assess the quality of the Nation’s drinking-water supply and advance knowledge of the natural and human factors that influence surface- and ground-water quality. This project will increase the understanding of the source, fate, and transport of contaminants as well as supply the information needed to assess physical and chemical changes to Long Island’s aquifer system on both a local and regional scale. It will benefit Federal, State, and local governments by providing standardized, quality-assured data that will contribute to the protection of human health. Data collected from this study will be stored in national databases available to the public, which can be used in concert with results from current and historical USGS investigations to advance knowledge of the regional hydrologic system. The USGS’s ability to provide wide dissemination of standardized results will be beneficial to water purveyors throughout Nassau County.

Approach

The U.S. Geological Survey (USGS) will sample groundwater monitoring wells in Nassau County for CECs that are primarily screened in the Magothy aquifer. All monitoring well samples will be analyzed for 1,4-dioxane, per- and polyfluorinated substances (PFAS), chlorofluorocarbons (CFCs), methyl tert-butyl ether (MTBE), and trihalomethanes (THMs). All well monitoring information, and well record and sample results, will be stored in the USGS National Water Information System (NWIS) database (https://nwis.waterdata.usgs.gov/ny/nwis/nwis).