Sentinel Monitoring of Groundwater for Contaminants of Emerging Concern to Provide Advanced Warning for Supply Wells on Long Island, New York

Science Center Objects

Problem The groundwater supply of Nassau and Suffolk Counties is prone to contamination from past and current land uses, including practices related to agriculture, industry, and residential development, because the soils and underlying sediments are generally composed of sandy, permeable materials that allow contaminants to move readily from the land surface into the groundwater below. Of in...

The groundwater supply of Nassau and Suffolk Counties is prone to contamination from past and current land uses, including practices related to agriculture, industry, and residential development, because the soils and underlying sediments are generally composed of sandy, permeable materials that allow contaminants to move readily from the land surface into the groundwater below. Of increasing concern are the human-derived contaminants stemming from on-site disposal of residential wastewater and industrial processes.
The centralized distribution of water through purveyors to most residents provides them with a reliable source of potable water that is consistently monitored at the wellhead. However, increased demands on the aquifer system have accelerated the downward flow of younger groundwater into the deeper parts of the system from which most wells withdraw water. This, in turn, has increased the potential for contaminants introduced at land surface (e.g. pharmaceuticals, 1,4-dioxane, and perfluorinated compounds) to reach supply wells sooner than under normal groundwater-flow conditions. Consequently, the types and concentrations of potential contaminants are often not foreseen until they reach the wellhead, which then requires the water supply to be treated, blended, or the well to be taken offline.
Contaminants of emerging concern (CECs), such as pharmaceuticals, 1,4-dioxane, and perfluorinated compounds (PFCs) have been detected in the Long Island aquifer system. Many of these compounds are unregulated but are monitored by public water systems. Advance detection of these CECs would allow water purveyors to better plan for treatment at the well head. It may also facilitate the ability to proactively address contaminants at the source rather than at the wellhead.
It is essential that CECs introduced at land surface be detected before they are drawn into supply wells. Knowledge of the fate and transport of CECs is critical to understanding and making informed decisions about groundwater quality and sustainability. The proposed monitoring of groundwater at sentinel locations throughout the two Counties would provide concerned parties with advanced warning of potential CEC contamination before it reaches supply wells.
The sole-source aquifer system of Long Island, which is relied on by the residents of Nassau and Suffolk Counties for abundant, potable drinking water, has increasingly been threatened by point and non-point sources of pollution. Precipitation, as well as wastewater disposal, provides recharge to the aquifer system, but both of these water sources can also carry natural and anthropogenic contaminants associated with wildlife and human activities. The rate and extent of contaminant transport depends on a variety of factors, including the solubility of a compound or mixture of compounds, ability of the vadose zone to filter (retain and [or] degrade) a contaminant, the type of sediments with which the water is in contact, and the continual geochemical evolution of groundwater along flow paths.
Such studies have resulted in the creation of unique and effective tools to evaluate the availability and suitability of groundwater for supply on Long Island. For example, analytical capabilities have been developed by USGS laboratories to detect hundreds of agricultural-, industrial-, and wastewater-related compounds at the parts-per-trillion level—thereby aiding in the detection of anthropogenic contaminants in groundwater as early as possible. The USGS has begun to implement these trace-level analytical methods in cooperation with the Suffolk County Water Authority (SCWA) and the New York State Department of Environmental Conservation (NYSDEC) to investigate the occurrence of CECs (pharmaceuticals, personal care products, and pesticides) in select SCWA supply wells and in observation wells. Data collected by the USGS—available from a publicly-accessible database—also compliment groundwater-quality samples collected and analyzed by the Suffolk County Department of Health Services, SCWA, and many water purveyors of Nassau County, all of which provide valuable data that, when synthesized, can be used to analyze for and track trends in impaired groundwater quality.
The primary objective of this proposed project is to build on existing water-resources programs in developing and monitoring a network of sentinel wells for the purpose of detecting contaminants in groundwater before they are captured by critical supply wells. Secondary objectives of the project are to maintain a publicly-accessible database of contaminants detected across Nassau and Suffolk Counties at sentinel locations. These objectives will ultimately provide the Long Island Commission for Aquifer Protection (LICAP) the information necessary to carry out its mission by identifying priorities for research and management related to Long Island’s sole-source aquifer system.
Water-quality samples will be collected once at sentinel well locations from an established groundwater observation-well network within the upper glacial aquifer. This observation-well network leverages the 32-well network of the National Water-Quality Assessment (NAWQA) Land-Use Study (LUS) that is currently being used to monitor current and legacy pesticides, pesticide degradates, major inorganics, and species of nitrogen and phosphorus associated with agriculture and residential turf grass maintenance (figure 1). An additional five observation wells will be selected in areas of concern identified in consultation with LICAP technical contacts. Locations would be identified upgradient of supply wells using USGS groundwater-level maps and flow models and Source Water Assessment Program (SWAP) results. These shallow wells may be screened in either the upper glacial or Magothy aquifer. The proposed sentinel network of 37 observation wells is expected to help provide advanced warning of potential contamination before it reaches the most vulnerable parts of Long Island’s supply-well network. All collected samples will be analyzed for pharmaceuticals (SH2440; appendix 1) and volatile organic compounds, including 1,4-dioxane (SH4437; appendix 2), as well as PFCs (CIN 50392; appendix 3) . Additional sample collection for pesticides (SH2437; appendix 4), nutrients (SH2755, nitrogen and phosphorus species; appendix 5), and major inorganics (SH2701, LC671, and LC657; appendix 6)
will be analyzed at the eight observation wells not included in the ongoing pesticide monitoring program. Data will be compiled, reviewed, and shared with water purveyors and regulators as soon as results become available. Following
USGS review and approval, all data will be served publicly via the National Water Information Service: Web Interface (NWISWeb, 
Standardized data-collection practices and methods developed by USGS regional and National studies will be followed (U.S. Geological Survey, variously dated). Replicate samples, equipment blanks, and laboratory controls will be collected and assessed for quality assurance and quality control (QA/QC) purposes. All water-quality samples will be analyzed at the USGS National Water Quality Laboratory (NWQL) in Denver, Co., using USGS NWQL methods for inorganic constituents and organic constituents except for PFCs. The USGS NWQL performance data are documented and available online at for organic constituents and for inorganic constituents. Samples for PFC analysis will be submitted to Maxxam Analytics in Mississauga, Ontario, through a subcontract of the USGS NWQL.

Project Location by County

Nassau County, NY, Suffolk County, NY