Regional Water-Quality Assessment of the Crystalline Rock Aquifers in New England, New Jersey, and New York

The following U.S. Geological Survey report has been completed as part of the National Water-Quality Assessment (NAWQA) of the New England crystalline rock aquifers: “Quality of Water from Crystalline Rock Aquifers in New England, New Jersey, and New York, 1995-2007”, U.S. Geological Survey Scientific Investigations Report 2011-5220, by Sarah M. Flanagan, Joseph D. Ayotte, and Gilpin R. Robinson, Jr.

Crystalline bedrock aquifers in New England and parts of New Jersey and New York (NECR aquifers) are a major source of drinking water. Because the quality of water in these aquifers is highly variable, the U.S. Geological Survey (USGS) statistically analyzed chemical data on samples of untreated groundwater collected from 117 domestic bedrock wells in New England, New York, and New Jersey, and from 4,775 public-supply bedrock wells in New England to characterize the quality of the groundwater. Some of the significant issues examined and findings from the study are listed below. See the full report for more details.

• Patterns in fluoride, arsenic, uranium, and radon distributions were discernible when the data were compared to lithology groupings of the bedrock, indicating that the type of bedrock has an effect on the quality of groundwater from NECR aquifers.
• Land use and population density were evaluated to explain patterns in water quality.
• Chloride to bromide (Cl:Br) mass ratios in the domestic well samples indicate that the groundwater was probably affected by at least three halogen sources: local precipitation and recharge waters, remnant seawater and connate waters evolved from seawater, and recharge waters affected by road salt.
• The groundwater in the NECR aquifers generally contained low concentrations of nitrate, VOCs, and pesticides.
• MtBE was detected more often in water samples with apparent ages of less than 25 years than in water samples with apparent ages greater than 25 years. This finding is consistent with the time period of high MtBE use in areas in the United States where reformulated gasoline was mandated.
• Concentrations of nitrate and gross alpha-particle activities were significantly greater in the water samples from the domestic wells than in samples from the public-supply wells. Concentrations of sodium, chloride, iron, manganese, and uranium were significantly greater in the water samples from the public-supply wells than in the samples from the domestic wells.
• The high frequency of detections for a wide variety of man-made and naturally-occurring contaminants in both domestic and public-supply wells shows the vulnerability of NECR aquifers to contamination. The highly variable water quality and the association with highly variable lithology of crystalline bedrock underscores the importance of testing individual wells to determine if concentrations for the most commonly detected contaminants exceed human-health benchmarks.

The report is available: http://pubs.usgs.gov/sir/2011/5220/