Science activity

Scientists are characterizing groundwater quality in principal aquifers, the primary source of the Nation's groundwater used for drinking. Concentrations of inorganic constituents, such as arsenic and nitrate, and organic constituents, such as pesticides and volatile organic compounds, are compared to benchmarks established for the protection of human health. Users can access an online tool to see how concentrations of pesticides, nutrients, metals, and organic contaminants in groundwater are changing during decadal periods across the Nation, and see in real time how chemical properties of groundwater at some sites are fluctuating. Groundwater quality data were collected from 5,000 wells between 1988-2001 (first sampling event) by the U.S. Geological Survey's National Water-Quality Assessment Project. Samples are collected in groups of 20-30 wells with similar characteristics called networks. About 1,500 of these wells in 67 networks were sampled about 10 years later between 2002-2012 (second sampling event) to evaluate decadal changes in groundwater quality. Between 2012 and 2016 (third sampling event), a subset of these networks has been sampled again, allowing additional results to be displayed on the web page: Decadal changes in groundwater quality. This is the third iteration of data added to the website, so this data release is referred to herein as Version 3.0. With the additional data, it is possible to evaluate changes in water quality between the 2nd and 3rd sampling event for 19 additional networks (35 total), changes in water quality between the 1st and 3rd sampling event for 15 additional networks (27 total), and changes across all 3 sampling events for 13 additional networks (27 total). A total of 78 networks have been sampled at least twice. Samples were obtained from monitoring wells, domestic-supply wells, and some public-supply wells before any treatment on the system.