DOI: 10.5066/p9pol486
title: Data used to evaluate drinking water quality in the glacial aquifer system, northern USA

description: This data release contains groundwater-quality data and well information for the glacial aquifer system in the northern USA. Water-quality data and well information were derived from a dataset compiled from three sources: The U.S. Geological Survey (USGS) National Water Information System (NWIS; USGS, 1998, 2002), the U.S. Environmental Protection Agency (USEPA) Safe Drinking Water Information System (SDWIS; USEPA, 2013), and numerous agencies and organizations at the state, regional, and local level. The data compilation of the National Water Quality Program's groundwater assessment team is an internal dataset informally referred to as the National Groundwater Aggregation (NGA). The current study of groundwater quality in the glaciated U.S. (Erickson and others, 2019) considers only parameters with benchmarks from wells in the national groundwater aggregation-data from springs were not used. Data were screened for sample dates of 2005 or later, and the most recent sample at each site was used. This data release includes a table of benchmarks and thresholds. &quot;Benchmark&quot; is a generic term for any standard, regulation, guideline, or criteria against which constituent concentrations are compared. The threshold is the value against which measured concentrations of constituents in water samples can be compared to help assess the potential effects of contaminants on water quality. The table of water-quality results includes the concentration of constituents relative to their health-based or non-health benchmark, and a flag to indicate if the concentration is low, medium, or high relative to the benchmark. A table of site information includes attributes for each well like the source of the water-quality data and well information, the state, water use code, depth (if available), and the 17 hydrogeologic terrane from Yager and others (2018). Each hydrogeologic terrane contains Quaternary sediment that is derived from a common depositional history and can be characterized by similar texture and thickness. Each of the 17 hydrogeologic terranes was divided into 30 equal-areas (cells) based on the method of Scott (1990). This cell number for each well is included in the table of site information. An equal-area assessment was used to show the proportion of the aquifer affected by high, medium, and low concentrations of selected constituents at the aquifer scale and terrane scale (Belitz and others, 2010). The equal-area cells were also used with population data (Erickson and others, 2019, supplemental information) to determine aquifer- and terrane-scale proportions of the population affected by high, medium, and low concentrations of selected constituents. A shape file of the hydrogeologic terranes and equal-area cells is included in this data release. A table of well construction information includes attributes for each well like the source of the well information, the state, well depth, screen length (if available), and the hydrogeologic terrane from Yager and others (2018). Information in this table is from a well construction database compiled from several sources to obtain information on well depths and screened intervals of domestic and public supply wells producing groundwater from Quaternary sediments in the U.S. within the glacial extent. Domestic-supply well data were compiled from a lithologic database (Bayless and others, 2017) as modified by Yager and others (2018), the USGS NWIS (USGS, 2016), and several state well log databases (Erickson and others, 2019, supplemental information). The state databases were accessed to add well records in areas where information from the lithologic and NWIS databases was sparse. Public-supply well data were compiled from the list of public water-supply wells in the water-use database of Yager and others (2018). This data release contains four tables and one shape file: Drinking_Water_QW_Glacial_Aquifer_System_Results.txt Drinking_Water_QW_Glacial_Aquifer_System_Sites.txt Well_Construction.txt Benchmarks.txt TerraneEqualAreas shape file