Drinking water quality in the glacial aquifer system, northern USA.

Groundwater supplies 50% of drinking water worldwide, but compromised water quality from anthropogenic and geogenic contaminants can limit usage of groundwater as a drinking water source. Groundwater quality in the glacial aquifer system, USA (GLAC), is presented in the context of a hydrogeologic framework that divides the study area into 17 hydrogeologic terranes. Results are reported at aquifer-system scale and regional (terrane) scale. This paper presents a quantitative assessment of groundwater quality in the GLAC using data from numerous sources for samples collected 2005-2013, compared to health-based and aesthetic (non-health) benchmarks, and evaluated with areal and population metrics. Concentrations above a benchmark are considered high. Trace elements are widespread across the study area, with an estimated 5.7 million people relying on groundwater with high concentrations of one or more trace elements; manganese and arsenic are most often at high concentration. Nitrate is found at high concentration in 4.0% of the study area, serving about 740 thousand people. Organic compounds including pesticides and volatile organic compounds are high in 2.0% of the assessed study area, with about 870 thousand people relying on groundwater with high concentrations of an organic compound. High arsenic and manganese concentrations occur primarily in the terranes with thick, stratigraphically complex, fine-grained glacial sediment, coincident with groundwater under reducing conditions (indicated by iron concentrations >100 µg/L); high nitrate is uncommon in those same terranes. When nitrate is high in thick, fine-grained, complex terranes, though, it is much more commonly associated with groundwater under more oxidizing conditions. Common geogenic trace elements occur at high concentration due to characteristic geologic and geochemical conditions. Conversely, anthropogenic nitrate and organic compounds are introduced at or near the land surface. High concentrations of nitrate or organic compounds are generally limited to areas in proximity where people live and use the chemicals.

Frequently co-occurring pesticides and volatile organic compounds in public supply and monitoring wells, southern New Jersey, USA.

One or more pesticides were detected with one or more volatile organic compounds (VOCs) in more than 95% of samples collected from 30 public supply and 95 monitoring wells screened in the unconsolidated surficial aquifer system of southern New Jersey, USA. Overall, more than 140,000 and more than 3,000 unique combinations of pesticides with VOCs were detected in two or more samples from the supply and monitoring wells, respectively. More than 400 of these combinations were detected in 20% or more of the samples from the supply wells, whereas only 17 were detected in 20% or more of the samples from the monitoring wells. Although many constituent combinations detected in water from the supply and monitoring wells are similar, differences in constituent combinations also were found and can be attributed, in part, to differences in the characteristics of these two well types. The monitoring wells sampled during this study yield water that typically was recharged beneath a single land-use setting during a recent, discrete time interval and that flowed along relatively short paths to the wells. Public supply wells, in contrast, yield large volumes of water and typically have contributing areas that are orders of magnitude larger than those of the monitoring wells. These large contributing areas generally encompass multiple land uses; moreover, because flow paths that originate in these areas vary in length, these wells typically yield water that was recharged over a large temporal interval. Water withdrawn from public supply wells, therefore, contains a mixture of waters of different ages that were recharged beneath various land-use settings. Because public supply wells intercept water flowing along longer paths with longer residence times and integrate waters from a larger source area than those associated with monitoring wells, they are more likely to yield water that contains constituents that were used in greater quantities in the past, that were introduced from point sources, and/or that are derived from the degradation of parent compounds along extended flow paths.