Selected anthropogenic contaminants in groundwater, Papio-Missouri River Natural Resources District, eastern Nebraska, 1992–2020

A study in cooperation with the Papio-Missouri River Natural Resources District was completed in 2019 to determine the concentration of contaminants of emerging concern (CEC) in groundwater in the Papio-Missouri River Natural Resources District, eastern Nebraska. Each well was sampled twice (in June and October or November) in 2019, totaling 34 samples. Samples were analyzed for 132 CECs, which include pharmaceutical, steroid hormone, and other organic chemicals. Seven of the 132 CEC analytes were detected in samples collected during this study. The most commonly detected CEC in this study was the antibiotic sulfamethoxazole. Other CECs detected in this study were nicotine, methyl-1H-benzotiazole (industrial product), acetaminophen (analgesic), caffeine, and metformin (diabetes medicine). None of the detected CECs have health-based water-quality standards. The agricultural herbicide atrazine was also sampled for and was detected in 15 of 26 samples from 8 wells, but all samples were below the established water-quality standard.

Nitrate, dissolved oxygen, and iron sampling results for 2010–19 and 1992–2020 were also assessed to determine the extent and trend of anthropogenic contamination in the Papio-Missouri River Natural Resources District. Nitrate as nitrogen was detected at a concentration greater than 4 milligrams per liter in 92 samples (19 percent), and detections in 36 samples (7.6 percent) exceeded 10 milligrams per liter, which is the U.S. Environmental Protection Agency’s maximum contaminant level for drinking water and Nebraska’s Title 118 maximum contaminant level for groundwater. Time series analysis showed that nitrate concentrations are not increasing or decreasing in any of the aquifers except for in three specific well nests, which are in phase 2 management areas. Dissolved oxygen results indicate potential denitrification throughout the Elkhorn alluvial aquifer; iron concentrations indicate potential denitrification in parts of the Missouri River alluvial aquifer.