These produced datasets include water-quality and quality assurance results collected by the USGS and other entities from 1952 to 2016 near the City of Poplar as well as throughout the East Poplar oil field, leachate results collected from drilling core within the Cretaceous Bearpaw Formation and Monoammonium phosphate (MAP) fertilizer results collected by the USGS in 2012. The handling and disposal of the brine has resulted in contamination of not only the shallow aquifers in the East Poplar oil field, but also the Poplar River (Thamke and Craigg, 1997; Thamke and Smith, 2014). The shallow aquifers are the only available source of potable groundwater in the area, and had provided water for more than 100 residents with household wells northeast of Poplar in addition to 2,900 residents that relied on the city of Poplar public water-supply wells. The city of Poplar, headquarters of the Fort Peck Tribal government, is down-gradient from multiple sources of brine and brine-contaminated groundwater in the East Poplar oil field. Data collected by the USGS during 2009–10 confirmed that water from the city of Poplar’s public water-supply wells were enriched in constituents that are present in oil-field brines (Peterman and others, 2010). As a result of the affected public-water supply wells, a pipeline was completed during 2011 that supplies treated water from the Missouri River to the city of Poplar and nearby residents, replacing the use of the shallow aquifers as a source of water (Debi Madison, Fort Peck Tribes, written commun., 2013).