Quality of groundwater used for public supply in principal aquifers of the Southwestern U.S.

Rosecrans, Celia

Quality of groundwater used for public supply in principal aquifers of the Southwestern U.S.

Tuesday, February 27, 2018: 8:50 a.m.

Celia Rosecrans , USGS, Sacramento, CA, CA

Marylynn Musgrove , USGS, Austin, TX

In 2013, the National Water-Quality Assessment (NAWQA) Project of the U.S. Geological Survey began a sampling effort focused on the quality of groundwater used for public supply in 20 principal aquifers across the Nation. Portions of four of these nationally identified principal aquifers─the Basin and Range basin-fill aquifer, the Basin and Range carbonate-rock aquifer, the Rio Grande aquifer and the High Plains aquifer─are located within the Southwestern U.S. NAWQA sampled 238 public supply wells from these four aquifers during 2013 to 2016. Samples were analyzed for a comprehensive suite of water-quality constituents, including major and trace elements (including hexavalent chromium), nutrients, pesticides, volatile organic compounds (VOCs), radionuclides, microbial indicators, pharmaceuticals, hormones, and groundwater age tracers. No exceedances of human-health benchmarks for drinking water were present in the samples collected for pesticides or VOCs. The most common exceedances frequencies of water-quality benchmarks relative to secondary standards were for salinity-related constituents: 30% of samples had high concentrations of dissolved solids, whereas exceedances of chloride, sulfate, and fluoride, ranged from 8% to 13%. The most common exceedance of a human-health benchmark for drinking water was for arsenic (12%). Exceedances for uranium (4%) and nitrate (0%) were low; these results contrast with previous NAWQA studies of shallow groundwater in these aquifers, where exceedances of human-health benchmarks for constituents such as arsenic, uranium, and nitrate occurred more frequently. Results are being evaluated to assess the relation of groundwater quality with natural and human-related factors. Most constituents that have exceedances of water-quality or human-health benchmarks in the four identified principal aquifers are derived chiefly from geologic sources, and generally are observed at higher concentrations in older, more geochemically evolved groundwater.

Celia Rosecrans, USGS, Sacramento, CA, CA

Celia Rosecrans is a hydrologist with the USGS in Sacramento, CA. Her scientific interest focuses on statistical prediction of water quality constituents in groundwater using random forest regression and boosted regression trees machine learning methods. Her recent work includes three-dimensional continuous probability models for aspects of redox conditions and pH in the groundwater system of the Central Valley California.

Marylynn Musgrove, USGS, Austin, TX

MaryLynn Musgrove is a Research Physical Scientist at the USGS Texas Water Science Center in Austin, Texas. Her research focuses on using geochemistry to better understand groundwater systems with a focus on both carbonate aquifers and aquifers of the western U.S.