Overview of Groundwater Quality in the Rio Grande Aquifer System

Groundwater historically has been the primary source of drinking water for communities and households throughout the Rio Grande Basin. Although the direct use of surface water for municipal water supply has been increasing in the basin, the limited availability of surface-water resources necessitates that groundwater will continue to be an important primary or secondary source of drinking water for many residents. In parts of several basin-fill aquifers of the Rio Grande aquifer system, concentrations of constituents with geologic sources, such as arsenic and dissolved solids, are high enough to limit the availability of groundwater that is suitable for drinking without treatment. Human-related contaminants, such as nitrate and volatile organic compounds, have been detected not only in shallow groundwater, but also in groundwater at depths used for domestic or public supply. Groundwater quality can be influenced by changes to the hydrologic system that result from development of water resources for agricultural and urban uses, such as increased groundwater withdrawals and increased recharge from the infiltration of excess irrigation water applied to crops and lawns. The National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey has developed conceptual models of important natural and human-related factors influencing groundwater quality of basin-fill aquifers in the Rio Grande aquifer system and across the southwestern U.S. Statistical models also have been created to estimate concentrations of arsenic and nitrate in groundwater of basins in the southwestern U.S. These conceptual and statistical models are intended to help the public understand where contaminants are likely to occur, assist water managers in assessing the potential effects of various basin-development scenarios on groundwater quality, and aid water suppliers in prioritizing areas for new groundwater development.