Assessing Groundwater Over Time in Gaines, Terry and Yoakum Counties, Texas

This report is part of a multi-phase study that is being done in cooperation with Llano Estacado Underground Water Conservation District, Sandy Land Underground Water Conservation District and South Plains Underground Water Conservation District. 

Declining groundwater levels have raised concerns about the amount of water available in the study area and the potential for water-quality changes. This report will help water managers make informed decisions about this finite resource.

USGS scientists developed a preliminary regional model of the hydrogeologic framework and geochemistry of the Ogallala, Edwards-Trinity and Dockum aquifers. USGS researchers assessed changes in groundwater levels and in nitrate and dissolved solids concentrations from early development (1930-60) to recent times (2005-15). Findings show localized areas of groundwater declines, as well as localized changes in nitrate and dissolved solids concentrations, over time. The new report is available online.

Results show significant water-level declines in the study area, with some areas showing a reduction of more than 100 feet. The largest area of groundwater-level decline in the Ogallala aquifer was found in Gaines County to the southwest of Denver City, Texas. Water level increases were found in the northern portion of the study area, near the Yoakum and Terry County boundary and in northeastern Gaines County. The area along the Yoakum-Terry county line showed a groundwater level increase of about 66 feet. These changes in water levels are likely due to differences in groundwater withdrawals over time, hydrogeologic structure, and interactions between aquifers in each area.

Scientists analyzed changes in nitrate and dissolved solids concentrations to determine how groundwater quality changed over time. Dissolved solids concentrations, an indicator of salinity, showed higher concentrations in the northeast portion of the study area, and varied changes over time in the Ogallala and Edwards-Trinity aquifers. In general, increases in nitrate concentrations were observed over time in some localized areas in the study area.

These results are guiding scientists in planning for the additional information needed for the next part of the study. USGS researchers are currently collecting additional data to further evaluate water quality and quantity, hydrogeologic structure and aquifer properties. A more detailed analysis and report will likely be completed in 2019.  

The USGS also developed a digital tool that allows partners to determine the depth of the water table and underlying aquifers at the click of a mouse. This tool allows resource managers to more readily assess groundwater conditions at any location.