Seasonal changes of groundwater quality in the Ogallala Aquifer

The Ogallala Aquifer extends beneath eight states in the Great Plains region of North America. It stretches from Texas to South Dakota and is among the largest aquifers in the world. In Texas, extraction of groundwater, primarily for cropland irrigation, far exceeds recharge resulting in a significant decline of the water table. In the Texas High Plains, this decline prompted restrictions set by a local water conservation agency in 2009 stating that in 50 years about 50% of the saturated thickness of the Ogallala Aquifer should be preserved. However, this restriction only addressed the quantity and not the quality of the remaining water. The quality of water extracted from the Ogallala Aquifer has been observed to change over time, especially over the length of a crop’s growing season. We measured water quality over a three-year period using an electrical conductivity sensor and measured depth to water at 20 locations across five counties in the Texas High Plains. Results show that when wells are actively pumping, water quality can change in complex and unpredictable ways. In some cases, water quality declined and in others water quality improved. This result has prompted us to further investigate the mechanisms involved in observed seasonal water quality changes.