SELENIUM, BORON, AND NITRATE CONCENTRATIONS IN GROUNDWATER OF THE SOUTHERN OGALLALA AQUIFER, TEXAS, USA

Abstract

Selenium, boron, and nitrate concentrations in 72 water wells in the southern Ogallala Aquifer were evaluated. The west Texas study area supports extensive cotton farming, livestock, and petroleum production. Approximately 32 percent of selenium observations exceeded the 20 µg/L advisory for irrigation water, and 10 percent of them exceeded the 50 µg/L standard for drinking water. However, only 2 percent of boron observations exceeded the 1,250 µg/L level for sensitive crops, and only 1 percent of nitrate concentrations exceeded the 44.3 mg/L drinking water standard. A significant positive association was found between selenium and boron concentrations; both solutes tended toward higher concentrations in shallower wells. However, nitrate showed generally higher concentrations in deeper wells; this pattern may reflect varying agricultural practices or intensity across the study area. Both agricultural activity and prevailing groundwater chemistry likely influence selenium, boron, and nitrate concentrations in the study area.