Nitrate and Chloride Concentrations in Groundwater beneath a Portion of the Trinity Group Outcrop Zone, Texas

Abstract

<p>Using a geographic information system and statistics, we evaluated spatial distributions of<br />nitrate and chloride concentrations in groundwater in an area of north-central Texas with agricultural activity,<br />in addition to oil and natural gas exploration and production. Data were compiled from 40 water wells sampled<br />in 2007. Nitrate concentrations in three wells exceeded the maximum contaminant level (44 mg/L) for drinking<br />water. The highest nitrate concentration was 149 mg/L, and concentrations were generally higher in shallower<br />wells. Chloride concentrations exceeded the 250 mg/L secondary drinking water standard in two wells, with no<br />significant association between chloride concentration and well depth. Results of this study suggest localized<br />human impacts, especially for nitrate, and identify areas warranting future monitoring.</p>