Modeling the Impact of CAFOs on Nitrate Contamination in the Middle Trinity Aquifer of Central Texas

Abstract

Elevated levels of nitrate, well in excess of drinking water standards, occur in the Middle Trinity aquifer underlying Central Texas. Agricultural businesses such as Concentrated Animal Feed Operations (CAFOs) are common in this region; improper management of waste, particularly manure, at these sites has resulted in the impairment of water resources by nutrients such as nitrogen. While several studies have investigated the impact of such chemicals released from CAFOs on the Bosque River, there have been limited attempts to characterize the vulnerability of the Middle Trinity aquifer, a major source of drinking water to the largely rural community. In this study, we have evaluated the risk of groundwater nitrate contamination via logistic regression techniques coupled with a GIS framework. Model inputs included hydrogeologic, geographic, land-use and climate data compiled from a variety of local and state sources. A unique aspect of this study is the development of a feature that captures the potential migration pathways from CAFOs by considering the gradient of the water table, proximity of CAFOs to drinking-water wells, and permitted waste application-rates at CAFOs. A logistic regression model for predicting nitrate contamination based on this feature demonstrated a statistically significant relationship (p < 10 -11 ), and the area under the ROC curve was 0.77. Future models will incorporate additional hydrogeologic variables such as depth to water table, soil properties, and annual rainfall. The results of this study highlight the need for promoting best management practices (BMPs) to minimize the impact of nutrients from CAFOs on natural ecosystems and human health.