Land Use and Its Impact on Groundwater Nitrate Contamination

This paper evaluates the efficacy of the Wellhead Protection Areas (WPAs) program in Nebraska as a water quality improvement tool. We employ a difference-indifferences (DiD) modeling framework to estimate changes in nitrate concentrations in groundwater before and after the implementation of WPAs, comparing locations within designated WPA areas to those outside. Specifically, we apply a staggered DiD design that explicitly accounts for variation in treatment timing across geographic units. The estimated average treatment effect on the treated (ATT) indicates that the WPA program is associated with a reduction in ground water concentrations.