Risk assessment formulation for nitrate leaching

TR Number



Journal Title

Journal ISSN

Volume Title


Virginia Tech


A framework for evaluating the risk of water pollution from the application of liquid dairy manure to agricultural fields was developed and applied. The GLEAMS (Groundwater Loading Effects of Agricultural Management Practices) (Ver 2.1) model was used to simulate NO₃-N leaching below the root zone for different land application rates of liquid dairy waste for fields in Georgia and Texas. Probability distributions of yearly-maximum nitrate concentrations were developed for each application rate at each site using the simulated nitrate concentrations. The probability of failure (exceeding 10 mg/L NO₃-N) for each application rate was determined from its corresponding distribution. An appropriate fine for farmers based on probability of failure for different land application rates was determined through economic analysis. The expected risk to farmers in monetary terms was determined for each application rate based on possible fines and the probability of failure. The monetary risk of nitrate leaching to ground water was compared to the social value of ground water.

The probability of failure for liquid dairy waste application rates between 200 to 800 kg·N/ha/yr ranged from 0.0022 to 0.74 for Tifton, GA. The probability of failure for liquid dairy waste application rates between 0 and 1000 kg·N/ha/yr ranged from 0.00 to 0.85 for Overton, TX. The maximum application rate that was environmentally acceptable for both Texas and Georgia was 250 kg·N/ha/yr based on the probability of failure. Fines of $1100/ha and $700/ha for the Georgia and Texas sites, respectively, would provide farmers with economic incentives not to exceed an application rate of 250 kg·N/ha/yr. These fines resulted in risks to farmers of $814/ha in Georgia for 800 kg·N/ha/yr application rate and $595/ha in Texas for 1000 kg·N/ha/yr rate. This compares with a social value ranging from $860/ha to $1432/ha of clean ground water.



risk assessment, nitrate leaching, NPS pollution