Assessment of nitrate contamination of groundwater using stastical methods

Irrigation schemes have the potential to increase in the concentration of nitrate in shallow groundwater. Historically effects assessment has focused one of two approaches. For the near field assessment, aquifer parameters are assumed uniform and representative, with cumulative effects largely ignored. For far field assessments, bucket models are commonly used that rely on assumptions of inflows and outflows of water and conservative assumptions on contaminants to assess downstream concentrations.

This paper presents an approach where the variability and uncertainties in data and our understanding of the groundwater systems, land use practices, climate and other factors that may influence nitrate contamination are acknowledged. Through the use of Monte Carlo simulation techniques, realistic estimates of potential contamination are made.

The advantage of this methodology is that it acknowledges the occurrence of adverse events, that when combined may lead to high estimates in nitrate concentrations. The methodology is able to assign probabilities to these events, such that while they are possible, the significance or weight given to such predictions is realistic. The Central Plains Water Enhancement Scheme provides an example of the use of these techniques that focus on the magnitude of the expected change in nitrate concentrations across the plains.