Concepts and methods of quantitative assessment of risk to groundwater resources

This work presents a two-dimensional approach of risk assessment method
based on the quantification of the probability of the occurrence of contaminant
source terms, as well as the assessment of the resultant impacts. The risk is
calculated using Monte Carlo simulation methods whereby synthetic
contaminant source terms were generated to the same distribution as
historically occurring pollution events or a priori potential probability
distribution. The spatial and temporal distributions of the generated
contaminant concentrations at pre-defined monitoring points within the aquifer
were then simulated from repeated realisations using integrated mathematical
models. The number of times when user defined ranges of concentration
magnitudes were exceeded is quantified as risk. The utilities of the method
were demonstrated using hypothetical scenarios, and the risk of pollution from
a number of sources all occurring by chance together was evaluated. The
results are presented in the form of charts and spatial maps. The generated risk
maps show the risk of pollution at each observation borehole, as well as the
trends within the study area. This capability to generate synthetic pollution
events from numerous potential sources of pollution based on historical
frequency of their occurrence proved to be a great asset to the method, and a
large benefit over the contemporary methods.