Geochemical modelling for mine site characterization and remediation

Although substantial advances in geochemical modelling have improved our ability to understand and improve mine site characterization and remediation, the limitations of modelling are often underappreciated. Modelers must have expertise in chemistry, geology, hydrology, geochemistry, and microbiology. Those who use codes must understand inorganic chemistry, thermodynamics, and kinetics for water-rock interactions. They must understand that code output is only useful insofar as they understand the limitations of the database and the built-in assumptions. A brief overview of geochemical code development in this paper reveals strengths and weaknesses in modelling capability. Because early predictions of water quality after mine closure often bear little resemblance to actual conditions, this approach should not be relied upon for permitting. Complex large-scale mine sites are not readily amenable to future predictions of hydrogeochemical conditions through modelling, however, modelling can constrain the possible and probable processes that give rise to specific water compositions. Modelling can also help guide remediation planning to find the most cost-effective alternative. Examples are provided for the Questa, New Mexico natural background study, the Summitville Mine, Colorado, and the Pinal Creek Basin, Arizona acid-contaminated aquifer.