ALCHEMI: A chemical equilibrium model to assess the acid-base chemistry and speciation of aluminum in dilute solutions

This chapter describes a chemical equilibrium model, ALCHEMI, which is used to evaluate the response of drainage water to acidic deposition, and provides some example applications. The program ALCHEMI can be used as a subroutine within comprehensive acidification models to calculate pH, acid neutralizing capacity as well as the speciation of AI and CT. Alternatively, it may be used to conduct thermodynamic calculations of interest or to help evaluate monitoring data. The chapter also discusses a description of the thermodynamic data, numerical techniques and model limitations. Uncertainty in model output originates from error in measured chemical input data and/or thermodynamic data. The chapter summarizes an analysis of uncertainty in chemical equilibrium calculations due to variability in: inorganic chemical equilibrium constants, measured inorganic chemical components, and estimates in measured values of dissolved organic carbon and equilibrium constants for the organic analog models.