Improvements to the Program Geochem

Abstract

Abstract The computer program GEOCHEM is widely used by soil scientists for the equilibrium chemical speciation of aqueous solutions. Two program shortcomings have been observed and are described. The first is that the program interprets pH as a concentration term, rather than as the negative logarithm of the proton activity. This can result in significant speciation errors, especially when ionic strength is relatively high and when reactions of interest involve H + raised to an exponent >1. The second involves the gradual drift in conditional constants used by the program during runs involving cases with varying ionic strengths. Source code modifications are presented to correct both program flaws.