A compartmentalized solute transport model for redox zones in contaminatedaquifers 2. Field-scale simulations

This paper, the second of two parts [see Abrams and League, this issue], re ports the field-scale application of COMPTRAN (compartmentalized solute tra nsport model) for simulating the development of redox zones. COMPTRAN is fu lly developed and described in the companion paper. Redox zones, which are often delineated by the relative concentrations of dissolved oxygen, have b een observed around the globe. The distribution of other redox-sensitive sp ecies is affected by redox zonation. At the U.S. Geological Survey's Cape C od research site, an anoxic zone containing high concentrations of dissolve d iron has been observed. Field data were abstracted from the Cape Cod site for the one-dimensional and two-dimensional COMPTRAN simulations reported in this paper. The purpose of the concept-development simulations was to de monstrate that the compartmentalized approach reported by Abrams et al. [19 98] can be linked with a solute transport model to simulate field-scale phe nomena. The results presented in this paper show that COMPTRAN successfully simulated the development of redox zones at the field scale, including tre nds in pH and alkalinity. Thermodynamic constraints were used to prevent lo wer-energy redox reactions from occurring under infeasible geochemical cond itions without imposing equilibrium among all redox species. Empirical meth ods of reaction inhibition were not needed for the simulations conducted fo r this study. COMPTRAN can be extended easily to include additional compart ments and reactions and is capable of handling complex velocity fields in m ore than one dimension.