ABSTRACT
The East German lignite dump sites are characterized by strongly mineralised and acidic pore waters. To evaluate possible effects for the surrounding areas, a prediction with a reactive transport model is necessary. There are two main difficulties of reactive transport modelling. The first is the fine spatial and time discretization which is necessary to avoid smearing and oscillation of the concentration field. The second problem is the calculation of small negative concentrations caused by a objectionable discretization of the nondiagonal dispersion fluxes. The paper presents biefly some algorithms of the program MODCALIF — CHEM which overcome these problems.
