The One-Dimensional Transport with Inflow and Storage (OTIS) as shown by several example applications is a model that may be used in conjunction with field-scale data to quantify hydrologic processes (advection, dispersion, and transient storage) and certain chemical reactions (sorption and first-order decay).
A second model, OTEQ (One-dimensional Transport with EQulibrium chemistry), combines the transport mechanisms in OTIS with a chemical equilibrium submodel that considers complexation, precipitation/ dissolution, and sorption. OTEQ may be used to quantify the geochemical processes affecting trace metals.