Modeling two-dimensional subsurface flow, fate and transport of microbes and chemicals

A two-dimensional model to simulate the subsurface flow, microbial growth-degradation, and transport and biodegradation of chemicals in groundwater environments (2DFATMIC) is developed. The model is designed to obtain the fluid velocity field and to solve the advective-dispersive transport equation coupled with biodegradation and microbial biomass production. The water flow through saturated-unsaturated media and the fate and transport of seven components (one substrate, two electron acceptors, one trace element, and three microbial populations) are modeled. The Richards' equation is solved by the finite element method, and seven partial differential equations describing the transport of microbes and chemicals are approximated by a modified Lagrangian-Eulerian numerical procedure (adapted zooming and peak capturing algorithm) that completely eliminates numerical dispersion and oscillation. This model also considers the effect of density on flow and on the fate and transport of microbes and chemicals. In other words, groundwater density and dynamic viscosity change with concentrations of chemicals and microbes, such that the flow and transport are coupled. Applications have been made to systems involving nitrate-based respiration, oxygen-based respiration, or multiple electron acceptors respiration.