Viral Flow and Transport in the Unsaturated Zone
Order No: FOS 82

VIRTUS (Viral Flow and Transport in the Unsaturated Zone) is a predictive finite difference model for virus fate and transport in unsaturated soil. The model allows the virus inactivation rate to vary based on soil temperature. The model supports unsteady flow, transport in layered soils, different virus inactivation rates for adsorbed versus freely suspended virus particles, and the flow of heat through soils. It is assumed that viruses are introduced at the soil surface. VIRTUS is based on mass conservation of a contaminant in porous media and couples the flow of water, viruses, and heat through soil.

The model can be used to estimate the number of viruses that reach the groundwater after traveling through the soil from a contamination source. The upper boundary condition for flow is described in terms of total water flux and includes the effects of precipitation and evaporation. For heat flow, the upper b.c. is also expressed as a flux condition and includes heat influx with rain water, evaporation/ condensation, short wave radiation, sensible heat, and long wave radiation. The upper condition for virus transport includes virus infiltration with rain. The bottom of the profile is a fixed water table elevation with constant soil water content and temperature.

For virus transport at the lower boundary a third-type b.c. is chosen. Model predictions were compared to measured data of virus transport in several laboratory column studies, and were within the 95% confidence limits of measured concentrations.

VIRTUS is a public domain research code, distributed with source code, executable image and example data sets. The documentation includes theory, user's instructions, and example problems.


Intel 80i86 processor with math coprocessor, 640 Kb (low) RAM, DOS 5.0 or higher, at least 1 Mb free disk space, CGA graphics or higher

Authors: M.V. Yates and Y. Ouyang (Univ. of Calif., Riverside) and S.R. Yates (USDA Salinity Laboratory).