Virus Transport during Transient Unsaturated and Steady-State Saturated Flow Conditions in Memphis Aquifer Sand

The overall goal of this research was to determine the effect of transient unsaturated flow conditions on the transport of a virus in aquifer material. It was hypothesized that viruses would be transported at the same rate and over the same distance as the migration of the wetting front and that virus retention during transient unsaturated flow would be similar to that during steady-state saturated flow. Virus transport during transient unsaturated horizontal flow was experimentally compared with its behavior under steady-state saturated vertical flow. In the transient flow experiment, virus (ΦX174) suspension was introduced into an initially air-dry repacked Memphis aquifer sand column with zero inflow head. In the steady-state saturated experiment, the sand was pre-saturated with water prior to virus injection at a constant inflow rate. Results obtained by sectioning the columns show that total (retained and free) virus concentrations decreased exponentially with the travel distance, and the decline was similar under transient unsaturated flow to steady-state saturated flow. Virus concentrations near the inlet in the Memphis aquifer sand columns were more than an order magnitude greater than the virus concentration of the influent solution in both experiments. A novel approach to quantifying virus retardation during transient unsaturated flow is proposed based on the centroids of the relative saturation and virus concentration versus relative distance functions. The results indicate similar virus retardation factors during transient unsaturated flow as compared to steady-state saturated flow. This may be a result of reduced air-water-solid interfaces as the wetting front moves through the soil during unsaturated transient flow.