Mechanisms of coliphage (phiX174 and/or MS2) transport and fate in the presence and absence of manure suspension were studied in saturated column experiments. In the presence of manure suspension, little inactivation occurred and the transport was controlled by deposition. The deposition followed a power law distribution with depth, and the magnitude increased with decreasing sand size. Comparison of the cumulative size distribution of manure components in the suspension initially and after passage through sand, suggested that particles retained by mechanical filtration decreased the effective pore size and potentially induced straining of phiX174. A 2-site kinetic deposition model was used to estimate the magnitudes of attachment and straining in the presence of manure suspension, and provided a good description of the data. Modeling results indicated that straining and attachment increased with decreasing sand size due to smaller pores and higher surface area, respectively. In the absence of manure suspension, phiX174 and MS2 transport was controlled by inactivation induced by the solid phase. This conclusion was based upon comparison of coliphage transport behavior at 5 and 20 degrees C, mass balance information, and numerical modeling. Comparison of phiX174 transport data in the presence and absence of manure suspension revealed much higher effluent concentrations in the presence of manure. This difference was attributed to lower inactivation and higher detachment rates. The observed coliphage transport behavior suggests that viability of viruses may be enhanced in the presence of manure suspensions, and that transport studies conducted in the absence of manure suspension may significantly underestimate the transport potential of viruses in manure contaminated environments.