Land-applying animal wastes potentially exposes humans and animals to fecal pathogens, either by direct contact with soil and produce, or via ground water contamination. Some of these organisms are Salmonella, certain pathogenic Escherichia coli strains, protozoa such as Cryptosporidium and Giardia, and enteric viruses. Whether soil adequately filters these pathogens before they reach ground water depends on the interaction of porosity, texture, depth, water content, rainfall intensity and duration, and soil management.
Coyne, Mark S.; Stoddard, C. S.; Grove, John H.; and Thom, William O., "Infiltration of Fecal Bacteria Through Soils: Timing and Tillage Effects" (1996). Soil Science News and Views. 21.