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We present theoretical and experimental work on Cryptosporidium parvum oocysts to characterize their transport behavior in saturated, sandy sediments under strictly controlled conditions. Column experiments are implemented with three different sands (effective grain size:  180, 420, and 1400 μm) at two different saturated flow rates (0.7 and 7 m/d). The experiments show that C. parvum oocysts, like other colloids, are subject to velocity enhancement. In medium and coarse sands, the oocysts travel 10−30% faster than a conservative tracer. The classic clean-bed filtration model is found to provide an excellent tool to estimate the degree of C. parvum filtration. Experimentally determined collision efficiencies, α, range from 0.4 to 1.1. The magnitude of α is consistent with the known physical and chemical properties of the oocyst and the transport medium and compares well with, e.g., measured collision efficiencies of …