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Beef feedlot runoff is a potential environmental contaminant. As such, its proper management is required to preserve water quality. Primary treatment of feedlot runoff often relies on sedimentation techniques, thus accurate knowledge of feedlot runoff physical properties is required. This study characterized the physical and chemical properties of runoff effluent from earthen and concrete beef feedlots in Iowa with the objective of providing the necessary information to improve solid settling basin design and performance. Study results indicated there was a difference between the settleability of runoff from earthen and concrete lots. Particle size distribution and particle density measurements indicated that the poorer settleability of concrete lot runoff was primarily caused by lower particle densities, 1.470.17 g/cm3 for concrete lots as compared to 1.89 0.11 g/cm3 for earthen lots. Runoff composition was analyzed before and after settling to relate nutrient reduction to solids removal. Results indicate an average of 41 g-TKN/kg-TS and 16 g-TP/kg-TS removed by settling.