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Runoff from Iowa State Universitys 380 head beef cattle concrete feedlot was treated via solids settling, then soil infiltration followed by a small constructed wetland, and ultimately discharged via a vegetated waterway to a nearby stream. Concentrations and nutrient mass flows were reduced dramatically. The treatment system removed over 97% of the Kjeldahl nitrogen (TKN) and ammonia nitrogen, 94% of total phosphorus, and 93% of total solids. The majority of the water quality improvement occurred during the soil filtration process, while flow through the wetland and a vegetated waterway provided polishing of the filtered effluent. Phosphorus concentrations were monitored in soil profiles in the infiltration area over the five years of the project and no buildup was observed. The passive treatment system can very effectively protect surface water quality below open beef feedlots.