Excessive concentrations of phosphorus can cause deterioration of surface waters by eutrophication. Some industrial byproducts can be utilized to filter dissolved P through a P filtering structure. The objectives of this study are to test the performance of a passive P filter structure filled with steel slag as filter material and estimate the life-span of the steel slag when used as a P sorbing material (PSM) under field conditions. The experimental design for the study is a split plot with main plots of filter material (steel slag or pea gravel) and subplots of fertilizer (P applied or no P applied).  Plastic tub-shaped containers filled with steel slag are placed in trenches at the bottom of ‘U3’ bermudagrass [Cynodon dactylon L. (Pers.)] plots located on a 5% slope. Natural rainfall runoff is collected and filtered then conducted by subsurface drain pipes to parshall flumes. Isco 6700 series (Isco, Lincoln, NE) automatic samplers are used to measure flow rates each minute and sample runoff passing through the flumes every 5 min. Pre-filtered runoff flows into collection tanks continuously during each runoff event for use in comparing the average P concentration in pre-filtered runoff with the average P concentration in post-filtered runoff.