June 16, 2021

Drainage of tile-riser inlets allow direct discharge of surface water into tile drainage systems, effectively bypassing soil filtration processes and negatively affecting water quality. Blind inlets have gained recent popularity in allowing for both depression drainage and removal of suspended particulate matter by filtration through a sand/gravel layer. This paper summarizes blind inlet development and all published studies, provides new data from dissection of the longest-operating blind inlet that was recently de-commissioned, and discusses new ideas for the future of blind inlets, given certain shortcomings. Previous studies, as well as current soil analysis of the 12-yr old blind inlet, confirmed the ability of blind inlets to reduce sediment and particulate phosphorus (P), with an overall removal efficiency of at least 40% for each. In addition to sediment and particulate P, soil sampling revealed the ability of the blind inlet to capture several pesticides: glyphosate, atrazine, S-metolachlor, and metabolites. Traditional blind inlet sand media are unable to remove appreciable amounts of dissolved P compared to alternative media such as steel slag. Enhanced removal of dissolved constituents could be easily achieved through the use of P sorption materials and organic materials such as biochar, as well as a combination with tile-drain filters.

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