Rain gardens and biofiltration basins have become common urban stormwater tools, but underdrains, often included to prevent flooding during extreme events, may inadvertently contribute to nutrient pollution by transporting phosphorus and nitrogen downstream before adequate infiltration occurs. In Minneapolis, where high infiltration rates are common, the city evaluated whether underdrain caps could promote infiltration in city-owned biofiltration basins. An inventory of 86 potential sites was created, followed by field inspections to assess viability. Previous monitoring confirmed soil infiltration rates were sufficient that capping would not risk prolonged ponding. A list of 37 viable sites was provided to the Public Works Surface Water and Sewers Operations and Maintenance group, which installed caps at 20 sites in 2024. Preliminary findings suggest capping underdrains is a low-cost, low-effort intervention to reduce nutrient loading and promote infiltration. Future work includes continued monitoring of installed caps, assessing remaining viable sites, and exploring implementation at Park Board and University-owned locations.