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Underground sand filters are a generally accepted stormwater management practice in the Twin Cities Metro Area (TCMA). However, there is not explicit design guidance in the Minnesota Stormwater Manual and many designs do not offer direct maintenance access to the sand media layer. This study evaluated the performance of six underground sand filters within the TCMA. At each site, we evaluated performance based on the measured filtration rate and removal of five common pollutants in stormwater runoff (TSS, TP, OP, TDP, and E.coli. The six underground sand filters were not consistently effective at removing pollutants. Removal effectiveness was highly variable for TSS, TP, TDP, and OP, with some pollutant concentrations increasing between the inlet and outlet of the filter. Conversely, we did find removal of E. coli to be consistent and effective at four of the six sites.
Todd Shoemaker has 20 years of experience in water resources and environmental engineering and serves as a Senior Water Resources Engineer at Stantec. His primary interests include watershed and stormwater management; green stormwater infrastructure modeling and design; hydrologic/hydraulic and water quality computer modeling; ravine and stream bank stabilization; and floodplain management and regulation.