Often, there is nowhere to retrofit a stormwater pond or infiltration basin to treat this runoff in developed areas. In these tight spots, we need a device that requires very little land but achieves high levels of pollutant removal. These underground tanks route stormwater through three chambers one to remove big particles of sediment, another to remove fine particles, and a final one to filter out dissolved pollutants. Unlike stormwater ponds or infiltration basins, they do not help control flooding or downstream erosion because they cannot detain much water.
Initial tests suggest that the multi-treatment tanks are doing their jobs quite well.
The Department of Natural Resources and U.S. Geological Survey will have better data when they complete the MTT study later this year. This summer, Madison will be testing another stormwater treatment device called a stormceptor. Like MTTs, stormceptors fit into tight spots and remove pollutants from the first flush of runoff. Unlike MTTs, stormceptors do not remove dissolved pollutants. Therefore, they are most appropriate for removing solids, oil and grease from general street and parking lot runoff.