Stormwater Monitoring in Rapid City

Executive Summary

Rapid City has implemented programs to improve stormwater quality in response to the “Phase II Final Rule” guidelines issued by the U.S. Environmental Protection Agency (USEPA). In 2008, the City of Rapid City requested that USGS provide assistance in developing strategies for a stormwater monitoring plan that would focus on helping to evaluate the effectiveness of the City’s improvement programs.  Pilot monitoring activities were initiated during 2008 in the Arrowhead drainage, and were expanded in 2010 to include the Meade-Hawthorne drainage in order to provide comparison of water-quality results between a fully developed basin (Meade-Hawthorne) and a mixed-landuse basin (Arrowhead).

The consistently higher bacteria and total suspended solids concentrations in the Meade-Hawthorne drainage may be indicative of the relative lack of sediment controls (detention ponds, vegetated channels, wetlands), compared to the controls and lower level of development in the Arrowhead basin. Arrowhead basin’s drainage contains about 90 percent open or natural channels, compared to just 21 percent in the Meade-Hawthorne basin.

Three constructed stormwater control structures were sampled in 2010–11 to assess the ability of these to remove sediment and bacteria. Similar to other studies across the Nation, data collected on these structures support the conclusion that dry detention basins are not as effective at bacteria removal compared to wet retention ponds with a permanent pool.

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