The purpose of this study is to evaluate the stormwater management effectiveness of installed underground sand filters in the Twin Cities Metro Area. The Minnesota Stormwater Manual includes guidance for the design and pollutant removal efficiency of surface and one type of underground sand filters. The most popular variety of underground sand filter, however, does not offer clear access to the sand media layer and is not included in the Minnesota Stormwater Manual. Maintenance is extremely limited by this design, which calls into question whether they can actually achieve the same removal efficiency as their above ground counterparts, and whether those efficiencies degrade over time. There is limited data regarding performance of in situ underground sand filters to assist in this evaluation.
Some underground systems in the Metro have been installed for a decade, but their long-term performance has not been evaluated. Award of this grant would provide funding to investigate underground filtration performance and answer the following questions:
- Are systems being maintained?
- Are systems meeting performance goals?
- What is the expected lifespan of an underground filtration system?
- How often should maintenance be performed?
- Should these systems continue to be considered a viable water quality BMP?