Steiger Lake, in northeastern Carver County, has historically experienced good water quality, with in-lake nutrient concentrations below the thresholds for the 303d Impaired Waters List. However, in 2008 the average concentration was 44 μg/L, which did not meet the goal set by the Minnehaha Creek Watershed District (MCWD). MCWD took the step to proactively protect the lake while its water quality was still relatively good and retained SRF to perform a feasibility study of options to provide treatment for two upstream sub-watersheds.
The study investigated the feasibility, size, and scope of a wet detention pond or other best management practice to provide treatment at the site of a drained wetland. The water treatment goal was to remove at least half of the total phosphorus load projected to be contributed by the two sub-watersheds under the ultimate 2020 development conditions. A variety of alternatives were investigated, including a large wet detention basin covering the majority of the site and three different wetland restoration options. The study also looked at the potential to expand an existing stormwater pond, located across TH 5 from the wetland, to assist with phosphorus removal.
We used XP-SWMM and PondNet to evaluate the potential of the various alternatives to obtain the desired phosphorus reductions. Each scenario included probably costs, expected pollutant removal efficiencies, and construction concerns. Based on this study, MCWD chose to move forward with a full restoration of the wetland and retained SRF to perform the final design and prepare construction documents.
Construction was completed in 2013 with the plant establishment inspections continuing for the next three growing seasons.
CLIENT: Minnehaha Creek Watershed District