Location: Eagan, MN
Application: Infiltration and Treatment
Number of Basins: 1
Product Used: 8’-0” DoubleTrap & two 10′-0” SiteSaver
Number of Pieces: 98 + 10 panels
Total Water Stored: 38,269 cf
Owner: City of Eagan, MN
Consulting Engineer: Stantec
General & Installing Contractor: Meyer Contracting
The Eagandale Industrial Park Neighborhood Street Revitalization is one of the City of Eagan’s 2021 projects involving roadway resurfacing, utility enhancements, street signage replacement, and stormwater quality improvements. Besides the road repairs and new infrastructure, this project focused on reducing the quantity of suspended solids, sediment, and phosphorus from stormwater going into LeMay Lake.
The project is in the watershed of LeMay Lake, which the Minnesota Pollution Control Agency determined in 2014 to be impaired with too much phosphorus. Federal and state regulations require studies and a plan to reduce sources of impairments. A 2015 study determined that Eagan’s stormwater phosphorus needed to be reduced by 27 percent. The City is implementing several projects to improve the lake’s water quality; estimates are that this project’s phosphorus removal fulfills the City-required watershed reduction.
Stantec, the engineering firm consultant for the project, conducted a feasibility study of the watershed to evaluate potential locations and suitable soils for Best Management Practices (BMPs). The maze of underground utilities under the roadways limited the available space for regional stormwater improvements. After the examination, the team located an area under West Service Road with just enough space and great soils to infiltrate stormwater runoff.
The civil consultant then worked with StormTrap to design a cost-effective solution that met the project’s stormwater treatment needs. An integrated system incorporating two SiteSaver hydrodynamic separators and an 8’-0’’ DoubleTrap basin. The City chose the system for providing open access for maintenance and the durability of the concrete structure underneath the street section.
The system, designed as a “treatment train in a vault,” has an internal junction chamber that splits the stormwater flows entering the system between the two SiteSaver devices. The water quality units capture trash, floatables, sediment, and phosphorus. Stormwater then flows into the 8’-0’’ DoubleTrap vault and fills the bottom before water bypasses the internal overflow weir. To infiltrate as much stormwater as possible, the system’s footprint was maximized by connecting the main StormTrap vault to a clean-out vault through a series of underdrains and aggregate, which saved costs. This allows up to 4’ of water to infiltrate for every storm event, increasing the system’s phosphorus- and sediment-capture efficiency.
Meyer Contracting installed the system in less than a week in the Fall of 2021. The project reduces about 35 pounds of phosphorus per year and provides over 38,000 cubic feet of stormwater storage. Todd Shoemaker, PE, Senior Resources Engineer at Stantec, stated that “it was great to work with StormTrap in this project from design to construction.”