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Hansen Park Iron-Enhanced Sand Filter

Hansen Park Iron-Enhanced Sand Filter and Dam
Hansen Park Iron-Enhanced Sand Filter

Location:  New Brighton, Minnesota
Client:  Rice Creek Watershed District

Overview

Hansen Park is in the Rice Creek Watershed District (RCWD) in New Brighton, Minnesota. This park, along with other areas in the District, was prone to extreme flooding and storm damage. These floods led HEI and the RCWD to create a $7.2-million project, the Long Lake Targeted Watershed Demonstration Program, which is partially funded through a Clean Water Fund grant from the Minnesota Board of Water and Soil Resources. 

Getting the Facts Straight

In 2013, the cities of New Brighton, St. Anthony Village, and Roseville petitioned to create the Basic Water Management Project. The project would address stormwater management and flooding within the drainage area of Ramsey County Ditch 2, which flows into the Hansen Park pond. This petition launched the RCWD and HEI into the first phase of this project: analyzing current conditions of the drainage area and how they could be improved with the Basic Water Management Project. 
Through this analysis, HEI proposed the Hansen Park project as a solution for water quality and flooding. The City of New Brighton took HEI’s findings and incorporated the project into an amended petition. On June 11, 2014, the RCWD accepted the amended petition and began to work in earnest to develop the background information and concept plans for the Hansen Park project.

Getting a Design in Place

HEI worked with stakeholders to design the multi-benefit project. This design married together several innovative best management practices, including: 
  • Three-stage dam and outlet design
  • Targeted removal of sediments causing phosphorous loading
  • Unique iron-enhanced sand filter that will treat discharge on a 24/7 basis

To be sure we had a full understanding of the site, our drone team captured videos of the existing site. They have continued to visit the site and take more videos to ensure the construction continues as planned.

However, no matter how much we try to plan there are some things that are simply out of anyone’s control.

Mother Nature Has Other Plans

To begin this construction project, HEI oversaw 60,000 cubic yards of material dredged from the site. When construction plans and schedules were set, our team banked on freezing January and February temperatures to set a firm foundation. They also planned on the freezing temperatures only causing a minimal soil swell. This would make dredging and removal much easier than with a larger swell. 

When construction began in 2016, the temperatures were just as cold as anticipated and everything seemed to be running smoothly. Then, in mid-January, temperatures sky-rocketed. Dark surfaces absorb more energy than light, so even though snow stuck around, the very soil we were settled on warmed too much. Instead of the firm ground we planned for, we were suddenly sinking in muddy slush, digging up sloppy soils, and removing just over half the tonnage of sediment a day than we originally planned.

With these difficult conditions, our crew unexpectedly had to coordinate with multiple landfills that would accept the soils and, eventually, extend the dredging and removal schedule into the next winter.

Despite the frustration of a warm season, our team found an inexpensive fix to the seemingly costly problem: wood chips. The wood chips acted as a thermal barrier, preventing soils from warming and giving us a firm foundation to work on. 

Even with these weather woes, construction of the iron-enhanced sand filter was successfully completed in the fall of 2018.

Funding the Project

With a budget of $4 million, Hansen Park is the largest (and most complicated) project in RCWD history. To fund this massive undertaking, the RCWD pulled from a $3-million Targeted Watershed Demonstration Project (TWDP) grant they were awarded in 2014. With a required $2-million match from the District, this grant covered $1.5-million of the $4-million project.