Sand filter for Lower Prior Lake put in near Sand Point Beach

Prior Lake American

An iron-enhanced sand filter basin near Sand Point Beach in Prior Lake is now complete, which could mean cleaner water and prevent thousands of pounds of algae from growing each year, a water resources expert said.

The city of Prior Lake and the Prior Lake-Spring Lake Watershed District collaborated on the project and held a grand opening for it on Wednesday.

“You would rarely see any one entity standing before you on anything significant that doesn’t have two, three, four stakeholders,” Prior Lake Mayor Kirt Briggs said during the grand opening. “We don’t get anything done if we don’t talk to each other.”

Maggie Karschnia, water resources project manager for the district, said the iron-enhanced sand filter basin captures stormwater and removes nutrients that shouldn’t be in the lake. The iron in the basin has an electrical charge that attracts phosphorus before it can encourage the growth of algae.

The basin can keep 24 pounds of phosphorus from entering the lake each year. As a result, algae in Lower Prior Lake will be reduced by as much as 12,000 pounds, according to the watershed district website.

“It means a lot for water quality going into the lake,” Karschnia said.

Lower Prior Lake is the last lake in a chain of three that also includes Spring Lake and Upper Prior Lake. Water moves along channels from Spring Lake on down.

All three are listed as “impaired waters,” according to the Minnesota Pollution Control Agency website. Impaired waters don’t meet one or more of the state’s water quality standards, which include maintaining certain amounts of pollutants in the water, protecting the water for beneficial uses and protecting high-quality or unique waters, according to the agency.

The watershed district is attempting to prevent Lower Prior Lake off of a state listing for impairment of aquatic recreation associated with high algae levels and poor water quality, Karschnia said. Spring Lake and Upper Prior Lake are on that list.

“Impaired and polluted are kind of the same,” Watershed District Water Resources Specialist Jaime Rockney said. There’s standards we like to meet, and if they don’t meet the standards, they’re considered impaired.”

Spring Lake is listed as impaired for aquatic consumption, aquatic life and aquatic recreation.

Aquatic life impairment means the number and diversity of fish, plants, or macroinvertebrates are not at healthy levels, Minnesota Pollution Control Agency Project Manager Chris Zadak said. The aquatic consumption impairment designation puts limits on how many fish from the lake can be eaten, while aquatic recreation impairment means recreational activities, such as swimming, are limited due to algae blooms.

The upper and lower Prior Lakes are listed as impaired in two categories each, including a proposed aquatic life impairment designation for Lower Prior lake. Zadak said the classification stemmed from “non-native aquatic species and riparian lakeshore development.”

“The district has this impairment on its radar,” Karschnia said, adding that the watershed district is awaiting more information and direction from the Minnesota Pollution Control Agency.

The filter basin also requires maintenance over time, she added. As a result of the captured phosphorus, the basin will begin to grow plants that will need to be raked out. The sand will also have to be tilled and redistributed, and the iron will need to be replaced at some point.

The city of Prior Lake will conduct the long-term maintenance on the basin.

“It became something larger, and it was just a really great opportunity for a partnership project,” Karschnia said.

The entire project, titled the “Sand Point Beach Park Project” also included the expansion of two stormwater ponds and a prairie restoration. The project is one of several dedicated to improving and maintaining the water quality of Lower Prior Lake. Others include an iron-enhanced sand filter, prairie planting and wetland enhancement at Fish Point Park, shoreline restoration at Watzl’s Beach and bio-infiltration basins — which is a sand filter without the iron — at Indian Ridge Park and Fairlawn Shores.

For the Sand Point Beach Park Project, the watershed district received a three-year, $142,000 Clean Water Partnership Grant from the Minnesota Pollution Control Agency. The district was required to match up to 50 percent of that but ended up contributing more than 50 percent of the grant for the projects, Karschnia said.

The iron-enhanced sand filter basin at Sand Point Beach was $144,000. The total cost of the project including the basin, the expansion of the ponds and the prairie restoration was $336,000.

“This project is important because we’re making an investment to protect a resource that is doing well,” Karschnia said. “They always say an ounce of prevention is worth a pound of cure, and we definitely believe that.”