A creek will be diverted through a filtration system to purify its water and remove phosphorous pollution that would otherwise enter Dutch Lake.
Elroy and Sara Kuglin watched a backhoe and a bulldozer maneuver over the half-frozen mud on their hay field recently near the west metro city of Mound.
Grading the field to its original slope was the final stage of an innovative filter system designed to improve water quality in nearby Dutch Lake.
Renae Clark, project manager for the Minnehaha Creek Watershed District (MCWD) that installed the filter, said the concept is simple: Dig a trench the length of a football field and about 15 feet wide, fill it with a mixture of sand and iron filings, and divert a creek through the trench to purify the water.
"The filter uses sand mixed with iron filings to both react with dissolved phosphorus and remove it from the water," Clark said.
Phosphorus is a problem because too much of it dissolved in water causes excessive algae growth that turns lakes green and smelly.
One pound of phosphorus can grow an extra 500 pounds of algae in a lake, according to studies.
Hundreds of lakes in Minnesota fail to meet clean water standards because of too much phosphorus. Water managers are seeking cost-effective ways to reduce the amount of fertilizer that runs off agricultural fields and lawns. They also want to remove phosphorus that has already entered wetlands and streams and is headed for lakes.
The Kuglins have lived on their six-acre hobby farm for 40 years. The field, just off Game Farm Road in Mound, slopes to the creek.
The couple sold an easement near the creek to the watershed district.
"It's been an interesting project to watch develop," said Sally Kuglin.
The creek flows intermittently, she said, when melting snow or downpour rains cause an upland wetland to overflow.
Clark estimates the filter system cost $272,000 and will intercept 30 pounds of phosphorus annually.
Water is diverted into the trench, she said, where it filters vertically through the sand mixture and underlying rocks. The clean water then percolates into perforated underground pipes and is routed back to the creek. The system is expected to last at least 10 years before the sand and iron filings will need to be replaced, she said.
Model for cleanup
Clark said similar systems have been used to remove pollutants from overflowing storm water ponds, but this is the first time the district has used it with wetlands.
MCWD administrator Eric Evenson said the idea is to create a model that can be used in similar situations near Lake Minnetonka and elsewhere.
The district will monitor the phosphorus levels above and below the filter system to measure how efficiently it's working.
The creek drains about 600 acres, or one-third of the entire sub-watershed that empties into Dutch Lake, Clark said.
The sources of the phosphorus in the area come from horse manure, crop fertilizer and decaying wetlands plants, she said.
Another part of the watershed is more residential, Clark said, and Dutch Lake would also improve if lawn and storm water runoff were reduced in that area.
While the overall goal is to reduce phosphorus entering Dutch Lake by 42 percent, the improvements could also help Jennings Bay in Lake Minnetonka, which lies further downstream.
In the district's water quality report card, Jennings Bay was tied for the worst grade among Minnetonka's 30 bays in 2011. Dutch Lake is listed on the state's list of "impaired waters" because of too much phosphorus.
After three weeks of digging, installing the filter system and adding cover, the Kuglin field sported a long, muddy scar as the bulldozer made its final passes across the slope. Crews will cover the area with straw mulch, Clark said, and seed it in a few weeks.
"By June this will look like a hay field again," she said.
Tom Meersman • 612-673-7388