Burnsville gives annual State of the Lakes report
Crystal Lake, one of three Burnsville lakes on Minnesota’s Impaired Waters List, may be coming off in 2018.
The 291-acre lake, which has a public beach and boat launch and many lakeshore homes, has for the last 10 years exceeded state standards for water clarity and phosphorus concentration, said Daryl Jacobson, the city’s water resources specialist. The lake’s level of chlorophyll-a is close to the state standard, he said.
Failing two of those three measures gets a lake put on the impaired list; passing two of the three gets a lake delisted. The measurements are averaged over 10 years. The next list comes out in 2018.
“I think it is very likely that it could be removed from the list,” Jacobson told the city’s Parks and Natural Resources Commission on Monday during his annual State of the Lakes report. “I think that’s some good news. There’s been a lot of work done in the Crystal Lake watershed over the last 15 years as well.”
The state Pollution Control Agency notified the city in January the lake may be delisted, Jacobson said. About 40 percent of Minnesota’s lakes and streams are impaired by “conventional pollutants,” according to the MPCA.
The other Burnsville lakes on the impaired list are Alimagnet and Keller, which share territory with Apple Valley.
The 104-acre Lake Alimagnet experienced sharply rising levels of phosphorus and chlorophyll-a in the last three years, while its visual clarity fell from 0.9 meters in 2014 to 0.7 in 2016.
“That’s the opposite of what we’re looking for,” Jacobson said.
Aluminum sulfate treatments to reduce phosphorus are planned this year in two ponds on the Burnsville side that drain most of the city’s stormwater that reaches the lake, Jacobson said. The Vermillion River Watershed Joint Powers Board landed a $216,000 state grant for the project and is adding $75,000 of its own funds, Jacobson said. Burnsville is kicking in $125,000, he said.
The project will include an iron-enhanced filter bench for each pond. Iron filings will filter phosphorus after rainfalls, Jacobson said.
Altogether, officials hope to remove 26 pounds of phosphorus annually from the Burnsville side of the lake, he said.
Last year the two cities stocked Alimagnet with 2,000 largemouth bass — predators intended to reduce the glut of growth-stunted sunfish that feed at the lake bottom and stir up phosphorus, Jacobson said.
In the 53-acre Keller Lake, phosphorus levels rose slightly from 2014 to 2016, chlorophyll-a levels fell sharply and clarity rose from 0.8 meters to 1.0. The city’s clarity goal for Keller, 1.8 meters, was set in 2002, is unrealistic for a shallow lake of 8 to 9 feet and will likely be reset, Jacobson said.
A large underground stormwater treatment system being built this summer at Crystal Beach Park is expected to remove about 72 pounds of phosphorus annually from water draining to Keller, Jacobson said. Two years ago Apple Valley built a stormwater pond to remove about 50 pounds, he said.
The 60-acre Lac Lavon — a former gravel quarry that filled with water when mining was done — has very low pollutant levels, a small watershed draining to the lake and a stellar clarity reading of 4.4 meters.
“That lake’s really in great shape,” Jacobson said.
The 27-acre Earley Lake was removed from the Impaired Waters List in 2012, Jacobson said. From 2014 to 2016 pollutant levels fell and clarity rose from 1.4 meters to 1.7.
The 58-acre Sunset Pond experienced a slight drop in phosphorus the last three years but nearly a tripling of chlorophyll-a. Clarity was at 1.8 meters last year and 2.2 in 2014.
The 11-acre Twin Lake South has experienced increases in phosphorus and chlorophyll-a and a drop in clarity, from 2.1 meters in 2014 to 1.9 last year.
The 14-acre Wood Pond has experienced a rise in the pollutants and fluctuating clarity levels — 1.3 meters in 2014, 2.5 in 2015 and 1.8 last year.
Aluminum sulfate treatment is planned this year to contain internal loading from sediments in the lake, Jacobson said. A street reconstruction project last year included some underground filters to treat stormwater entering the south side of the lake.
“I think Wood Pond is definitely trending in the right direction,” Jacobson said.