Lake Okabena's health to be addressed
WORTHINGTON — For years, people have debated just what or who is contributing phosphorus to the waters of Lake Okabena that lead to the stinky, unsightly algal blooms during the summer months.
Without accurate data from pollutant sources, however, the Okabena-Ocheda Watershed District has difficulty pointing a finger at any one culprit. The farmers say it isn’t them — that it’s city residents who put too many chemicals on their lawn or let grass clippings and other pollutants flow into the city’s stormwater system. Meanwhile, city residents point to the farmers.
Now, the OOWD is hoping to get some answers.
The watershed district recently received approval from the Minnesota Pollution Control Agency to conduct its own tests on the lake in advance of the state-mandated Total Maximum Daily Load (TMDL) study. The MPCA is planning a study of the entire Missouri River basin, which encompasses portions of Rock, Nobles, Pipestone and Murray counties.
“They’ll set loading limits for various categories based on monitoring that’s been done in the past, but we were a little uncomfortable that they weren’t doing any additional monitoring and looking at real numbers in the Okabena-Ocheda Watershed District. Rather, they were going to use numbers calibrated from a watershed like Worthington,” said OOWD Administrator Dan Livdahl during an Okabena-Ocheda-Bella Clean Water Partnership Joint Powers Board meeting early Friday morning.
Livdahl said putting load limits on Lake Okabena without using actual figures could “get kind of hairy” and possibly cost the watershed and the city of Worthington significantly more money.
The Clean Water Partnership last completed a study on Lake Okabena 20 years ago.
Since receiving approval from the MPCA to conduct its own surveys in advance of the TMDL, Livdahl said he requested proposals from three different engineering firms to conduct the lake study. He recommended the joint powers board approve Wenck Associates Inc., Maple Plain, to evaluate the phosphorus sources in the lake.
The total cost of the study is $53,558, with the MPCA agreeing to pay $23,400. Joint Powers Board member Steve Johnson moved to fund $26,000 from the Clean Water Partnership, with the remainder to come in the form of labor provided by the watershed district. With the motion’s passage, Livdahl said it’s possible the lake study will begin yet this fall. The MPCA wants to complete its study in 2014.
“The report will be useful to the MPCA,” he added. “The state will look at where soil erosion, phosphorus and stream bank erosion are going on, (as well as) the Worthington storm sewer system, and coming up with a good estimate of how much pollution is coming from that.”
Also taken into account is wind deposition — how much soil is blown during the winter months onto the snow and ending up in the lake.
Ultimately, the results of the study will be used by the MPCA when it write its TMDL plan for the Missouri River basin. Meanwhile, Livdahl told the board it may want to do more locally to address some of the issues, and that could mean applying for grants to help fund projects.
“If we cut off all of the pollution, we’ll still have a dirty lake,” he said. “If you’re looking at options you can do in the lake, we’re really limited because the lake is shallow. We’ve got essentially 10 to 15 feet of sediment down there that’s really high in nutrients. If you take off that top layer (by dredging), down below might be even worse.”
Board member Rolf Mahlberg said the group needs to find out what illnesses the lake has before talking about prescribing fixes.
“It will be intriguing to find the data,” he added. “Everybody thinks it’s someone else.”
Also discussed at Friday’s meeting was the need to stabilize Okabena Creek north of Oxford Street, behind the Sanford Clinic and Solid Rock Assembly.
The stabilization project has been discussed for several years, and the creek was recently surveyed by Larry Mick, thanks to funding from the E.O. Olson board.
Worthington City Engineer Dwayne Haffield said the streambank erosion is contributing to the sediment coming into Lake Okabena, and will need to be addressed eventually.
Despite attempts to find more environmentally friendly ways of solving the erosion problem, Haffield said the stabilization project will need to be fixed with riprap.
“What we would do to stabilize that is essentially bring some slopes up to better manage (the creek) and then riprap,” Haffield said. “Bottom line, we’re looking at — this is rough estimates — looking at around $700,000.
“There’s been a lot of talk about projects we could do for water quality — this is one that’s been coming up,” he added. “It’s definitely a project that could be considered as a recommendation from this board to the city for clean water.
“It’s literally and figuratively an eroding problem.”
Because the project hasn’t been identified in a TMDL, Haffield said it would be a “tough sell” for grant funds.
Livdahl said state legacy funds may also be difficult to access for the project, since they have a history of selecting projects that include vegetation and creating wildlife benefit.
“Riprap, for this site, is the right answer, but it isn’t something the state will get excited about and want to fund,” he added.
It is possible the work could be divided so the expense would be spread out over more than one year.
Survey work was also discussed to determine sedimentation rates in Lake Okabena and Sunset Bay. When Sunset Bay was cleaned out in the 1960s, it was done to create a stormwater basin. It has been filling in with sediment ever since, and in 1997, Livdahl said they were told the basin had about 30 years of capacity before it would need to be cleared out.
Now halfway through that 30-year span, Livdahl said they should see what’s happening with sediment levels in both Sunset Bay and Lake Okabena.
They can have surveys done at approximately 300 different points on the two water bodies for a cost of approximately $2,500.
The joint powers board offered support for the survey, which could be conducted this fall.
Daily Globe Reporter Julie Buntjer may be reached at 376-7330.