The long-running campaign to clean up Veterans Memorial Lake took another step forward Monday night when the Great Bend City Council approved the application of a chemical jolt to help eliminate the toxic blue-green algae.
What is considered a low dose of liquid alum (5,600 gallons) will be injected into the lake via pumps through the existing oxygen diffusers, said Terry Hoff, Great Bend’s human resources director who has overseen the project. This will start in April and take about three weeks.
“Our goal is to shock the lake,” Hoff said.
Hoff stressed that this so called alum micro-floc system is safe and non-toxic to people and pets since it is such a low concentration. The treatment has been reviewed and blessed by the Kansas Department of Health and Environment.
The aim of this process is to reduce phosphorus levels in Vets, he said. It is the phosphorus that feeds the algae.
The initial treatment will cost $16,000, $14,00 for the alum and $2,000 for the pumps and tubing required to apply it, Hoff said. All the work will be done by city personnel, which cuts the cost of the operation.
The alum was the less-expensive of two options. Hoff said the city also looked at Phoslock system from SePRO of Carmel, Ind., the quote for which was $29,900.
After this initial treatment, phosphorus levels and other water quality parameters in the lake will continue to be monitored, he said. The need for additional alum applications will be evaluated.
But, “this is not a final solution,” Hoff said. “We still have to address all the factors that introduce phosphorus into the lake.”
The flocks of geese that have made their home at Vets, along with the waste they create, are one of the key sources of that contamination. Keeping them off the water will be an ongoing battle, Hoff said.
“We will continue aggressive efforts,” he said. The use of various noise makers to scare the birds away will continue as needed.
But, there is also the storm water that flows into the lake, carrying phosphorus-laden lawn fertilizers. In addition to public education on this, attempts to use vegetation to filter the run-off will be implemented.
Hoff said they want to return the lake to a normal ecological level and once again make it a safe and enjoyable asset to the community. They also want to eventually restock it with fish.
But, “this will take time,” Hoff said.
How does the alum work?
On contact with water, alum forms a fluffy aluminum hydroxide precipitate called floc. Aluminum hydroxide (the principle ingredient in common antacids such as Maalox) binds with phosphorus to form an aluminum phosphate compound.
This compound is insoluble in water under most conditions so the phosphorus in it can no longer be used as food by algae organisms, Hoff said. As the floc slowly settles, some phosphorus is removed from the water.
The floc also tends to collect suspended particles in the water and carry them down to the bottom, leaving the lake noticeably clearer. On the bottom of the lake the floc forms a layer that acts as a phosphorus barrier by combining with phosphorus as it is released from the sediments.
A long road
This journey started a year ago, well actually longer.
Troubles with algae in Vets date back to 2010. Over the years, the algae has tainted the water green and has even led the KDHE to issue warnings about coming in contact with it.
A year ago, the city contracted with consulting firm, CH2M Hill, of Englewood, Colo., to develop a multi-step plan to remediate the problem. The use of alum was one recommendation from the consultants.
Among the steps were public education, reducing the introduction of phosphorus, minimizing the goose population and a mapping of the lake floor contours. These have all been done or are on-going.
A biological survey of life in the lake was also planned. However, a massive fish kill last summer rendered this step obsolete.
“We were devastated at the time,” Hoff said. “But, there was a silver lining.”
The kill allowed the city to turn off the oxygen diffusers which were installed to help infuse oxygen into the water for the fish. This made it easier to conduct surveys of the lake and easier to manage the goose issue.
As the process continues, Hoff said monitoring will also continue.