Phosphorus treatment for L.S. includes alum
BY PAM STEVENS | MANAGING EDITOR
While phosphorus is important to the health of Lake Stevens high levels can result in water quality deterioration and unwanted algae blooms.
This past year the City of Lake Stevens has had to post three warnings of toxic blue-green algae blooms due to the phosphorus levels in the lake.
Twenty years ago the phosphorous levels in that lake were not controlled. Since then four aerators were placed in the deepest part of the lake which maintained phosphorous levels and kept them at a minimum.
“The aerator system works by putting oxygen into the deepest portion of the lake where it is needed to maintain a phosphorus bond with the iron in the sediment,” City Public Works Director Mick Monken explained. “Over the years, the continued loading of phosphorus from natural and imported materials (such as fertilizers, soaps, septic systems, and improper disposal of vegetation debris) has exceeded the capacity of the aerator and iron sediment control.”
Now the aerator has almost hit its life span making it imperative for the city to come up with a plan to treat the phosphorous in the lake.
“The City and County have been working for the past several years to determine a long range sustainable solution to deal with the phosphorus problem. The alternatives considered were continuing with aeration, aeration with alum treatment, and alum alone,” Monken said. “After reviewing the options for public health, environmental protection, and cost/benefit the conclusion was that alum alone was the lowest cost with the highest benefit solution that could meet these criteria.”
They are also planning an education effort for citizens who live in and around the lake to help keep the public informed as to how they can help keep phosphorous levels lower.
Monken explained that alum, or aluminum sulfate, is already commonly used in treating drinking water and is safe and effective in low doses.
“It is considered by the State Department of Ecology to be an effective and safe treatment for managing phosphorus,” he said. “This practice is commonly used in several lakes within Washington and throughout the country for treating phosphorus.”
The first alum treatment in Lake Stevens will take place this summer and will continue annually.
“It is estimated that the alum treatment alone solution will be a similar cost to what is being budgeted for the existing aerator system,” Monken said. “In addition to these costs, the aerator system has an estimated replacement cost of $4 million, which if considered into the overall cost, makes the alum treatment a significantly lower long range cost saving.”
The city will present its education effort as well as new regulations sometime this year.