Alum treatment complete
On Wednesday, May 8th, HAB Aquatic Solutions finished the alum treatment on Normandale Lake in Bloomington. The alum was applied via an alum treatment barge, which was refilled from tanks stationed at the Normandale Lake boat launch. The treatment began on Tuesday, May 7th, and was mostly completed then to take advantage of the calm weather.
What is alum?
Alum (aluminum sulfate) is a nontoxic liquid. Its use in lakes began in the early 1970’s and is used to reduce the amount of phosphorus in the water. Phosphorus is the nutrient that fuels algae growth. Reduced phosphorus levels can lead to lower amounts of algae. Alum is most often used to control phosphorus release from the lake bottom sediments (internal loading).
When aluminum is applied to a lake as a solution of alum (aluminum sulfate), it forms an insoluble aluminum hydroxide floc that settles to the lake bottom. The aluminum binds with phosphorus in the sediment to prevent it from recycling back into the water column. Conducting the alum treatment before aquatic plants are reestablished in the lake allows the aluminum floc to reach the sediment more evenly.