The Green Lake Alum Treatment Begins!

From Rob Zisette, Principal Scientist, Herrera, Inc.
  and the Seattle Parks Department
Photos by Richard Flemimg

The 2016 Green Lake alum treatment will start at about 7:30 am on Tuesday April 5. Conducted by HAB Aquatic Solutions, the treatment is expected to be conducted from 6:30 am to 7 pm for five straight days ending on Saturday April 9. The treatment will be monitored on a full-time basis in accordance with the water quality monitoring plan and permit conditions. The monitoring plan is an appendix of the treatment plan that can be found at the project website.

The barge ready to be refilled. It will spread the alum treatment 12 hours a day for several days.

The alum will be applied near the water surface. It removes phosphorus from the water column as it forms small clumps and settles. It then covers the bottom sediments to further prevent the internal release of phosphorus from the sediments. The alum treatment is effective immediately upon application.

The tanker truck filling the storage tanks on the shore.

The alum treatment is intended to reduce phosphorus levels in the lake, limiting cyanobacteria (blue-green algae) blooms and improving recreational use of the lake. The alum treatment is applied from a barge on the lake. The treatment is pumped from a truck staged in the parking lot through hoses that will run over the Green Lake path to the barge. These hoses will require a small ramp to allow Green Lake path users to travel safely over them.

Algal scum on the lake, before the treatment.

Previous lake-wide alum applications in 1991 and 2004 effectively limited algae blooms and improved water quality. The alum treatment is expected to be effective for up to 10 years. The alum treatment plan was developed as part of the 2016 Green Lake Phosphorous Management Plan.

If you have additional questions about the project please contact Chris Mueller, Seattle Parks and Recreation project manager at chris.mueller@seattle.gov or 206-684-0998.