Monthly Archive: April 2016

From Rob Zisette, Principal Scientist, Herrera, Inc.
Photos by Richard Flemimg and Rob Zisette

Water goes from green to blue after the alum treatment

The 2016 Green Lake alum treatment was successfully conducted by HAB Aquatic Solutions over a 6-day period from April 5 – 10. As planned, a total of 81,744 gallons of aluminum sulfate (alum) and 40,905 gallons of sodium aluminate (buffer) were applied evenly over the entire lake. The treatment was monitored on a full-time basis in accordance with the water quality monitoring plan and permit requirements. The treatment increased water transparency (Secchi depth) from 9 to 19 feet and changed the color from green to blue, and had no effect on the lake pH or dissolved oxygen concentrations.

The treatment boat spread alum and buffer evenly over the entire lake 12 hours a day for 6 days.

Alum and buffer were trucked to the lake from as far away as Edmonton, Alberta, and stored in separate tanks contained in a parking lot near the Small Craft Center. Each chemical was pumped through hoses from the storage tank to tanks on the treatment boat in the lake. A ramp was constructed over the hoses to allow use of the foot path throughout the entire treatment period.

A tanker truck filled storage tanks on the shore.

Alum and buffer were injected into the water surface through paired hoses from tanks on the treatment boat. The injected chemicals formed small particles that settled to the lake bottom, removing phosphorus and algae from the water column as they settled. The settled aluminum binds to phosphorus in the bottom sediments to reduce the internal release of phosphorus from the sediments to the water, and limit the growth of algae and toxic cyanobacteria in the lake during the summer. The treatment goal is to prevent future closures of the lake to recreational uses due to toxic cyanobacteria for up to 10 years. The treatment plan and more information can be found on the project website.

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.

Click image to see alum treatment coverage.

Room opens for socializing and conversation at 6:45 PM

• Introductions
• Richard Fleming
  • Recent Activities at Green Lake
• Rob Zisette
  • Update on Alum Treatment
• Richard Fleming
  • A To-Do List for Green Lake. Participants can suggest things within the park that need maintenance, upgrades, and/or other actions. Bring Suggestions, identifying locations if appropriate. Photos may be helpful.
  • Suggestions will be assembled into a To-Do list for review at FOGL’s May meeting and then submitted to the Parks Department
• Ellen Hewitt
  • Webmaster’s Report
• Gayle Garman
  • Treasurer’s Report
• Next Meeting – May 24, 2016
• Adjourn

Friends of Green Lake (FOGL) is a non-profit group in Seattle, Washington, whose mission is to ensure a healthy Green Lake for wildlife and recreation, for today and tomorrow.

At our January Friends of Green Lake meeting, Dick Johnson, the Parks Division Director, asked FOGL to provide a list of things that needed to be done at Green Lake Park. A major portion of our April meeting will address compiling a To-Do List. You are invited to attend, participate, and contribute your ideas.

Examples of ideas that have been suggested so far are:

• Develop a Vegetation Management Plan for the lake’s shoreline.
• Return the Green Lake Community Center rooms that are currently being used as Parks’ Department offices to public use for classes and meetings.
• Remove willow branches that were cut and left in the cattails near the turtle logs. The branches provide an unwanted bed for blackberries, shading out the cattails and eliminating nesting habitat for the blackbirds.

To have the most effect, FOGL’s list must be well-ordered, identify issues, and contain suggestions for appropriate corrective measures. If you have suggestions for the Green Lake To-Do List, it would be very helpful to have you submit your suggestions and concerns via the Contact tab “Your Message” area on the Friends of Green Lake website, or otherwise mail your input to:

You can use the following format to input your suggestions or concerns:

You may also present your input at the FOGL meeting in the Board Room at The Hearthstone on Tuesday, April 26th, 7:00 pm. An action committee will be formed and there will be voting on the projects at the May meeting.

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.