King County to clean up Lake Hicks algae with alum

2005 Archived News

In an effort to control algae blooms and clean up Lake Hicks in White Center, King County plans to apply chemicals to the four-acre urban lake in Lakewood Park on Monday, April 11.

Once a favorite swimming and fishing hole, the lake has been plagued with poor water quality for many years. Very high phosphorus concentrations have lead to frequent, dense and sometimes toxic cyanobacteria (blue-green algae) blooms, which have resulted in permanent closure of the beach for swimming due to safety concerns. The lake is categorized under the Federal Clean Water Act (1972) as 'impaired' by excessively high phosphorus concentrations. It will remain closed to swimming after the chemicals are applied.

Though much smaller in scale, both the problem and solution are very similar to the Green Lake cleanup project undertaken by the City of Seattle in 2004.

To clean up the lake, about 2,500 gallons of aluminum sulfate (alum) will be pumped into Lake Hicks. Alum is a chemical compound often used in wastewater treatment and sometimes as a food additive. Because alum on its own would make the lake too acidic to support aquatic life in the lake, about 1,000 gallons of a second chemical, sodium aluminate, will be applied simultaneously to 'buffer' the alum, maintaining near-neutral pH in the lake. The addition of alum and sodium aluminate to the lake will pose little risk to humans, aquatic plants, and wildlife.

When the chemicals are added to the water, a flaky white solid 'floc' will form. Aluminum in the floc will chemically bind phosphorus dissolved in the water, and then sink to form a layer on the bottom that will limit internal phosphorus recycling from lake sediments. The treatment should result in dramatic improvements to the water quality and appearance of the lake.

The chemicals will be pumped from large temporary tanks in the parking lot to a boat with two tanks, one for each chemical. The boat will then traverse the lake pumping the alum and buffer into the water. The boat will need to refill its tanks 15-20 times to complete the treatment.

If the weather on Monday April 11 is too windy or rainy to do the treatment, the lake will be treated on Tuesday, April 12 (weather permitting).

Other facts:

• The lake is in King County's Lakewood Park: SW 112th St. and 10th Ave SW in the White Center neighborhood of unincorporated King County.
• Lake Hicks is also known as Lake Garrett
• The surface area of lake is approximately four acres
• Average depth of the lake is 3 meters (10 feet)
• Max depth is 5.5 meters (18 feet)
• Surface area, average and max depth vary with water level changes

For questions or more information about the planned alum treatment, contact Michael Murphy at the King County Department of Natural Resources and Parks: 206-296-8008 or michael.murphy@kingcounty.gov.