A diagram portraying how the potential oxygenation system works during the May 20 Blackman Lake cyanobacteria meeting.
Photo by Michael Whitney.
SNOHOMISH — To alleviate the algae issues at Blackman Lake, consulting scientists are pitching the city either apply treatments to the lake or install an underwater system that pipes in oxygen.
The lakebed is releasing phosphorous from its deep sediment. It’s contributing to an overabundance of nutrients in the water.
The nutrient-rich imbalance creates lake conditions in which toxic blue-green algae thrives, and oxygen for fish gets suppressed and depleted.
Both suggestions tackle the imbalance. Treatments cap down the phosphorus. Oxygenation would prevent any stagnation.
The oxygenation system has a $350,000 upfront cost, but little else than routine maintenance and electrical power annually each year after, as long as the machine doesn’t get damaged.
A long series of treatments over 20 years would cost $700,000 to do two treatments a year, or $1.4 million to do four treatments a year, from numbers presented by consultant Rob Zisette.
About 15 people attended a Blackman Lake cynaobacteria plan presentation May 20, including Mayor Linda Redmon.
Redmon said installing the oxygenation system is her preference, from her initial reaction, because long-term it would cost less and be an alternative to putting chemicals in the lake.
“It’s worth a look,” Redmon said to the Tribune, but she’d have to see if it’s feasible.
Snohomish has used new technologies before, Redmon said, pointing to the biofilter “bacteria hotels” installed at its wastewater plant about 14 years ago. The biofilters worked to get Snohomish back into regulatory compliance about preventing sewage discharge overruns into the Snohomish River.
The city could put a treatment into the lake as soon as this fall, Zisette said, as the basic permits are easy to get.
Treatments are the usual route. Somebody drops them into the lake from a boat. Area lakes such as Lake Stevens were cleared up this way.
Setting up an oxygenation system could take a year or more.
The oxygenation system is capable of not getting clogged with the lakebed sediment it’s stirring up, he said. The oxygenation also will decompose sediment faster because of aerobics.
Zisette suggested funding conduits for these projects. These could be establishing a lake management taxing district, usually from nearby lakeside owners; using money in the city stormwater budget that’s funded through utility taxes; obtaining government grants; pinging state Legislators for dollars; or setting a special purpose tax district for the lake.
Zisette’s team plans to finish up the plan next month and take public comments to mid-June. The final recommendation plan should be delivered to council by July.
In the presentation, Zisette suggested the city takes the route of oxygenation.
Nearby residents collected a year’s worth of water samples from the lake for testing. The program also collected from stormwater entering the lake.
It aided scientists to conclude the lakebed’s the primary source of phosphorus.
In summertime, there’s a swell of pollution from waterfowl. Some 20% of the phosphorus comes from them at its peak.
Few amounts of phosphorus is coming from the creek, the stormwater system or seeping in through the watershed, summer results saw.
Water predominantly goes out of the lake through Swifty Creek.
The draft report and slides are on the city’s Blackman Lake web page within www.snohomishwa.gov.
Identify toxic algae
• Cyanobacteria, called “blue-green algae,” often looks like a mat of paint on the water.
• Cyanobacteria is a liver toxin, eye irritant and skin irritant.
