Kent city officials hope an upgrade to the aerator system at Lake Fenwick helps improve water quality. COURTESY PHOTO, City of Kent

Kent city officials hope an upgrade to the aerator system at Lake Fenwick helps improve water quality. COURTESY PHOTO, City of Kent

Aerator system retrofit to improve Lake Fenwick water quality in Kent

City upgrade to cost about $900,000

A retrofit of an aerator system is expected to improve water quality at Kent’s Lake Fenwick, where twice in October the toxin levels were above the State Department of Health recommended guidance thresholds.

The Kent City Council in December approved acceptance of a $189,789 grant from the King County Flood Control District to help pay for the upgrade to the aerator system, first installed in 1994 to help isolate the phosphorus and reduce the potential for harmful algal blooms in the lake.

The cost of the entire project is estimated at about $900,000, city environmental specialist Meara Heubach told the council at its Dec. 3 Committee of the Whole meeting. City staff also is seeking a $200,000 grant from the county. The aerator system pipes oxygen to the middle of Lake Fenwick, 25828 Lake Fenwick Road.

“The grant we got is one piece of the puzzle,” Heubach said. “With funds already received, including this, and if we get the other grant, it will still leave $231,000 that we expect to get from city drainage funds.”

Kent gets monies from the Flood Control District, funded by property taxes, as part of its Sub-Regional Opportunity Fund, of which 10 percent of the levy collected within each jurisdiction is granted back to the city to be used for stormwater or habitat projects.

Excess phosphorus in the lake comes from stormwater inputs from the surrounding Lake Fenwick watershed that lead to the toxic algal blooms that have regularly occurred over the last few years, according to city documents.

Lake Fenwick is a 303d waterbody, which is the state Department of Ecology’s list of impaired waterbodies because of its phosphorus pollution.

Councilmember Les Thomas asked Heubach if fertilizer used by property owners in the area causes the problem.

“Fertilizers from lawns washes down into lake and has phosphorus,” Heubach said. “There are other factors, but the main factor is pollution from the neighboring areas.”

The improved aerator system is expected to make a difference.

“Oxygen has helped, but it’s never been enough to eliminate a problem level of phosphorus, so we will retrofit the aerator and upgrade equipment,” Heubach said.

Crews are expected to start the repairs this year. The city hired a consultant in 2010 to analyze the aerator system and it was determined that the amount of phosphorus pollution in the lake exceeds the aerator’s capacity, according to city documents. Some existing infrastructure at the lake remains in good condition, so city staff determined it would do a complete retrofit of the existing system rather than a complete rebuild.

Thomas asked whether the studies indicated that the retrofit will solve the problem or just help a little.

“We monitor lake and studies in 2010 suggest this will go far to solve the problem,” Heubach said. “Another step would be aluminum treatments into the lake to also help the aerator, but aluminum is expensive now. That could be part of the solution, but right now we will focus on the aerator.”

The state Department of Health in October said people should not swim, consume lake water or engage in other water-contact activities at Lake Fenwick due to unsafe levels of algal toxin microcystin. Warning signs were posted.

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