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Improperly mixed chemicals culprit in fish deaths

By John Larson

Tacoma Weekly
jlarson@tacomaweekly.com
Published on: August 14, 2008

Chemicals applied to Wapato Lake last month in an effort to eliminate algae were improperly mixed, which led to dead fish floating in the water in the days after the treatment on July 25. Rob Plotnikoff, a scientist with water monitoring firm Tetra Tech, provided information to Metro Parks Commission during their Aug. 11 meeting.

Workers from TeeMark of Aitkin, Minn., applied the chemicals, which were transported to the lake in tanker trucks. Two chemicals were used. The active ingredient is alum, an acid, and the other, sodium aluminate, serves as a buffer to balance the pH of the water.

The solution had 7 percent more alum than what the specifications called for, while the sodium aluminate was under-applied by 4.9 percent of the specified amount.

The situation is being monitored by the state Department of Ecology and Department of Fish and Wildlife, as well as Tacoma/Pierce County Health Department.

Steve Knauer, director of parks and building services for Metro Parks, also spoke to the commissioners.

On Aug. 12 a crew removed debris from the bottom of the lake, much of it items that were not visible before the chemical treatment made the water substantially clearer.

The clearer water has attracted more geese that now have a better view of potential food in the lake. Geese have been an ongoing problem in local parks because of the large amount of droppings they produce. “We obviously want to get a hurdle on that soon,” Knauer remarked.

Testing of the lake Aug. 11 revealed pH levels were between 4.80 and 4.88. The level has increased .5 percent from two weeks ago, according to Plotnikoff. The target is six. To reach this, Plotnikoff advised adding sodium bicarbonate, the active ingredient in Tums and similar medications. He described it as “a very benign” substance that offers the safest and fastest way to balance the pH.

He advised purchasing one ton of the substance, as purchasing it by the ton carries a cost reduction for buying in bulk quantities. This would be around $1 a pound, according to Plotnikoff. He envisions a two-part process that would put 1,200 pounds into the lake, with another 800 pounds available if needed.

One citizen, Curt Mehlhaff, addressed the council. “This looks like a chemistry experiment gone terribly awry,” he said.

Mehlhaff urged the commissioners not to heed Plotnikoff’s advise, as it could be the equivalent of dumping a ton of salt into the lake.

“This has potential pitfalls and more embarrassment written all over it.”

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