MITCHELL, S.D. (AP) — Coring samples taken from a South Dakota lake have revealed the volume of sediment laden with algae-producing phosphorus may be up to eight times what was earlier estimated.

The samples from Lake Mitchell that were taken in February have put the $7.2 million estimate for a lake cleanup project into question.

At a recent meeting the Mitchell City Council approved 7-1 to spend an additional $80,000 to refine the project's costs over eight weeks, The Daily Republic reported . Council members said they're reluctant to spend the planned $385,000 toward the phase one of the lake cleanup, especially given the added uncertainties.

Council member Mel Olson proposed spending the $80,000 to get a better cost estimate.

"To get some answers, we've got to spend some dough," Olson said.

Lake consultant Mike Sotak said he couldn't produce a better cost estimate without working through the results of the core samples. He said the sediment found "presents a challenge."

"I don't know what this means with the $7.2 million project," Sotak told council members.

Previous estimates said about 250,000 cubic yards of the lake would need to be dredged, but information from the February study shows the total is closer to 2 million cubic yards.

Sotak stressed that not all of the sediment may need to be dredged.

The depth of the material containing phosphorus varies widely around the lake. Deep areas could be capped with clay and neutralizing alum to reduce algae blooms.

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Information from: The Daily Republic, http://www.mitchellrepublic.com