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Scott G Winterton, Deseret News
Sediment buildup below Tibble Fork Dam is seen on Tuesday, Aug. 23, 2016.

SALT LAKE CITY — Last August's sediment release during the restoration of the Tibble Fork Dam is prompting Utah water quality regulators to seek more than $145,000 in penalties and reimbursement from the dam's operators.

About 5,200 fish died in a 2-mile stretch of the American Fork River in Utah County after 5,000 cubic yards of metals-laden mud washed into the waterway on Aug. 22.

Utah Division of Wildlife Resources employees Mike Slater and Stuart Bagley use electrification tools to identify fish mortality in the American Fork River below Tibble Fork Dam on Tuesday, Aug. 23, 2016. | Scott G Winterton, Deseret News

The dam and reservoir, operated by the North Utah County Water Conservancy District, serves downstream irrigators that include farmers and cities.

In a proposed settlement agreement signed Thursday, the water district agreed to pay $52,500 in penalties and nearly $93,000 in reimbursement to the Utah Division of Water Quality to cover sampling and monitoring costs incurred from Aug. 23 to Sept. 5.

The district also agreed to monitor the river until its health is restored to prerelease conditions.

"We want to ensure that the water quality of the American Fork River is restored and that residual sediments from the release don’t degrade the river or threaten public health or aquatic life in the future,” said Walt Baker, water quality director. “Most importantly, we want to make sure that this kind of incident doesn’t happen again.”

The settlement includes a requirement of monitoring in multiple locations along the river, as well as canals that serve farms and fields. The penalty is set under state law and determined based on impact to public health and the environment.

The water district was issued a notice of violation in late September for the sediment release, which was first reported by a member of Trout Unlimited who was fishing on the American Fork River.

The dam was in the midst of a $7.3 million restoration project in conjunction with the U.S. Department of Agriculture's Natural Resources Conservation Service when the release happened.

As the last of the water was being drained from the reservoir, inflows from a mountain stream cut through a chunk of ground and washed it downstream into the river. The metals that include lead and arsenic are waste from a legacy mining operation.

The American Fork River was shut down for weeks for public access and had notices posted for people to steer clear.

While there was concern the contaminants may pose hazards for downstream water users, state regulators say testing shows metal levels are below federal standards in drinking water wells tied to Tibble Fork, and the river is now safe for recreation.

Paul Burnett, director of Trout Unlimited's Utah Water and Habitat Program, said the organization remains concerned that the river is restored to ecological health.

"Our primary interest is ensuring that this settlement agreement reflects the full recovery of this valuable resource and that objective targets have been developed. Recovery may require more resources than have been identified in the draft settlement agreement,” Burnett said.

"Equally important as recovery is ensuring that events like the one last summer … do not happen again, neither here nor in other valuable rivers and streams,” he added. “Our waterways are more than a conduit for water. Thousands of people value what our rivers and streams bring to our communities."

Trout Unlimited's Brian Wimmer shows dead fish due to sediment in the water below Tibble Fork Dam on Tuesday, Aug. 23, 2016. He joined Utah Division of Wildlife Resources employees Mike Slater and Stuart Bagley (not pictured) in identifying fish mortality in the American Fork River below the dam. | Scott G Winterton, Deseret News

The settlement agreement is open to public comment over a 30-day period that begins Friday and runs through May 1.

Comments can be sent to Kevin Okleberry at kokleberry@utah.gov or P.O. Box 144870, Salt Lake City, UT 84114-4870.