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Rocky Mountain Power has agreed to pay just more than $15,000 in penalties to the state Division of Water Quality to resolve last summer's release of coal ash into the Price River.

According to the proposed settlement, which is pending approval by the Division of Water Quality while the state collects public comment, Rocky Mountain Power agreed to pay a $13,000 penalty for the spill, and will also reimburse the state for just over $2,000 in administrative expenses accrued while responding to the incident.

The utility has also agreed to conduct a follow-up environmental assessment of the long-term impact of the coal ash on the health of the Price River. An estimated 2,370 cubic yards of coal ash — laden with 13.9 pounds of arsenic and 35.9 pounds of lead — washed into the Price River on Aug. 4 during a flash flood. Samples taken downstream following the flood contained elevated levels of iron and aluminum.

Paul Murphy, a spokesman for Rocky Mountain Power, said the utility is taking responsibility for the spill and is committed to monitoring the river and taking corrective action if necessary.

"We are responsible for it," he said, "and we will continue to work with the Department of Environmental Quality and with local residents to make sure everything is right."

Walt Baker, director of the Utah Division of Water Quality, said he believed the "modest" penalty is fair, given that the state does not believe the spill will result in any long-term environmental damage and that it appears to have been the result of factors outside the utility's control.

Baker said the state believes that the flash flood was the result of an unexpectedly large storm event. "Sometimes Mother Nature throws a curve ball," he said, "and it certainly did in this regard."

Brian McInerney, a hydrologist with the National Weather Service, said the Price area did appear to have flash flooding that day, but it was not clear just how severe it was. This particular landfill is in a blind spot not visible to National Service Radar.

An engineering consultant hired by Rocky Mountain Power estimated that the storm produced 2 inches of precipitation between 2-4 p.m., which would qualify as a 100- to 400-year event. A 100-year event is when the storm is so large that, statistically, it is expected to happen only once in 100 years.

The flooding washed debris into a temporary stormwater collection system that had been put into place while the landfill was under construction. The debris clogged up the collection system, which had been built to withstand a 50-year storm event, and allowed floodwater to wash directly through the landfill, cutting a 550-foot-long gully in the coal ash pile, according to the settlement agreement.

While anything over an inch of rain per hour is capable of producing a flash flood, McInerney said that rate of rain isn't unusual during the late summer in the Price area. In order to produce an abnormally large flash flood, he said, Price would need to get more than 2 inches of rain per hour.

Baker said the state did not attempt to independently verify Rocky Mountain Power's reports of abnormally intense rainfall.

"That's not rocket science, and we'd be able to do that," he said, "but we're not sure that is consequential relative to the settlement of this."

Baker said the "jury is still out" on whether the spill could have been averted had Rocky Mountain Power had different stormwater controls in place.

The landfill's stormwater collection system is being modified to accommodate larger storms, according to the settlement agreement. The state will collect public comments until Jan. 20. Comments should be emailed to kokleberry@utah.gov or mailed to the Department of Environmental Quality, Division of Water Quality, 195 North 1950 West, P.O. Box 144870, Salt Lake City, Utah 84114-4870.