A U.S. appeals court said more information is needed before determining whether a company operating a Colorado gold mine illegally polluted a river by discharging wastewater into collection ponds that seeped into the ground and migrated to the nearby waterway.

A three-judge panel of the Denver-based 10th U.S. Circuit Court of Appeals reversed a lower court’s 2022 decision, which had found in favor of Colorado residents and local nonprofit groups. They had argued that under the federal Clean Water Act that High Mountain Mining needed a permit to discharge pollution like magnesium and potassium from its mine southwest of Denver into a tributary of the South Platte River.

The 10th Circuit said the mine's unlined ponds may well have caused the contamination alleged in the lawsuit, but the lower court should have considered more factors when determining whether the ponds were the "functional equivalent" of a direct pollution source under the Clean Water Act, which would require a permit.

Writing for the court, Circuit Judge Timothy Tymkovich said the decision is one of the first to address the appropriate application of the U.S. Supreme Court’s 2020 decision in County of Maui v. Hawaii Wildlife Fund, which established a legal framework to determine whether pollution that reaches waterways through groundwater is subject to regulation.

While the lower court considered important elements of the test outlined in that decision like the distance between the ponds and the river, the type of ground wastewater needed to travel through and the amount of time it would take for water to make the journey, Tymkovich said it should have analyzed other factors as well. Looking at other factors like how much the pollution is diluted or changed before it reaches the river is important given the complex typography surrounding the mine, he said, and thousands of other active mines in the region might face similar claims.

The decision reversed a $500,000 penalty for violating the Clean Water Act and sent the case back to the lower court.

An attorney for the Colorado residents and local nonprofit groups, which sued in 2019, said no other court has asked for such an exhaustive review but that they hope the lower court will give them an opportunity to address other factors the 10th Circuit said should have been addressed.
Representatives for High Mountain did not immediately respond to a request for comment. The company had argued the plaintiffs had not provided sufficient evidence that pollution from its ponds entered the river.

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