DENVER (AP) — Colorado, the U.S. government and a gold mining company have agreed to resolve a longstanding dispute over who’s responsible for continuing cleanup at a Superfund site that was established after a massive 2015 spill of hazardous mine waste that fouled rivers with a sickly yellow sheen in three states.

The proposed settlement announced Wednesday would direct $90 million to cleanup at the Bonita Peak Mining District Superfund site in southwest Colorado, according to the U.S. Environmental Protection Agency and Denver-based Sunnyside Gold Corp.

A U.S. District Court in New Mexico would approve the proposed settlement after a public comment period.

Sunnyside, which owns property in the district, and the EPA have been in a long-running battle over the cleanup. The EPA has targeted Sunnyside to help pay for the cleanup, and the company has resisted, launching multiple challenges to the size and management of the project.

An EPA-led contractor crew was doing excavation work at the entrance to the Gold King Mine, another site in the district, in August 2015 when it inadvertently breached a debris pile that was holding back wastewater inside the mine.

An estimated 3 million gallons (11 million liters) of wastewater poured out, carrying nearly 540 U.S. tons (490 metric tons) of metals, mostly iron and aluminum. Rivers in Colorado, New Mexico and Utah were polluted.