WASHINGTON — The head of the Environmental Protection Agency was remorseful Tuesday after an EPA safety team accidentally caused 3 million gallons of wastewater to spill from an abandoned mine in Colorado, turning a major waterway a bilious yellow hue.

“This is a tragic and unfortunate incident, and EPA is taking responsibility to ensure that it is cleaned up,” said EPA Administrator Gina McCarthy. “The most important thing throughout this is ensuring the health and safety of the residents and visitors near the river. “

“EPA is an agency whose core mission is ensuring a clean environment and protecting public health, so it pains me to see this happening,” she continued. 

The Aug. 5 spill released lead, arsenic, cadmium and other dangerous contaminants from the former Gold King Mine site into a creek that flows into the Animas River. That river flows into the San Juan River and down through New Mexico, raising concerns about downstream pollution.

The EPA was at the site investigating ongoing water releases from mines in the area and assessing whether it could take additional remediation measures. The agency said the team at the site misjudged the pressure that had built up at the entrance of the mine.

The Gold King Mine has been out of use since 1923, and is one of thousands of abandoned mine sites across the country. There are 22,000 abandoned sites in Colorado alone, local NPR affiliate KUNC reported. For many of these mines, the previous owners are long gone, leaving the EPA on the hook for cleanup and spill prevention.

Someone at the agency clearly screwed up here, which has led to lots of public outcry in the region targeted at the EPA, and to the administrator’s contrition Tuesday. But as others have pointed out, there are various reasons cleanup at this and other sites has been complicated.

As the Durango Herald has reported, the EPA wanted to declare abandoned mines around the region a Superfund site, which would increase the amount of funds available for cleanup. But residents and government officials in the area pushed back because they were worried about the impact a Superfund declaration would have on tourism.

EPA and local officials recently reached an agreement that the agency would work on cleaning up the ongoing pollution from the mines without declaring a Superfund site, which is what prompted the work that led to last week’s accident. McCarthy said Tuesday that the incident occurred “when one of our contracting teams was using heavy equipment to enter the Gold King Mine … to begin the process of pumping and treating the contaminated water inside.” 

The Denver Post has also reported on another issue that has hindered cleanup at mine sites in the state: concerns about liability in the event of an accident. Because of the current interpretation of the Clean Water Act, environmental groups and state governments have feared taking on cleanup because they could be held liable for costs if something goes wrong. The EPA moved to reduce the legal liability in 2012, and Colorado’s congressional delegation has sought to amend the Clean Water Act to make it easier for third-party “Good Samaritans” to help with cleanup. But those legislative efforts have not been successful so far.

McCarthy plans to travel to Colorado and New Mexico on Wednesday to inspect response efforts, where she’ll likely get an earful from residents.