Colorado health scientists have opposed a global mining giant’s push to raise by 43 times the statewide limit for molybdenum pollution of streams, revealing that discharges from the open-pit Climax Mine already may pose public health risks to Summit County communities.
The Colorado Department of Public Health and Environment water-quality scientists said, in a recommendation to state commissioners, that Climax Molybdenum’s proposed hike “would be acutely lethal to aquatic life” and probably not protective of people.
A Climax report on molybdenum exposures in Colorado “demonstrates that current levels of molybdenum in drinking water may pose a public health risk to communities downstream” of the mine, CDPHE scientists said in filings reviewed by The Denver Post.
State data show molybdenum discharges from the Climax Mine above Leadville in recent years increased to levels 10 times higher than the current statewide limit of 210 parts per billion. CDPHE water-quality control commissioners granted Climax a “temporary modification.” When it expired, the commissioners extended the modification to provide more time to complete a study of molybdenum.
CDPHE officials Tuesday declined to discuss this issue.
Federal Environmental Protection Agency officials, who oversee Colorado’s compliance with the Clean Water Act, informed state commissioners last week that the EPA would allow a limit higher than what Climax Molybdenum is proposing, according to a document filed Friday.
A regional EPA spokesman issued a prepared statement saying the EPA’s filing is “preliminary,” confirming that “our initial review indicates that the proposed standard would protect water supply uses,” but declined to further discuss this issue
State commissioners often follow EPA guidance in setting pollution limits sufficient to protect people while accounting for variability and uncertainty.
A subsidiary of the $46 billion mining company Freeport-McMoRan, Climax Molybdenum runs the Climax Mine, located above Leadville, which discharges wastewater into Tenmile Creek, headwaters in the Colorado River Basin that flow into Denver Water’s Dillon reservoir, the main drinking water supply for 1.4 million Denver residents.
Climax officials cited three rat studies the company helped fund in asking CDPHE to relax the statewide water quality limit for molybdenum in streams used for domestic water to 9,000 ppb billion from 210 ppb. Climax also wants limits for waterways used for agricultural irrigation raised to 1,000 ppb from 160 ppb.
EPA recommendations submitted to the CDPHE said a molybdenum limit for streams tapped for drinking water of 10,000 ppb “would be protective … and consistent with Clean Water Act requirements.” However, EPA regional officials said in the document filed Friday that they would not object if Colorado’s commission “chooses to be more conservative and adopts a more stringent table value standard of 9,000 ug/L (ppb) as proposed by Climax Molybdenum Company.”
The EPA “must review and act upon any revised standards once they are adopted by the commission for them to be in effect under the Clean Water Act,” the agency’s statement said. “If the commission chooses to retain current standards, EPA will not have an approval or disapproval role.”
The relaxed pollution limits could reduce water-treatment costs at the Climax Mine. Climax Molybdenum also runs the Henderson Mine near Empire and a mill in Grand County.
Previously, when Colorado water-quality control set the agriculture limit at 300 ppb, EPA officials favored a more cautious approach, prompting state officials to tighten the limit to 160 ppb.
The CDPHE scientists submitted their recommendation Friday to state commissioners, who are scheduled to deal with the matter in December.
Denver Water is opposing the push for a looser statewide limit, along with downstream communities including Frisco, the Copper Mountain resort and people to the west along the Eagle River.
“We want to make sure the commission sets a standard that is protective of human health,” said Boulder-based attorney Steve Bushong, a former aquatic scientist who represents a coalition of downstream communities. “Tenmile Creek and the Eagle River are used for public drinking water supplies. Therein lies the concern. This standard needs to be right. It needs to be adequately conservative.
“The appropriate water supply standard is important because existing concentrations of molybdenum in Tenmile Creek and at Copper Mountain at times are more than 10 times higher than the current molybdenum standard.”
Denver Water treatment plants lack the capacity to remove molybdenum, which in trace amounts can be healthy. While data on human toxicity is limited, chronic ingestion of molybdenum can cause diarrhea, stunted growth, infertility, low birth weights and gout, and can also affect the lungs, kidneys and liver.
Climax officials have told state water quality commissioners their proposal “is not based on any intent or need to increase molybdenum in Climax discharges, and, in particular, Climax does not intend to change its mining or water treatment process in a manner that would cause an increase in the historical discharge of molybdenum into Tenmile Creek.”
The Climax Mine above Leadville opened in 1918 and closed in 1987. Freeport-McMoRan reopened it in 2012. It employs 355 workers.
