Officials to launch investigation into Central City/Clear Creek superfund site

Traces of heavy metals near residential areas prompts further study

Andrew Fraieli
Posted 8/4/22

Investigations will soon begin into mine waste piles near residential areas within Clear Creek County and beyond to look for further evidence of heavy metals like lead and arsenic that may impact surface waters.

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Officials to launch investigation into Central City/Clear Creek superfund site

Traces of heavy metals near residential areas prompts further study


Investigations will soon begin looking into mine waste piles near residential areas within Clear Creek County and beyond to seek further evidence of heavy metals like lead and arsenic that may impact surface waters.

The Colorado Department of Public Health and the Environmental Protection Agency hosted multiple public meetings recently to answer questions pertaining to the investigation and elaborate on what the investigation and clean-up will look like.

The area being investigated consists of the entire Clear Creek watershed, about 400 square miles — including most of Clear Creek County, and parts of Gilpin and Jefferson counties —  and is called the Clear Creek/Central City Superfund Site. What prompted the investigation was the possible evidence of heavy metals in mine waste piles near residential areas in 2018 during a routine 5-year study of the site, according to CDPHE Remedial Project Manager Kyle Sandor.

The metals, mainly lead and arsenic, caused the CDPHE and EPA to label the superfund site as possibly “not protective of human health.” In other words, the metals “may pose an unacceptable risk,” said Superfund and Assessment Unit Leader Mary Boardman.

Previous work and investigations have been done by the CDPHE and EPA on mine waste piles within the superfund site, but the factors that determine “unacceptable risk” change as they gain a better understanding of the effects of lead and other heavy metals, and, compared to previous work, this investigation is specifically within residential areas.

“The work that we did for surface water, we largely think we’ve done that work, so during the last five year review period, we identified these residential mine waste piles as potentially needing further assessment,” said Sandor.

Over 500 mine waste piles near residential properties were identified, according to Sandor, and letters were sent to 143 property owners where homes were within 125 feet of those piles. They hope to get permission to access at least 100 different properties to draw top-soil samples and create a data set to guide the clean-up process.

Previous Superfund Work

According to the most recently available reports, the superfund site was created in 1983 due to impacts by historic mining activity in the area.

“Historic mining and milling activities resulted in the watershed becoming contaminated with heavy (trace) metals, significantly impacting aquatic life and potentially threatening human health,” the report said.

Multiple actions have already been taken by the CDPHE and EPA to address these issues, called “Operating Unit” sites.

“Just a way to divide an area of the site for investigation and eventual cleanup," Sandor said. 

There have been four already: OU1 in 1987 addressed mine discharges; OU2 in 1988 addressed waste piles and stormwater controls for mine tailings near those same mines; OU3 in 1991 was due to reassessments of the OU1 mines and resulted in further capping of waste piles and active treatment of mine discharges; and OU4 in 2004 was more capping and other clean-up actions of the North Fork of the Clear Creek subwatershed.

Investigation Steps

After the 2018 sampling showed signs of heavy metals, the superfund site was actually labeled "Current Human Exposure Not Under Control,” in September of 2021, according to the EPA.

Funds were then received from the EPA to hire a consultant and begin the investigation, according to Sandor. This consisted of analyzing aerial photography of the site, looking for potential mine waste piles by sparsity of vegetation and discoloration of material at the surface, among other factors, leading to the over 500 identified piles.

“The sample results confirmed our suspicion that there may be risk associated with those piles, but there was such a small data set that we couldn’t say for certain that the results were representative of the whole study area,” Sandor said, which is why the investigation was and is necessary.

The letters sent asking for access to properties for soil sampling did only go to owners of properties that have a mine waste pile within 125 feet of a residence though, not the residence itself. But, maps of the locations of piles, and a draft report are currently being worked on, said Sandor, and will be released publicly when completed.

Within this investigation stage, the CDPHE and the EPA will use analysis of samples to determine site specific clean-up goals, according to Sandor. 

“The goal is not to be following a federal lead standard, or arsenic standard, but to be able to come up with clean-up goals that are specific to the area and allow us to clean up to a level that is still protective of human health based on the data we collect, versus national input,” he said. “It will allow us more flexibility in our clean-ups while still ensuring we’re being protective.”

Following federal or state standards may require larger clean-ups, he continued.

Boardman elaborated that they may end up with even more stringent clean-up goals, it all depends on the data they collect.

The example Boardman gives is higher concentrations of heavy metal in a pile on a cliff, compared to a lower concentration pile near a school. The pile near a school will be cleaned first, with the cliff pile possibly not cleaned at all because few people may ever go there.

Tthe investigation is expected to be finished by the end of 2024 going into 2025, according to Sandor. After that, a proposed plan will be released by the EPA for public comment, before a “record of decision” is created which will “kind of memorialize the clean-up options and goals for this part of the site,” Sandor said.

The Clean-up

Actual clean-up is expected to start in late 2025, potentially early 2026, according to Sandor. He sees it as a mix of land-use control and physical cleanup, but it’s too early to tell what the “ultimate cleanup goals are.”

Elaborating on options, Sandor said there was removal, which would consist of fully removing the waste pile and bringing it to an external site such as the Church Placer Waste Rock Repository — created from a previous OU. Part of their work will be checking the capacity of that repository, with possible plans of expansion or further use outside its initial design, but he specified it was not a strong option for the areas being looked at.

Another option is capping, which consists of covering the pile with a material like dirt or asphalt and has been used extensively already. And a final option is land-use control — not allowing residences to be built within a certain area of the pile.

Long-term goals, according to Sandor, are working with local governments to have a “institutional control,” a notice or restriction, for home buyers that will inform them they may need to test for mine waste — depending on the area — and how to go about that. “This way, we don’t have to come back in 10 years and there’s another slew of people moved into houses near waste piles and we have to go through this process again,” he continued.

“If we could implement a land-use restriction that still protects human health, than that’s the ultimate goal,”  Boardman said.

They also are looking at interim plans that allow immediate action on piles that may affect young children and nursing mothers — people most at risk from these heavy metals — as they assess them.

The  Data Needed

Sandor and Boardman both acknowledge the worries of property owners over liability due to these mine waste piles, and the labeling of the area as a super fund site. Sandor elaborates that the superfund site’s original purpose was to look for impacts on surface water quality issues.

“One of the issues we have identified with the study area approach is that it casts a wide net, and some ambiguity as to what is part of the site and what isn’t,” he said. “Moving forward we intend on making it really clear what piles we’ve identified, if we consider it part of the site and if it may require restrictions in the future, or clean up work immediately.”

Boardman explains as well that this is the phase of the investigation to find the metal and give a “hard boundary” to those areas so to release others from the study area.

The best way for them to do that, she continued, is access to those people’s properties to get that data. The bigger the area, the more samples needed. More samples, higher quality data, and better assessments of what areas will need to stay within the study area.

Clear Creek, superfund site, mine tailings, water contamination, Central City, EPA, soil sampling


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