Results of Expanded Adit Sampling at Gold King Mine

EPA routinely samples water at the adit (entrance portal) of the Gold King Mine for metals, as they are the expected contaminants related to the Aug. 5 release.

At the request of La Plata County, Colorado, EPA collected water and sediment samples at the mine entrance to test for an expanded suite of potential contaminants. These contaminants include volatile and semivolatile organic compounds, polychlorinated biphenyls (PCBs), dioxins, radiological components and additional types of metals.

The levels of nearly all these potential contaminants were below residential and recreational levels. The total metals analysis of surface water found cadmium, cobalt, copper and manganese above risk-based screening levels for recreational use. However, the levels of metals found in surface water at the mouth of a hard-rock mine would not be considered unusual considering the highly mineralized geology of this location. Additionally, there is no recreational use of the water at this location and very little human exposure.

A review of all results is provided here for both surface water and sediment sampling. The data files are below.

Note: It should be noted that some of these results were compared to residential risk-based screening criteria. A comparison of detections in surface water or sediment in an isolated mining area to soil or drinking water criteria for residential exposures is not EPA practice or policy. Such comparisons are not appropriate because such uses are not made of water flowing directly from a mine adit. However, this comparison was conducted in this instance to demonstrate the very low risk associated with these detections.

Surface Water:

The surface water sample from the Gold King Mine adit was analyzed for volatile and semivolatile organic compounds, polychlorinated biphenyls (PCBs), dioxins, metals, and radiological components.

The levels of organic compounds detected in the surface water samples do not pose a human health risk.

No volatile and semivolatile organic compounds or PCBs were detected in the surface water sample.

All detections of dioxins in surface water were at levels below the reporting limit for the analysis and, therefore, reported as estimated amounts.

The total metals analysis of surface water found cadmium, cobalt, copper and manganese above risk-based screening levels for recreational use. However, the levels of metals found in surface water at the mouth of a hard-rock mine would not be considered unusual considering the highly mineralized geology of this location. Additionally, there is no recreational use of the water at this location and very little human exposure.

Radiological components in surface water were also measured. Radium, thorium and uranium were either not detected, detected below reporting limits or detected at very low levels; uranium was also below a risk-based screening level for residential exposures.

Sediments:

The sediment sample was analyzed for volatile and semivolatile organic compounds, PCBs, dioxins, metals and radiological components.

The levels of organic compounds detected in the sediment samples do not pose a human health risk. Of the volatile and semivolatile compounds analyzed, only acetone and 3- and 4-methylphenol were detected in the sediment sample. In both cases, the detections were below reporting limits for the analyses and, therefore, reported as estimated.

Dioxins are byproducts of incomplete combustion of chemical compounds, volcanic action and forest fires. Therefore, they are found throughout the environment, including isolated forested areas. The very low detections of dioxins were below residential soil screening levels.

All metals found in the sediment were below risk-based screening criteria for recreational use.

La Plata County Analysis:

Two sets of samples were obtained on Sept. 21, 2015, one of which was provided to La Plata County for analysis. The analysis of La Plata County’s samples can be found at http://www.co.laplata.co.us/i_want_to/gold_king_mine_information Exit Because different laboratories with different protocols were used by EPA and La Plata County to analyze the two separate samples, there may be a difference in the associated results. Such variations are to be expected and do not reflect an error in data collection or analysis.

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