Weighing the impact of the Gold King Mine spill – and hundreds of inactive mines like it

By Ronald R. H. Cohen
Colorado School of Mines

Earlier this month, contractors for the Environmental Protection Agency (EPA) trying to characterize the quantity and quality of water from the Gold King Mine in Colorado accidentally disturbed a blockage retaining water in the abandoned mine. The breach led to the release of about three million gallons of water contaminated with acidity, metals and other pollutants into the Animas River.

Since then, the EPA has released an analysis of the water quality and bottom sediments during and after the mine spill plume passed through locations in Colorado. In addition, I have located and perused some data for the Animas River before the spill. The EPA also released Task Orders and Statements of Work for the Gold King Mine from 2013 to 2015.

All of these documents permit us to create a picture of the activities taking place when the spill occurred and its impact. They provide a glimpse into the extent of ongoing toxic discharges from abandoned mines and hint at the scale of the challenge in containing contaminated water from hundreds or even thousands of mines similar to the Gold King Mine.

Impact of the Gold King spill

First, to put the spill quantity in perspective, the overall contaminated water discharge of abandoned mines in Colorado is estimated to equal at least one Gold King disaster every two days.

There are at least 230 inactive mines in Colorado spilling thousands of gallons per minute into local waterways, according to state officials. The EPA has estimated that 40% of river headwaters in the West are impaired by acid mine drainage flowing from metal mines.

In Colorado, state health officials determined on August 20 that discharges from the 230 old mines have contaminated 1,645 miles of rivers and streams.

The EPA, meanwhile, bypassed its typically long quality assurance/quality control approval processes to reveal some analyses of the water column on August 9, just a few days after the spill.

The data suggest that the Animas River water was back to pre-spill levels of the toxic metals. Notice that I say “pre-spill” levels and not natural background levels. The Animas River has been receiving effluent from the abandoned and inactive mines for more than 100 years. The metal levels are elevated above natural background even without the Gold King spill.

Heavy metals flow through it

It should be noted that the data were reported as dissolved metals and total metals. Dissolved metals are molecules that have dissolved within water, much the way salt does. Total metals also include metals attached to the fine, solid particles – similar to soil and “mud” particles.

The toxic metals that are a threat to human drinking water are the dissolved metals and are the ones I refer to when comparing with pre-spill concentrations. The metals attached to the particles are an immediate threat to humans only if the water is acidic, as acidic water could dissolve some of the metals on the solid particles. The solid-bound metals could be a long-term threat to the aquatic ecosystem if present in large enough quantities and long enough to pass through the food web.

Water monitoring on the Animas River near Durango, Colorado on August 14 2015. | Eric Vance/EPA

Immediately after the spill, people were correctly concerned about the solid particles – that is, suspended solids that haven’t dissolved in water – from the spill settling onto the bed of the Animas River. What do the data indicate?

The EPA took some preliminary samples of the spill material on the bed of the Animas. There are different ways to classify the potential toxicity of metals on solids. ERL (Effect Range Low) values are the lowest concentration of a metal that produce adverse effects in 10% of the studies reporting harmful effects. ERM (Effect Range Medium) designates the level at which half of the studies reported harmful effects.

Metal levels on the sediment samples taken after the plume of the spill passed Durango, Colorado were above the ERL levels and at or only slightly above ERM. Interestingly, those metal levels were lower than those found in the Animas River upstream of the spill at a site not affected by the spill.

In other words, there was no elevated threat above pre-spill levels. That suggests to me that the contamination in the bed of the Animas due to the spill was not as bad as feared, or at the very least, the spill did not significantly worsen water quality compared to the ongoing pollution from abandoned mines.

It also supports the prediction immediately after the spill that the impact was transitory and the river would return to “normal” after the spill plume passed by. High water during spring snowmelt should scour, suspend, dilute and wash any residual spill sediment on the bed downstream.

Earlier concerns of a blow-out

Headlines appeared nationally that the EPA had known that there was a potential for a spill, implying that the EPA was incompetent in addressing the threat and causing the spill.

However, a look at available documents suggests that the private contractor was there to install facilities to address just that issue. They were to install a conveyance (pipe) to draw off water to minimize the risk of a blowout or spill while characterizing the magnitude of the water behind the blockages. From the Action/Work Plan of May 2015:

It is proposed to re-open the Gold King Mine portal and workings to investigate the conditions to assess the on-going releases. This will require the incremental de-watering and removal of such blockages to prevent blowouts. The work is intended to take place in late Summer or Fall, 2015. In addition, the secondary purpose of the work is to attempt to identify and characterize specific water flows into the mine and evaluate potential means to mitigate those flows if possible.

This reflects the EPA’s concern from 2014:

The Gold King Mine has not had maintenance of the mine working since 1991, and the workings have been inaccessible since 1995 when the mine portal collapsed. This condition has likely caused impounding of water behind the collapse. In addition, other collapses within the workings may have occurred creating additional water impounding conditions. Conditions may exist that could result in a blow-out of the blockages and cause a release of large volumes of contaminated mine waters and sediment from inside the mine, which contain concentrated heavy metals.

Thus, the EPA contractors were there to attempt to understand just how large the problem was. As they began their operations, the blowout and spill occurred. The water impounded behind the blockages far exceeded expectations.

Given the lack of adequate documentation of the underground workings and amount of discharge of water into the mine, estimation of just how much volume is there is guesswork. This guess didn’t work.

Whenever there is a human endeavor, there is risk: risk of failure or accident. Gold King Mine is a prime example.


Ronald R. H. Cohen is Associate Professor of Civil and Environmental Engineering at Colorado School of Mines

This article was originally published on The Conversation.

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