Hardrock metal mining is a large-scale industrial activity that disturbs large areas of land and generates large volumes of solid waste. Unlike other industries the location of a mine is dictated by the location of the ore body. Many ore bodies and mines are located on public land administered by the US Forest Service (USFS) and the US Bureau of Land Management (BLM). In the western United States extensive precious and heavy metal mining started in the 1880s and, for the next 70 to 80 years, was a major industry in many states, including Colorado. At that time hardrock mining utilized some of the most advance technology and engineering of any major industry in the world. However, environmental controls were very limited or non-existent and, as a result, transport of acidic water with high concentrations of dissolved and suspended metals and from abandoned mines is currently causing serious environmental damage.
The BLM has estimated that there may be as many as 30,000 abandoned mines on BLM managed land that need assessment and approximately 2800 are known to have an environmental impact. The Forest Service has estimated that there may be 27,000 -39,000 abandoned mines on lands managed by the USFS and that approximately 20% pose an environmental risk. The Environmental Protection Agency (EPA) has calculated that 40 percent of river headwaters in the West are impaired by acid mine drainage. Nationwide more than 75 mine sites have been designated as Superfund sites. Ownership of abandoned mines on public and private lands is often difficult or impossible to establish for hardrock mines that stopped operating in the 1920s – 1940s. There is no state or federal program or dedicated funding for systematically inspecting abandoned mines and, as a result, adequate inventories and preliminary assessments of legacy hardrock mine have not been completed.
Mining districts are often large (watershed scale), and occur in complex geologic and hydrologic settings and often include many individual mines. The most problematic legacy mine sites are districts where vein / replacement deposits were mined by underground methods. Underground mines typically need to be dewatered to expose the ore body for mining. Prior to the federal Clean Water Act (CWA) water pumped or drained from operating underground mines was discharged directly to streams and rivers – often with inadequate or no treatment. Water management is an even more difficult problem at abandoned mine sites where contaminated mine water discharges from underground workings. Groundwater flowing into and out of abandoned underground workings flows through mineralized rock and becomes contaminated with dissolved and suspended metals (primarily cadmium, copper, lead, arsenic, manganese, zinc). Where ore bodies contain significant sulfide minerals, oxidation of these minerals produces acid. Metals and acid are then transported from major mine-related sources via: surface runoff, groundwater flow and stream flow. Fish and other aquatic life in streams and adjacent riparian zones are particularly vulnerable to high concentrations of metals. Contaminated drainage from these mines can discharge to rivers above intakes for public water supply systems resulting in exceedance of SDWA MCLs.
The Problem in CO
Within Colorado there are more than 20,000 abandoned mines. The US EPA estimates that approximately 230 of these mines are draining into the headwaters of the state’s rivers and contaminating more than 1300 miles of rivers and streams. These mines are concentrated along the Colorado Mineral belt (Fig. 1) and include the districts around Silverton, Ouray, Lake City, Leadville, Buena Vista, Montezuma, Central City and Boulder / Gold Hill. Discharge from mines in these districts impact sections of the Animas, Uncompahgre, Gunnison, Eagle, Arkansas, Big Thompson and South Platte Rivers. Ten Colorado mining sites have been listed, with the concurrence of the State of Colorado, as SUPERFUND sites under EPA CERCLA authorities (Table 1).
Table 1 – Superfund mine sites in Colorado
California Gulch – Leadville
Smuggler Mine – Aspen
Bonita Peak –Silverton
Captain Jack Mine –Ward
Nelson Tunnel – Creede
Central City / Clear Creek mining district
Uravan – uranium
Denero Tunnel – Leadville
Pennsylvania Mine – Peru Cr.
Rico –St. Louis Tunnel
There are two main issues related to abandoned mines – safety and remediation of environmental impacts. Safety work involves closing off access to keep people and animals from entering abandoned mines. In Colorado the Inactive Mine Program, within the Colorado Division of Reclamation, Mining and Safety (DRMS), with a staff of about 20 people, is focused primarily on mine safety work. DRMS receives approximately 2 million dollars per year from the Federal Office of Surface Mining to fund mine safety work. Safety issues have been addressed at over 6000 mines in Colorado.
Remediation at abandoned mines that are discharging contaminated mine water is a more difficult and expensive problem. Depending on site hydrology and the nature and extent of the underground workings, environmental remediation and closure involves either permanent water treatment or use of hydraulic controls to manage mine waters. Discharge rates from Colorado’s abandoned mines vary significantly – from a few gallons per minute (gpm) to more than 1000 gpm. Cumulative discharge from the 230 draining mines in Colorado probably exceeds 7000 gpm (10,000,000 gallons per day). State agencies don’t monitor combined flow. Many of these mines have been discharging contaminated water for 80-100 years. It is difficult to estimate the metals loading to streams and rivers from these discharges but it is likely tens of millions of tons per year. Mine remediation work is constrained because there are no dedicated funds for remedial work at abandoned mines. DRMS participation is limited to providing technical support to remedial projects managed by the USFS, BLM or EPA. In 2014, state mining officials spent $1.5 million on six mine cleanup projects — down from $4.5 million in 2013 based on diminished funding from federal agencies. In total, approximately $12.3 million was spent on mine reclamation work in Colorado between 2009 and 2014.
Gold King Mine
In August 2015 an EPA contractor, while attempting to stabilize the portal area at the Gold King mine in the Cement Creek watershed above Silverton, CO, accidently caused the release of approximately 3 million gallons of water stored in the underground workings. The release occurred over a 9 hour period. The total amount of metals entering the Animas River as a result of the release was estimated to be 540 tons–mainly iron and aluminum. An estimated 99 % of this metals load was derived from abandoned mine waste piles located outside the Gold King Mine. As a result, 97% of the metals load associated with the release was suspended material –not dissolved in the water. Approximately 90% of the total load settled out in the Animus River bed sediments downstream of the confluence with Cement Creek. The total metals load associated with the release was comparable to the amount of metals carried by the river in one to two days of high spring runoff. However, the concentration of metals during the peak of the plume passage was much higher than historic spring runoff conditions.
It is very important to put the Gold King Mine release in the context of the environmental degradation from abandoned mines in the upper part of the Animas River watershed. There are hundreds of abandoned mines in the upper Animas River watershed and dozens of mines in upper Cement Creek watershed. Significant metal loading to the Animas River and its upper tributaries has been ongoing for decades. The Cement Creek watershed, a tributary to the Animus River, is eroded into large exposed ore bodies and has never had significant fish or riparian life due to natural conditions. The August 2015 release of a slug (plume) of mine water from the Gold King mine was not an environmental disaster. The volume of the Gold King release was equivalent to four to seven days of the ongoing discharge from the mine. Sampling conducted after the release has indicated clearly that dissolved metals concentrations had decreased to pre-release levels by the time the plume reached the San Juan River. In the upper Animus River metals concentrations decreased to pre-release levels a few weeks after the release and stayed at pre-release levels over the winter of 2015-2016. Subsequent monitoring data has not indicated any significant impact to aquatic life in the Animus River. State and tribal water quality standards were exceeded only occasionally during the nine months after the release. This condition has been a common occurrence in the watershed for decades.
Funding and Legislation
Assessment, prioritization and environmental remediation at abandoned mine sites has been constrained by outdated laws and regulations that are ambiguous or incompatible regarding liability and compliance with environmental law. As a result there has been a chronic lack of funding to address the problem. Characterization, risk assessment and remediation / restoration at large legacy mine sites are very expensive and typically take 10 years or longer. Unlike coal mining and oil and gas production, hard-rock mining companies have historically not been required to pay royalties or other fees to address the cost of abandoned mines. The 1872 mining law, which, amazingly is still in effect, gives discoverers the right to stake mining claims to extract precious and heavy metal deposits from public lands. The law applies to all public domain lands unless withdrawn or set aside for specific use (about 270 million acres). No federal royalty has been required and there are no environmental reclamation or remediation requirements in the law. The provisions of this law are clearly in conflict with the Clean Water Act. In 2009 reform legislation was introduced in both the US Senate and House of Representatives. The proposed law would require royalty payments by mining operations on public lands with the potential to raise $100 million per year. The Congress has taken no action on this legislation.
None of the Federal agencies most involved in mine cleanups (EPA, USFS and BLM) have dedicated programs or funding for abandoned mine characterization and cleanup. The Federal Bureau of Mines, which employed highly trained mining engineers and hydrologists, was abolished in 1996. As stated above more than 75 mine sites have been designated as Superfund sites across the nation. Most of these are legacy sites. The Superfund, which included funds from a tax on industry, was discontinued during the George Bush Administration. Since then legacy mine sites have to compete with other high priority sites for EPA CERCLA funds which are taxpayer dollars. There is currently no tax on the mining industry to generate funds to cleanup legacy mine sites. A study by the Denver-based Center for Western Priorities used Government Accountability Office data to estimate clean-up costs for 5105 abandoned mines on public lands in Colorado at over $1 billion. The analysis uses GAO estimates of 5105 abandoned mines on federal land in Colorado.
With the elimination of the tax on industry that provided funds for the Superfund, the US EPA and State environment agencies began using other CERCLA authorities and CWA authorities and grants to help communities with legacy mines address the environmental degradation issues. This community based effort, while utilizing an inclusive stakeholder approach, was constrained by inadequate funding for legacy sites where contaminated mine water discharges to streams or shallow groundwater and by inflexible provisions of the CWA. Under the federal CWA, anyone who 1) does a partial cleanup but does not meet federal CWA standards, or 2) unintentionally makes the problem worse, can be subject to enforcement and /or citizen lawsuits under the CWA or CERCLA. During the past ten years the US Congress has considered Good Samaritan legislation that would establish a permit system to allow a Good Samaritan (as defined in bill) to cleanup inactive or abandoned mine site and would shield the permittee from CWA/ CERCLA liability for actions taken under the permit. Strict requirements would be established as to who can be a good samaritan, which sites are eligible and what must be included in permit. At least one of the bills would allow for limited recycling of tails /wasterock to the extent that it is necessary for and directly related to the cleanup. As of 2017 none of these bills have become law and there is no effort in the current Congress.
A long term solution to environmental degradation related to legacy hardrock mine sites includes four key policy elements:
- Funding needs to be generated via a tax on the mining industry.
- Liability under the CWA has to be managed to allow for private sector organizations and businesses to participate in mine site cleanup
- Community involvement – many legacy mine sites occur near towns that have a historical significance and a long, proud mining tradition. Environmental remediation /restoration must include extensive community involvement, maintaining a mining heritage and partnerships between communities and State / Federal Government.
- Innovative use of current authorities including Brownfields and voluntary cleanup programs – with appropriate oversight.
Mike Wireman, National Ground-Water Expert, USEPA (retired)
April 5, 2017