Legacy Mine Closure: Managing and Identifying your Risk

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The mining industry is an essential cornerstone of our modern society. Without minerals harvested from the earth, there’d be no smartphones, computer chips or cars. But in the past, extracting minerals from the ground has been a complex and sometimes damaging process. Abandoned and legacy mines across the United States may pose risks to the environment and humans.

Although no longer operating, these mines still need to be evaluated, closed and reclaimed appropriately. Known as legacy brownfield sites, these old operations are often governed by a complex framework of federal and local laws, and it can be challenging for owners or managers to know where to begin the closure process. If you, your company or agency manages legacy mine sites, here are a few actions to consider when evaluating your risk and planning for a closure.

Understand the Regulations

If you’re not certain which regulatory laws apply to a mine site, the first step is to understand legal liabilities and responsibilities. The applicable regulatory framework depends on the lead agency assigned to the project, and this can vary based on the location and size of the site. For example, if the site is located on Forest Service-administered lands then the lead agency is typically the Forest Service. At times, depending on the site and complexity of the mine, the Environmental Protection Agency (EPA) can also be the lead agency.

Federal lead agencies typically regulate these sites under Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) regulations. CERCLA laws provide a method to identify and prioritize sites and evaluate cleanup approaches. CERCLA gives the lead agency the authority to perform removal and remedial actions at hazardous waste sites and assigns the financial responsibility for cleanup costs to “responsible parties.” Owners and managers of legacy mine sites can find lots of guidance on how to approach CERCLA closure from the EPA.

If the lead agency is designated as a state environmental department (Department of Environmental Quality, etc.), then closure must fall under state regulations rather than federal. Most state regulations are similar in nature to CERCLA, but the specifics vary by state. 

In certain circumstances, elements of the Resource Conservation and Recovery Act (RCRA), which typically applies to operating mines, can also come into play. The specifics of mine location, operation and contaminants matter. Specific types of hardrock waste are exempt from the regulations for hardrock waste in RCRA Subtitle C thanks to the Bevill Amendment. Hardrock waste generated during mineral extraction (waste rock and overburden), beneficiation (crushing, grinding) and from certain ore processing are exempt. But even this exemption is not always straightforward. Not all states recognize the Bevill Amendment, so it is important to do your homework on state regulations and rules. 

Environmental Investigation/Characterization

The first step toward eventual mine closure is often site investigation to characterize the extent of contamination and site impacts. Owners and operators need to understand the extent of any potential contamination, and how its classification will impact the legal framework for reclamation and closure.

Hiring an experienced environmental professional to develop and implement a site characterization plan can give owners a better understanding of potential environmental risks and liabilities. The plan often focuses on characterizing soil, rock and water at the site. The first step is often to figure out if a site has been impacted by historical activities or other background conditions. This can be challenging at mine sites, because metal concentrations are usually naturally elevated (hence the location of the mine) and regulatory cleanup levels can be significantly less than background concentrations at the site. This is especially challenging at older legacy mine sites that weren’t required to perform initial site characterization before opening the mine, as is standard practice today.  

Environmental scientists use several tests to assess the mobility and migration potential of metals from solid media. These include the Toxicity Characteristic Leaching Procedure (TCLP), Synthetic Precipitation Leaching Procedure (SPLP) and Acid-Base Accounting (ABAs). The TCLP is used to determine if a waste is classified as “hazardous waste” under the CRA and needs to be handed and disposed separately—unless it qualifies as exempt under the Bevill Amendment. SPLP tests are used to evaluate the in-situ mobility of metals under nature rain conditions, and ABAs are static tests to estimate the potential for solid media to form Acid Rock Drainage (ARD)—a significant issue for mines with high sulfide orebodies. 

Potential Discharges

Legacy mines always face the possibility of waste discharges into nearby ecosystems if not properly maintained. If the site is near residential neighborhoods, waterways, wetlands or other sensitive areas, the risks to humans and the environment are magnified.

If there’s any potential impact to endangered or threatened species under federal protection, the risks and costs associated with mine closure are likely to rise. More sensitive or highly-protected ecological receptors near your site typically mean greater risk to the environment and owner. Mine owners who are uncertain of the scope of potential ecological impacts near their sites may consider requesting an ecological survey to understand these local receptors.

Public Access to the Site

Any amount of public access to a mine site, even unauthorized access, can be extremely risky for owners. Ideally, sites should be physically secured with fencing and other barriers to keep people clear of potential contamination and other physical hazards. Even if the site itself is secure, nearby public use areas such as hiking trails, parks or even neighborhoods can magnify the liability risk. It’s important to identify these risks and develop strategic approaches to minimize exposure as a result of unauthorized access to the site.

Geohazards

Geophysical hazards such as unstable waste rock slopes, aging underground workings and hazardous openings create a two-fold challenge to mine owners. They can pose an immediate physical threat to infrastructure on and off-site and increase the chance of a release to the environment. Tailings ponds are often impounded by levees and dams. If these dams/levees experience seepage or even failure, serious environmental impacts can result. Slopes, levees and other potential hazards should be carefully evaluated and addressed through reclamation and closure. Post-reclamation monitoring and operation/maintenance is an important step to ensure the hazards addressed in the reclamation process remain in place and effective.

Closing

The biggest key to managing risks from legacy mining sites is simple—act now, not later, and have a plan. Qualified environmental professionals can be helpful in performing site characterization, risk assessments, engineering, and navigating the rapidly-shifting maze of environmental regulations. GeoEngineers’ environmental scientists and engineers have years of experience in the mining industry and are happy to answer any questions you might have about mine closure and applicable regulations.

Questions? We have answers.