Chapter 9 MODERN TAILINGS MANAGEMENT

• Jurisdiction: United States

Mining Law
Chapter 9

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MODERN TAILINGS MANAGEMENT
Benjamin Machlis Kayla Weiser-Burton Dorsey & Whitney LLP Salt Lake City, UT

M. BENJAMIN MACHLIS a Partner at Dorsey & Whitney LLP in Salt Lake City. Ben has extensive experience in matters involving state and federal regulations regarding solid and hazardous waste (RCRA), hazardous materials transportation (HMR), toxic chemicals (TSCA), water quality (CWA), community right-to-know laws (EPCRA) and remediation of contaminated property (CERCLA). Ben has been recognized by Mountain States Super Lawyers® as a "Rising Star" in Environmental practice in 2014 through 2019. He has served as Young Professionals Committee Chairman (2016-2017) of the Rocky Mountain Mineral Law Foundation, as a member of the Board of Directors of Utah Open Lands and as an adjunct faculty member at the S.J. Quinney College of Law.

I. Introduction and Background on Tailings Storage Facilities

For the vast majority of mining operations, the extraction of target minerals is accomplished by milling the ore to a fine particle size and further processing that milled ore to extract the target minerals from the ore. The resulting mixture of the economically worthless fraction of the ore body--water and residual process chemicals--is referred to as tailings. While some mines with underground operations use a fraction of the tailings to backfill the underground workings, the volume of tailings generated necessitates the placement of tailings in surface facilities. Along with the mine workings and waste rock (mined material that does not contain sufficient mineralization to be processed) storage facilities, these surface tailings storage facilities ("TSFs") are often the largest pieces of infrastructure at any mine site.

Recent failures of TSFs and the impact such failures have on human life and the environment have put a spotlight on the design, construction, maintenance, and closure of TSFs. This spotlight has brought a renewed focus on the mining industry to adhere to a higher standard of care, the exploration of innovative technologies to better manage tailings, and enhanced regulatory structures for TSFs. The global mining industry also responded to these recent TSF failures by establishing, along with non-industry global partners, a set of standards for the industry to adhere to throughout the lifecycle of a TSF. However, these standards are not binding on all of the mining industry, leaving a potentially significant gap in the enforcement of these standards. After providing a brief background on TSFs and recent TSF failures, this paper reviews the development of the new Global Industry Standard on Tailings Management ("GSTM" or the "Standard") and examines the regulatory structures of the states within the United States with significant mining operations to assess the status of adoption of the key aspects of the Standard suitable for regulatory uptake.

A. Traditional Tailings Storage Facility Design

The most commonly used tailings management technology is to deposit tailings as a flowable slurry in a surface impoundment designed to contain the flowable mass of tailings. Generally, these TSFs are located in a manner that takes advantage of local topography to provide some of the containment with the construction of a tailings dam at one (or more) locations to complete the containment of the materials. Once deposited, the slurry segregates over time, allowing the water to be pumped off the top and, generally, recirculated to the processing facility for use as make up water. The most common types of dams used for containment are:

• Upstream Tailings Dams - these facilities are started by the construction of a pervious starter dam. As tailings are deposited in the facility, the slurry segregates, and the solids adjacent to the starter dam dewater sufficiently to form the foundation of the next dam raise.¹

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Because this method of construction relies on previously deposited tailings for structural stability, it is not suitable for use in all climates and many have called for a prohibition on its use.²
• Centerline Tailings Dams - these facilities are started by the construction of a starter dam. As tailings are deposited in the facility, successive raises of the embankment are placed vertically on the centerline of the prior section. The upstream portion of each raise is structurally supported by deposited tailings, but the downstream portion is supported by native land.³

• Downstream Tailings Dams - these facilities are started by construction of an impervious starter dam. As the facility fills, successive raises of the embankment are constructed on the downstream slope of the previous dam raise. Accordingly, the dam crest moves downstream with every raise of the embankment.⁴

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In addition, some traditional tailings facilities are constructed in a single stage where the initial embankment is built at a sufficient size to contain all tailings anticipated to be placed in the TSF.

B. Alternative Tailings Storage Management

In recent years, new technologies have been developed to manage tailings in a manner intended to provide a higher margin of safety and environmental protection. The most commonly discussed alternative management strategy is dry-stack, where tailings are dewatered by centrifuge, vacuum, belt press, plate and frame, or screw filtration methods. Depending on the degree of filtration, the result is a wet or dry cake tailings material. The resulting tailings can be pumped (wet cake), trucked or conveyer-belted (dry cake) to the disposal site. The filtered tailings are designed to be a more stable mass than traditional slurry tailings, and in the case of dry cake tailings, can be compacted and managed in piles or stacks that resemble the management structures for coarser grained waste rock. Dry stack tailings management is intended to address some of the safety and environmental concerns associated with traditional tailings management by removing the liquid prior to placement of the material. Notably, the term "dry stack" is a bit misleading as even dry cake tailings retain a certain amount of moisture content. Because the material is generally very fine-grain, in certain climates, precipitation infiltration may create concerns about the generation of contaminated seepage or liquefaction of the dry stacked tailings. Accordingly, questions have been raised for facilities proposing to use dry stack tailings in the United States, most notably for the Twin Metals project in Minnesota, about the nature and robustness of the containment structures necessary for dry stack TSFs.

Other proposed mining projects in the United States are also exploring alternative technologies. For example, the Black Butte Copper Project in Montana recently obtained final permit authorization for a mine that incorporated dewatered and cemented paste tailings in the design of its TSF.⁵ While the cemented paste tailings are designed to create a non-flowable mass, the TSF was still designed to the same safety and environmental control standards that would have been required if traditional slurry deposition technology were employed.⁶ Notably, both Twin Metals' proposed use of dry-stack and Black Butte's proposed use of cemented paste were criticized by environmental organizations as unproven and unsafe tailing management proposals.

C. Recent Tailings Storage Facility Failures

Over the last decade, a number of TSF failures have caught global attention and brought a spotlight on the design, construction, management, and closure of TSFs. Two particular events stand out.

On August 4, 2014, a catastrophic loss of containment occurred at the Mount Polley Mine in British Columbia.⁷ The failure resulted in over 25 million cubic meters of tailings and wastewater being released into nearby waterways.⁸ The Mount Polly TSF had been constructed with embankments on three sides and natural topography providing containment on the fourth side of the TSF.⁹ After the incident, the

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BC government and local indigenous groups convened an expert panel to investigate and prepare a report on the failure of the TSF.¹⁰ The report concluded that the failure was mainly due to faulty design, a failure to plan raises of the embankment adequately in advance, and inadequate water balancing.¹¹ The panel noted that the "related absence of a well-developed tailings beach violated the fundamental premise of design as a tailings dam, not a water-storage dam."¹²

On January 25, 2019, Dam I at the Corrego do Feijao mine in Brumadinho, Brazil failed resulting in the release of a mudflow that killed more than 250 people.¹³ In addition to the significant loss of life, this incident caught global attention because there was high quality video of the TSF failure and ensuing mudflow. According to the expert panel report commissioned by the mine operator, the TSF was constructed using the upstream method in ten successive raises of the embankment over its operational life.¹⁴ The expert panel report concluded that a design that resulted in a steep upstream slope angle, poor water management during operations, a lack of sufficient internal drainage, the brittle structure of the tailings, and increased regional precipitation all contributed to the failure of the TSF.¹⁵

II. The Global Industry Standard

On the heels of Mount Polley and other catastrophic events, the Brumadinho tailings dam failure put a fresh spotlight on the mining industry and the management of tailings. As the International Council on Mining & Metals ("ICMM"), an organization comprised of twenty-eight of the largest mining companies in the world, notes on its website:

This was a pivotal moment for the sector and one that demanded decisive and appropriate action. The solution required our industry to unite, work collaboratively and develop a tangible offering to strengthen the safety of tailings facilities to prevent future failures, and

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