East Helena Slag Pile Community Survey

Please review the background information before filling out the survey on the next page. Click to see a PDF of the information with all figures.

East Helena Slag Pile
The 16-million-ton slag pile at the former ASARCO lead smelter is a defining feature on the landscape in East Helena. (See Figure 1.) The pile occupies 65 acres and rises 150 feet above ground (equivalent height of a 15-story building). (See Figure 2.) The black, glass-like slag pile was created by pouring molten slag—the byproduct of smelting ores to produce lead bullion. The pile grew over the 110-plus years that ASARCO operated the smelter.

The slag pile consists of “fumed slag” (FS) and “unfumed slag” (UFS). From 1940 to 1982, zinc was recovered from FS before it was poured onto the pile. (See Figure 2.) After shutdown of the fuming plant in 1982, ASARCO poured the ±2-million-ton “upper lift” of UFS, which contains zinc and other metals. (See Figure 3.) Most of the pile —±13 million of the 16 million tons—is fumed.

Groundwater Impacts
While precipitation causes all slag to leach metals to groundwater, the upper lift of UFS is the source of 75% of the remaining selenium. To prevent selenium from loading to groundwater, EPA has approved the final remedial action at the former smelter, which entails grading and capping the UFS with an estimated 2-foot-thick vegetated soil cover. A similar, thinner vegetated soil cover will be placed over the rest of the slag pile.

Slag Recycling Project
In 2021, METG began working with Metallica—an international metals trading company—on a recycling project designed to remove the upper lift of UFS. (See Figure 4.) Slag was crushed, transported by rail to Canada, and shipped to the Korea Zinc (KZ) smelter (in South Korea) for “fuming” to extract zinc and other valuable metals and use the remaining byproduct to manufacture cement. Metallica had planned to ship ±30,000 tons of slag per month to remove ±2 million tons of UFS in 5 years. Since 2021, Metallica has transported almost 145,000 tons of UFS to KZ, but supply chain and transshipping issues delayed delivery of the required slag quantities. KZ terminated its contract with Metallica in June 2024, pausing the recycling project. To resume recycling, Metallica or METG would need to find a new slag purchaser and resolve transshipping issues. Currently, shipping costs are high, and a viable purchaser has not been identified (There are no zinc smelters in North America that can handle the quantities of UFS from East Helena). Removal of UFS will no longer be feasible once the slag pile is capped.

Benefits of Removing Upper Lift of Unfumed Slag

• Reduces pile height by 50% if entire upper lift is removed (see Figure 5)
• Removes primary, remaining source of groundwater selenium contamination
• Shortens the construction time required to grade and cap slag pile by ±1 year
• Allows slag sale proceeds to fund other East Helena cleanup activities
• Reduces cost to cap slag pile, leaving more funds available for other cleanup activities

Other Facts

• Pursuing the UFS recycling will delay capping the slag pile (which is the final action to remove the largest source of selenium contamination to groundwater).
  • However, groundwater quality has significantly improved as a result of cleanup measures implemented at the Site. The off-site selenium plume has receded by ¾ of a mile since 2016. (See Figure 6.)
• A large portion of the slag pile will remain in place and be capped regardless of whether the upper lift is removed.
• Capping will involve regrading and vegetating the pile so it will look more natural.
• Recycling requires crushing, which could increase contaminant leaching to groundwater; however, monthly groundwater monitoring to date has shown no increased leaching to groundwater.
• Grading and capping the pile will take ±2 years to complete.
• EPA is evaluating placing soil excavated from East Helena residential yards onto the slag pile, which would increase its height and delay capping by several years.