UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8, MONTANA OFFICE FEDERAL BUILDING, 10 West 15TH Street, Suite 3200 Helena, MT 59626-0096 Phone 866-457-2690 www.epa.gov/region8 Ref: 8SEM-RBC February 3, 2020 MEMORANDUM SUBJECT: FROM: TO: Parrot Tailings mining waste remedial decisio /s -~ iority Soils Operable Unit Joseph Vranka, Section Chief O~l Superfund Remedial Section C/ File/Administrative Record for the 2020 Butte Priority Soils Operable Unit Record of Decision Amendment The responsiveness summary portion of the 2020 Butte Priority Soils Operable Unit (BPSOU) Record of Decision Amendment contains the Environmental Protection Agency's (EPA's) response to comments, including comments which question why the EPA did not include the Parrot Tailings removal as part of EPA's remedial decision for the BPSOU. This memorandum further describes the EPA decision making regarding this issue and describes EPA's concerns regarding the potential adverse effects the removal of the Parrot Tailings may have on the BPSOU remedial groundwater capture and treatment system. As explained in the responsiveness summar1/, the EPA did not include the removal of the Parrot Tailings in the remedy described in its 2006 BPSOU Record of Decision because EPA's analysis-particularly its analysis contained in the 2004 BPSOU Focused Feasibility Study of the Metro Storm Drain (now referred to as the BPSOU Subdrain); Phase II Remedial Investigation/Feasibility Study Final Feasibility Study (the FFS) - demonstrated that even if accessible portions of the Parrot Tailings were removed, many secondary sources of groundwater contamination within the BPSOU would remain such that groundwat~r standards for human health would not be obtained for the BPSOU alluvial aquifer in a reasonable time frame. Thus, under EPA's remedial authority, the removal of the Parrot Tailings waste was not appropriate, in EPA's view. The State of Montana disagreed with that view in its 2006 letter of partial concurrence on the 2006 BPSOU Record of Decision. In 2015, the EPA conducted a review of data collected after the 2006 Record of Decision, primarily by the State of Montana and other independent parties, to assess its potential impact on the conclusion that the removal considered in the FFS would not bring the BPSOU alluvial aquifer into compliance with groundwater standards. The EPA found the following: More waste is located downgradient of the alluvial aquifer groundwater divide than previously understood. As a result, the FPS-defined partial removal action would result in removal of a smaller portion of the total waste in the area. Under the partial removal alternative under consideration in the FFS, 48 acres of waste would be left in place downgradient of the groundwater divide and upgradient of the removal. The water
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8, MONTANA OFFICE
FEDERAL BUILDING, 10 West 15TH Street, Suite 3200 Helena, MT 59626-0096
Phone 866-457-2690 www.epa.gov/region8
Ref: 8SEM-RBC
February 3, 2020
MEMORANDUM
SUBJECT:
FROM:
TO:
Parrot Tailings mining waste remedial decisio/s - ~ iority Soils Operable Unit
Joseph Vranka, Section Chief O~l ~ Superfund Remedial Section C /
File/Administrative Record for the 2020 Butte Priority Soils Operable Unit Record of Decision Amendment
The responsiveness summary portion of the 2020 Butte Priority Soils Operable Unit (BPSOU) Record of Decision Amendment contains the Environmental Protection Agency's (EPA's) response to comments, including comments which question why the EPA did not include the Parrot Tailings removal as part of EPA's remedial decision for the BPSOU. This memorandum further describes the EPA decision making regarding this issue and describes EPA's concerns regarding the potential adverse effects the removal of the Parrot Tailings may have on the BPSOU remedial groundwater capture and treatment system.
As explained in the responsiveness summar1/, the EPA did not include the removal of the Parrot Tailings in the remedy described in its 2006 BPSOU Record of Decision because EPA's analysis-particularly its analysis contained in the 2004 BPSOU Focused Feasibility Study of the Metro Storm Drain (now referred to as the BPSOU Subdrain); Phase II Remedial Investigation/Feasibility Study Final Feasibility Study (the FFS) - demonstrated that even if accessible portions of the Parrot Tailings were removed, many secondary sources of groundwater contamination within the BPSOU would remain such that groundwat~r standards for human health would not be obtained for the BPSOU alluvial aquifer in a reasonable time frame. Thus, under EPA's remedial authority, the removal of the Parrot Tailings waste was not appropriate, in EPA's view. The State of Montana disagreed with that view in its 2006 letter of partial concurrence on the 2006 BPSOU Record of Decision.
In 2015, the EPA conducted a review of data collected after the 2006 Record of Decision, primarily by the State of Montana and other independent parties, to assess its potential impact on the conclusion that the removal considered in the FFS would not bring the BPSOU alluvial aquifer into compliance with groundwater standards. The EPA found the following:
■ More waste is located downgradient of the alluvial aquifer groundwater divide than previously understood. As a result, the FPS-defined partial removal action would result in removal of a smaller portion of the total waste in the area.
■ Under the partial removal alternative under consideration in the FFS, 48 acres of waste would be left in place downgradient of the groundwater divide and upgradient of the removal. The water
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quality under the waste to be left in place is severely impacted and would re-contaminate the removal area.
• With the relocation of the groundwater divide, significantly more critical infrastructure (roads, railroads, pipelines) overlies waste impacting groundwater flowing toward the BPSOU Subdrain, making a more complete removal impracticable.
, · - • Th~ FFS-defined removal action itself would expose the tailings to atmospheric oxygen, which could worsen acid generation and metals dissolution in the tailings that would be left in place.
• The FFS-defined removal action includes removal of the tailings and organic silt, but the slag and overburden would be returned to the excavation as fill. Based on the SPLP tests, the slag is also
· leachable and should not be used as fill.
• Based on the new understanding of geochemical attenuation mechanisms in the middle alluvium, zinc and copper are contained within zinc phyllosilicates and manganese oxides. Solid-phase mineral precipitation is controlling zinc and copper concentrations, not adsorption.
• The capacity of the aquifer to attenuate zinc and copper is not limited by a finite number of adsorptiem sites. Zinc and copper will continue to precipitate in these mineral phases indefinitely.
• The cleanup time to completely leach (dissolve) zinc from one mile of aquifer containing zinc kerolite wa~ c~nservatively estimated to be 13,077 years, under an ideal removal scenario. This estimate is dependent on pH. Any implementable removal scenario under consideration would be less than ideal conditions and would extend these cleanup time estimates.
• Post-removal groundwater COC concentrations at LAO show initial reductions. However, the concentrations have not improved since 2002 and appear to be reaching a new equilibrium. Based bn the limited available data, concentrations in many locations remain above human health standards. Furthermore, concentrations remain well above aquatic life standards, and water treatment is still required.
• Analyses of these new data did not change EPA' s the conclusions reached in the FFS that partial reilJoval of the Parrot tailings will not be effective at attaining groundwater standards. Leaching from upgradient wastes left in place following a partial removal action would re-contaminate the removal area. Secondary sources within the alluvial aquifer would affect groundwater for a significant period of time under the most optimistic conditions and· significantly longer under a partial removal scenario. Furthermore, no savings in long-term treatment costs would be realized, because under any removal scenario, groundwater treatment would remain necessary to protect aquatic life in Silver Bow Creek.
This analysis did not support alteration of EPA's 2006 remedial decision to leave the Parrot Tailings in place and to focus remedial efforts on the collection and treatment of contaminated groundwater before the groundwater enters Blacktail Creek and Silver Bow Creek below the confluence with Blacktail Creek, which are perennial surface water bodies within the BPSOU. Data obtained since the 2015 evaluation does not alter the EPA's views regarding this view.
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The State of Montana continues to disagree with EPA's position. In 2016, the Montana Natural Resource Damage Program amended its 2013 Butte Area One Restoration Plan to include the Parrot Tailings Waste Removal Project. In September 2019, the State further amended the Butte Area One Restoration Plan, the Upper Clark Fork River Basin Aquatic and Terrestrial Resources Restoration Plans and the Upper Clark Fork River Restoration Fund/Butte Groundwater Restoration Plan to further provide for the funding of this project. All of these documents are contained in the administrative record for the 2020 BPSOU Record of Decision Amendment.
Phase 1 of the Parrot Tailings Waste Removal Project has been implemented by the Montana Natural Resource Damage Program, and Phase II is in the planning stages.
As _the State's September 17, 2019 Response to Public Comments notes, use of natural resource damage restoration funds for the Parrot Tailings Waste Removal Project is an appropriate use of the State's natural resource damage funds obtained through various settlements between the State of Montana and the Atlantic Richfield Company1• EPA agrees with the State's determination that removal of tailings and other wastes is an appropriate use of restoration funds, and supports the State's efforts here.
The EPA has supported the State's efforts by agreeing to the release of $16.5 million in settlement funds previously set aside for the remediation of the Streamside Tailings Operable Unit to the Montana Natural Resource Damage Program for'tlse .with the Parrot Tailings Waste Removal Project. EPA has generally coordinated with the Montana Natural Resource Damage Program on this project through review of documents and other general coordination activities. Finally, the EPA facilitated the State's monetary settlement of $20.5 million with the Atlantic Richfield Company contained in the proposed BPSOU Remedial Design/Remedial Action and Operation and Maintenance Consent Decree, and understands that the State intends to apply·some of those·proceeds towards the Parrot Tailings Waste Removal Project.
As noted above, the EPA has concerns that the Parrot Tailings Waste Removal Project may adversely impact the BPSOU remedial groundwater capture and treatment system, through oxidation of the
groundwate\§ont.,n an1wor through changes in the flow direction or the alluvial groundwater. See, EPA's I 11!> '. ii.letter to the Montana Natural Resource Damage Program, which is also part of the administrative record for the 2020 BPSOU Record of Decision Amendment. The EPA worked cooperatively with the State and the Atlantic Richfield Company to include provisions in the proposed BPSOU Partial Remedial Design/Remedial Action and Operation and Maintenance Consent Decree to allow, under certain conditions, for claims against the State of Montana to address such adverse impacts if they occur. The EPA will continue to work cooperatively with the Montana Natural Resource Damage Program to proactively monitor and address concerns as both the Parrot Tailings Waste Removal Project and the BPSOU remediation are implemented.
1. In 2007, the State issued a Butte Area One Restoration Draft Conceptual Restoration Plan and Planning Process. This document - a precursor to the current, amended Butte Area One Restoration Plan - calls for the removal of the Parrot Tailings waste under natural resource damage authority. This document, attached to the 2008 Consent Decree for the Clark Fork River Operable Unit and For Remaining State of Montana Clark Fork Basin Natural Resource Damage Claims, was the basis of the $28 million settlement between the State of Montana and the Atlantic Richfield Company for outstanding natural resource damage claims related to the alluvial aquifer in Butte described in that Consent Decree.
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