GALLATIN CORRECTIVE MEASURES STUDY
SCOPE OF WORK AND SCHEDULE
Gallatin Chemical Works 8800 Industrial Park Lane Belgrade, Gallatin County, Montana 59714
RCRA Permit No. MTD098712456
Date: February 14, 2025
Prepared by:
Calderwood & Harkness LLP Matter No. 1039-00003
in coordination with
Pinnacle Creek Environmental, LLC 320 Willowbrook Drive, Suite 100 Bozeman, Montana 59715
Prepared for:
Torchlight Mining Corp. and Torchlight Specialty Chemicals, Inc.
Consent Decree Reference: United States of America and State of Montana v. Torchlight Mining Corp. et al. Civil Action No. 9:24-cv-00087-DWM United States District Court for the District of Montana, Missoula Division
CMS Final Report Submission Deadline: June 14, 2026
CONFIDENTIAL — PREPARED AT THE DIRECTION OF COUNSEL — ATTORNEY WORK PRODUCT — SUBJECT TO ATTORNEY-CLIENT PRIVILEGE
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I. INTRODUCTION AND PURPOSE
1.1 Background
This document sets forth the Scope of Work and Schedule for the Corrective Measures Study ("CMS") to be conducted at the Gallatin Chemical Works facility (the "Gallatin Site" or "Facility") located at 8800 Industrial Park Lane, Belgrade, Gallatin County, Montana 59714. The CMS is being undertaken in accordance with the requirements of the Resource Conservation and Recovery Act ("RCRA"), 42 U.S.C. §§ 6901 et seq., and the terms of the Consent Decree entered (or expected to be entered) in United States of America and State of Montana v. Torchlight Mining Corp. et al., Civil Action No. 9:24-cv-00087-DWM, before the Honorable Donald W. Molloy, Senior U.S. District Judge, United States District Court for the District of Montana, Missoula Division (the "Consent Decree").
The Gallatin Site encompasses approximately 145 acres of industrially zoned land within the Belgrade city limits in Gallatin County, Montana, situated in the greater Bozeman metropolitan area. The Facility has been in active operation since 1993 as a specialty chemical manufacturing facility. Principal product lines include flotation reagents, sodium xanthate, and dithiophosphate collectors used extensively in mining and mineral processing operations throughout the western United States and Canada. The manufacturing processes conducted at the Facility involve the use and handling of carbon disulfide ("CS₂"), sodium hydroxide, alcohols, phosphorus pentasulfide, and various organic solvents, which collectively generate multiple hazardous and non-hazardous waste streams requiring active management.
The Facility is operated by Torchlight Specialty Chemicals, Inc. ("TSC"), a Delaware corporation (EIN: 47-3819204). TSC is a wholly owned subsidiary of Torchlight Mining (U.S.) Inc. ("TM(US)"), a Delaware corporation serving as the U.S. holding company for domestic mining and chemical operations. TM(US) is, in turn, wholly owned by Torchlight Mining Corp. ("TMC"), a corporation incorporated under the Canada Business Corporations Act, with its principal office in Toronto, Ontario. TMC is dual-listed on the Toronto Stock Exchange and the New York Stock Exchange under the ticker symbol TRC. As of the date of this Scope of Work, TMC's consolidated market capitalization is approximately $4.2 billion (CAD). TMC serves as the parent guarantor under the Consent Decree for all remediation obligations at the Gallatin Site and the three other sites covered by the Consent Decree.
The Facility is currently active and will remain operational throughout the CMS and the subsequent period of corrective measures implementation. The CMS and associated investigative and remedial activities must therefore be planned and conducted in a manner that accommodates ongoing manufacturing operations, maintains worker safety, and minimizes disruption to production processes while achieving the environmental objectives established by the Consent Decree and applicable regulatory requirements.
1.2 Regulatory Context
The Gallatin Site is a RCRA Corrective Action facility operating under RCRA Permit No. MTD098712456, issued by the Montana Department of Environmental Quality ("MT DEQ") under the State's authorized RCRA program. The Facility's hazardous waste management activities are subject to the requirements of RCRA Subtitle C, as codified in 40 C.F.R. Parts 260 through 270, and the corresponding provisions of the Montana Hazardous Waste Act, Montana Code Annotated §§ 75-10-401 et seq., and the implementing regulations at ARM Title 17, Chapter 53.
The United States Environmental Protection Agency ("EPA"), acting through Region 8, and the State of Montana, acting through the Office of the Attorney General and MT DEQ, filed a civil enforcement action against TMC, TM(US), and TSC alleging multiple violations of federal and state environmental statutes at the Gallatin Site and three additional facilities owned or operated by the corporate family. The alleged violations at the Gallatin Site include:
(a) RCRA § 3004 (42 U.S.C. § 6924): Operation of an unpermitted hazardous-waste storage unit at the Facility, specifically a concrete-pad storage area utilized for temporary accumulation of hazardous waste containers in excess of the 90-day generator accumulation time limitations, without a RCRA Part B permit or interim status authorization.
(b) RCRA § 3005 (42 U.S.C. § 6925): Failure to perform corrective action at three identified Solid Waste Management Units ("SWMUs") at which releases of hazardous waste or hazardous constituents to soil and groundwater have been documented, as required by the corrective action provisions of the Facility's RCRA permit.
(c) Clean Water Act ("CWA") § 301 (33 U.S.C. § 1311): Fourteen documented exceedances of Montana Pollutant Discharge Elimination System ("MPDES") permit effluent limits for carbon disulfide ("CS₂") and total suspended solids ("TSS") occurring between January 2021 and June 2024. These exceedances constitute unauthorized discharges of pollutants in violation of the Facility's MPDES permit and the national pollutant discharge elimination system requirements of the CWA.
The CMS is required under Section VII.B of the Consent Decree entered (or expected to be entered) in Civil Action No. 9:24-cv-00087-DWM. EPA Region 8, headquartered in Denver, Colorado, is the lead regulatory office for the Gallatin facility for purposes of RCRA corrective action oversight, CMS review and approval, and corrective measures selection. The State of Montana, Department of Environmental Quality, is a co-plaintiff in the enforcement action and retains concurrent oversight authority with respect to state-authorized RCRA permit requirements and MPDES permit compliance. State coordination for the litigation and regulatory matters is led by Annika Hedstrom, Assistant Attorney General, Montana Attorney General's Office, Environmental Bureau, Helena, Montana.
1.3 Purpose of the CMS
The purpose of the CMS is to:
(a) Evaluate and develop corrective measures alternatives that will effectively address releases of hazardous waste and hazardous constituents from the three identified SWMUs at the Gallatin Site, remediate CS₂ contamination in groundwater, and address volatile organic compound ("VOC") contamination in subsurface soils, thereby achieving compliance with applicable federal and state environmental standards and protecting human health and the environment.
(b) Provide a technically sound and defensible basis for the selection of final corrective measures by EPA, in consultation with MT DEQ, ensuring that the selected remedy is both protective and cost-effective, and that it appropriately balances the relevant evaluation criteria established by RCRA corrective action guidance.
(c) Ensure compliance with the Consent Decree remediation schedule, pursuant to which the final CMS report is due no later than June 14, 2026, which is twelve months after the anticipated Effective Date of the Consent Decree.
(d) Support the broader remediation objectives established by the Consent Decree across all four sites, while focusing specifically on the technical and economic characteristics unique to the Gallatin Site.
The estimated total remediation cost for the Gallatin Site is approximately $42.8 million over a 15-year implementation and monitoring period. The net present value ("NPV") of this obligation, calculated using a 3% discount rate consistent with the Consent Decree's financial assurance provisions, is approximately $34.1 million. These cost estimates are preliminary and are based on Pinnacle Creek Environmental, LLC's ("Pinnacle Creek") current assessment of likely remedial technologies and implementation costs. The estimates will be refined through the CMS process as additional site characterization data become available and corrective measures alternatives are developed in greater detail.
1.4 Relationship to Consent Decree
This Scope of Work is prepared in reference to the substantially final agreed Consent Decree text dated February 3, 2025, and the execution version dated February 19, 2025, which was subsequently lodged with the Court for the requisite public comment period and judicial approval. The Consent Decree resolves the civil claims asserted by the United States and the State of Montana against TMC and its subsidiaries arising from environmental violations at four facilities owned or operated by the Torchlight corporate family.
The CMS for the Gallatin Site is one component of TMC's comprehensive remediation obligations under the Consent Decree. The four sites covered by the Consent Decree are:
(i) Ridgecrest Mine — Ridgecrest, Elko County, Nevada;
(ii) Gallatin Chemical Works — Belgrade, Gallatin County, Montana (the subject of this Scope of Work);
(iii) Bonanza Creek Mine — Bonanza Creek, Clearwater County, Idaho; and
(iv) Kanawha Bend Chemical Plant — Kanawha Bend, Kanawha County, West Virginia.
The total nominal remediation obligations across all four sites under the Consent Decree are approximately $343.5 million. The total NPV of these obligations, calculated at a 3% discount rate, is approximately $245.1 million. The Gallatin Site remediation obligation of $42.8 million (nominal) represents approximately 12.5% of the total nominal remediation costs across all four sites. The Consent Decree establishes site-specific schedules, performance standards, and completion criteria for each facility, and the CMS for the Gallatin Site must be conducted in coordination with the corrective action programs underway or planned at the other three sites to ensure efficient allocation of corporate resources and consistent technical approaches where appropriate.
The Consent Decree further requires the establishment of comprehensive financial assurance mechanisms, the appointment of an independent court-approved monitor, and the payment of stipulated civil penalties, all of which are described in greater detail in subsequent sections of this Scope of Work.
II. SITE DESCRIPTION AND OPERATIONAL HISTORY
2.1 Site Location and Physical Description
The Gallatin Chemical Works facility is located at 8800 Industrial Park Lane, Belgrade, Gallatin County, Montana 59714. The Facility occupies approximately 145 acres of industrially zoned land within the Belgrade Industrial Park, situated approximately 2.5 miles northwest of downtown Belgrade and approximately 9 miles west-northwest of downtown Bozeman. The Belgrade-Bozeman metropolitan area has a combined population of approximately 65,000, and the area has experienced substantial residential and commercial growth over the past two decades.
The Facility lies within the Gallatin Valley, a broad intermontane basin underlain by Quaternary alluvial and glacial outwash deposits. General site topography is relatively flat, with gentle northwest-to-southeast slopes consistent with the regional alluvial fan surface. Ground surface elevations across the Facility range from approximately 4,470 feet above mean sea level (AMSL) at the northwestern boundary to approximately 4,455 feet AMSL at the southeastern boundary, representing an average gradient of approximately 0.3 percent.
Surrounding land use is predominantly industrial and agricultural. The Belgrade Industrial Park extends to the north and east of the Facility, with light manufacturing and warehousing operations occupying adjacent parcels. Agricultural lands, primarily irrigated hay and grain fields, adjoin the Facility to the south and west. The nearest residential development is the Meadow Creek subdivision, located approximately 1.2 miles east-southeast of the Facility boundary. The nearest public school (Meadow Creek Elementary) is located approximately 1.8 miles east of the site.
The East Gallatin River, a tributary of the Gallatin River and ultimately the Missouri River, flows in a generally northerly direction approximately 1.4 miles east of the Facility. Several irrigation ditches, including the Middle Creek Ditch and the Highland Ditch, traverse the area south and west of the site. No perennial surface water features are located within the Facility boundaries, although a constructed stormwater retention basin occupies approximately 2.5 acres in the southeastern portion of the property.
The physical layout of the Facility includes the following principal areas and structures:
(a) Manufacturing Complex (Buildings A through D): Four interconnected steel-frame industrial buildings totaling approximately 185,000 square feet, housing sodium xanthate production (Building A), dithiophosphate collector production (Building B), flotation reagent blending and packaging (Building C), and quality control and analytical laboratories (Building D).
(b) Raw Material Storage Area: A concrete-pad area of approximately 45,000 square feet used for storage of bulk raw materials, including carbon disulfide, sodium hydroxide, phosphorus pentasulfide, and various alcohols. Bulk liquid storage includes six above-ground storage tanks with a combined capacity of approximately 480,000 gallons.
(c) Product Storage and Shipping: Warehouse facilities of approximately 60,000 square feet with rail siding and truck loading docks.
(d) Waste Management Areas: Including the three identified SWMUs, a 90-day hazardous waste accumulation area, and a non-hazardous solid waste roll-off container staging area.
(e) Process Water Treatment System: An on-site wastewater treatment plant with a design capacity of 150,000 gallons per day, including equalization, chemical precipitation, air stripping, biological treatment, and clarification units, discharging treated effluent under MPDES Permit No. MT-0029874.
(f) Stormwater Management Infrastructure: Including collection drains, oil/water separators, a stormwater retention basin, and permitted stormwater outfalls.
(g) Administrative Offices: A two-story office building of approximately 12,000 square feet housing facility management, environmental health and safety, and administrative functions.
(h) Maintenance and Utility Buildings: Including an electrical substation, a natural gas metering station, a maintenance shop, and a parts warehouse.
2.2 Operational History
Torchlight Specialty Chemicals, Inc. commenced manufacturing operations at the Gallatin Chemical Works in 1993, following construction of the initial manufacturing facilities (Buildings A and B) in 1991–1992. The Facility was developed on previously undeveloped agricultural land acquired by TM(US) in 1990. No prior industrial operations are known to have occurred on the property.
The Facility was designed and constructed to produce specialty chemicals for use in the mining and mineral processing industry, capitalizing on the proximity to major mining operations in Montana, Idaho, and Nevada. The principal product lines manufactured at the Facility include:
(a) Sodium Xanthate (Sodium Ethyl Xanthate and Sodium Isopropyl Xanthate): Produced by the reaction of carbon disulfide with sodium hydroxide and the appropriate alcohol (ethanol or isopropanol) under controlled temperature conditions. Sodium xanthate is used as a collector in the froth flotation of sulfide mineral ores.
(b) Dithiophosphate Collectors (Sodium Diethyl Dithiophosphate and Sodium Diisopropyl Dithiophosphate): Produced by the reaction of phosphorus pentasulfide with the appropriate alcohol, followed by neutralization with sodium hydroxide. Dithiophosphate collectors are used in flotation circuits for copper, lead, zinc, and gold ores.
(c) Flotation Reagent Blends: Custom-formulated blends of collectors, frothers, depressants, and modifiers tailored to specific ore types and customer specifications.
The primary raw materials used at the Facility include carbon disulfide (CS₂), sodium hydroxide (50% solution), ethanol, isopropanol, phosphorus pentasulfide, methyl isobutyl carbinol (MIBC), and various specialty chemicals. Carbon disulfide is the most significant raw material from an environmental and safety perspective due to its volatility, flammability, and toxicity. The Facility receives CS₂ by rail car in quantities of approximately 1.2 million gallons per year.
Waste streams generated by the manufacturing processes include:
(a) Process wastewater containing residual CS₂, xanthate decomposition products, alcohols, and suspended solids;
(b) Spent reaction residues classified as RCRA hazardous waste under the characteristic (D001 — ignitability; D003 — reactivity) and listed (K-listed from specific sources) waste codes;
(c) Off-specification product requiring rework or disposal;
(d) Contaminated personal protective equipment, rags, and laboratory wastes;
(e) Air emissions from process vents, storage tank breathing losses, and fugitive sources, controlled by a thermal oxidizer and activated carbon adsorption systems; and
(f) Stormwater runoff from production areas requiring treatment prior to discharge.
The Facility expanded production capacity in 1998 with the construction of Building C (flotation reagent blending) and again in 2005 with the addition of Building D (analytical laboratories). Waste management practices at the Facility have evolved over time. In the period from approximately 1993 to 2008, waste management operations included the use of areas that are now identified as SWMUs 1, 2, and 3, as described in Section III.2 below. EPA's 2019 Compliance Evaluation Inspection ("CEI") identified concerns regarding waste management practices at these areas, and a subsequent RCRA Facility Investigation ("RFI") confirmed releases of hazardous constituents to soil and groundwater.
The unpermitted hazardous-waste storage unit identified by EPA in the 2019 CEI consisted of a concrete-pad storage area in the northwestern portion of the Facility where containerized hazardous waste (principally spent reaction residues in 55-gallon drums and 275-gallon intermediate bulk containers) was stored for periods exceeding the 90-day generator accumulation time limitations of 40 C.F.R. § 262.17, without the Facility having obtained a RCRA Part B permit or interim status authorization for storage. EPA's inspection records document that on the dates of inspection, the storage area contained approximately 180 drums and 24 intermediate bulk containers of hazardous waste, with the earliest accumulation start dates preceding the inspection date by more than 150 days.
The Facility's RCRA Permit No. MTD098712456 was originally issued by MT DEQ in 1995 and has been renewed and modified on multiple occasions. The current permit term expires on December 31, 2027. The permit authorizes the treatment, storage, and disposal of specified hazardous wastes and incorporates corrective action requirements for identified SWMUs. The permit will require modification to incorporate the corrective measures selected through the CMS process.
2.3 Environmental Setting
Geology and Hydrogeology
The Gallatin Site is underlain by Quaternary alluvial deposits consisting of interbedded sands, gravels, silts, and clays deposited by the Gallatin River and its tributaries. These alluvial deposits extend to depths of approximately 80 to 120 feet below ground surface ("bgs") across the Facility, overlying Tertiary sedimentary bedrock of the Bozeman Group. The shallow alluvial aquifer, which is the principal aquifer of concern for the CMS, is composed of the upper 40 to 60 feet of alluvial deposits and is generally unconfined to semi-confined, with localized clay lenses providing intermittent confinement.
Depth to groundwater beneath the Facility ranges from approximately 12 to 22 feet bgs, varying seasonally in response to irrigation recharge and precipitation patterns. Seasonal groundwater fluctuations of 3 to 5 feet have been documented in Facility monitoring wells. Hydraulic conductivity of the shallow alluvial aquifer has been estimated from slug tests and pumping tests to range from approximately 25 to 150 feet per day, with a geometric mean of approximately 65 feet per day. The effective porosity is estimated at 0.25 to 0.30.
Groundwater flow in the shallow alluvial aquifer is generally to the east-southeast, consistent with the regional groundwater flow pattern in the Gallatin Valley. The horizontal hydraulic gradient across the Facility ranges from approximately 0.003 to 0.006 ft/ft, yielding estimated average linear groundwater velocities on the order of 0.5 to 1.5 feet per day. These velocities indicate that contaminated groundwater originating from the source areas at the Facility could potentially migrate significant distances in the downgradient direction over multi-year timeframes.
Surface Hydrology. As noted in Section 2.1, no perennial surface water features are located within the Facility boundaries. The constructed stormwater retention basin in the southeastern portion of the property collects and manages stormwater runoff from production and material handling areas. Treated process wastewater is discharged to an unnamed drainage ditch that flows east-southeast to the East Gallatin River, approximately 1.4 miles from the Facility.
Stormwater from the Facility is managed through a series of collection drains, oil/water separators, and the retention basin, with permitted discharges under MPDES Permit No. MT-0029874. The stormwater management system was designed to handle the 25-year, 24-hour storm event, although capacity limitations during high-intensity precipitation events have contributed to some of the documented MPDES exceedances.
Climate and Meteorological Conditions
The Gallatin Valley experiences a semi-arid continental climate characterized by cold winters, warm summers, and relatively low annual precipitation. Mean annual precipitation at the Belgrade Airport station (National Weather Service Cooperative Station No. 240645) is approximately 15.2 inches, with the majority occurring as rain from April through June and as snow from November through March. Mean annual temperature is approximately 43°F, with mean January temperatures of approximately 20°F and mean July temperatures of approximately 67°F.
These climatic conditions are relevant to contaminant transport and remedy design in several respects: (i) the relatively low precipitation limits recharge to the shallow aquifer, affecting contaminant migration rates and the feasibility of natural attenuation processes; (ii) freezing conditions from approximately November through March constrain the seasonal window for certain field investigation and construction activities; and (iii) the semi-arid climate supports evaporative treatment technologies but also limits the effectiveness of certain biological treatment approaches that are temperature-dependent.
Sensitive Receptors. The shallow alluvial aquifer is a significant water resource in the Gallatin Valley, and numerous domestic and agricultural wells are completed in this aquifer in the vicinity of the Facility. A survey of Montana Bureau of Mines and Geology well records and MT DEQ's Ground Water Information Center database indicates that approximately 35 domestic water supply wells and 12 agricultural/irrigation wells are located within a 2-mile radius of the Facility. The nearest known domestic water supply well is located approximately 0.75 miles east-southeast of the Facility boundary, along the projected path of groundwater flow from the site.
The City of Belgrade operates a municipal water supply system served by several high-capacity production wells completed in the deeper alluvial and Tertiary aquifer systems. The nearest municipal production well is located approximately 2.8 miles east-northeast of the Facility. While the deeper aquifer system is generally hydraulically separated from the shallow alluvial aquifer by intervening clay units, the potential for vertical hydraulic communication through natural or anthropogenic pathways must be evaluated as part of the CMS.
Ecological receptors in the vicinity include the East Gallatin River and associated riparian habitat, wetlands along the Middle Creek Ditch corridor, and agricultural lands that may be irrigated with groundwater from the shallow aquifer. The East Gallatin River supports populations of brown trout, rainbow trout, and whitefish, and is classified as a B-1 waterbody under Montana's surface water quality standards.
III. NATURE AND EXTENT OF CONTAMINATION
3.1 Summary of Contaminants of Concern
Based on the results of the RCRA Facility Investigation ("RFI"), EPA Compliance Evaluation Inspections, historical groundwater and soil monitoring data, and MPDES discharge monitoring reports, the following contaminants of concern ("COCs") have been identified at the Gallatin Site:
Carbon Disulfide (CS₂) in Groundwater. Carbon disulfide is the primary groundwater contaminant of concern at the Facility. CS₂ has been detected in monitoring wells at concentrations ranging from below the method detection limit to a maximum detected concentration of 890 micrograms per liter (µg/L), measured in monitoring well MW-7 during the October 2023 quarterly sampling event. The federal Maximum Contaminant Level ("MCL") for carbon disulfide under the Safe Drinking Water Act is 10 µg/L (established by EPA as a non-zero Maximum Contaminant Level Goal under 40 C.F.R. Part 141). The maximum detected concentration of 890 µg/L therefore exceeds the MCL by a factor of approximately 89. Montana's groundwater quality standard for CS₂, adopted by reference to the federal MCL, is also 10 µg/L. The CS₂ contamination in groundwater is attributable to releases from manufacturing process areas, raw material handling and storage, and the SWMUs identified at the Facility.
Xanthate Decomposition Products in Soil and Groundwater. Sodium xanthate and its decomposition products, including carbon disulfide (which is both a raw material and a xanthate decomposition product), carbonyl sulfide, and various organic sulfur compounds, have been detected in soil and groundwater samples collected from areas associated with xanthate production and waste management. The fate and transport of xanthate decomposition products in the subsurface environment are complex and require further characterization as part of the CMS data gap evaluation.
Volatile Organic Compounds (VOCs) in Subsurface Soils. Toluene and xylene have been detected in subsurface soil samples at concentrations exceeding risk-based screening levels in areas associated with solvent storage, waste management, and manufacturing operations. Toluene concentrations in soil range from below the method detection limit to 48 milligrams per kilogram (mg/kg), and xylene concentrations range from below the method detection limit to 31 mg/kg. These VOC detections are found at depths ranging from approximately 4 to 18 feet bgs, with the highest concentrations generally associated with the SWMU source areas.
Total Suspended Solids (TSS) in Effluent Discharge. The Facility's treated process wastewater effluent has exceeded the MPDES permit limits for total suspended solids on multiple occasions. TSS, while not a hazardous constituent per se, is a regulated parameter under the MPDES permit that serves as an indicator of treatment system performance and has direct implications for the quality of discharged effluent reaching receiving waters. The MPDES permit limit for TSS is 30 mg/L (monthly average) and 45 mg/L (daily maximum). Exceedances of both the monthly average and daily maximum limits have been documented.
3.2 Solid Waste Management Units (SWMUs)
Three Solid Waste Management Units have been identified at the Gallatin Site through the RCRA Facility Investigation process and EPA compliance evaluation inspections. Each SWMU is described below:
SWMU-1: Former Chemical Reagent Waste Storage Area. SWMU-1 is located in the northwestern portion of the Facility, approximately 200 feet north of Building A (sodium xanthate production). The area encompasses approximately 12,000 square feet (approximately 0.28 acres) and consists of a partially bermed, unlined earthen pad that was historically used from approximately 1993 to 2008 for the temporary storage and staging of containerized chemical reagent waste, including off-specification sodium xanthate product, spent reaction residues, and contaminated process materials. Waste containers historically stored at SWMU-1 included 55-gallon steel drums and 275-gallon intermediate bulk containers (totes). Evidence of container corrosion, spillage, and surface staining was documented during EPA's 2019 CEI. Soil sampling conducted during the RFI revealed elevated concentrations of CS₂, xanthate decomposition products, and VOCs in soils beneath and adjacent to the former storage area, with contamination extending to depths of approximately 12 feet bgs.
SWMU-2: Process Wastewater Evaporation Pad. SWMU-2 is located in the central-southern portion of the Facility, approximately 150 feet south of Building B (dithiophosphate collector production). The area encompasses approximately 18,000 square feet (approximately 0.41 acres) and consists of a concrete-lined but deteriorated pad that was used from approximately 1995 to 2012 as an evaporation and volume-reduction area for process wastewater and washdown water that could not be accommodated by the wastewater treatment system during peak production periods. The concrete lining of the pad exhibits visible cracking, spalling, and joint deterioration, and the RFI confirmed that the liner integrity had been compromised, allowing infiltration of process wastewater to the underlying soils and the shallow alluvial aquifer. Groundwater monitoring wells installed downgradient of SWMU-2 have consistently shown elevated CS₂ concentrations, and this area is believed to be a significant contributing source to the CS₂ groundwater plume.
SWMU-3: Former Drum Storage and Staging Area. SWMU-3 is located in the eastern portion of the Facility, approximately 100 feet east of the product storage warehouse and adjacent to the rail siding. The area encompasses approximately 8,500 square feet (approximately 0.20 acres) and was historically used from approximately 1993 to 2015 for the storage and staging of both empty and full drums of raw materials, intermediates, and waste. Waste handling practices at SWMU-3 included the consolidation and overpacking of leaking or damaged containers, which contributed to localized soil contamination. Soil boring data from the RFI indicate the presence of toluene and xylene contamination in the vadose zone beneath SWMU-3 at concentrations above risk-based screening levels, extending to depths of approximately 15 feet bgs.
Releases from all three SWMUs have been documented through the RFI process and are summarized in the RFI Final Report (Pinnacle Creek Environmental, LLC, September 2024), EPA CEI reports (2019, 2021), and historical facility monitoring records. The combined releases from these SWMUs, together with releases from manufacturing process areas and material handling operations, have resulted in the CS₂ groundwater plume and soil contamination conditions that are the subject of this CMS.
3.3 Groundwater Contamination
CS₂ Plume Delineation
The CS₂ groundwater plume at the Gallatin Site has been delineated through a network of 24 monitoring wells installed during the RFI and prior facility investigation programs. The plume originates from multiple source areas within the Facility, with the highest concentrations observed in the vicinity of SWMU-2 (process wastewater evaporation pad) and SWMU-1 (former chemical reagent waste storage area).
The lateral extent of the CS₂ plume, as defined by the 10 µg/L (MCL) isoconcentration contour, extends approximately 2,800 feet in the downgradient (east-southeast) direction from the primary source area at SWMU-2. The plume width, measured perpendicular to the groundwater flow direction, is approximately 900 feet at its widest point. The leading edge of the plume, at the most recent sampling event (October 2023), was detected at monitoring well MW-21, located approximately 2,800 feet east-southeast of SWMU-2, at a concentration of 14 µg/L. The plume appears to be approaching steady-state conditions in the downgradient direction based on comparison of plume extent over the most recent five years of monitoring data.
Vertically, CS₂ contamination is present primarily in the upper 30 feet of the saturated zone, corresponding to the upper portion of the shallow alluvial aquifer. Depth-discrete sampling conducted at nested monitoring well clusters indicates that CS₂ concentrations decrease significantly below approximately 40 feet bgs, suggesting that the lower portion of the alluvial aquifer and the underlying Tertiary bedrock are not significantly impacted. However, additional vertical characterization may be warranted in the source areas where higher concentrations are present.
Concentration Distribution. CS₂ concentrations in the source area (vicinity of SWMU-2 and SWMU-1) range from approximately 200 to 890 µg/L, with the maximum concentration of 890 µg/L detected in monitoring well MW-7, screened from 15 to 25 feet bgs, approximately 75 feet downgradient of SWMU-2. Concentrations diminish progressively in the downgradient direction, with concentrations of approximately 50 to 150 µg/L at distances of 500 to 1,000 feet from the source, and concentrations of approximately 10 to 30 µg/L at distances of 2,000 to 2,800 feet from the source. This attenuation pattern is consistent with the combined effects of dispersion, sorption, and natural degradation processes, although the relative contribution of each process requires further evaluation.
Xanthate Decomposition Product Distribution
Xanthate decomposition products, including carbonyl sulfide and various organic sulfur compounds, have been detected at lower concentrations than CS₂ in groundwater, generally co-located with the CS₂ plume but at levels that are typically an order of magnitude lower. The behavior of these compounds in the subsurface, including their degradation rates and potential to generate secondary contaminants, is a data gap to be addressed in Phase 1 of the CMS.
Monitoring Well Network
The Facility's groundwater monitoring network currently consists of 24 monitoring wells, including 6 upgradient background wells, 12 compliance monitoring wells within and immediately downgradient of the plume, and 6 sentinel wells at the plume margins. Groundwater samples are collected quarterly for a comprehensive analyte list that includes CS₂, VOCs, xanthate decomposition products, general chemistry parameters, and metals. Laboratory analyses are performed using EPA Method 8260D (VOCs including CS₂), EPA Method 8270E (semi-volatile organic compounds), and standard methods for general chemistry parameters. Historical groundwater monitoring data extending back to 2005 are available for analysis of concentration trends and natural attenuation rates.
3.4 Soil Contamination
VOC contamination, primarily toluene and xylene, has been documented in subsurface soils at the Gallatin Site in areas associated with the three SWMUs and adjacent material handling areas. The affected soil area, as defined by the extent of VOC detections above risk-based screening levels, encompasses approximately 4.5 acres in aggregate across the three SWMU areas and adjoining zones.
Soil contamination at SWMU-1 consists of CS₂, toluene, and xylene at depths of approximately 4 to 12 feet bgs, with maximum toluene concentrations of 48 mg/kg and maximum xylene concentrations of 31 mg/kg. Soil contamination at SWMU-2 is dominated by CS₂ and xanthate decomposition products at depths of approximately 3 to 18 feet bgs, extending through the vadose zone to the water table. Soil contamination at SWMU-3 consists primarily of toluene and xylene at depths of approximately 5 to 15 feet bgs, with lower concentrations of CS₂.
Soil characterization data have been collected through a total of 42 soil borings and associated laboratory analyses conducted during the RFI. Soil samples were analyzed for VOCs (EPA Method 8260D), semi-volatile organic compounds (EPA Method 8270E), metals (EPA Methods 6010D and 7470A), and total petroleum hydrocarbons. Additional soil sampling is anticipated as part of the CMS supplemental investigation to refine the lateral and vertical extent of contamination and provide data necessary for remedy design and cost estimation.
3.5 Surface Water and Effluent
The Facility's MPDES Permit No. MT-0029874 authorizes the discharge of treated process wastewater and stormwater to the unnamed drainage ditch that ultimately flows to the East Gallatin River. The permit establishes effluent limits for multiple parameters, including CS₂ (daily maximum of 20 µg/L) and TSS (monthly average of 30 mg/L; daily maximum of 45 mg/L), among others.
Between January 2021 and June 2024, a total of 14 documented exceedances of MPDES permit effluent limits for CS₂ and TSS were recorded in the Facility's Discharge Monitoring Reports ("DMRs") submitted to MT DEQ. Of the 14 exceedances, 8 involved CS₂ effluent limit violations (with maximum reported effluent CS₂ concentrations of up to 62 µg/L, approximately three times the daily maximum limit) and 6 involved TSS limit violations (with maximum reported effluent TSS concentrations of up to 87 mg/L, approximately twice the daily maximum limit). The exceedances were concentrated during periods of high production volume and during spring runoff events when stormwater inflow exceeded the treatment system's hydraulic capacity. A detailed tabulation of the 14 exceedances, including dates, parameters, reported concentrations, and applicable limits, is provided in Appendix E.
The current effluent treatment system, which was constructed in 1993 and upgraded in 2003, utilizes equalization, chemical precipitation with ferric chloride, air stripping for CS₂ removal, activated sludge biological treatment, and secondary clarification. The system's design capacity is 150,000 gallons per day, but actual influent flows during peak production and wet weather periods have exceeded 200,000 gallons per day, resulting in reduced treatment effectiveness and the documented permit exceedances. Deficiencies in the treatment system, including the age and condition of the air stripping tower packing, insufficient equalization volume, and inadequate stormwater segregation, have been identified as contributing factors. Evaluation of effluent treatment system upgrades or replacement is a key component of the CMS alternatives analysis.
IV. CORRECTIVE MEASURES OBJECTIVES
4.1 Overall Objectives
The corrective measures to be evaluated through the CMS shall be designed to achieve the following objectives:
(a) Protect human health and the environment from further releases of hazardous waste and hazardous constituents from the SWMUs and other areas of contamination at the Gallatin Site, and mitigate the risks posed by existing contamination in soil, groundwater, and surface water.
(b) Achieve compliance with RCRA corrective action standards as set forth in 40 C.F.R. Part 264, Subpart F, and the corresponding provisions of the Montana Hazardous Waste Act and implementing regulations, including the media cleanup standards and performance criteria applicable to corrective measures at RCRA facilities.
(c) Attain groundwater cleanup levels for CS₂ of 10 µg/L or less, equal to the federal Maximum Contaminant Level, and achieve compliance with applicable Montana surface water quality standards in groundwater that discharges to or has the potential to impact surface water bodies, including the East Gallatin River.
(d) Remediate VOC-contaminated soils (toluene, xylene, and CS₂) to levels that are protective of groundwater quality (i.e., concentrations that will not leach at rates sufficient to cause groundwater concentrations to exceed cleanup levels) and direct-contact exposure pathways (i.e., concentrations that do not pose unacceptable risk to human health through dermal contact, ingestion, or inhalation of soil vapors by workers or future occupants).
(e) Achieve and maintain compliance with all MPDES permit effluent limits at the Facility's permitted discharge point(s), including the CS₂ and TSS limits that have been the subject of documented exceedances, through upgrade or replacement of the existing effluent treatment system.
(f) Satisfy the performance standards and completion criteria established in the Consent Decree, including time-certain milestones for remedy implementation and operation, demonstration of compliance with cleanup levels through performance monitoring, and ultimately the attainment of final remediation objectives sufficient to warrant termination of the Consent Decree's environmental monitoring and reporting obligations for the Gallatin Site.
4.2 Applicable or Relevant and Appropriate Requirements (ARARs)
The CMS will identify and evaluate all federal and state requirements that are applicable or relevant and appropriate to the corrective measures alternatives under consideration. Preliminary identification of potential ARARs includes the following:
(a) Federal RCRA Corrective Action Standards (40 C.F.R. Part 264, Subpart F): Including the requirements for corrective action at SWMUs, groundwater monitoring and cleanup standards, and the standards for final corrective measures design and implementation.
(b) Montana Surface Water Quality Standards (ARM 17.30.600 *et seq.*): Establishing the beneficial use classifications, numeric criteria, and narrative standards applicable to surface waters that may be affected by releases from the Facility, including the East Gallatin River (classified as a B-1 waterbody).
(c) Montana Groundwater Quality Standards (ARM 17.30.1001 *et seq.*): Establishing the numeric standards for groundwater quality, including adoption by reference of federal MCLs and Montana-specific standards for parameters not addressed by federal regulations.
(d) MPDES Permit Requirements (Montana Code Annotated § 75-5-401 *et seq.* and ARM 17.30.1301 *et seq.*): Including the technology-based and water-quality-based effluent limits established in the Facility's MPDES permit, and the requirements for compliance with anti-degradation standards.
(e) Montana Hazardous Waste Act (Montana Code Annotated §§ 75-10-401 *et seq.* and ARM Title 17, Chapter 53): Including the state-authorized RCRA program requirements for hazardous waste treatment, storage, disposal, and corrective action.
(f) Federal and State Maximum Contaminant Levels (MCLs): Including the MCL for CS₂ (10 µg/L), the MCL for toluene (1,000 µg/L), and the MCL for xylenes (10,000 µg/L), as established by EPA under 40 C.F.R. Part 141 and adopted by reference under Montana's groundwater quality standards.
(g) Additional ARARs: Any additional federal, state, or local requirements identified during the CMS process, including but not limited to air emission standards applicable to remediation activities (e.g., NESHAP requirements for air stripping units), construction and building permit requirements, and solid waste disposal requirements for excavated contaminated soils.
4.3 Cleanup Levels
The following cleanup levels will serve as the preliminary performance standards for the CMS alternatives evaluation. These levels are subject to refinement based on the results of the CMS risk assessment and site-specific analyses, and are subject to EPA approval:
Site-specific risk-based cleanup levels for toluene and xylene in soil will be developed during Phase 2 of the CMS using standard risk assessment methodologies, including EPA's Soil Screening Guidance and Regional Screening Level calculator, with consideration of the industrial land use classification of the Facility and the protection of groundwater quality through soil leaching pathway analysis. Cleanup levels for xanthate decomposition products will be established based on a compound-specific risk assessment, taking into account the available toxicological data, exposure pathways, and environmental fate and transport characteristics of these compounds.
V. SCOPE OF WORK — CMS ACTIVITIES
5.1 Phase 1: Data Gap Evaluation and Supplemental Investigation
5.1.1 Existing Data Review
Pinnacle Creek Environmental will conduct a comprehensive review and evaluation of all existing environmental data for the Gallatin Site, including but not limited to:
(a) RFI Final Report (Pinnacle Creek Environmental, LLC, September 2024) and all supporting data packages;
(b) EPA Compliance Evaluation Inspection reports (2019 and 2021) and associated sampling data;
(c) Historical groundwater monitoring data (2005–present), including quarterly analytical results, water level measurements, and plume maps;
(d) Soil boring logs, soil analytical results, and geotechnical data from all investigation programs;
(e) MPDES Discharge Monitoring Reports (2018–present);
(f) Process water treatment system design documents, operating records, and maintenance logs;
(g) RCRA permit application documents, permit modifications, and compliance history;
(h) Facility waste generation and management records, manifests, and land disposal restriction notifications;
(i) Air monitoring and emission inventory data; and
(j) Any other relevant environmental data, reports, or records maintained by TSC, EPA, or MT DEQ.
5.1.2 Data Gap Identification
Based on the existing data review, Pinnacle Creek will prepare a Data Gap Evaluation Report identifying the specific data needs that must be addressed through supplemental investigation in order to support the development and evaluation of corrective measures alternatives. Anticipated data gaps include, but may not be limited to:
(a) Refined delineation of the downgradient and lateral margins of the CS₂ groundwater plume, particularly in the east-southeast direction toward domestic water supply wells;
(b) Vertical characterization of CS₂ distribution in the deeper portions of the shallow alluvial aquifer beneath source areas;
(c) Assessment of natural attenuation processes for CS₂ in groundwater, including biodegradation rates, geochemical indicators, and daughter product formation;
(d) Additional soil characterization at and between SWMUs to refine the volume and mass of contaminated soil requiring remediation;
(e) Geotechnical data necessary to support remedy design, including soil bearing capacity, permeability, and constructability considerations for cap and cover systems;
(f) Aquifer testing data (pumping tests) to refine hydraulic parameters used in groundwater modeling for pump-and-treat remedy design; and
(g) Characterization of the xanthate decomposition product fate and transport properties in the subsurface.
5.1.3 Supplemental Investigation Activities
Following EPA review and approval of the Supplemental Investigation Work Plan, Pinnacle Creek will conduct the following field activities:
(a) Supplemental Soil Sampling: Installation of additional soil borings at and between the three SWMUs and in areas identified as data gaps, with collection of continuous soil samples for laboratory analysis. It is estimated that approximately 15 to 20 additional soil borings will be required, each extending to depths of approximately 20 to 30 feet bgs.
(b) Supplemental Groundwater Characterization: Installation of up to 8 additional monitoring wells, including both shallow and deep completions, to refine plume delineation and provide data for remedy design. New wells will be designed with appropriate screen intervals, constructed in accordance with Montana well construction standards (ARM 36.21.801 et seq.), and developed to ensure representative groundwater quality data.
(c) Geotechnical Investigation: Performance of geotechnical borings and laboratory testing (grain size analysis, Atterberg limits, permeability, unconfined compressive strength) at locations relevant to remedy design, including the SWMU areas where engineered caps or covers may be considered, and areas where treatment system foundations or other structures may be constructed.
(d) Aquifer Testing: Performance of constant-rate pumping tests at two to three locations within the CS₂ plume to refine the estimates of hydraulic conductivity, transmissivity, storativity, and specific yield. Pumping test data will be used to calibrate a groundwater flow model for pump-and-treat remedy design and optimization.
(e) Natural Attenuation Assessment: Collection of groundwater samples for geochemical parameters indicative of natural attenuation processes, including dissolved oxygen, oxidation-reduction potential, nitrate, sulfate, dissolved iron, dissolved manganese, and dissolved gases (methane, ethene, ethane). These data will be used to evaluate the potential for monitored natural attenuation as a component of the groundwater remedy.
5.1.4 Phase 1 Timeline
Phase 1 activities will commence within 60 days of the Consent Decree Effective Date. Based on an expected Effective Date of June 14, 2025, the Phase 1 commencement date is approximately August 13, 2025. Specific Phase 1 milestones are set forth in the Master Schedule in Section VIII.
5.2 Phase 2: Development of Corrective Measures Alternatives
5.2.1 Technology Identification and Screening
Pinnacle Creek will identify and screen potential corrective measures technologies applicable to each contaminated medium and each type of source or exposure pathway requiring remediation at the Gallatin Site. The technology screening will consider the full range of available remediation technologies, including but not limited to:
SWMU Source Control and Closure/Capping:
(a) Engineered cover/cap systems (low-permeability soil covers, geomembrane caps, evapotranspiration covers);
(b) Soil stabilization/solidification;
(c) Excavation and off-site disposal at permitted hazardous waste or Subtitle D facilities;
(d) In-situ treatment (chemical oxidation, enhanced bioremediation); and
(e) Institutional controls and deed restrictions.
CS₂ Groundwater Plume Treatment:
(a) Pump-and-treat systems (groundwater extraction with above-ground treatment by air stripping, activated carbon adsorption, advanced oxidation, or biological treatment);
(b) In-situ chemical oxidation (ISCO) using permanganate, persulfate, or Fenton's reagent;
(c) In-situ enhanced bioremediation through substrate addition;
(d) Monitored natural attenuation (MNA) as a stand-alone remedy or in combination with active treatment;
(e) Air sparging/soil vapor extraction (AS/SVE) combinations for source area and dissolved-phase treatment in the upper saturated zone; and
(f) Permeable reactive barriers.
VOC Soil Remediation:
(a) Soil vapor extraction (SVE);
(b) Excavation and off-site disposal;
(c) In-situ chemical oxidation;
(d) Ex-situ thermal treatment; and
(e) Bioventing/biostimulation.
Effluent Treatment System Upgrade or Replacement:
(a) Upgrade of existing air stripping system (repacking, increased tower capacity);
(b) Addition of granular activated carbon polishing units;
(c) Construction of new equalization and stormwater management facilities to reduce peak hydraulic loading;
(d) Advanced oxidation processes (UV/H₂O₂, ozone) for enhanced CS₂ destruction; and