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National Priorities List

The city of Butte, Montana, is known as the “richest hill on Earth” because it contains one of the largest deposits of copper ore ever discovered in the United States, along with significant amounts of silver, zinc, manganese, and other minerals. Rich ore deposits made Butte and the nearby town of Anaconda the center of more than a century of extensive mining, milling and smelting activity, starting in Butte in the 1860’s. At their peak these operations employed many thousands of people, and included over 300 mines, more than 19 mills and smelters, and an extensive network of railroad lines that carried over 20 billion pounds of copper to the rest of the nation. A byproduct of these operations was the creation of waste rock, mill tailings, smelter slag, and other waste that was disposed of in the Butte area, impacting the soil, groundwater, and surface water in Silver Bow Creek, which flows through the center of Butte.

In 1982, the U.S. Environmental Protection Agency (EPA) proposed to add approximately 28 miles of Silver Bow Creek to the Superfund National Priorities List (NPL). The listing process evaluates initial information about a contaminated site, and that information is used to prioritize sites for further investigation and remedial action. EPA placed the Silver Bow Creek Site on that list in 1983,1 and expanded the Site boundaries in 1987.2

Today the Silver Bow Creek/Butte Area NPL Site includes the creek, floodplain and hillside areas impacted by former mining, milling and smelting activity in Butte and Walkerville; the stormwater systems in Butte and Walkerville that drain to the creek corridor; an extensive network of underground mine tunnels and workings in the historic mining district that are below the groundwater table; and a former open pit mine known as the Berkeley Pit.

Remedy Enforcement Actions for BPSOU

After placing a site on the NPL, EPA has four tools it can use to continue the investigation and begin to clean up and remediate the contamination. EPA can:

  • Perform work itself and seek to recover its costs from the Potentially Responsible Parties (PRPs) in a cost-recovery lawsuit;
  • Order PRPs to perform work through an administrative order;
  • Seek a court order requiring PRPs to perform and/or pay for the work; and
  • Enter into a settlement with PRPs who are willing to perform all or portions of the work.

EPA has used every one of these tools at the Butte Priority Soils site. It has conducted some of the work itself, starting in 1982. Beginning in 1988 EPA – working in consultation with Montana Department of Environmental Quality (DEQ) – also issued a series of administrative orders requiring Atlantic Richfield Company (Atlantic Richfield) and other potentially liable parties, including Butte-Silver Bow, to perform removal actions, and to investigate and remediate the contamination generated by former mining, milling and smelting activity.

These administrative orders are listed below. Each order has a number that identifies the EPA Region that issued it (in this case, EPA Region 8) and the year when it was issued. For example, Order No. CERCLA VIII-88 was issued by EPA Region 8 in 1988. Where EPA performed the work, no order number is listed. Orders that require work which is ongoing today are identified below as “ongoing” work:

  • Walkerville Time Critical Removal Action I (TCRA), Order No. CERCLA-VIII-88-05
  • Timber Butte TCRA, Order No. CERCLA-VIII-89-21
  • Butte Priority Soils Operable Unit (BPSOU) TCRAs, Orders Nos. CERCLA-VIII-90-1, CERCLA-VIII-90-12
  • BPSOU EE/CA Administrative Order on Consent No. CERCLA-VIII-91-13
  • Colorado Smelter TCRA, Order No. CERCLA-VIII-92-04
  • Anselmo Mine Yard & Acquisition /Silver Hill TCRA, Order No. CERCLA-VIII-92-23
  • Walkerville TCRA II - EPA performed work
  • Railroad Beds TCRA, Order No. CERCLA-VIII 2000-02 (ongoing)
  • Stormwater TCRA, Order No. CERCLA-VIII 95 58 (ongoing)
  • Walkerville TCRA III - EPA performed work
  • Lower Area One EE/CA Administrative Order on Consent No. CERCLA-VIII-90-14
  • Lower Area One Non-Time Critical Removal Action (NTCRA), Order No. CERCLA-VIII-92-17 (ongoing)
  • Manganese TCRA - EPA performed work
  • BPSOU Residential Soils/Waste Dumps NTCRA, Order No. CERCLA-VIII-94-21 (ongoing)
  • EPA and Atlantic Richfield both participated in the Clark Tailings RCRA action (1998), and the Butte Mine Flooding related pump vault interceptor (2002).
  • Remedial Investigation and Feasibility Study (“RI/FS”) for the BPSOU, Administrative Order on Consent Docket No. CERCLA-VIII-92-18. The RI/FS and a subsequent supplemental feasibility report studied options for final remedies for BPSOU.
  • Partial Remedial Design/Remedial Action Implementation, Operation and Maintenance, Order No. CERCLA-08-2011-0011 (ongoing)

EPA and the U.S. Department of Justice also filed a lawsuit against Atlantic Richfield Company in 1989 in federal court in Montana, seeking to hold the company responsible for all contamination at the Site. Atlantic Richfield answered the complaint, raising defenses and asserting counterclaims that sought to hold other liable PRPs, including federal agencies, responsible for the contamination those parties contributed or caused. The parties have amended the complaint, answer and counterclaims several times, and have conducted extensive discovery into various sources of contamination at the Site.3

In a separate but related lawsuit filed in federal court in Montana in 1983, the State of Montana sought to recover natural resource damages from Atlantic Richfield under CERCLA and state law. The State alleged that contamination from past mining, milling, mineral processing and related activities in Butte and Anaconda had injured fish and wildlife, surface and ground water, soil and habitat.4 The State sought to recover damages for resources that would not be restored by EPA’s remedies for the site. A trial to resolve disputes over liability and damages began in March 1997 and ceased in 1998, before trial was complete.

In 1998 Atlantic Richfield reached a partial settlement of remedy and natural resource damage claims involving a 26-mile segment of Silver Bow Creek and the associated floodplain, beginning just outside the city of Butte and extending west to the Warm Springs Ponds. The settlement was incorporated into the Streamside Tailings Operable Unit Consent Decree and approved by the court in 1999.5

As part of that consent decree, the parties agreed to enter a series of future settlement negotiations to resolve disputes over liability for remedy work and costs at different areas within the larger Site. Each negotiation is limited to a portion of the Site, and begins after EPA selects a final remedy for that portion of the Site. Litigation over the Butte Priority Soils Operable Unit remedy and related costs was suspended in order to provide EPA with sufficient time to select a final remedy for that area, and to give the parties additional time to attempt to negotiate a consent decree to implement some or all of the final remedy.

Remedy Selection

In December 2004, EPA, in consultation with DEQ, analyzed remedial action alternatives and proposed what it deemed to be the most appropriate remedy for the BPSOU and adjacent residential areas in a Proposed Plan. Pursuant to CERCLA, 42 U.S.C. § 9617, EPA published notice of the plan in a local newspaper and provided the public with an opportunity to comment on it.

Atlantic Richfield, the State of Montana, and Butte-Silver Bow each submitted comments on EPA’s proposed remediation plan, presenting different views of the feasible, cost-effective and appropriate remedy for contamination that impacts Silver Bow Creek. In general:

  • Montana DEQ supported a remedy that would remove tailings buried in the former and the current creek corridors, characterizing these wastes as a threat to groundwater and surface water in Silver Bow Creek.
  • Montana’s natural resource trustee indicated that if tailings remained in place, the trustee would continue to seek damages from responsible parties to restore or replace water resources impacted by former mining operations. Atlantic Richfield supported EPA’s proposed plan for a remedy that would leave the tailings in place and use other methods to improve and protect water quality in the creek. These technologies included continued operation of a groundwater collection and treatment system in the historic creek corridor, and the construction and operation of additional catch basins to collect and treat contaminated stormwater, to significantly reduce the amount of metals that can flow into the creek.6 Since that remedy would not restore all water resources in Butte to the condition they would be in without any metal or other contamination, Atlantic Richfield recognized that further action – involving further litigation and/or settlement - would be needed to resolve the State’s claims for natural resource damages.
  • Butte-Silver Bow supported the plan to leave tailings in place, so long as Atlantic Richfield would: i) fund the design, construction, operation and maintenance of the other remedies; ii) include funds to repair and upgrade deteriorating portions of the existing municipal stormwater system that impact water quality in the creek; and iii) provide funds to restore, redevelop and improve the Butte community, in order to protect local taxpayers from the potentially high costs of these and other remedies and restoration projects.7

On September 25, 2006, EPA issued a Record of Decision (“2006 Record of Decision”) selecting further remedial actions to be implemented at the BPSOU. DEQ concurred in some, but not all, of the remedy actions described in that decision. DEQ did not concur with the decision to leave the Parrot Tailings, Diggings East Tailings and the North Side Tailings in place, reiterating its belief that the tailings removal would improve groundwater quality and increase the long-term effectiveness and permanence of the creek remedy.8

After receiving additional environmental data and analysis and other new information, on July 18, 2011, EPA issued an Explanation of Significant Differences (“2011 ESD”), which modified the 2006 Record of Decision, describing changes to the remedy and ground water monitoring requirements.

On July 20, 2011, EPA issued a unilateral administrative order requiring Atlantic Richfield, Butte-Silver Bow, and other responsible parties to implement certain remedial design, remedial action, operation and maintenance activities at the BPSOU to implement the remedies EPA selected in 2006 and 2011.

A vast amount of environmental data was collected and analyzed after the original record of decision was issued in 2006 and the explanation of significant differences was issued in 2011. Essential remedy components and methods were tested to evaluate their effectiveness. Based on that work, the parties are now in a better position to evaluate the feasibility and effectiveness of further work to reduce the amount of metals that flow into Silver Bow Creek by:

  • Removing and capping more mine waste sources on Butte Hill, to reduce the potential for metals to erode into stormwater;
  • Operating and maintaining more catch basins and other remedy structures to collect and treat more contaminated stormwater before it reaches the creek;
  • Further improving the Butte-Silver Bow stormwater sewer system in order to reduce the amount of metals that reach Silver Bow Creek during storm events;
  • Collecting and treating more contaminated groundwater to reduce potential impacts to the creek;
  • Removing more floodplain waste from portions of Blacktail Creek and Silver Bow Creek; and
  • Moving Silver Bow Creek out of the slag canyon and into a new, clean channel across the former Butte Reduction Works site.

After implementing these types of remedies on a smaller scale in portions of the site, the parties now have a more complete and holistic view of the remedies that are effective, feasible, and that work in the Butte environment. This information has been carefully analyzed and used to identify scientifically sound, technically feasible, cost-effective options for completing a permanent and sustainable remedy for the BPSOU.

After receiving this additional environmental data and analysis, and other new information, on April 11, 2019, EPA published notice of a Proposed Plan (“2019 Proposed Plan”) to further amend the 2006 Record of Decision/2011 ESD, taking new information and analysis into account. EPA provided an opportunity for written and oral comments from the public. Atlantic Richfield, the State of Montana, Butte-Silver Bow and members of the public all provided comments.

On February 4, 2020, after considering the public comments and other information in the administrative record, EPA issued a Record of Decision Amendment (“2020 Record of Decision Amendment”) modifying the 2006 Record of Decision/2011 ESD to provide for, among other things, certain changes in surface water standards within the BPSOU, and to further define certain surface and groundwater and soil remedial requirements at the BPSOU and residential areas outside the BPSOU, but within Silver Bow County DEQ concurs in the amendments.

EPA’s final remedy for the BPSOU is set forth in the 2006 Record of Decision, as modified by the 2011 ESD, and as further modified by the 2020 Record of Decision Amendment. All three documents are attached as Appendix A to the proposed partial consent decree for the BPSOU.

A copy of the proposed consent decree for the Butte Priority Soils Operable Unit and its appendices is available on the Consent Decree page of this website.

The proposed consent decree contains the additional work requirements, work scope and work plans that the settling parties propose to use to design, construct, operate and maintain the final remedy described in the consent decree. These documents describe what the remedy will include, how the work will be done, how it will be monitored to evaluate its effectiveness, and how it will be maintained to ensure it continues to be effective in the future.

Additional information about the work conducted at the BPSOU is included in the Completing the Remedy page of this website, and on EPA’s website.

1 48 Fed. Reg. 40658 (September 8, 1983)

2 52 Fed. Reg. 27627 (July 22, 1987)

3 The lawsuit is called United States v. Atlantic Richfield Company, Case No. CV-89-39-BU-SEH filed in the US District Court of Montana.

4 The lawsuit is called Montana v. Atlantic Richfield Company, Case No. CV-83-217-HLN-SEH filed in the US District Court of Montana.

5 The settlement was documented in two consent decrees – one in the lawsuit filed by the U.S., and one in the lawsuit filed by State. Collectively, the two settlements provided the State with funds to implement a stream and floodplain remedy coordinated with restoration work in the portion of Silver Bow Creek that begins outside the City of Butte and flows downstream into the Warm Springs Ponds. At the same time, Atlantic Richfield settled the majority of the natural resource damage claims brought against it by the State, the United States and the Confederated Salish and Kootenai tribes. Atlantic Richfield settled the remaining natural resource damage claims pending against it in 2008, in connection with two consent decrees for the Clark Fork River Operable Unit , subject to certain reserved rights.

6 Atlantic Richfield comments on EPA’s Proposed Plan for the Butte Priority Soils remedy (March 2005), and EPA’s responses to them (2006), are included in the 2006 Record of Decision for BPSOU, at App. C, Section 2.

7 Butte-Silver Bow’s comments on EPA’s Proposed Plan for the Butte Priority Soils remedy (March 2005), and EPA’s responses to them (2006), are included in the 2006 Record of Decision for BPSOU, at App. C, Section 2.

8 Letter from Richard Opper, Director of Montana DEQ, to Max Dodson, EPA 8 Regional Administrator, regarding State’s Partial Concurrence in the Butte Priority Soils Record of Decision (Sept. 2006). The letter is included in the 2006 ROD, at App. C, Section 1.