BPSOU Remedy


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The volume of water required to cover 1 acre of land (43,560 square feet) to a depth of 1 foot. Equal to 325,851 gallons or 1,233 cubic meters.


An illness or condition characterized by sharpness or severity of sudden onset.


The government entities responsible for enforcing Superfund orders and overseeing remediation activities.


Habitats and ecosystems that exist in bodies of water.


A geologic formation composed of materials such as sand, silt, or gravel that can store and supply groundwater to wells or springs.

Background Level

The average presence of an element, like arsenic or copper, as it occurs naturally in the surrounding environment.

Base Flow

Sustained flow of a stream, in the absence of direct runoff from storm events or snowmelt. Natural or base flow is sustained largely by groundwater.


Relating to or occurring at the bottom of a body of water.

Best Management Practices (BMPs)

Usually refers to an approach designed to utilize best technological and maintenance procedures to reduce water pollution. With regard to remediation construction, BMPs are used to minimize impact to water quality, such as preventing erosion and runoff.

Butte Hill

The historic mining district in the city limits of Butte, atop a rich deposit of copper and other minerals.

Butte Treatment Lagoons

The groundwater treatment facility operated by Atlantic Richfield in a wetlands setting.


A layer of soil, clay or other material installed over the top of a closed landfill or repository to minimize water from seeping into the enclosure. A cap also acts as a barrier to keep people or animals from coming into contact with the covered substance.

Catch Basin

A receptacle located at the point of discharge into a sewer, designed to retain materials that could potentially block up a sewer pipe. A manhole in a city street is an example of a catch basin. A system of channels and catch basins have been installed to capture storm water runoff in Butte. Additional catch basins will be included in the proposed modifications.


Comprehensive Environmental Response, Compensation and Liability Act, the 1980 federal law that established the Superfund program. See “Superfund” below or visit the EPA website for more information.

Clean Water Act

Codified in 1972, the Act establishes structures for the regulation of pollutant discharges into the waters of the U.S., giving the EPA the authority to establish water quality criteria and set wastewater standards for industry.


Actions taken to deal with a release or threatened release of hazardous substances that could affect public health or the environment. The term “cleanup” is sometimes used interchangeably with the terms “remedial action,” “removal action,” “response action” or “corrective action.”


Conformity in fulfilling official requirements


Where two or more rivers or streams flow together.

Consent Decree

A legal document, approved by a federal court judge, that formalizes an agreement reached between the EPA and potentially responsible parties (PRPs) on cleanup actions. A consent decree describes the action PRPs will take and is subject to public comment. It is used for remedial designs and remedial actions or final cleanups.


A remediation method that seals off all possible exposure pathways between a hazardous disposal site and the environment. It generally includes capping and institutional controls.

Contaminants of Concern (COC)

(Also refers to “constituents of concern.”) Contaminants that have been shown through chemical analysis to pose potential risk to human health or an ecological system.


The presence of chemicals in the air, water, or soil that may harm people or the environment. Often these chemicals are the result of human activities.

Cubic Yard

Defined as the volume of a cube with sides of one yard in length. A cubic yard of material can be spread to cover 100 square feet (10 x 10 ft. area) at 3 inches of depth.

Drainage Basin

A land area where precipitation runs off into streams, lakes, rivers and reservoirs.


The sum of all external conditions affecting the life, development and survival of an organism.


The federal Environmental Protection Agency which was established in 1970 by President Nixon. The EPA brought together parts of various government agencies involved with the control of pollution.

Explanation of Significant Differences (ESD)

A document prepared by U.S. EPA to explain its reasons for making a ‘significant change’ to a remedy component, while preserving the overall remedy approach. Examples of such significant changes include: 1) a significant increase (or decrease) in the volume of waste to be removed, which significantly alters the cost and time required to complete the remedy; 2) a significant change in cleanup levels that can be achieved with the selected cleanup method (for example, treating water to a different standard with the same plant); or 3) a decision that it is not feasible to construct a waste landfill on site, and a requirement to transport the waste to a landfill off-site for disposal. More examples can be found in A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other Remedy Selection Decision Documents, at Chapter 7 (U.S. EPA 1999).

Feasibility Study (FS)

The analysis of potential cleanup actions for a Superfund site. The FS usually recommends the selection of a cost-effective and long-term alternative and starts as soon as the remedial investigation (RI) is complete. Together they are commonly referred to as the RI/FS.


The relatively flat and typically dry swath of land that runs alongside a stream, river, or lake that may become flooded during storm events or snowmelt.

Fundamental Change

A fundamental change is one that fundamentally changes the nature of the remedy selected for the site. Fundamental changes must be explained and documented in an amendment to the Record of Decision. Examples of fundamental changes include: 1) replacing a treatment method that failed during pilot testing with a new remedy to excavate and dispose of the waste off-site; 2) replacing a waste containment remedy that failed with a new remedy that requires waste treatment, or waste excavation and disposal off-site; or 3) making a determination to issue technical impracticability waiver for a cleanup goal that is unattainable or impracticable to meet in an area, along with a decision to contain waste in that area, rather than attempting (and failing) to treat it. More examples can be found in A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other Remedy Selection Decision Documents, at Chapter 7 (U.S. EPA 1999).


The supply of fresh water found beneath the earth’s surface (usually in aquifers) which is often used for supplying wells and springs.

Heavy Metals

Metallic elements with high atomic weights such as mercury, chromium, cadmium, copper, arsenic and lead.

Hydraulic Control

The use of science and engineering to control the flow of water. At BPSOU, hydraulic controls will control the movement of contaminated groundwater and stormwater into the creeks.

Institutional Controls

Measures such as access and deed restrictions that separate people from a source of contamination. More than one institutional control may be used at a site.


Key Remedial Elements Construction Completion Report. Visit the BPSOU Statement of Work, Appendix D to the BPSOU Consent Decree article for more information.

Lead Agency

The federal agency (or state agency operating pursuant to a contract or cooperative agreement) that has primary responsibility for coordinating response actions under the National Contingency Plan.

Low Impact Development

Adopting processes based on nature to protect water quality and aquatic habitat, such as streambank restoration.


Montana Department of Environmental Quality, the state agency responsible for laws and regulations designed to protect human health and the environment.

Metro Sewer

Butte’s wastewater treatment plant that was upgraded starting in 2014 to improve quality of Silver Bow Creek and water in the Clark Fork River basin.

Metro Storm Drain (MSD)

A water channel built in the 1930s as a federal work project to reduce flooding and efficiently carry urban and industrial wastes to Silver Bow Creek. Atlantic Richfield has worked with EPA and MDEQ to remediate mine wastes found in the MSD.

Mine Waste

By-products of mining activities where minerals are separated from ores.

Modified Remedy

A change to an EPA-approved Record of Decision (ROD) that occurs when new treatment technologies become available that could be applicable to a site, or when assessments of work completed or data collected indicate a need to adjust a remediation plan in order to make it more effective.

Monitoring Wells

Wells drilled at specific locations where groundwater can be sampled at selected depths and studied to determine the direction of groundwater flow and the types and amounts of contaminants present.

National Priorities List (NPL)

The EPA’s list of hazardous waste sites targeted for cleanup under Superfund.

Operable Unit

A sub-area or sub-unit of a Superfund site. Superfund, or NPL, sites are often divided into operable units to make cleanup more manageable, especially with large sites such as those in the Clark Fork River Basin.

Operations and Maintenance

Activities conducted at a Superfund site after the cleanup is finished to ensure the remedy is effective and operating properly.


Generally, any substance introduced into the environment that adversely affects the usefulness of a resource.

Potentially Responsible Party (PRP)

Those entities or individuals identified by the EPA as potentially liable under CERCLA for cleanup costs. PRPs include generators and present or former owners of facilities or real property where hazardous substances have been stored, treated or disposed of, as well as those who accepted hazardous substances for transport.

Railroad Corridor

An example of successful re-use in Butte. A combination of waste removal and capping took place along railroad tracks throughout Butte. Abandoned tracks were removed and replaced by pedestrian trails. Active lines were cleaned.

Record of Decision (ROD)

A public document that specifies which cleanup alternative EPA has selected for a Superfund site. The ROD is created from information generated during the Remedial Investigation/Feasibility Study (RI/FS).


Under the Montana Metal Mine Reclamation Act, the return of lands disturbed by mining to a post-mining use. (Note: this does not mean that lands are required to be returned to a pre-mining condition.)


In Superfund, a remedy is something that addresses historic substance releases to protect human health and the environmentFor the purposes of the BPSOU CD, the remedy will address wastes generated during historic mining operations and further protect the environment.  

Remedial Action (RA)

The actual construction or implementation phase of a Superfund cleanup that follows remedial design.

Remedial Design (RD)

After a cleanup method is selected, a specific design is developed for the cleanup action.

Remedial Investigation (RI)

A study designed to determine the nature and extent of contamination at a Superfund site. The RI lists cleanup alternatives and is conducted prior to the feasibility study (FS).


In relation to remediation, a location where excavated wastes and materials can be stored safely.


Any action or combination of actions to restore, rehabilitate, replace or acquire the equivalent of injured natural resources and services.

Retention and Detention Basin

Man-made water features designed to control runoff, flooding or stormwater and improve the quality of downstream water. Detention ponds, known as “dry ponds,” provide flood control measures. Retention ponds hold a permanent pool of water and are referred to as “wet ponds.” Some ponds are constructed to serve as both detention and retention facilities.

Retroactive Liability

Parties can be held liable for releases that occurred prior to December 1980 when Congress enacted CERCLA.

Riparian Habitat

Areas adjacent to rivers and streams that support plants and wildlife.

Risk Assessment

A study to estimate the potential health and environmental effects of exposure to chemicals. A risk assessment supplements a remedial investigation.


Loose particles of sand, clay, silt and other substances that settle at the bottom of a water body. The particles originate from eroding soil and from decomposing plants and animals.

Settling Defendant

For the purposes of the Butte Priority Soils Operable Unit Consent Decree, Atlantic Richfield Company and the City and County of Butte-Silver Bow. 


The property addressed by remediation activities that are intended to improve the conditions of soil, surface water, groundwater or air associated with the property.


A glass-like by-product of the smelting process, where a metal has been separated from its ore (rocks or materials that occur naturally in the Earth).


Surface runoff produced by melting snow.

Source Area

(Also non-point source and area source.) Water pollution caused by stormwater or snowmelt moving over an area, washing natural and man-made pollution into a water body. In BPSOU, 178 source areas spanning 422 acres have been reclaimed since the 1990s.


Water that runs off from land as the result of precipitation events, such as heavy rainfall or snow melt.


The water discharge that occurs in a natural or man-made channel.


The Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) of 1980 that authorizes the federal government to respond to actual or potential releases of hazardous substances that may endanger the public health or the environment. The act was amended in 1986 by the Superfund Amendments and Reauthorization Act (SARA).

Surface Water

A river, lake, creek or other body of water that formed above the ground.


Waste separated out from the milling of mineral ores.

Technical Impracticability Evaluation

An assessment of what is practically possible to achieve with known remediation technologies; usually refers to groundwater remediation. A technical impracticality evaluation performed in Butte concluded aquatic life standards can be met in Silver Bow Creek most of the time during base flow conditions; metals concentrations have and will continue to improve during normal high flow conditions when the remedy construction is complete; and impacts from stormwater runoff will be further reduced when additional BMP basins are in place.

Unilateral Administrative Order (UAO)

Under Superfund, gives EPA the authority to order parties to perform cleanup work under certain conditions.

Water Quality Standards

Adopted by states and approved by the EPA. Standards cover the use of a water body and the water quality criteria which must be met to protect the designated use.


An area that is regularly saturated by surface or groundwater.