The terms described below are used throughout this Web site and related documents when discussing transmission line siting and construction.

A - C | D - E | F - M | N - O | P - R | S - U | V - Z

Alternative/Alternate: Options that a federal agency considers to address the significant issues and meet the purpose of and need for a proposed project in an environmental analysis. Also used to describe other routes under consideration.

Bureau of Land Management (BLM): A federal agency under the U.S. Department of the Interior that is responsible for carrying out a variety of programs for the management and conservation of resources on 258 million acres. The BLM manages multiple resources and uses, including energy and minerals, timber, forage, recreation, wild horse and burro herds, fish and wildlife habitat, wilderness areas, and archaeological, paleontological and historical sites. The BLM has been designated as the lead federal agency for the environmental review of the Gateway West Transmission Line Project.

Constraint: A resource or condition that potentially limits transmission line routes, including areas that are closed by regulations (e.g. municipal airports) or where impacts would be very difficult or impossible to mitigate due to resource protection and other legal requirements.

Cooperating Agency: For the purposes of this project, a cooperating agency must have some level of jurisdiction in conjunction with the federal and/or state permitting agencies. A cooperating agency must also possess special expertise or knowledge regarding the impacts that the proposed action will have on local, regional or state land use plans, policies and controls. State, local, tribal and other federal entities may be recognized as cooperating agencies, as appropriate. Participation requires a signed Memorandum of Understanding between the cooperating agency and the BLM.

Corridor: For the purposes of this project, the corridor is either: 1) the geographic area within which a transmission line is located or planned to be located. Typically used to develop a working alignment for the initial screening of alternatives. If an environmentally sensitive area is found, the transmission line alignment can be shifted within the corridor to avoid adverse impacts to the sensitive area; or 2) a linear area designated by law or in a land use plan that is the preferred location for placement of linear rights of way such as transmission lines.

Current: The movement of electrons through a conductor; measured in amperes or amps.

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Distribution Line (e.g., 12.5 kV; 34.5 kV): Lines used for transmitting energy to its end use, including commercial facilities, small factories or a small transformer outside a group of houses.

Easements: Agreements that give the utility company the right to use the land owned by the individual for a specific purpose. Most commonly, negotiations directly with private property owners determine easement rights and restrictions for using portions of the land that remains owned by the individual.

Electromagnetic Fields (EMF): Invisible forces created by any electric charge. The word “electromagnetic” is a combination of two words; electro (electric) and magnetic. Electric fields are the result of the strength (voltage) of the electric charge. Magnetic fields are the result of the motion (current) of the charge. Wherever electricity is used, EMFs are present.

Eminent Domain: When a utility company acquires property for public use through a court action, in which a court decides that the proposed subsequent use is in the public interest and also determines the compensation to be paid to the owner.

Energy: In the electric utility industry, it represents the amount of power used or transmitted over a given amount of time.

Environmental Impact Statement (EIS): Required by the National Environmental Policy Act (NEPA), an EIS is a comprehensive public document that analyzes the impacts of a major federal action significantly affecting the quality of the human environment. When complete, it is a tool for decision making as the EIS describes the positive and negative environmental effects of a proposed action, describes alternative actions and provides an analysis of environmental impacts and ways to mitigate such impacts. An EIS examines physical and biological resources, resource uses, fire management, special designations, and social and economic conditions.

Extra-High Voltage Transmission Lines (230 kV; 345 kV; 500 kV): Used for transmitting electrical energy over great distances.

  • Higher voltage lines are more efficient than lower voltage lines. A higher voltage transmission line will result in fewer losses than a transmission line with a lower voltage.
  • Higher voltage lines often have "bundled" conductors, meaning that multiple wires are hung from the same insulator. This increases the amount of power that can be carried on a single circuit.

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Geographic Information System (GIS): A computer representation of data that is geographically distributed in three dimensions. These data can be generated and displayed to show their physical location. Each data set with a certain type of information constitutes a “layer” in the GIS. GIS layers can be superimposed to show the spatial relationships of different items.

Integrated Resource Plan (IRP) (also known as the Energy Plan for the Future): A comprehensive look at present and future demands for electricity, as well as a plan for meeting those demands.

Kilovolt(s) or kV: A unit of energy equal to 1,000 volts.

Lattice Tower: A freestanding steel framework tower that is often used for cross-country lines with voltages above 100 kilovolts.

Lead Agency: The agency or agencies preparing, or having taken primary responsibility for preparing, an environmental document as required by NEPA. For the Gateway West Transmission Line Project, the BLM is the lead agency.

Mitigation: Compensation for the loss of a resource’s function and/or value resulting from permanent impacts.

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National Environmental Policy Act of 1969 (NEPA): Federal statute that contains procedures to ensure that federal agency decision makers take environmental factors into account. The two major purposes of the NEPA process are citizen involvement and better informed decisions.

Notice of Intent (NOI) developed by the BLM and USFS: The notice submitted to the Federal Register for the project states the BLM and USFS intent to prepare an environmental impact statement (EIS) for the proposed transmission line and provides background information on the proposed project in preparation for the scoping process.

Opportunity: A resource or condition that can accommodate a transmission line route, including existing utility or transportation corridors.

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Power: The rate at which work is done. The basic unit of measure for power is the watt (w).

Purpose and Need (NEPA): Under the National Environmental Policy Act of 1969 (NEPA), the need to take an action may be something the agency identifies itself, or it may be a need to make a decision on a proposal brought to it by someone outside of the agency, for example, an applicant for a permit. Alternatives are measured against how well they meet the underlying need and best achieve the purposes to be attained.

Purpose and Need (project proponent): As identified by an applicant or proponent of a project, the purpose and need describes the intended outcome of the project and the compelling reason why it is being proposed. Alternatives are measured against how well they meet the underlying need and best achieve the purposes to be attained.

Public Scoping Report: A report developed by the BLM that documents public outreach efforts and summarizes the comments received during the public scoping period.

Record of Decision (ROD): The document that is prepared to substantiate a decision based on an EIS. The Record of Decision (ROD) is the final step for the BLM and USFS in the EIS process. The ROD states the final agency decisions, identifies the alternatives considered and discusses mitigation, enforcement and monitoring commitments.

Right of Way (ROW): Public land authorized to be used or occupied pursuant to a right of way grant. A right of way grant authorizes the use of a right of way over, upon, under, or through public lands for construction, operation, maintenance and termination of a project.

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Sage Grouse Lek: A gathering area for male sage grouse for the purposes of a competitive mating display.

Scoping: Public scoping is the process that federal agencies use to identify public issues and concerns relating to management actions on federal lands.

Source Station: A power station that is the receiving point for energy from distant generation delivered over high voltage power lines.

Stray Voltage: Stray Voltage is an extraneous voltage that appears on grounded surfaces in buildings, barns and other structures, including utility distribution systems.

Study Area: The geographic area addressed by the analysis in a plan or study.

Substation: A station used to transform one voltage to another and for protecting and controlling transmission and distribution lines. A substation is used to raise voltages for long distance transmission and to lower transmission voltages for distribution to the end users. Without substations, generation would have to be located very close to the customer load.

Sub-transmission Lines (69 kV; 138 kV; 161 kV): Lines used for transmitting electrical energy between substations that are close to one another (up to approximately 100 miles). These lines will typically not carry as much energy as the extra-high voltage lines.

Threatened Species: Any species that is likely to become endangered within the foreseeable future throughout all or a significant part of its range.

Transmission Lines: A transmission line is used to conduct electricity between two points. Without high voltage transmission lines, generation would have to be located at or near where the energy is used.

United States Forest Service (USFS): A federal agency under the Department of Agriculture that manages 193 million acres of public land for multiple uses and benefits and for the sustained yield of renewable resources such as water, forage, wood, recreation, fish and wildlife habitat, wilderness areas, and archaeological, paleontological and historical sites.

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Volt: The measure of electrical “pressure”.

Voltage: The electrical potential difference between two points expressed in volts.

West-wide Energy Corridor (WWEC) Programmatic EIS: Considers 11 contiguous western states for the possible construction, operation, maintenance, and decommissioning and dismantling of energy infrastructure such as oil and gas pipelines and electric transmission lines. The states considered are Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming (

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