Major Source in the United States
Major Source in Environmental Law
Under the 1970 Clean Air Act, a pollution source is considered a major source if it is stationary and has the potential to emit 100 tons per year or more of a regulated air pollutant. The Clean Air Act Amendments of 1990 made the definition more inclusive by lowering the threshold of 100 tons per year for certain facilities: those that emit hazardous air pollutants or those located in an air district that has not attained the national air quality standards for the pollutant they discharge. See hazardous air pollutants; National Ambient Air Quality Standards; National Emission Standards for Hazardous Air Pollutants; nonattainment areas.
A stationary source may consist of more than one building. For purposes of determining the status of the facility, the government aggregates all facilities managed by the same person if they are near each other. The pollutant tonnage considered is not what the source actually emits but what it is capable of emitting. This figure is based on facility design: how much pollution would the source generate if it were operating at peak capacity? In some situations, if the source owner or manager agrees to limit plant operations so that it does not exceed certain levels, and if those levels are enforceable by the government, the Environmental Protection Agency (EPA) may consider actual emissions instead of potential emissions when deciding whether or not the source is major. Several courts have also determined that if the source is modifying its facility, the EPA should consider past operating practices to calculate future emissions.
Hazardous air pollutant dischargers are considered major sources if they have the potential to emit 10 tons per year or more of one hazardous air pollutant or 25 tons per year of any combination of hazardous air pollutants. In nonattainment areas for any of the criteria pollutants (ozone, nitrogen oxides, sulfur dioxide, lead, and small particulates), a source may be considered major at a level as low as 10 tons per year if it discharges the pollutant the area is having trouble with.
Once a facility is designated a major source, a permitting requirement for operation as well as other restrictions are triggered. All of the pollutants it emits will be regulated. For example, if a plant discharges 100 tons per year of nitrogen oxides but is below that amount for sulfur dioxide, it is still a major source. When the permit is written, it will include limits for sulfur dioxide as well as nitrogen oxides. A new major source or existing major facility that wants to modify its plant or operation is also required to go through preconstruction review and permitting before it can begin construction. Minor sources are not regulated to the same degree.
Based on “Environment and the Law. A Dictionary”.