MPCA strives to ensure Minnesota's outdoor air is healthy for all to breathe.
Conducting an Air Emission Risk Analysis (AERA) is one way the MPCA works to protect the environment and enhance human health. The AERA process is used to evaluate and quantify the potential human health risks due to the air pollution emitted by a proposed project. Screening tools, computer models and inhalation health benchmarks are used to assess the potential cancer and non-cancer health risks of a project’s air emissions.
To assesses the potential cumulative risks of a project in a community the MPCA considers nearby facilities, background contamination, and local land use activities, such as the farming or fishing occurring in an area. Further contextual information, such as the locations of nearby schools and hospitals, is collected to identify potential routes of exposure and sensitive populations.
The results from a risk analysis are used to describe the potential risks posed to the individuals that would experience the highest level of exposure and incorporates the MPCA Environmental Justice Policy. The results of the analysis are referenced in the MPCA environmental review process to determine a project’s potential for significant environmental impact and to inform alternative proposals. Information from AERAs may also be employed to determine air permitting limits or monitoring requirements for facilities.
Is an AERA required?
An AERA will be requested under any of the following conditions:
- An Environmental Assessment Worksheet is required by Minn. R. 4410.4300, subpart 15.
- An Environmental Impact Statement is required by Minn. R. 4410.4400 and the project increases air emissions of a single pollutant (excluding greenhouse gases) by 250 tons per year or more after the use of control equipment.
- An Environmental Impact Statement is required by Minn. R. 4410.4400 and the facility or project increases air emissions of combined greenhouse gases by 100,000 tons per year or more after the use of control equipment.
- Environmental Review staff determine an air assessment is needed for a mandatory Environmental Assessment Worksheet or an Environmental Impact Statement and criteria air modeling is deemed necessary.
All mandatory AERAs must fulfill Environmental Review’s requirement for an analysis of cumulative potential effects.
Discretionary and voluntary AERAs
Discretionary AERAs may be requested by MPCA management after considering all project information including:
- Substantive comments received during a public comment period that might be resolved through the AERA process.
- Significant public interest indicates a need for further analysis prior to public notice.
- The location of the facility is of concern or there are uniquely sensitive receptors near the facility.
- The amount or types of emissions from the facility are of concern.
MPCA's authority to regulate air emissions
The Clean Air Act requires the US EPA to regulate the emissions of 187 specific air toxics, also referred to as Hazardous Air Pollutants or HAPs. Instead of promulgating ambient air quality standards for these pollutants, the US EPA regulates HAPs through National Emission Standards for Hazardous Air Pollutants (NESHAPs). In Minnesota, potential health effects from air toxics are further reviewed using the AERA process and accompanying risk screening tools. These tools are routinely updated to ensure the most current toxicity and air modeling information is used to assess the potential for adverse health impacts.
The MPCA has the authority to gather information that pertains to MPCA rules or statutes. Representatives of the MPCA may examine records or request access to property to obtain information in accord with Minn. Stat. § 116.091. The MPCA may also craft permit conditions to prevent pollution and to protect human health and the environment (Minn. Stat.§ 116.07, subd. 4a and Minn. R. 7007.0800, subp. 2). A permit applicant is required to provide all applicable information. Minn. R. 7007.1000, subp.2 provides the authority to deny a permit when there is potential for adverse effects to human health or the environment.
What is included in an AERA?
The types of information incorporated into an AERA may be general assumptions that provide high-end screening estimates, or detailed information providing risk estimates more specific to a facility’s operating conditions.
Levels of air modeling refinement may be illustrated as a pyramid. At the base are screening assumptions that are sufficient to protect public health and can be applied to many types of facilities. For example, one protective assumption is that a facility will operate 24 hours a day for 7 days a week. Higher up the pyramid, the refined assessment illustrates conditions very specific to a facility and its surroundings. The risk estimates in most AERAs are based on intermediate levels of refinement.
If AERA risk estimates are below facility risk guidelines when using screening level assumptions, a project may proceed without further refined modeling. If the initial screening risk estimates are above facility risk guidelines, refinements may be made to better reflect a facility’s operating conditions. These refinements may apply to any step of an AERA and are described in the AERA Guide.
What are facility risk guidelines?
Upon completion of an AERA, quantitative risk results are compared to the following facility risk guidelines developed in collaboration with MDH and consistent with U.S. EPA guidance.
- Total facility cancer risk below or at: one in 100,000 (1E-05)
- Total facility hazard index below or at: one
How to submit an AERA
The required forms to complete an AERA are available on the Forms and Tools section of the AERA webpage. Step by step directions for completing the AERA forms are provided in the AERA guide. Following the guide and its associated forms will promote the efficient review of a facility’s submittal.