This section addresses frequently asked questions and issues related to an AERA. It also contains helpful information for consultants and facilities conducting an AERA. For further information see the AERA Guide.
Project proposer questions
The AERA is generally done as part of an Environmental Assessment Worksheet and/or an air emission permit application or permit amendment application and is submitted in conjunction with those documents. The MPCA may also request that an AERA be completed in the event that there are concerns or complaints about health and/or environmental risk by the public who may be in the vicinity of the emission sources. Our suggestion for initially approaching an AERA is to first learn about the process. The next step is to complete the Risk Assessment Screening Spreadsheet (RASS) and supporting forms or to contact one of the staff listed on this webpage. More specific guidance can be found in the Air Emission Risk Analysis (AERA) Guide.
An AERA must first be completed by the project proposer and preparation time will vary depending on the certainty of emission factors, chemicals that will be emitted, complexity of emission sources and how much plans change from the initial construction plans. Once the AERA has been submitted to the MPCA, staff review the document, request supporting information, and prepare summary documents that can be used to inform an EAW or permit. The timeline for an AERA will coincide with the schedules established for the EAW or permit. Previous AERAs have typically taken from one month to six months to complete. The length of time required for a project depends on several factors including Agency work load, the quality of the submittals received by the Agency and the responsiveness of the project proposer to MPCA information requests.
The most expeditious approach generally means thorough planning and active engagement on the part of the project proposer and facility representatives. The AERA’s primary function is to provide complete and correct information to the public and to decision-makers. To facilitate that, there are several things that a project proposer can do to keep a project on track:
- Allow a reasonable amount of time between application and initial construction dates.
- Talk with MPCA staff to determine what information is needed prior to submittals.
- Provide complete information in the application and submittals; follow AERA guidance.
- Meet with MPCA staff regularly and respond to requests in a timely manner.
- Provide MPCA staff with the information they request and need.
Proposers may have the option of requesting that their air permit be formally expedited which, in turn, may expedite the review of the AERA. The company is charged for this service based on the amount of staff time required. This is highly dependent on availability of staff and resources and should not be relied on as the best option.
The AERA provides guidance and is not a rule; therefore a facility does not have to use the tools provided by the MPCA. However, the MPCA staff believes that using the AERA guidance, forms, and RASS and MPCA tools will expedite the review necessary for the Environmental Review and air permitting processes by providing reviewers assurance that toxicity values and modeling data are applied correctly. The MPCA staff strongly recommends using the RASS and MPCA guidance whenever feasible.
No, inhalation health benchmarks are not “bright lines” or regulatory standards. The AERA should not be viewed as a pass/fail exercise. There are several factors that influence risk management recommendations. Some factors are quantitative (safety factors in emission rates, certainty in toxicity values, refinement of dispersion modeling, etc.) while other equally important considerations are qualitative (proximity to nearby residences and businesses, how frequently the facility will operate, compliance history, etc.). All of these issues may affect the conclusions from an EAW or whether a permit is ultimately issued.
A team of program managers from the MPCA makes recommendations regarding the adequacy of a facility’s AERA results and its air permit based on staff recommendations. The managers may decide to approve permit issuance, require MPCA staff to evaluate certain aspects of a project further, or gather more information on a topic of public interest.
MPCA managers make risk management decisions based on staff recommendations that provide a total picture of the facility. They review and consider the staff summary and recommendation along with permit or environmental review issues. This includes, but is not limited to:
- the type of permit,
- the amount of emissions,
- the types of control equipment to be installed,
- the proposed monitoring or testing,
- the previous experience with the industry,
- the safety factors in emission rates,
- the certainty in toxicity values,
- the refinement of dispersion modeling,
- the proximity to nearby residences and businesses,
- how frequently the facility will operate,
- the compliance history at an existing facility,
- local community concerns, and
- other issues that may be related to the proposed project.
The MPCA strives to balance all of these concerns to the best of its ability.
The AERA summary form includes the following:
- Risk estimates
- Facility location information (including the nearest resident)
- Nearby land use and zoning information
- Conformity with the RASS and approved toxicity values
- Unique chemical or toxicity information
- Verification of emission rates
- Verification of modeling results
- Maps and information identifying the locations of maximum impact
- Fish consumption pathway analysis (if applicable)
- A description of how conservative or refined the analysis is
- Any important circumstances or considerations specific to the project
- Comments from the Minnesota Department of Health (if applicable)
- Analysis of mercury emissions
- If applicable, a summary of the cumulative air emissions risk analysis
This list will vary depending on applicability to each specific project. The impact analysis also contains a recommendation as to whether or not any mitigation should be required by the permit.
While MPCA staff must make a final recommendation on an AERA for a project, the project proposer may disagree with a certain position or approach the Agency takes. We would encourage the consultant and facility representative to bring these issues to our attention early in the process, and to contact the assigned section manager if they are unable to resolve the issue at the staff level. At that time, managers will talk with MPCA staff regarding the dispute and make a decision as to whether or not any changes are necessary. This decision will be based on the specific needs of the project as well as deference to standard MPCA practices.
The MPCA has a hierarchy of chemical and toxicological databases that it uses complete risk assessment calculations. As toxicity values are updated in the separate databases based on new scientific information, the MPCA updates its own list of chemical information. This is done primarily with input from the Minnesota Department of Health. The chemical values used are known as Inhalation Health Benchmarks (IHBs). The IHBs can be found in the Risk Assessment Screening Spreadsheet (RASS).
Multi-pathway Screening Factors were developed to analyze potential risk from persistent, bioaccumulative and toxic (PBT) chemicals and are defined as the ratio of the risk from the indirect exposure pathway (e.g., oral or non-inhalation) to the risk from the inhalation exposure pathway. The MPCA has applied Multi-pathway Screening Factors to the maximum estimated inhalation risk in the RASS. The MPCA staff developed the factors in the RASS using the Industrial Risk Assessment Program (IRAP-h View) software, a computer program developed by Lakes Environmental Software that incorporates the algorithms contained in US EPA’s Human Health Risk Assessment Protocol for Hazardous Waste Combustors (HHRAP).
Multi-pathway Screening Factors were developed for both cancer and chronic non-cancer endpoints for adult farmer and adult resident scenarios but not for the fish consumption pathway due to the great number of variables inherent in estimating fish concentrations. For most volatile compounds, the inhalation risks are higher than the non-inhalation risks, so the Multi-pathway Screening Factor will be less than one. On the other hand, chemicals that accumulate in the food chain may have relatively high non-inhalation risks and a multi-pathway screening factor greater than one. Multi-pathway screening factors were only developed for pollutants with ratios greater than one. For a list of multi-pathway screening factors, see the Risk Assessment Spreadsheet (RASS).
The completion of an AERA has both indirect and direct benefits. Facilities that complete an AERA may initially determine that the potential human health risk posed by emissions from their facility is unacceptable. Based on these preliminary results, the project proposer may choose to improve emission controls or efficiencies within the plant prior to submitting their AERA results and thereby reduce emissions from their facility (e.g., pollution prevention measures). Emission reductions (risk reductions) may also occur as a direct result of the AERA process and recommendations on how to mitigate potential risk. Some examples of mitigation include process improvements, product substitutions, diesel idling prevention measures, voluntary mercury limits, and stack testing to better characterize emissions. Recommendations such as these are discussed with the project proposer to ensure that they are feasible and will be effective. In some cases, facilities have worked together with the MPCA and the Minnesota Technical Assistance Program (MnTAP) to reduce air emissions and implement pollution prevention measures. These measures, in some cases, have helped to reduce operating costs and to address community concerns regarding odors or potential health risks. For more information about potential projects and Pollution Prevention practices, see Industry Best P2 Practices or MnTAP.
Yes. Certain types of emission sources do not need to be included in the quantitative assessment, as described below.
Exclude an “insignificant activity” as defined in Minn. R. 7007.1300 (and its associated emissions) from the quantitative risk analysis if:
- the activity emits a pollutant that does not have an inhalation health benchmark listed in the RASS, or
- the activity emits a pollutant that is also emitted by sources/units already included in the emission inventory, and the contribution of the individual activity is less than 1% of the total emission inventory for a pollutant (hourly for acute and annual for chronic).
If an emissions source does not meet one of these two tests, then it should be included in the RASS. Some types of insignificant activities can emit substantial amounts of air toxics or small amounts of highly toxic pollutants; these should not automatically be excluded from the AERA process.
Internal combustion engines associated with emergency generators and fire pumps are not quantitatively assessed. Further discussion of these sources is required in the qualitative portion of the AERA. See section 3.3.2 of the AERA Guidance for the definition of “emergency generator” and additional guidance related to describing these emission units.
Emergency generators are also generally excluded from the AERA process, however, a facility may choose to include these sources in the RASS (to the extent possible) or address them qualitatively in an AERA. These sources would not be excluded from a Cumulative Air Emissions Risk Analysis that might be completed in addition to the AERA.
The AERA is a “screening” level analysis and therefore, should be based on assumptions that are protective of public health, particularly with respect to emission rates and inhalation health benchmarks. But a project proposer may choose how much specificity or refinement they want to add, particularly in the areas of emission estimates and modeling, which may be more representative of actual operating scenarios. In almost any project, there are pros and cons to presenting information that is likely an overestimate of risk, not the least of which is ease of communicating the likely actual scenario to the public. However, MPCA staff and project proposers ultimately have to describe how close to reality (i.e., expected conditions) the analysis is. If a project proposer submits information that is likely to underestimate risk, MPCA staff may ask them to re-evaluate the information or substitute more health-protective inputs themselves. It may expedite the review process if proposers or their consultants provide information regarding uncertainties in the assessment, including assumptions that may overestimate and underestimate risks.
An important element of a human health risk assessment is the transparent communication of uncertainty and variability. A portion of the uncertainty in a final risk estimate stems directly from the assumptions used to characterize potential human exposures. The USEPA and MPCA recommend estimating risks based on a set of default exposure assumptions, called the “Reasonable Maximum Exposure” (RME). One approach to communicate the uncertainty associated with the default exposure assumptions is to provide risk estimates using multiple human exposure assumptions. Risk results using central tendency human exposure factors should not replace risk estimates based on the RME and should not be considered a refinement to screening level risk assessments that follow MPCA’s Air Emissions Risk Analysis (AERA) guidance. Including central tendency exposure estimates would generally be appropriate in larger multi-pathway risk assessments, where more discussion of uncertainty is warranted. Information to estimate potential human health risks using central tendency values for human exposure factors can be found on the Multi-pathway Risk Analysis webpage.
Who to contact
- Kristie Ellickson, 651-757-2336