4 The record articles

Navigating State-Specific Air Toxics Programs

Posted: July 31st, 2017

Authors: All4 Staff 

Hazardous Air Pollutants (HAP), also commonly referred to as Toxic Air Pollutants (TAP) or air toxics, are those pollutants that are known or suspected to cause cancer or other serious health effects, such as reproductive effects, birth defects, or adverse environmental effects.  We’re all familiar with the technology-based approach used by U.S. EPA to regulate air toxics through their development and implementation of Maximum Achievable Control Technology (MACT) standards.  Many of us have also had exposure to the Risk and Technology Review (RTR) process, which is conducted by U.S. EPA every eight years after a MACT standard has been set for U.S. EPA to determine if revisions to existing MACT standards are necessary to protect human health.

However, many states make the decision that it’s not enough to simply incorporate Federal MACT standards to safeguard public and environmental health.  The following states incorporate additional requirements into their permitting rules or policies which must be considered by new and modified sources: California, Delaware, Georgia, Iowa, Louisiana, Massachusetts, Michigan, Minnesota, Mississippi, Nebraska, New Hampshire, New York, North Carolina, Oklahoma, Oregon, Texas, Virginia, and West Virginia.  Other states require air toxics evaluations for existing sources as part of operating permit renewal applications (e.g., New Jersey). In this article, we’ll provide a broad overview of unique air toxics programs in some of the states we often work in – namely Georgia, Maryland, Michigan, New Jersey, and Texas.

If your facility is either located in one of the states discussed herein, or in another state with its own unique air toxics requirements, we encourage you to stay vigilant regarding such requirements as state agencies are starting to lean more heavily on their own regulations given the downturn in regulatory activity at the Federal level. For those of you with operations outside of states with unique state-specific air toxics programs, consider the fact that state requirements such as those detailed in this article may require a bit more planning, strategy, and analysis.


In the State of Georgia, a Toxics Impact Assessment (TIA) must be conducted for new and modified sources of air toxics pursuant to the State’s “Guideline for Ambient Impact Assessment of Toxic Air Pollutant Emissions.”  The obligation to conduct such an assessment stems from Title 391‚ Chapter 3‚ Rule 1‚ Section 2‚ (2)(a)(1) and (2)(a)(3) of the Georgia Air Quality Control Regulations and the air toxics of concern are listed in Appendix A of the referenced guidance document.  For such pollutants, the Georgia Environmental Protection Division (GEPD) requires calculation of an acceptable ambient concentration (AAC), air quality modeling of a predicted ambient impact, and a comparison of the modeled result with the AAC.  This first series of steps is regarded as “screening” after which more in-depth analysis may be required.  This initial step includes a screening level air dispersion modeling evaluation, using U.S. EPA’s SCREEN3 air dispersion model, to predict Maximum Ground Level Concentrations (MGLCs) from a given facility.  The MGLCs are then compared to the calculated AACs established using toxicity data from the Integrated Risk Information System (IRIS) and Occupational Safety and Health Administration (OSHA) Time Weighted Average (TWA) and ceiling Permissible Exposures Limit (PEL) standards (PEL-TWA, PEL-C).  If an MGLC exceeds a respective calculated AAC, additional analyses may be required including a site-specific risk assessment, the use of alternative toxicity data, safety factors, or alternative methods of impact assessment.  If, after performing a site-specific risk assessment, it is determined that it is infeasible to comply with an AAC or not possible to demonstrate that the cumulative hazard risk index is below 1, then GEPD may, at their discretion, require installation of New Source MACT, which for the purpose of the referenced guidance document means “the control technology which reflects the maximum degree of reduction in emissions of hazardous air pollutants that the Director determines is achievable by the source, provided that such control technology is no less effective than the level of emission control which is achieved in practice by the best controlled similar source.”

An understanding of the various data required to perform the TIA, the assumptions and limitations inherent to the dispersion model, the basis for calculation of the AAC (with special consideration to the acquisition of pollutant toxicity data, adjustment of toxicity data for potential public exposure in excess of occupational exposure, application of safety factors, and averaging periods), and the general comparative procedure for determining toxic pollutant impact is required when performing a TIA in Georgia.


In the State of Maryland, both new and modified sources of air emissions must be evaluated with respect to the following state-specific TAP requirements found at Code of Maryland Regulations (COMAR) 26.11.15:

  • COMAR – Requirement to Quantify Emissions
  • COMAR – Control Technology Requirements
  • COMAR – Ambient Impact Requirement

An applicant’s first obligation, under COMAR, is to quantify the emissions of TAP from the premises.  For a new source (constructed or reconstructed after July 1, 1988), any of the listed pollutants in COMAR or .07 plus any other air pollutant that is considered a health hazard as defined by OSHA is considered a TAP.  For existing sources (constructed prior to July 1, 1988), only pollutants listed in COMAR or .07 are considered TAPs.

Next, new sources and certain existing sources must perform a Best Available Control Technology for Toxics (T-BACT) analysis pursuant to COMAR  Similar to a Best Available Control Technology (BACT) analysis conducted in support of a Prevention of Significant Deterioration (PSD) project, the procedure for conducting a T-BACT analysis involves the top-down identification of available air pollution control options (i.e., starting with the most effective); performing an analysis of energy, economic, and environmental impacts; and selecting the most effective control alternative not otherwise eliminated as T-BACT.

Maryland also requires that an applicant demonstrate that premise-wide emissions and off-site impacts (as determined by air dispersion modeling) of each TAP will not adversely affect public health based upon established benchmarks (i.e., screening levels).  In general, if premise-wide emissions are calculated as being less than the maximum allowable emissions or if the off-site impact of the premises-wide emissions of each TAP is less than the screening levels for the TAP, adverse public health effects would not be expected.


In the State of Michigan, new and modified sources of air emissions are potentially subject to the following State air toxics regulations:

  • R 336.1224 – T-BACT Requirement for New and Modified Sources of Air Toxics
  • R 336.1225 – Health-Based Screening Level Requirement for New or Modified Sources of Air Toxics

Michigan’s Health-Based Screening Level Rules require each new or modified emissions unit that is required to obtain a Permit-To-Install (PTI), and which emits a Toxic Air Contaminant (TAC), to ensure that the emissions of TAC associated with the project are not more than predicted maximum allowable emission rates.  Making such predictions involves review of the Michigan Department of Environmental Quality (MDEQ) “List of Screening Levels (ITSL, IRSL, and SRSL)” to identify Initial Threshold Screening Levels (ITSLs), Initial Risk Screening Levels (IRSLs), and Secondary Risk Screening Levels (SRSLs).  Through this review, a facility determines what applicable ITSL, IRSL, and SRSL thresholds apply for use in a subsequent air dispersion modeling analysis.  The air dispersion modeling analysis determines if the TAC emissions associated with a project exceed the applicable ITSL, IRSL, or SRSL.

Notwithstanding the exemptions provided at R336.1224(2)(a) through (d), R 336.1224 (Rule 224) requires that certain new or modified emissions units for which a PTI application is required, and for which any of the following conditions exist, shall not cause or allow the emission of TAC in excess of the maximum allowable emission rate based on the application of T-BACT:

  • The maximum allowable emissions rate of a TAC from the proposed new or modified emissions unit or units exceeds 0.1 pound per hour or less for a carcinogen or 1.0 pound per hour for any other TAC, or
  • The applicable ITSL determined for the TAC is less than or equal to 200 micrograms per cubic meter, or
  • The applicable IRSL determined is less than or equal to 0.1 micrograms per cubic meter.

If T-BACT is required, the applicant must identify and apply the maximum degree of emission reduction which the MDEQ determines is reasonably achievable for each process that emits TACs, considering energy, environmental, and economic impacts, and other costs.  Similar to T-BACT analysis required by the State of Maryland, the procedure for conducting a T-BACT analysis in Michigan involves identification of available control options; performing an analysis of energy, economic, and environmental impacts; and selection of the most effective control alternative not otherwise eliminated to represent T-BACT.

New Jersey

The State of New Jersey’s air toxics risk assessment requirements apply to the following types of emissions sources:

  • New and modified sources of air pollution required to have an air pollution control pre-construction permit and that emit air toxics above the thresholds listed in N.J.A.C. 7:27-8, Appendix 1, Table B [Reporting and State of the Art Threshold for HAPs (Potential to Emit)], and
  • New and modified sources at major facilities with existing Operating Permits that emit air toxics listed in N.J.A.C. 7:27-22, Appendix Table B, and
  • Existing facilities advised by New Jersey Department of Environmental Protection (NJDEP) that they must carry out a facility-wide assessment.

There are two methods of performing such a risk assessment in New Jersey:

  • Risk Screening
  • Comprehensive Risk Assessment

Risk screening is the most commonly executed type of assessment and is typically performed by NJDEP staff but may be optionally carried out by an applicant prior to application submittal.  The approach includes both first- and second-level screening, where first-level screening essentially overestimates cancer and noncancer risks through its utilization of generalized worst-case assumptions, worksheet calculations, and air impact values (in lieu of air dispersion modeling).  In doing so, sources with emissions of TAC that exceed New Jersey’s risk guidelines, and thereby may pose a significant health risk to its citizens, are identified as requiring closer scrutiny through the second-level screening process.  Second-level screening is a refinement of first-level screening that relies upon stack- and source-specific data, representative meteorological data, and the AERMOD atmospheric dispersion modeling system.  NJDEP staff typically conduct second-level risk screening at the expense of the applicant, but an applicant may also carry out the procedure with verbal approval by NJDEP.   In such cases, submittal of an air quality modeling protocol is sometimes required.

In certain cases, applicants are notified by NJDEP that they must prepare a Comprehensive Risk Assessment (CRA).  Examples of sources that could trigger a CRA include coal-fired power plants, incinerators (e.g., municipal solid waste, hazardous waste, medical waste, etc.), and larger stationary sources. For such cases where a comprehensive risk assessment is requested, the applicant is also responsible for submittal and approval of a risk assessment protocol, and, in the case of certain RCRA hazardous waste combustion facilities, submittal and approval of a multi-pathway risk assessment protocol.  The applicant is also responsible for paying fees to cover NJDEP’s review of a comprehensive risk assessment.

Comprehensive risk assessments involve both air dispersion modeling and, in cases where an ingestion exposure pathway exists, deposition modeling.  They also include a hazard identification step, a dose-response assessment, an exposure assessment, and risk characterization step to be performed consistent with the guidelines presented in NJDEP’s “Technical Manual 1003: Guidance on Risk Assessment for Air Contaminant Emissions.”


The Texas Commission on Environmental Quality (TCEQ) requires preparation of a Health Effects Analysis through the State’s document “Air Quality Modeling Guidelines.” This Health Effects Analysis establishes off-property Ground-Level Concentrations (GLCs) of contaminants resulting from proposed and/or existing emissions sources and evaluates those GLCs for their potential to cause adverse health or welfare effects against published Effects Screening Levels (ESLs).  The published ESLs are based on an air toxic’s potential to cause adverse health effects, odor nuisances, vegetation effects, or materials damage.

The procedure for performing a Health Effects Analysis is three-tiered. Under the initial Tier I approach, maximum off-property short- and long-term GLCs are compared to the respective ESL for the contaminants under review.  If the maximum off-property short- and long-term GLCs are equal to or less than the ESLs for the contaminants under review, adverse health or welfare effects are determined to be not expected.  If the maximum off-property short- and long-term GCL is above the respective ESL, it is not necessarily indicative that an adverse effect will occur, but does indicate that further evaluation under Tier II is warranted.

The Tier II approach is performed with acknowledgment of whether the locations of the GLCs are industrial or non-industrial.  For industrial receptors, if the maximum off-property short- and long-term GLCs are equal to or less than two times the respective ESLs, adverse health or welfare effects would not be expected.  For non-industrial receptors, if the maximum off-property short- and long-term GLCs are equal to or less than the respective ESLs, adverse health or welfare effects would not be expected.  However, if the maximum off-property short- and long-term GLCs for industrial receptors are greater than two times the respective ESLs, adverse health or welfare effects would be expected.  Similarly, if the maximum off-property short- and long-term GLCs for non-industrial receptors are greater than the respective ESLs, adverse health or welfare effects would be expected.

Tier III is a refinement of the Tier I and II approaches, which rely solely on predicted concentrations.  Tier III goes further by incorporating additional case-specific factors such as land use, magnitude of predicted concentrations, frequency of predicted exceedance, or toxic effect caused by the contaminant to factor in additional information about the potential for exposure and occurrence of adverse health and welfare effects.


Where applicable, state air toxics programs are a required component of many air permitting projects and compliance with the state-specific requirements, as defined by each rule, must be demonstrated to be granted authorization to proceed.  While sharing many basic components, air toxic program interpretation and execution can vary significantly from state to state and a thorough understanding of the applicable program is crucial to a successful permitting project.

ALL4 has conducted air quality modeling studies and risk analyses in support of a variety of regulatory and permitting projects including, but not limited to, state air toxics programs.  We offer extensive experience applying air dispersion models, regional modeling analysis, understanding and interpreting the results, and integrating the results into the permitting process, compliance demonstrations, or strategic planning for future operations. We’ve worked closely with state meteorologists, U.S. EPA regulatory and technical staff, toxicologists, and air dispersion model developers. We understand the technical aspects of the models and the regulations governing the use of air dispersion models.  For questions related to the regulation of air toxics in your state, feel free to contact us.  For specific modeling needs, don’t hesitate to reach out to any of our talented ALL4 modeling team members.


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