4 The record articles

Residual Risk and Hazardous Air Pollutants – Why the Rules of the Game Can Change

Posted: August 4th, 2014

Author: All4 Staff 

The U.S. Environmental Protection Agency (U.S. EPA) maintains a website that identifies dates of upcoming rulemakings in various stages (Notice of Proposed Rulemaking; Final Rule, etc.) to be published in the Federal Register. A review of this website reveals that several upcoming proposed rules and final rules are associated with Residual Risk and Technology Review (RTR) Amendments to National Emission Standards for Hazardous Air Pollutants (NESHAP). Furthermore, as described in ALL4’s blog posted on June 30, 2014, U.S. EPA recently published revisions to two (2) NESHAPs for the petroleum industry related to an RTR. Most environmental professionals are familiar with NESHAPs, which are commonly referred to as maximum achievable control technology (MACT) standards, and are codified at 40 CFR Part 63. The Part 63 NESHAPs have been in effect since the 1990s, so what is happening with these regulations and what exactly does RTR mean? To answer that question, we first must go back to the 1990 amendments to the Clean Air Act (CAA), and review the approach established to regulate HAPs.

Brief History of NESHAPs

Under the CAA of 1970, hazardous air pollutants (HAPs) were regulated by a risk-based program and NESHAPs were established for individual pollutants at a level that would ensure the protection of public health with “an ample margin of safety.”[1] These standards were codified at 40 CFR Part 61; for example, Subpart E to 40 CFR Part 61 contains standards for mercury emissions from stationary sources that process mercury ore to recover mercury; use mercury chlor-alkali cells to produce chlorine gas and alkali metal hydroxide; and incinerate or dry wastewater treatment plant sludge. The approach established under the 1990 amendments to the CAA changed course, requiring the development of technology-based emission standards for categories of sources (e.g., Subpart S to 40 CFR Part 63 established NESHAPs for the pulp and paper industry). These technology-based NESHAPs must reflect the maximum degree of HAP emission reductions achievable after considering cost, energy requirements, and non-air quality health and environmental impacts.[2] The MACT standards are in the form of design, equipment, work practice, or operational standards, and the minimum control level for a NESHAP is referred to as the “MACT floor.” It is interesting to note that the MACT floor is established on a pollutant-by-pollutant basis. Under a pollutant-by-pollutant approach, U.S. EPA sets limits based on the best performance of individual plants for individual pollutants rather than the best performing plant across all the pollutants. This approach has been the bane of industry for several years and has been the impetus behind multiple litigation actions. Until April 2013, industry has been unsuccessful in overturning this approach, largely due to legal actions related to a MACT standard for medical waste incinerators, in which the courts have denied industry petitions to revise the approach because they did not raise the issue in the public comments on the original 1997 incinerator MACT standard. However, in April 2013, the door may have been opened to revise the approach due to industry opposition to the Utility MACT standard because that standard is a new standard for a new source category – stay tuned.[3]

Though the Part 63 NESHAPs were established without regard to the toxicity and risk of a given HAP regulated by the standard, the intent of the MACT standards was to reduce a majority of the HAP emissions and the associated risk.[4]

For additional discussions on the MACT floor process, please refer to Dan Holland’s blog post and my blog post from November 7, 2013.

[1] U.S. EPA, Residual Risk Report to Congress, EPA-453/R-99-001, March 1999 (U.S. EPA, March 1999)

[2] Federal Register, Volume 79, No. 125, June 30, 2014 (79 FR 36880)

[3] “EPA Fights Multiple Legal Attacks In Suit Over MACT for Existing Utilities” Clean Air Report – www.InsideEPA.com – April 25, 2013 (Clean Air Report, April 2013).

[4] 79 FR 36880

RTR Process

Section 112(f)(2) of the CAA directs U.S. EPA to conduct risk assessments on each source category subject to MACT standards, and to determine if additional standards are needed to reduce residual risks. Section 112(d)(6) of the CAA requires U.S. EPA to review and revise the MACT standards, as necessary, taking into account developments in practices, processes and control technologies.[5] These reviews are required to occur no less frequently than every eight (8) years (although the review process is certainly behind schedule). An important distinction as part of this review is that U.S. EPA is not required to recalculate the MACT floor.[6] This aspect is related to two (2) court cases that are now the impetus of a congressional movement to revise U.S. EPA’s approach to RTRs, including the need to redo the MACT floor-setting processes established in in 1990 amendments to the CAA each time it conducts an RTR.[7]

Similar to the 1970 CAA, Section 112(f)(2) of the 1990 amendments to the CAA also requires U.S. EPA to determine for the Part 63 NESHAPs whether the standards provide an ample margin of safety to protect public health. U.S. EPA generally follows two (2) steps to evaluate the residual risk for its RTR process:[8] 1) determining the acceptable risk, and 2) determining if a standard provides an ample margin of safety to protect human health.

Determining Acceptable Risk

So what is acceptable risk? In the development of NESHAPs for Benzene Emissions from Maleic Anhydride Plants, Ethylbenzene/Styrene Plants, Benzene Storage Vessels, Benzene Equipment Leaks, and Coke By-Product Recovery Plants (Benzene NESHAP; 54 FR 38044, September 14, 1989), U.S. EPA determined that if the risk to the “maximum exposed individual” is no higher than approximately one (1) in 10,000, that risk level is considered acceptable.[9] U.S. EPA further explained that the maximum individual risk is based on the estimated risk that a person living near a plant would have if (s)he were exposed to the maximum pollutant concentrations for 70 years. The one (1) in 10,000 criterion is considered as a benchmark by U.S. EPA, and is not necessarily a bright line for acceptable risk, meaning that other health measures and factors are considered when establishing acceptable risk. If risks are found to be unacceptable, U.S. EPA cannot consider cost when identifying standards necessary to reduce the risks to acceptable levels.

Determining an Ample Margin of Safety

The ample margin of safety is “the level at which the standards must be set, unless an even more stringent standard is necessary to prevent, taking into consideration costs, energy, safety and other relevant factors, an adverse environmental effect.”[10] CAA Section 112(f)(2)(A) stipulates that if a HAP classified as a known, probable, or possible human carcinogen does not reduce lifetime excess cancer risks to the individual most exposed to emissions from a source in the category to less than one (1) in 1,000,000, U.S. EPA must promulgate residual risk standards for the source category , as necessary, to provide an ample margin of safety to protect public health. As such, U.S EPA may adopt standards equal to the existing MACT standard if it determines that the existing standard is sufficiently protective. Otherwise, U.S. EPA is charged to revise the standard in order to provide an ample margin of safety to project public health.  U.S. EPA’s overall objective, as started in the Benzene NESHAP, is to provide maximum feasible protection against risks to health from HAPs by (1) protecting the greatest number of persons possible to an individual lifetime risk level no higher than one (1) in 1,000,000, and (2) limiting to no higher than approximately one (1) in 10,000 the estimated risk that a person living near a plant would have if (s)he were exposed to the maximum pollutant concentrations for 70 years.

[6] 79 FR 36880

[7] “Waxman, Advocates Urge D.C. Circuit to Force Stricter EPA MACT Rules” Clean Air Report – www.InsideEPA.com – June 19, 2014 (Clean Air Report, June 2014)

[8] 79 FR 36880

[9] Ibid.

[10] Ibid.

Risk Assessment Process

So how does U.S. EPA estimate the risks posed by the MACT standards? U.S. EPA conducts a risk assessment that provides estimates of the maximum individual risk posed by HAP emissions from a source in a MACT standard; the hazard index for chronic exposures to HAP with potential to cause non-cancer health effects; and the hazard quotient for acute exposures to HAP with potential to cause non-cancer health effects. The risk assessment also provides estimates of the distribution of cancer risks within the exposed populations, cancer incidence, and an evaluation of the potential for adverse effects for a MACT standard.[11] The process consists of eight (8) steps, as summarized below:

  1. Estimate and compile actual emissions and identify emission release characteristics, using Information Collection Requests (ICRs) from affected facilities. The ICRs typically provide source locations, release characteristics (stack height, exhaust temperature, exhaust flow rate, etc.), annual emission rates, and supporting data such as stack testing results and inventories developed based on industry emission factors.
  2. Estimate and compile MACT allowable emissions, which are typically requested as part of the ICR process.
  3. Conduct air dispersion modeling to estimate HAP concentrations in ambient air, estimate long-term and short-term inhalation exposures to individuals residing within 50 kilometers of the modeled source, and estimate individual and population-level inhalation risks using the exposure estimates and quantitative dose-response information.
  4. Conduct a multi-pathway human health exposure and risk assessment, which is a screening analysis examining the potential for significant risks due to exposures via routes other than inhalation (e.g., ingestion) using fate and transport modeling techniques.
  5. Assess risks considering emissions control options to evaluate pre- and post-control risk. This enables an evaluation of current and emerging technologies to identify more effective control technologies to incorporate into the MACT standard, if appropriate.
  6. Conduct environmental risk screening assessment to examine the potential for adverse environmental effects using fate and transport modeling techniques.
  7. Conduct assessments to put the NESHAP source category risks into context by examining the risks from the entire “facility,” where the facility includes all HAP-emitting operations within a contiguous area and under common control. In other words, U.S. EPA examines the HAP emissions not only from the source category emission points of interest, but also emissions of HAP from all other emission sources at the facility for which it has data.
  8. Consider the uncertainties in the emission datasets, where in the context of exposure and risk assessment, the term “uncertainty,” encompasses both variability in the range of expected inputs and screening results due to existing spatial, temporal, and other factors, as well as uncertainty in being able to accurately estimate the true result. Model uncertainty concerns whether the selected models are appropriate for the assessment being conducted and whether they adequately represent the movement and accumulation of environmental HAP emissions in the environment.

In addition, U.S. EPA conducts a technology review focused on the identification and evaluation of developments in practices, processes and control technologies that have occurred since the MACT standard was promulgated. Where U.S. EPA identifies such developments, in order to evaluate if it is necessary to revise the MACT standard, consideration is given to the technical feasibility of applying these developments, and the estimated costs, energy implications, non-air environmental impacts, as well as considering the emission reductions. U.S. EPA also considers the appropriateness of applying controls to new sources versus retrofitting existing sources.[12]

Typically, U.S. EPA considers any of the following to be a “development:”

  • Any add-on control technology or other equipment that was not identified and considered during development of the original MACT standard.
  • Any improvements in add-on control technology or other equipment (that were identified and considered during development of the original MACT standard) that could result in additional emissions reduction.
  • Any work practice or operational procedure that was not identified or considered during development of the original MACT standard.
  • Any process change or pollution prevention alternative that could be broadly applied to the industry and that was not identified or considered during development of the original MACT standard.
  • Any significant changes in the cost (including cost effectiveness) of applying controls (including controls considered during the development of the original MACT standard).
  • Findings from a review of information from other sources, such as state and/or local permitting agency databases and industry-supported databases.

Parting Thoughts

This article describes the general process in which U.S. EPA assesses risks to public health and the environmental as it pertains to the historical implementation of NESHAPs. The process is not performed in a vacuum. As described in the risk assessment section, U.S. EPA’s process is largely dependent on information from the regulated facilities. This is where you can help your own cause, particularly as it relates to the emissions submittal process for the ICR for a given MACT standard. By providing complete information as part of the ICR, U.S. EPA more reliable and representative data to assess the residual risk. Furthermore, participating individually or as part of an industry trade group to submit comments during the various phases of an RTR rulemaking enables additional information to be considered for the final determinations. Now that you have a better understanding of the RTR process, you have the tools to make on-going compliance with your applicable NESHAPs a bit more bearable, even if the rules of the game change in the future.

[11] Ibid.

[12] Ibid.


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