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The National Association of Clean Air Agencies (“NACAA”) submitted comments to the United States Environmental Protection Agency (“EPA”) addressing the proposed:

National Emission Standards for Hazardous Air Pollutants Stationary Combustion Turbines Residual Risk and Technology Review (“RTR”)

See 84 Fed. Reg. 15046 (April 12, 2019).

NACAA describes itself as the national, non-partisan, non-profit association of air pollution control agencies in 41 states, including 114 local air agencies, the District of Columbia and four territories.

The comments address three topics:

• Facility-Wide and Cumulative Risks
• Concentrations at Census Tract Centroids
• Acute Exposure

As to facility-wide and cumulative risks, NACAA states that the proposed RTR includes in its analyses facility-wide assessments exposures from multiple sources in the same category; analysis of the ingestion route of exposure for some persistent and bioaccumulative pollutants; and aggregate cancer risk from all carcinogens and aggregated noncancer Hazard Quotients for noncarcinogens affecting the same target organ.

EPA is encouraged to “broadly consider the full impact of multiple pollutants and emission points affecting the local community in its regulations.” Concern is expressed that the estimated cancer maximum individual risk is 2,000-in-1 million predominantly due to the contributions of ethylene oxide The agency is urged to use the to use the updated Integrated Risk Information System risk value for the constituents in setting regulations that will ameliorate risks from exposure to the constituent from this or other source categories.

In addressing concentrations at census tract centroids, NACAA states that EPA used long-term concentrations affecting the census blocks within 50 kilometers of each facility. It states that this dilutes the effect of sources’ emissions by estimating the impact at the centroid of the census block instead of at the property line or wherever the maximum exposed individual is. It is recommended that the agency:

. . . identify and use the truly maximum individual risk, irrespective of its location in the census block, rather than using the predicted chronic exposures at the census block centroid as surrogates for the exposure concentrations for all people living in that block.

Finally, as to Acute Exposure, concern is expressed that EPA is still using Acute Exposure Guideline Levels or Emergency Response Planning Guidelines to address exposures in the residual risk assessments. It is argued that such limits were developed for accident release emergency planning and are not appropriate for assessing daily human exposure scenarios.

A copy of the comments can be downloaded here.