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Federal Register / Vol. 86, No. 3 / Wednesday, January 6, 2021 / Rules and Regulations
basis for each model assumption used;
and to show the sensitivity of the modeled results to alternative assumptions. These proposed requirements also directed the EPA to give explicit consideration to high quality studies that explore a broad class of parametric dose-response models, non-parametric models that incorporate fewer assumptions, various threshold models, and models that investigate factors that might account for spatial heterogeneity.
The EPA received significant comment on the 2018 proposed rule regarding the proposed 40 CFR 30.6
requirement that the EPA evaluate the appropriateness of using default assumptions, including assumptions of a linear, no threshold dose-response.
The vast majority of commenters asserted that the EPA should not focus the requirement to evaluate the appropriateness of using default assumptions specifically on linear, no threshold dose-response. In the 2020
SNPRM, in response to these comments, the EPA proposed a variation of the regulatory text which did not include the phrase including assumptions of a linear, no threshold dose-response, because this could imply that the regulation is specific to those particular assumptions.
The EPA also received significant comment on the 2018 proposed rule about the proposed 40 CFR 30.6
requirement to clearly explain the scientific basis for each model assumption used and to present analyses showing the sensitivity of the modeled results to alternative assumptions. Most commenters contended that such a requirement would be overly burdensome and unnecessary. They recommended that the EPA should present sensitivity analyses only on the most significant assumptions.
Considering these comments, in the 2020 SNPRM, the EPA clarified that the use of the terms model assumptions, assumptions and models in the proposed regulatory text at 40 CFR 30.6
apply to the critical assumptions that drive the models analytic results, not to each assumption used in the model. The EPAs proposed revision of the 40 CFR
30.6 regulatory text reflected this clarification.
After considering comments on both the 2018 proposed rule and the 2020
SNPRM, the EPA has determined that this rule should apply to dose-response data rather than dose-response data and models. Given the specificity of 40 CFR
30.6 to dose-response data and models, and in particular dose-response models, the EPA is not finalizing 40 CFR 30.6.

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The EPA is adapting one provision of 40
CFR 30.6 as a factor in 40 CFR 30.5 in determining the consideration to afford pivotal science for which the doseresponse data are not available for independent validation. Specifically, the EPA is finalizing as a factor in 40
CFR 30.5 the consideration that the EPA
would give to high quality studies that explore a broad class of parametric dose-response models, non-parametric models that incorporate fewer assumptions, various threshold models, and models that investigate factors that might account for spatial heterogeneity.
Further, because the EPA is not finalizing any part of the provision that is specific to assumptions and methods associated with dose-response models, comments on the proposed requirements related to these issues are moot. However, while the EPA is not finalizing the provisions in 40 CFR 30.6
that include the term uncertainty, the EPA is responding to these comments because the term uncertainty is used in 40 CFR 30.5. The EPA is also responding to comments on the proposed 40 CFR 30.6 provision incorporated as part of 40 CFR 30.5.
Some commenters contended that the EPAs use of the term uncertainty at 40 CFR 30.6 is vague. A few other commenters contended that the EPA
should include specific requirements in 40 CFR 30.6 as to the scope of an analysis of uncertainty. The EPA
disagrees with the suggestion that the term uncertainty is vague or that there is significant ambiguity about what should be in the scope of a characterization of uncertainty. The characterization of uncertainty is a key factor in the assessments that the EPA
conducts. It is a component of various EPA guidelines e.g., Framework for Human Health Risk Assessment to Inform Decision Making, Ref. 36 that the EPA relies upon in conducting its assessments. The scope of the uncertainty analyses that the EPA
conducts necessarily varies across assessments and actions. The intent of this regulation is not to force uncertainty analyses into a one-size-fitsall approach, as that is not practical, good policy, or good science. Thus, a regulation of internal procedures, such as this one, does not require a regulatory definition for a term that is already a key component of current EPA practices and guidelines and EPAs assessment process.
Several commenters contended that the proposed 40 CFR 30.6 requirement that the EPA give explicit consideration to high quality studies that explore a broad range of parametric dose-response or concentration-response models and
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to non-parametric models that incorporate fewer assumptions could force the EPA into situations in which it applies dose-response models that are not appropriate for the data being assessed. The EPA notes that the final regulatory text in 40 CFR 30.5 does not require that a specific type of doseresponse model be applied to a particular situation. Rather, in determining the consideration to afford pivotal science for which the doseresponse data are not available for independent validation, the EPA will evaluate, as appropriate, the extent to which the study considered a broad range of parametric dose-response or concentration-response models, a robust set of potential confounding variables, nonparametric models that incorporate fewer assumptions, various threshold models across the dose or exposure range, and models that investigate factors that might account for spatial heterogeneity.
G. Administrators Exemption In the 2018 proposed rule, the EPA
proposed that the Administrator could grant case-by-case exemptions to the requirements in proposed 40 CFR part 30 when compliance with those requirements is impracticable proposed 40 CFR 30.9. In the 2020 SNPRM, the EPA modified proposed 40 CFR 30.9 to be consistent with other changes proposed in the 2020 SNPRM, such that the Administrator could grant case-bycase exemptions to the requirements in proposed 40 CFR part 30 under specific conditions for which compliance with the requirements in proposed 40 CFR
part 30 is impracticable.
Some commenters supported the Administrators exemption provision in proposed 40 CFR 30.9 while others opposed it. Commenters expressing support for the exemption provision noted that exemptions may be needed to account for lawful and reasonable restrictions on underlying data and models. Commenters expressing opposition to the exemption provision raised concerns about the Administrator granting exemptions from the requirements in proposed 40 CFR part 30. These commenters contended that the Administrator may lack the scientific expertise to make the appropriate exemption decisions and that the Administrator, as a political appointee, could be biased. Some public commenters recommended that the exemption process require formal consultation with EPA career scientists, the EPAs SAB, or another Agency advisory committee.
The EPA also received comment on the following proposed conditions
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