The comments reflect interagency review of the draft rule under EOs 12866 and 13563. They are 

subject to further policy review.

Page 1 of 6

Comments on the Socio-Economic Analysis (same comments for both ONG & Natural Gas documents):

Page 7/8: The discussion of results mentions only some of the results in the table and not all and the 

rational for this is not clear. Could EPA explain further? Also, in the discussion of changes EPA uses 

variable terms: sometimes ‘modest increases’, sometimes ‘similar’, sometimes ‘greater’, sometimes 

‘increases’. It is not clear what is meant by all these different terms. It would also be helpful if EPA 

discussed any statistical analyses that were conducted to see if any of the differences are statistically 

significant. If no statistical analyses were conducted, this should be very clearly stated. We encourage 

EPA to pursue statistical analyses and suggest that perhaps taking comment on suggested approaches 

would be helpful.

EPA Response: We did not perform tests for statistical significance. It is likely that most of the 

differences noted would be statistically significant because of the sample sizes of the nationwide data 

and the people at risk greater than 1 in a million. However, there may be select cases where the sample 

size of people at risk greater than 1 in a million is insufficient to show a statistically significant difference 

with the nationwide data. We will include some text in the demographics reports explaining this.

Page 8: in the uncertainty discuss, the Census bureau does not refer to “typical uncertainties” when 

describing errors in filling out and transcribing forms. Please delete this language consistent with 

changes in previous preamble discussions.

EPA Response: We will delete the language.

Comments on the draft risk assessment:

General comment: Should the document also have some discussion of allowable risk? This is in the 

preamble, but not clear it is discussed elsewhere.

EPA Response: We did not perform a separate risk assessment for allowable emissions, so we did not 

include risk estimates for allowable emissions in the risk assessment document. To estimate the MIR for 

the source category based on allowable emissions, the baseline risk assessment results for the higher risk 

facilities were scaled based on knowledge of the control status of sources and the 1 ton per year 

alternative emission standard. This analysis is included in a separate memo to the docket.

We note that in discussion of human inhalation exposure (section 2.3) there is a bias toward estimating 

risk high. This discussion, particularly as it relates to the MIR, should carry over to the preamble when 

EPA is discussing whether or not risks are acceptable.

EPA Response: We discuss in Section 2.3 how human activity and mobility do not bias MIR or incidence. 

Because of this, we do not feel it is necessary to include preamble language on the subject.

Page 13/14: the discussion of formaldehyde risks should be updated in light of the recent NAS report 

which is now available. While EPA may still be digesting, NAS made some clear statements:

at page 42, regarding the Conolly/CIIT model “Although the committee finds that testing of 

alternative models and the variability in model parameters is consistent with EPA’s cancer 

guidelines, some of the more extreme model scenarios should not have been used as a basis for 

rejecting the BBDR approach. In particular, adjustments of parameter values associated with 

mutation, birth, and death rates of initiated cells used in EPA’s analysis of alternative models 
The comments reflect interagency review of the draft rule under EOs 12866 and 13563. They are 

subject to further policy review.

Page 2 of 6

that yielded the most extreme deviations from the Conolly et al. (2004) low-dose extrapolations 

also produced unrealistically high added risks for humans at concentrations that have been 

observed in the environment of occupationally exposed workers (100% incidence at 

concentrations as low as about 0.1-1 ppm). Thus, the committee recommends that

manipulations of model parameters that yield results that are biologically implausible or 

inconsistent with the available data be discarded and not used as a basis for rejecting the 

overall model. The committee concludes that the existing BBDR models were developed from 

an impressive exposure- and time-dependent database on the modes of actions of 

formaldehyde in rats and monkeys; exquisitely detailed dosimetry models in rats, monkeys, and 

humans; and sparse data on humans that required scale-up of key model parameter values 

from animal studies and other biologic data and epidemiologic observations to constrain the 

human model predictions. The scope of the research makes this one of the best-developed 

BBDR models to date for any chemical, even with its acknowledged uncertainties.”

At page 43: “The committee acknowledges and agrees with EPA that the Conolly et al. (2003, 

2004) models, like most models, contain weaknesses and tenuously supported assumptions. 

Conolly and co-workers felt that they made several conservative assumptions in their models—

use of hockey-stick rather than Jshaped models for cell proliferation, use of overall respiratory 

tract cancer incidence in humans to calculate basal mutation rates, and use of an upper bound 

on the proportionality parameter relating DPX to mutation. EPA pushed that concept further by 

making even more conservative assumptions within the models that cumulatively resulted in 

radical departures from the results of the Conolly et al. models with regard to low-dose 

extrapolation of tumor incidence. The committee notes that EPA forced changes in the model 

parameter values in a direction that yielded more conservative results rather than one that 

yielded a best fit to the data. The committee is also concerned that EPA directed substantial 

effort toward refuting many of the assumptions and conclusions of the Conolly et al. (2003, 

2004) models rather than trying to fill the data gaps that were clearly articulated by the models. 

One of the major strengths of the Conolly et al. models is that the developers had to reconcile 

all the data or specify why they could not be reconciled. The integrated model structure allows 

one to identify uncertainties clearly and how they may affect model behavior. Conolly and coworkers were clear on that point and expressed the need for new data that could anchor many 

of the parameter values that had to be optimized from rather sparse data sets. Regardless, the 

committee recommends that for completeness and transparency the BBDR models published 

by Conolly et al. (2003, 2004), with the flaw in one numeric approach identified by EPA

corrected, be used in the draft IRIS assessment and that the results be compared with those of 

the approach that was used in the draft assessment.”

At page 44: “Furthermore, EPA, on the basis of extreme alternative model scenarios, chose not 

to use the BBDR models developed by Conolly et al. (2003, 2004); however, the committee 

questions the validity of some of these scenarios and recommends that the BBDR models 

developed by Conolly and co-workers be used (with the flaw in one numeric approach identified 

by EPA corrected), that the results be compared with those of the approach currently presented 

in the draft IRIS assessment, and that the strengths and weaknesses of each approach be 

discussed.”

Based on NAS comments, for transparency in the risk assessment and preamble, we suggest 

that EPA present risk numbers using the CIIT value as well as the older IRIS value. EPA can then 

take comment on the range of values presented.
The comments reflect interagency review of the draft rule under EOs 12866 and 13563. They are 

subject to further policy review.

Page 3 of 6

EPA Response: We conclude that adding this discussion is unnecessary for several reasons. First, the IRIS 

assessment of formaldehyde is in the external peer review phase, and it is appropriate to address the 

NAS comments within the IRIS assessment instead of this rulemaking. Also, formaldehyde is not a risk 

driver for either source category. The emissions from the categories are low (Storage and Transmission: 

0.06 TPY; Production: 2 TPY). Formaldehyde is a driver for facilitywide risks, but those will be addressed 

under a separate action for RICE.

Page 22: EPA mentions that if benzene risks exceed 1 in a million, EPA will evaluate the impact of using 

the low end of the range. It is not clear that EPA has done this transparently or robustly enough in the 

preamble and risk assessment. We suggest greater discussion, noting, as per the IRIS file, that both ends 

of the range are equally plausible.

EPA Response: We conclude that the discussion of the benzene URE range in Section 2.7, along with the 

table footnotes of the lower-end results, and additional language in the source category results sections 

are sufficient. 

Page 26, in section 3.2, please discuss the cancer risks using both sides of the benzene range equally. 

There should be two estimates in all cases for the number of people at risk, each time a risk number is 

provided (similar edits for preamble as well).

EPA Response: We will add some language to discuss the results at the lower end of the range.

Page 27, when discussing the max acute HQ, please provide what the number would be if an alternative 

to the REL was used.

EPA Response: We include HQ estimates based on reference values other than the REL in the results 

table. We have not discussed these in the text because the HQ values are less than 1. The discussion 

focuses on those cases where the HQ exceeds 1 and the refined estimates for those cases. We do not 

perform any refinements for cases of HQ less than 1.

Table 3.2-1 and 4.2-1- please always provide a range of benzene values in each row (for cancer risks and 

population exposures). For non cancer, please give max acute HQ using values other than the REL.

Since benzene is a risk driver, more than just footnote 16 is needed, a range of values should be in all 

tables where benzene is a risk driver.

EPA Response: We conclude that the discussion of the benzene URE range in Section 2.7, along with the 

table footnotes of the lower-end results, and additional language in the source category results sections 

are sufficient. Population exposure estimates are not scalable with the cancer URE, so we couldn’t 

provide a range for that anyway.

Page 29, when discussing formaldehyde risks, please also present what risks would be if CIIT value was 

used.

EPA Response: See formaldehyde response above.

Section 5.2- please include a specific discussion regarding the range of plausible benzene risks.
The comments reflect interagency review of the draft rule under EOs 12866 and 13563. They are 

subject to further policy review.

Page 4 of 6

EPA Response: We already include a discussion of the benzene range in Section 2.7. We conclude that 

this discussion, along with the table footnotes of the lower-end results and additional language in the 

source category results sections are sufficient. The Section 5.2 discussion is about general dose-response 

uncertainties and is not pollutant-specific.

Comments on the RIA:

In all tables, please clarify that except for VOC benefits, all other health benefits should clearly be noted 

as co-benefits.

EPA Response: Health benefits associated with exposure to ozone and PM2.5 are not “co-benefits” of the 

NSPS. The purpose of the NSPS is to control criteria pollutants, and VOCs are being controlled as 

precursors to these secondarily formed criteria pollutants. The purpose of the NESHAP is to control 

HAPS, thus health benefits associated with exposure to HAPs are also not “co-benefits”. We will ensure 

that climate benefits are properly characterized as co-benefits throughout the RIA.

Section 4.4, (page 4-9), when discussing risk drivers, please be more transparent regarding the 

confidence in the values. For instance, EPA has low confidence in the acrolein values and this certainly 

should impact the NATA results and interpretation. Footnote 20 is not sufficiently transparent. 

EPA Response: We will clarify the footnote.

Page 4-10, the discussion of the acrolein/acetaldehyde values should also take into account confidence 

in the values. Often lower IRIS values are driven by higher uncertainties (3 orders of magnitude of 

uncertainty factors added to the point of departure).

EPA Response: We will add a clarifying footnote.

Page 4-11 and elsewhere (page 4-12), please delete language that says “due to methodology and time 

limitations..” we believe that EPA has had sufficient time to try to do a better job quantifying HAP 

benefits. Suggest simply taking comment on methodologies and suggested approaches. We would 

appreciate EPA committing to attempt to quantify these values. 

EPA Response: We will revise the language to say “due to data and methodology limitations”. 

Section 4.4.3 Formaldehyde: please update discussion to reflect NAS report. (See comments on risk 

assessment)

EPA Response: Formaldehyde has been deleted from RIA.

Comments on the preamble:

Page 176-179: please update formaldehyde discussion (see comments regarding risk assessment). In 

light of NAS comments, EPA should be more supportive and continue to present results with CIIT 

modeling.
The comments reflect interagency review of the draft rule under EOs 12866 and 13563. They are 

subject to further policy review.

Page 5 of 6

EPA Response: See response on formaldehyde comment above.

Page 206/207- please discuss use of a plausible risk range for benzene cancer risks. Footnote 41 is not 

sufficient as benzene is a risk driver.

EPA Response: In addition to footnote 41, we have added footnotes to the risk results tables that state 

the impact of the lower end of the range.

Page 214- table 2 should in most columns present a range of equally plausible risk values based on the 

benzene range. For the column on max. acute risk, please also note what max acute risk would be with 

other acute screening values. Text discussion in section i (inhalation risk results) should also be revised 

to reflect a range of benzene values. (similar comments on table and text on page 226-229)

EPA Response: We have added footnotes to the risk results tables that state the impact of the lower end 

of the range, and we will add text to the discussion. In RTR preambles, we have limited the presentation 

of acute HQ results to those based on the lowest available acute dose-response value, which, in most 

cases, is the REL. We state this in a footnote in the tables.

Page 215- table 3, please see comments above and revise table and text to reflect benzene range. When 

discussing formaldehyde risk, please also present a range which includes the CIIT value as per NAS 

recommendations. Similar comment for page 229.

EPA Response: Same response as for table 2.

Page 220- again, please provide benzene range. Considering the low end of the range as well as the 

conservatism in the exposure assumptions, it is not clear that EPA has provided a full weight of the 

evidence discussion when making an unacceptable determination.

EPA Response: We conclude that the inclusion of footnotes and text elsewhere in the preamble is

sufficient to address the benzene URE range issue. Including discussion of the range in the acceptability 

discussion would not change the conclusion because the risks would still be deemed unacceptable at the 

lower end of the range.

Page 221, when discussing Acute HQ’s please provide max HQ using other available acute values. This 

should be in text.

We do discuss in that section (page 222) that “the highest estimated 1-hour exposure is less than 10 

percent of the AEGL-1 value.” 

Page 222/223- if EPA considers the range of benzene values, it’s not clear why the compliance 

alternative needs to be completely removed. To provide flexibility, EPA should discuss the option of 

perhaps needing to lower the 1 tpy threshold, but it’s not clear why it needs to go to zero to make risks 

acceptable. Further justification is needed. It would be helpful to include discussion/analysis of facilities 

that currently use the compliance alternative and what their risks numbers are. Suggest further 

discussion on page 234 as well.

Response in progress.
The comments reflect interagency review of the draft rule under EOs 12866 and 13563. They are 

subject to further policy review.

Page 6 of 6

Page 301- unclear that this conclusion regarding risks tracks with the rest of the preamble

EPA Response: If the comment refers to the text for Executive Order 13045, it does not seem to be 

inconsistent with the rest of the preamble. The EO text states that “.... EPA’s risk assessments (included 

in the docket for this proposed rule) demonstrate that the existing regulations are associated with an 

acceptable level of risk...” We do state earlier in the preamble that the 400 in a million based on 

allowable emissions is unacceptable. The EO text will be revised.