Response to Public Comments on the EPA's
                 Residual Risk and Technology Review for the
                Publicly Owned Treatment Works Source Category

                                 October 2017

Contents
Introduction	1
Risk Review	3
2.1	Risk Assessment Inputs	3
2.2	Risk Assessment Methods	5
2.2.1	Inhalation Risk Screening	7
2.2.2	Multipathway Screening	18
2.2.3	Cumulative Risk Assessment	20
2.3	Risk Assessment Results	25
2.4	Demographics	29
Technology review	32
Applicability	37
4.1	General Comments	37
4.2	Affected sources	39
4.3	Major Source Determination	40
4.4	Pretreatment	42
Emission Standards, Testing, and Monitoring	46
5.1	HAP Fraction Emission Limit	46
5.2	Alternative Standards	47
5.3	Monitoring	50
Compliance Dates	59
Reporting	60
Economic impacts	62
Startup, Shutdown, or Malfunction	64
Miscellaneous	68

Introduction

      Section 112(f)(2) of the Clean Air Act (CAA) directs the Environmental Protection Agency (EPA) to conduct risk assessments on each source category subject to maximum achievable control technology (MACT) standards and determine if additional standards are needed to reduce residual risks within 8 years after promulgation. Section 112(d)(6) of the CAA requires the EPA to review and revise the MACT standards, as necessary, taking into account developments in practices, processes, and control technologies at least every 8 years. The national emission standards for hazardous air pollutants (NESHAP) for Publicly Owned Treatment Works (POTW) (40 CFR part 63, subpart VVV) were promulgated in 1999 and most recently amended in 2002 and are due for review under CAA sections 112(f)(2) and 112(d)(6).
      The POTW NESHAP was included in a suit filed by Sierra Club and California Communities Against Toxics. The suit asked the D.C. District Court to compel the EPA to complete the residual risk and technology review (RTR) assessments required by the CAA. The August 27, 2015 court order specifies a promulgation date of October 16, 2017 for completing the RTR. In addition, on December 19, 2008, the D.C. Circuit Court vacated the startup, shutdown, and malfunction (SSM) exemption provisions in the General Provisions for non-opacity [40 CFR 63.6(f)(1)] and opacity [40 CFR 63.6(h)(1)] standards, and the EPA is evaluating the SSM provisions in subpart VVV in light of this decision. The EPA is also evaluating 40 CFR part 63, subpart VVV to determine if additional amendments are warranted -  and can be done within the limited time period provided by the court-ordered deadline - to ensure continuous compliance with the standard and to promote consistency with other standards.
      To address the RTR assessments, SSM exemptions, and other changes that are warranted, proposed amendments to subpart VVV were developed, signed by the EPA Administrator on December 6, 2016, and published in the Federal Register on December 27, 2016. A 90-day period ending March 29, 2017, was provided for the public to submit comments on the proposal to the EPA. The following sections of this document summarize the public comments received on the proposal and present the EPA's responses to those comments:
   Section 2 - Risk Review
   Section 3 - Technology Review
   Section 4 - Applicability
   Section 5 - Emission Standards, Testing, and Monitoring
   Section 6 - Reporting
   Section 7 - Compliance Dates
   Section 8 - Economic Impacts
   Section 9 - Startup, Shutdown, or Malfunction
   Section 10 - Miscellaneous Comments

      A total of 23 separate sets of written comments were received on the proposal. See www.regulations.gov, docket ID no. EPA-HQ-OAR-2016-0490, for the complete comments. Table 1 below lists the names of the commenters providing written comments, their affiliations, and the document numbers assigned to their comments. For simplicity, only the last four digits of the document number specific to each commenter are presented in this document (e.g., 0040, instead of EPA-HQ-OAR-2016-0490-0040).
          Table 1. List of Commenters on 40 CFR Part 63 Subpart VVV,
                   Proposed December 27, 2016 (81 FR 95352)
                       Docket No. EPA-HQ-OAR-2016-0490-
                                Commenter Name
                                  Affiliation
                                     0040
Curt McCormick
CWA Consulting Services, LLC
                                     0045
Isaac Smith
Advanced Placement U.S. Government and Politics student at West Bloomfield High School
                                     0046
Anonymous
--
                                     0050
Kay Anderson
American Bottoms Regional Wastewater Treatment Facility
                                     0052
--
Gulf Coast Waste Disposal Authority
                                     0053
Anonymous
--
                                     0054
Kay Anderson
American Bottoms Regional Wastewater Treatment Facility
                                     0056
Karnig Ohannessian
Department of the Navy
                                     0058
Sarah Van Frank
Butler County (OH) Water and Sewer Department
                                     0059
Cindy Cullen
Metropolitan St. Louis Sewer District
                                     0060
Paul Kent
Vanessa Wishart
Municipal Environmental Group  -  Wastewater Division
                                     0061
Emma Cheuse
Earthjustice[1]
                                     0062
Mark Feltner
Hampton Roads Sanitation District
                                     0063
Kevin Shafer
Milwaukee Metropolitan Sewerage District
                                     0064
Peter LaFlamme
Association of Clean Water Administration (ACWA)
                                     0065
Gail Good
State of Wisconsin, Department of Natural Resources
                                     0066
Matthew Todd
Residual Risk Coalition[2]
                                     0067
Peter Waite
Eli Lilly and Company
                                     0068
Kara Valentine
Steve Goans
State of Nebraska, Department of Environmental Quality
                                     0069
Pam Elardo
New York City Department of Environmental Protection
                                     0070
Cynthia Finley
National Association of Clean Water Agencies (NACWA)
                                     0071
Steven Jepsen
Southern California Alliance of Publicly Owned Treatment Works (SCAP)
                                     0072
Claudio Ternieden
Water Environment Federation
[1] On behalf of Sierra Club
[2] Comprised of the American Chemistry Council, the American Coke and Coal Chemicals Institute, The American Forest & Paper Association, the American Fuel & Petrochemical Manufacturers, the American Iron and Steel Institute, the American Petroleum Institute, the National Oilseed Processors Association, and the Rubber Manufacturers Association.

      In some cases, one or more commenters endorsed the comments by another commenter. In those cases, the endorsement is noted in the "Miscellaneous Comments" section. The comment summaries are numbered sequentially (e.g., 2.2.1-01, 02, 03, etc.) within each section and subsection.
Risk Review
Risk Assessment Inputs
      2.1-01 Comment:  Commenter 0061-A1 objected to the EPA's estimation of chronic exposure at the census block centroid instead of at the facility fence or property line. Furthermore, the commenter stated that the EPA made no effort to move receptor points closer to the facility to assess chronic or cancer risk, even where local residents live nearer to a facility than the census block centroid. According to the commenter, this conflicts with the recommendation of the Science Advisory Board (SAB), which has urged the EPA to consider "specific locations of residences."  The commenter stated that taking geographic variation out of the equation fails to properly account for exposure to the "individual most exposed to emissions" as required by section 112(f)(2)(A), and fails to provide an accurate estimate of risk. The commenter argued that estimating the annual average concentrations at the area-weighted centers of census blocks blatantly and artificially underestimates the risk estimated for people at the fence-line since the center of a census block is almost always further away from the facility than the fence-line. The commenter also noted that census blocks vary greatly in size, yet the EPA provides no evidence that it reviewed census block size or configuration to consider how concentrations of pollutants might vary within these blocks. Therefore, the commenter concluded, area-weighted centers of census blocks may be significantly underestimating exposure in some cases.
      Commenter 0061-A1 stated that the EPA's failure to adjust receptor points for residents living on the fence-line is particularly inexcusable given that the EPA's air dispersion model allows for such an adjustment, and that such an adjustment was appropriately made for the estimation of acute health risks. The commenter concluded that, having recognized that the maximum exposed individual for acute risks is likely present at the fence-line, the EPA cannot justify failing to analyze cancer and other chronic health effects in a similar manner.
 	2.1-01 Response: In a national-scale assessment of lifetime inhalation exposures and health risks from facilities in a source category, it is appropriate to identify exposure locations where it may be reasonably expected that an individual will spend a majority of his or her lifetime. In determining chronic risks, it is appropriate to use census block information on where people actually reside, rather than points at the property line, to locate the estimation of exposures and risks to individuals living near such facilities. Census blocks are the finest resolution available as part of the nationwide population data (as developed by the U.S. Census Bureau); on average, a census block is comprised of approximately 40 people and about 10 households. In the EPA risk assessments, the geographic centroid of each census block containing at least one person is used to represent the location where all the people in that census block live. The census block centroid with the highest estimated exposure then becomes the location of maximum exposure, and the entire population of that census block is assumed to experience the maximum individual risk. In some cases, because actual residence locations may be closer to or farther from facility emission points, this may result in an overestimate or underestimate of the actual annual concentrations (although there is no systematic bias for average levels). Given the relatively small dimensions of census block in densely-populated areas, there is little uncertainty introduced by using the census block centroids in lieu of actual residence locations. There is the potential for more uncertainty when the census blocks are larger, although there is still no systematic bias. The EPA concludes that the most appropriate locations at which to estimate chronic exposures and risks are the census block centroids because: 1) census blocks are the finest resolution available in the national census data; 2) facility fence-lines do not typically represent locations where chronic exposures are likely (i.e., people do not typically live at the fence-line of facilities); and 3) there is no bias introduced into the estimate of maximum individual risk (MIR) by using census block centroid locations. In its peer review of the methodologies used to estimate risks as part of the RTR rulemaking efforts, the EPA's SAB endorsed this approach.
            In addition to the approach described above, the EPA recognizes that where a census block centroid is located on industrial property or is large and the centroid is less likely to be representative of the block's residential locations, the block centroid may not be the appropriate surrogate. For this source categories, as described in the Residual Risk Assessment for the Publicly Owned Treatment Works source category in Support of the December 2016 Risk and Technology Review Proposed Rule (December 2016) in Docket Item No. EPA - HQ - OAR - 2016 - 0490-0012, in cases where a census block centroid was within 300 meters of any emission source (and therefore possibly on facility property), we viewed aerial images of the facility to determine whether the block centroid was likely located on facility property. Likewise, we examined aerial image of all large census blocks within one kilometer of any emission source. If the block centroid did not represent the residential locations within that block, we relocated it to better represent them and/or we added receptors for residences nearer to the facility than the centroid. For these source categories, we added several receptors for census blocks where the centroid location was not representative of the residential locations. Appendix 7 of the risk assessment document cited above provides additional information on these changes.
      2.1-02 Comment: Commenter 0061-A1 stated that toxic air pollutants emitted by POTW contribute to a wide range of serious health impacts. The commenter provided a summary of emissions from the modeling file and health impacts for 8 pollutants. The pollutants were: benzene, formaldehyde, toluene, ethylbenzene, polycyclic aromatic hydrocarbons, naphthalene, acetaldehyde, and hydrogen sulfide (H2S). The commenter noted that benzene is a known carcinogen and long term exposure can cause leukemia.
      The commenter noted that there is a pending petition to list H2S as a hazardous air pollutant (HAP) and emphasized the dangers of H2S, encouraging the EPA to list this pollutant as a HAP and regulate emissions from POTW. The commenter cited a Chemical Safety Board (CSB) report from 2002 regarding an incident when H2S gas leaked from a sewer manway at the Georgia-Pacific Naheola mill in Pennington, Alabama, in which several people working near the manway were exposed to the gas and two contractors were killed and eight people were injured. Commenter 0061-A1 also noted that CSB published a Safety Bulletin called "Sodium Hydrosulfide: Preventing Harm" in response to other similar incidents involving sodium hydrosulfide, and the EPA found that the science "shows that it can reasonably be anticipated to cause chronic health effects in humans" and threatens "significant adverse effects in aquatic organisms." The commenter also attached an article to their comment that was not specifically referenced in the text, but addresses worker safety at POTW, including a discussion about the adverse health effects from chronic exposure to low levels of H2S gas.
      2.1-02 Response: We appreciate the commenter's summary of emissions in the modeling file from source category emission units and the human health impacts associated with each of the 8 pollutants. While the human health impacts are supported with documentation, it is important to note that quantity, dispersion, and receptor location are important when determining human health impacts. Using these factors with the HEM-3 model, the EPA found that the risks from this source category were acceptable.
      The commenter provided references to several news reports regarding emissions from H2S in occupational settings and accidental releases. The commenter also mentions a petition submitted to the EPA to list H2S as a HAP. The commenter claims that the EPA has sufficient toxicity data on H2S to list and regulate it from publicly owned treatment works in this rulemaking. The EPA has received a petition to list H2S as a HAP under section 112(b) of the CAA. The EPA's process to review this petition is a separate process from the current RTR review of this source category. It would be premature to address H2S emissions under this RTR because the EPA has not yet made a determination on the petition to list H2S as a HAP.
Risk Assessment Methods
      2.2-01 Comment: Commenter 0052 supported the EPA's methodology and conclusion concerning the risk assessment conducted pursuant to 112(f).
      2.2-01 Response: We acknowledge the commenter's support for evaluating the public health risks associated with exiting POTW subject to subpart VVV.
      2.2-02 Comment: Commenters 0045, 0046, 0059, 0066, 0070, 0071 contended that the EPA has no basis for proposing new requirements because the EPA's proposed risk analysis shows that there is no health risk. Commenters 0045, 0046, 0059, 0066 added that the EPA's finding of no significant health risk means that the proposed $10,000 cost for the six POTW in the proposal is not justified. Commenter 0066 added that the EPA's previous assertion "we believe that the findings that underlie a section 112(f) determination should be key factors in making any subsequent section 112(d)(6) determinations for the related section 112(d) standard" (70 Fed. Reg. 19992, 20009 (Apr. 15, 2005)) contradicts the EPA's proposal to add new requirements.
      2.2-02 Response: The residual risk review and the technology review are required by separate sections of the CAA. Section 112(f) requires that 8 years after promulgation of the MACT standard the EPA must publish standards to provide an ample margin of safety to protect public health. Section 112(d)(6) requires that 8 years after promulgation of the MACT standard, the EPA must review and, as necessary, revise the MACT standard to reflect developments in practices, processes, and control technologies. These reviews are independent requirements of the CAA, and both requirements must be met. Nothing in the CAA specifies that the level of public health risks posed by the industry controls the determinations made under the section 112(d)(6) review about developments affecting the feasibility and cost of emission controls for the industry.
      2.2-03 Comment: Commenter 0066 argued that the CAA gives the EPA authority to make a residual risk determination only once for a given source category or subcategory, and that it does not provide authority for the EPA to undertake additional residual risk reviews for the same source category after the first (and only) review is completed. The commenter contended that the following statement in the proposal misstated the law because it suggests that the EPA may need to conduct a § 112(f) residual risk review for a given source category more than one time: "it will not be necessary to conduct another residual risk review under CAA section 112(f) for this source category 8 years following promulgation of the new standards for collection systems, merely due to the addition of these MACT requirements." (81 Fed. Reg. at 95373) The commenter argued that this statement is inconsistent with Section 112(f)(2)(A) of the CAA, which states "within 8 years after promulgation of standards for each category or subcategory of sources pursuant to subsection (d) of this section, [the Administrator must] promulgate standards for such category or subcategory if promulgation of such standards is required" to prevent unacceptable risk to health or the environment. The commenter argued that this language sets a deadline for promulgating a residual risk rule based on the date a MACT standard for a given source category is issued (i.e., 1999 for the POTW source category), not based on the date future revisions are made to those standards, because standards for the source category already exist.
      2.2-03 Response: To the extent the commenter interprets the EPA's statement as suggesting that the CAA requires a residual risk analysis under section 112(f)(2) every 8 years, the commenter is misinterpreting the EPA's statement in the proposal.  The EPA does not interpret section 112(f) as establishing a recurring requirement to conduct a residual risk analysis every 8 years.  Also, to the extent that the comment is addressing whether and under what circumstances the EPA could conduct subsequent residual risk analyses, or the extent to which the EPA could consider risk in future hypothetical rulemakings, that is beyond the scope of this rulemaking.  Nonetheless, the EPA notes that it disagrees with the comment to the extent that it suggests that this action limits the EPA's discretion to evaluate risk from the source category in future actions. With respect to the specific language cited by the commenter, the language at 81 FR 95373 merely indicated that a future risk reevaluation under section 112(f)(2) will not be necessary for POTW due to emissions from collection systems.
      2.2-04 Comment: Commenter 0061-A1 contended that the EPA was legally obligated by sections 112(d)(6) and (f)(2) of the CAA to perform a technology and community health risk review and set updated standards for POTW within 8 years after first setting standards, and updated standards for POTW are long overdue. The commenter stated that the EPA's failure to act has resulted in six major source POTW facilities emitting approximately 27 tons per year of toxic air emissions (include cancer-causing pollutants like acetaldehyde, formaldehyde and benzene) into local communities.
      2.2-04 Response: With respect to the first part of this comment (that the EPA was legally obligated to conduct the risk and technology review within 8 years and that updated standards are overdue), this is not a relevant issue for this rulemaking.  This issue was addressed in the lawsuit that ended with a consent decree setting deadlines for the EPA to conduct this risk and technology review. See Sierra Club v. McCarthy, No. 13-1639 (RMD) (D.D.C.). With respect to the second part of this comment (that six POTW have emitted approximately 27 tons of per year because of the EPA's failure to conduct the risk and technology review before now), the commenter does not explain how this contention is relevant to the issues before the EPA in this rulemaking. Again, this issue might have been relevant in the deadline suit in Sierra Club v. McCarthy, No. 13-1639, but the commenter does not explain why it is a significant comment here.
      2.2-05 Comment: Commenter 0061-A1 stated that the EPA must protect communities exposed to toxic air pollution from publicly owned treatment works. The commenter provided data to demonstrate the significance of toxic emissions from POTW and the size of the affected population, listing per facility HAP emission data for each of the six-major source POTW included in the proposal and indicating that they together annually emit at least 20 tons and possibly as high as 48.2 tons of HAP. The commenter pointed out that 2.2 million people live within 5 km of these POTW, and over 24 million people live within 50 km of these facilities.
      2.2-05 Response: We acknowledge the commenter's support for evaluating the public health risks associated with existing POTW subject to subpart VVV.
2.2.1	Inhalation Risk Screening
      2.2.1-01 Comment:  Commenter 0061-A1 stated that the EPA failed to use the best available reference values for a number of key HAP including benzene, and thus underestimated risk from these pollutants.
      Regarding cancer risk, commenter 0061-A1 recommended using the latest cancer potency values as published by the California EPA (CalEPA) in updated guidance in 2015. The commenter performed a comparison of the CalEPA values and those used by the EPA and claimed for some HAP (including 1,3 butadiene and benzene) the UREs are at least 72percent lower. The commenter also stated an emissions weighted analysis of the different potency values used by the EPA versus those recommended by CalEPA shows that cancer risk may have been two times higher had the EPA utilized up-to-date factors.
      Regarding non-cancer chronic risk, commenter 0061-A1 also recommended that the EPA use the latest chronic inhalation RfCs published by CalEPA in their 2015 guidance. The commenter claimed that the EPA's RfC for benzene is less protective than that published by CalEPA by two orders of magnitude.
      Regarding non-cancer acute risk, commenter 0061-A1 also recommended that the EPA use the up-to-date benzene value from CalEPA in its risk assessment and update the assessment accordingly. The commenter claimed that the acute reference value used to evaluate benzene exposure is two orders of magnitude too high, leading to a very significant underestimation of the acute non-cancer health hazards of benzene emissions from POTW. The commenter noted that the EPA used an acute reference exposure level (REL) of 1.3 milligrams per cubic meter (mg/m[3]), while CalEPA uses a value of 0.027 mg/m[3] based on the latest science.
      2.2.1-01 Response:  The EPA's chemical-specific toxicity values are derived using risk assessment guidelines and approaches that are well established and vetted through the scientific community, and follow rigorous peer review processes. The RTR program gives preference to the EPA values for use in risk assessments and uses other values, as appropriate, when those values are derived with methods and peer review processes consistent with those followed by the EPA. The approach for selecting appropriate toxicity values for use in the RTR Program has been endorsed by the SAB.
      The commenter recommended that the EPA use CalEPA's new toxicity values for several chemicals and provided some references for the approaches used to derive those values. The EPA scientists reviewed the information provided by the commenter regarding the CalEPA values and concluded that further information is needed to evaluate the scientific basis and rationale for the recent changes in CalEPA risk assessment methods and their application for individual toxicity values. Until the EPA has completed its evaluation, it is premature to determine what role these values might play in the RTR process. Although EPA uses many of CalEPA's toxicity values in the RTR risk assessment, we did not use the new CalEPA toxicity values as part of this current rulemaking.
      We disagree with the comment that the EPA should adopt the CalEPA acute REL for benzene. The EPA has an approach for selecting appropriate health benchmark values and in general, this approach places greater weight on the EPA derived health benchmarks than those from other agencies. The approach favoring the EPA benchmarks (when they exist) has been endorsed by the SAB, and ensures values most consistent with well-established and scientifically-based EPA policy.
      2.2.1-02 Comment:  Commenter 0061-A1 argued that the EPA unlawfully and arbitrarily treated risk as zero for some pollutants (i.e., at least, Dibutylphthalate), stating that just as National Lime Association, 233 F.3d at 642, requires the EPA to set emission limits for all HAPs, the EPA must assess the health risks for all listed HAPs. The commenter stated that the EPA underestimated health risks by not using the best available information on pollutants and by treating various types of risk as zero when the science shows risk is present. The commenter asserted that, just because the EPA has not yet developed a reference value for a pollutant, type of exposure, or type of risk, does not mean risk does not exist and can be ignored. The commenter suggested that the EPA develop default approaches to support the evaluation of risk from chemicals which lack chemical-specific data, as National Academy of Sciences (NAS) advises. One of the approaches detailed by the commenter is the inclusion of an uncertainty factor to account for the additional risk that a HAP likely causes, until such time as the EPA does have a reference value to use. The commenter added that if a default approach is not developed, the EPA should at a minimum engage in the interim in a qualitative assessment of the additional, missing risks, and account for them in its analysis.
      Commenter 0061-A1 also argued that some pollutants continue to have no reference values over 20 years after the CAA was amended and that the Integrated Risk Information System (IRIS) review process has been bogged down for many pollutants. The commenter asserted that, for pollutants currently under IRIS assessment, the EPA must use the best available scientific information from the IRIS review during current rulemakings. At minimum, the commenter concluded that the EPA must account for the lack of reference values or the lack of an up-to-date final IRIS assessment rather than not including any consideration of health risks caused by such pollutants.
      Finally, according to commenter 0061-A1, the EPA violated the notice and comment requirements by not providing public notice of all HAPs for which it did not evaluate cancer, chronic non-cancer, acute, or multipathway risk. The commenter contended that this prevented commenters from having a meaningful opportunity to present data to the EPA that may be useful in the EPA's evaluation of the risk from pollutants for which the EPA is currently treating as zero risk. The commenter stated that, in the response to comments, the EPA must confirm the list of pollutants for which it did not assess any quantitative value.
      2.2.1-02 Response:  This issue was addressed by the EPA's SAB in its May 7, 2010 response to the EPA Administrator. In that response, the SAB panel recommended that, for HAP that do not have dose-response values from the EPA's list, the EPA should consider and utilize, as appropriate, additional sources for such values that have undergone adequate and rigorous scientific peer review. The SAB panel further recommended that the inclusion of additional sources of dose-response values into the EPA's list should be adequately documented in a transparent manner in any residual risk assessment case study. We agree with this approach and have considered other sources of dose-response data when conducting our risk determinations under RTR. However, in some instances no sources of information beyond the EPA's list are available.
      For a tabular summary of HAPs that have dose response values for which an exposure assessment was conducted, refer to Table 3.1-1 of the Residual Risk Assessment for the Publicly Owned Treatment Works Source Category in Support of the December 2016 Risk and Technology Review Proposed Rule (December 2016), Docket ID No. EPA-HQ-OAR-2016-0490-0012.
      The EPA agrees that it is important to develop toxicity values for all HAP utilizing all credible and relevant toxicity information. The need to update assessments with newly available data as well as the need to complete toxicological assessments for all HAP lacking dose-response assessments increases the importance of Agency activities to streamline and fully utilize the EPA's already overloaded IRIS program. To that end, the EPA has always prioritized for IRIS assessments those HAP without dose-response values but with the greatest potential for public exposure. As a result of this prioritization, while not all HAP may have scientifically accepted dose-response values that can be used in residual risk assessments, it is clear that the vast majority of HAP which might carry the potential to significantly impact the results of residual risk assessments do, in fact, have credible dose-response values. Thus, while we are not yet at the point where we have determined dose-response values for all HAP, we are generally capable of deriving reasonable risk estimates for those HAP which dominate the risks from any one source category. In the course of each residual risk assessment, should we encounter HAP for which we have not determined dose-response values and which carry the potential to create significant risks, we point those out as uncertainties and target them for future IRIS assessments. In general, we strive to strike a balance in our assessments, meaning that while some factors likely lead to underestimates of risk, others likely lead to overestimates of risk. We conclude that the risk assessment for this source category is sufficient to support a decision on the acceptability of the risk and ample margin of safety.
      2.2.1-03 Comment:  Commenter 0061-A1 asserted that the EPA must recognize that chronic (non-cancer) risk-causing pollutants have no safe level of exposure, noting that the NAS recommends that cancer and chronic non-cancer risk assessment use the same approach in order to address the fact that very low levels of non-carcinogen exposures can pose health risks. The commenter noted that the use of reference doses (RfDs) for dose-response risk assessments of chronic non-cancer health effects may significantly underestimate risk, because the NAS defines the RfD or RfC as a dose "likely to be without an appreciable risk of deleterious effects" over a lifetime of exposure.
      Commenter 0061-A1 identified what they see as the problems with traditional toxicology as the basis for risk assessments, including the presumption that health effects are related to dose, and that a dose can be found for virtually all chemicals where no effect is found. The commenter claimed that the greatest public health threat of chemicals is for fetal exposure, meaning that the dose may be less important than the timing, and furthermore that for some toxic chemicals, the clinical effect can actually increase as the chemical concentration decreases, meaning that there is no safe level of exposure. For example, the commenter noted that a 2009 statement by the Endocrine Society stated that "[e]ven infinitesimally low levels of exposure, indeed, any level of exposure at all, may cause endocrine or reproductive abnormalities, particularly if exposure occurs during a critical developmental window. Surprisingly, low doses may even exert more potent effects than higher doses." The commenter also noted that a recent panel of twelve national endocrine disruptor specialists recently stated that "[for] every chemical that we looked at that we could find a low-dose cutoff, if it had been studied at low doses it had an effect at low doses."  The commenter further noted that a recent joint public statement by the American College of Obstetricians and Gynecologists and the American Society for Reproductive Medicine addressed the extraordinary vulnerability of in utero development.
      2.2.1-03 Response:  Chronic non-cancer dose response values used in the RTR program, including those derived by the EPA and similar authoritative agencies (e.g., Agency for Toxic Substances and Disease Registry (ATSDR) and CalEPA) represent chronic exposure levels that are intended to be health-protective. Those values are derived using an approach that is intended to not underestimate risk in the face of uncertainty and variability. When there are gaps in the available information, uncertainty factors (UFs) are applied to derive reference values that are protective against appreciable risk of deleterious effects. Uncertainty factors are commonly default values (e.g., factors of 10 or 3) used in the absence of compound-specific data; where data are available, data-derived extrapolation factors may also be developed using compound-specific information. When data are limited, more assumptions are needed and more default factors are used. Thus there may be a greater tendency to overestimate risk -- in the sense that further study might support development of reference values that are higher (i.e., less potent) because fewer default assumptions are needed. For some pollutants, however, there is a slight possibility that risks could be underestimated. Where data indicate a potential vulnerability of a specific lifestage, the EPA includes this information in its derivation of cancer and non-cancer dose-response values. In some instances, data are not available for a robust characterization of risk during a specific lifestage and, in that case, potential susceptibilities are accounted for by applying the appropriate uncertainty factors.
      The EPA agrees with the NAS that the recommendations on harmonization of cancer and non-cancer approaches are important issues in risk assessment and the EPA incorporates NAS recommendations as feasible. The NAS has agreed with the EPA, specifically on the derivation methodology of RfCs and RfDs, that the available scientific information does not always allow for assessment derivation issues to be fully considered and it has reviewed and supported the approaches currently used in the derivation of the RfCs and RfDs. The NAS has also recognized that many of the recommended changes for the IRIS Program will need to be incorporated over a number of years and further recommend continuation of the development of assessments as the recommendations are implemented (i.e., the process should not be halted until all recommendations can be enacted). As such, improvements will be made over time and existing assessments will need to be used in the interim. Further, the EPA has a legal obligation to proceed with regulatory action based on the best available data and tools. Because we use the best available data and tools, apply conservative assumptions, and take into account uncertainties, we tend to err on the side of overestimating risk in determining whether risk is acceptable.
      The commenter stated that there are problems associated with traditional toxicology presumption that health effects are related to dose, however the commenter does not provide any information to consider an alternative paradigm to risk assessment that would not include an analysis of dose response relationships in the risk assessment process.
      The commenter provided a reference to support the statement that there is no safe level of exposure and that for fetal exposure, the dose may be less important than the timing, and furthermore that for some toxic chemicals, the clinical effect can actually increase as the chemical concentration decreases. The review article on hormones and endocrine-disrupting chemicals focuses on a broad category of chemicals that appear to act at low concentrations. We disagree with the interpretation of the commenter on the referenced review. First, the authors of the review article do not conclude that there is no safe level of exposure for chemicals in general, not even for endocrine disruptors. We disagree with the comment that clinical effect increases as dose of the chemical decreases; rather, the authors of the review conclude that the effect of low doses of this group of chemicals cannot be predicted by effects observed at high doses, and they encourage investigators to make changes in chemical testing approaches to identify potential endocrine disruptors. We conclude that none of the information or conclusions in the review article conflicts with the EPA's determinations in this regulatory action.
      We agree with the comment that the regulatory community, including the EPA, should use conservative approaches to evaluate cancer risks especially when considering cancer risks to early life stages. When chemical-specific data is available on which age or life-stage specific risk estimates or potencies can be determined, default age dependent adjustment factors can be applied when assessing cancer risk for early-life exposures to chemicals which cause cancer through a mutagenic mode of action. With regard to other carcinogenic pollutants for which early-life susceptibility data are lacking, it is the Agency's long-standing science policy position that use of the linear low-dose extrapolation approach (without further adjustment) provides adequate public health conservatism in the absence of chemical-specific data indicating differential early-life susceptibility or when the mode of action is not mutagenicity. The basis for this methodology is provided in the 2005 Supplemental Guidance.
      2.2.1-04 Comment:  Commenter 0061-A1 stated that the EPA's cancer risk assessment for POTW does not adequately account for early-life exposure or the greater risk to and susceptibility of children. According to the commenter, the EPA must account for increased early-life susceptibility by applying age-dependent adjustment factors for all carcinogens emitted by a source category. The commenter noted that the EPA has restricted its application of age-dependent adjustment factors to those HAPs included in the EPA's list of carcinogens that act by a mutagenic mode of action. The commenter quoted a statement by NAS in 2009: "the EPA needs methods for explicitly considering in cancer risk assessment ... chemicals that do not meet the threshold of evidence that the agency is considering for judging whether a chemical has a mutagenic mode of action .... Special attention should be given to hormonally active compounds and genotoxic chemicals that do not meet the threshold of evidence requirements." The commenter pointed out that the EPA's 2005 Guidelines recognized that updates would be needed if more data became available, and claimed that such data are now available from the NAS and the California Office of Environmental Health Hazard Assessment (OEHHA), yet the EPA has not issued such updates to implement age-dependent adjustment factors for all carcinogens. Regarding pre-natal cancer risk, commenter 0061-A1 noted that the EPA's risk assessment does not take into account increased susceptibility to carcinogens due to pre-natal exposures, even for known-to-be mutagenic carcinogens, and that the EPA must do so for these as well as for all carcinogens. The commenter argued that despite the EPA's own recognition that exposures of concern include pre-conception exposures of both parents through adolescence, it has not developed adjustment factors for pre-natal exposures.[,] This omission from the EPA's 2005 Guidelines was noted by NAS. The commenter recommended that the EPA use the OEHHA methods and adjustment factors, as well as procedures to assess exposure during fetal development, to account for pre-natal susceptibility and exposures.[,][,] According to the commenter, OEHHA specifically discusses the use of a 10X adjustment factor for cancer risk to account for pre-natal (third trimester) to age 2 exposures, and the EPA should consider using this same factor.
      Regarding chronic non-cancer risk, commenter 0061-A1 asserted that exposure to toxic agents in the intrauterine stage of life has one of the most important, potentially irreversible impacts on life-long health, but the EPA's rules are insufficient to protect human health at the critical stage of embryonic development. The commenter stated that California EPA/OEHHA, in setting non-cancer RELs, considers that children may be outliers in terms of chemical susceptibility and on a case-specific basis adds a children's pharmacodynamic factor of 3-fold, making the inhalation risk for children as much as 10 times greater than adults. According to the commenter, most of the EPA's IRIS toxicity threshold values (reference concentrations and doses) used for chronic non-cancer risk assessment do not incorporate the latest science on increased susceptibility of children, and the EPA must consult and apply child-specific reference values, where available. The commenter argued that until the IRIS values fully account for the increased risk caused by early-life exposure to an emitted pollutant, the EPA should use the OEHHA child-specific reference doses or benchmarks available to assess chronic non-cancer health risk from ingestion for certain pollutants. The commenter asserted that the EPA should also assess such risk from inhalation by using standard methods to translate these values into child-specific reference concentrations to assess inhalation-based risk.
      Where child-specific reference values are unavailable, commenter 0061-A1 asserted that the EPA must consult science on early exposure impacts and use an additional default or uncertainty factor. Until the EPA has child-specific or child-based reference values available for a given pollutant, the commenter suggested that the EPA should apply a default or uncertainty factor of at least 10 to account for increased risk from early-life exposures for non-cancer risk in this rulemaking and other risk assessments. The commenter noted that this would be consistent with the NAS recommendation on the need for the EPA to use default factors to account for greater risk, with the science developed and considered by OEHHA, and with the 10X factor enacted by Congress in the Food Quality Protection Act (FQPA). As noted by the commenter, the FQPA provided that "an additional tenfold margin of safety for the pesticide chemical residue and other sources of exposure shall be applied for infants and children to take into account potential pre- and post-natal toxicity and completeness of the data with respect to exposure and toxicity to infants and children." Congress's recognition of the need to use this default factor provides a model that the EPA should consider and incorporate into its residual risk assessment, according to the commenter. The commenter stated that it would be appropriate and within the EPA's authority under CAA section 112(f)(2) to determine that the EPA must use a children's ten-fold margin of safety factor, to fulfill the CAA's "margin of safety" requirement. The commenter further noted that the EPA's current reference values are generally one order of magnitude less protective (i.e., larger) than the values that California has recognized as needed to protect children, based on the currently available science and a specific assessment of research relevant to early life exposures.
 	2.2.1-04 Response:  We disagree with the comment that this risk assessment underestimates risk to children and lacks consideration of early-life susceptibility. We acknowledge that population subgroups, including children, may have a potential for risk that is greater than the general population due to greater relative exposure and/or greater susceptibility to the toxicant. The assessments we undertake to estimate risk account for this potential vulnerability. With respect to exposure, the risk assessments we perform implicitly account for this greater potential for exposure by assuming lifetime exposure, in which populations are conservatively presumed to be exposed to airborne concentrations at their residence continuously, 24 hours per day for a full lifetime, including childhood. With regard to children's potentially greater susceptibility to non-cancer toxicants, the assessments rely on the EPA (or comparable) hazard identification and dose-response values which have been developed to be protective for all subgroups of the general population, including children.
      For example, a review of the chronic reference value process concluded that the EPA's RfC derivation processes adequately considered potential susceptibility of different subgroups with specific consideration of children, such that the resultant RfC values pertain to the full human population "including sensitive subgroups," a phrase which is inclusive of childhood. With respect to cancer, the EPA uses the age-dependent adjustment factor approach referred to by the commenter, but limits the use of those factors only to carcinogenic pollutants that are known to act via mutagenic mode of action, in contrast to the OEHHA approach, which uses them across the board for all carcinogens regardless of MOA. In lieu of chemical-specific data on which age or life-stage specific risk estimates or potencies can be determined, default age dependent adjustment factors can be applied when assessing cancer risk for early-life exposures to chemicals which cause cancer through a mutagenic MOA. With regard to other carcinogenic pollutants for which early-life susceptibility data are lacking, it is the Agency's long-standing science policy position that use of the linear low-dose extrapolation approach (without further adjustment) provides adequate public health conservatism in the absence of chemical-specific data indicating differential early-life susceptibility or when the mode of action is not mutagenicity. The basis for this methodology is provided in the 2005 Supplemental Guidance.
      We also disagree with the comment that the risk assessment for these source categories did not consider the groups that may be most at-risk (e.g., pregnant women and children). When the EPA derives exposure reference concentrations and URE for HAP, it also considers the most sensitive populations identified in the available literature, and importantly, these are the values used in our risk assessments. With regard to consideration of a potential vulnerability of a specific lifestage, including time period before conception, the EPA includes this information in its derivation of cancer and non-cancer toxicity assessments. For example, a prenatal developmental studies in rodents, when available, are regularly considered in IRIS toxicity assessments and data are then extrapolated to predict effects in humans. In some instances, the available literature is unavailable for a robust characterization of risk during a specific lifestage and in that case the potential susceptibilities are accounted for by applying the appropriate uncertainty factors.
            We disagree with the general comment that the EPA should adopt the California OEHHA child-protective scientific approach on for deriving health benchmarks. The EPA has an approach for selecting appropriate health benchmark values and in general, this approach places greater weight on the EPA derived health benchmarks than those from other agencies. The approach of favoring the EPA benchmarks (when they exist) has been endorsed by the SAB, and ensures use of values most consistent with well-established and scientifically-based the EPA science policy. The EPA is currently evaluating the most appropriate use for the California OEHHA child-specific reference doses. We note that there are currently no such values for HAP inhalation, therefore the current utility may be limited to PB-HAP, which may be associated with non-negligible ingestion exposures. This evaluation on appropriateness of these values in the context of the RTR Program and the EPA science policy is necessary prior to using these child-specific RfD.
      The estimated risks must also be considered in the context of the full set of assumptions used for this risk assessment. Our unit risk estimates for HAP are considered a plausible upper-bound estimate with an appropriate age dependent adjustment; actual potency is likely to be lower and could be as low as zero. Our chronic non-cancer reference values have been derived considering the potential susceptibility of different subgroups, with specific consideration of children. In addition, an extra 10X uncertainty factor is not needed in the RfC/RfD methodology because the currently available factors are considered sufficient to account for uncertainties in the database from which the reference values are derived. After considering these and other factors, we continue to consider the risks from emissions after application of the revisions to the NESHAP for these source categories to provide an ample margin of safety (consistent with the Benzene NESHAP framework).
      The EPA disagrees with the commenter that a children's default safety factor of 10 or more should be added to the EPA's reference values. In response to the 10X factor enacted by Congress in the FQPA (1996) to the EPA non-cancer reference value derivation, the Agency evaluated their methods for considering children's risk in the development of reference values. As part of their response, the U.S. EPA (i.e. the Science Policy Council and Risk Assessment Forum) established the RfD/RfC Technical Panel to develop a strategy for implementing the FQPA and examine the issues relative to protecting children's health and application of the 10X safety factor. One of the outcomes of the Technical Panel's efforts was an in depth review of a number of issues related to the RfD/RfC process (U.S. EPA 2002). The most critical aspect in the derivation of a reference value pertaining to the FQPA has to do with variation between individual humans and is accounted for by a default uncertainty factor (UF-H) when no chemical-specific data are available. The EPA reviewed the default UF for inter-human variability and found the EPA's default value of 10 adequate for all susceptible populations, including children and infants. The EPA also recommended the use of chemical-specific data in preference to default uncertainty factors when available (US EPA, 1994, 2011) and is developing Agency guidance to facilitate consistency in the development and use of data-derived extrapolation factors for RfCs and RfDs (U.S EPA, 2011). Additionally, the EPA also applies a database uncertainty factor (UF-D) which is intended to account for the potential for deriving an under protective RfD/RfC as a result of an incomplete characterization of the chemical's toxicity. In addition to the identification of toxicity information that is lacking, review of existing data may also suggest that a lower reference value might result if additional data were available.
      In conclusion, an additional uncertainty factor is not needed in the RfC/RfD methodology because the currently available factors are considered sufficient to account for uncertainties in the database from which the reference values are derived (and does not exclude the possibility that these uncertainty factors may be decreased or increased from the default value of 10).
2.2.2	Multipathway Screening
      2.2.2-01 Comment:  Commenter 0061-A1 stated that the EPA's multipathway risk assessment claiming that all PB-HAP did not exceed the Tier-1 screening emission rate is incomplete and underestimates risks. The commenter supported performing a multipathway (i.e., non-inhalation-based) risk assessment but stated that the EPA's multipathway analysis is deficient and could be improved by incorporating the following suggestions:
 EPA must perform a multipathway risk assessment on "allowable" emissions, not just "actual" emissions, which are likely underestimated.
 EPA must assess the non-inhalation-based risk created by POTW emissions of all PB-HAP, instead of restricting its multipathway risk screening assessment to 2-methylnaphthalene.
 EPA did not conduct a Tier 2 or 3 screening analysis when the EPA concluded that POTW in the category did not exceed the worst-case Tier 1 screening emission rate for 2-methylnaphthalene.
 Consistent with the 2004 guidance document and OEHHA 2012 Guidelines, the EPA must recognize the deposition of persistent HAPs as a source of soil contamination presenting a potentially significant route of exposure, particularly for children. The commenter argued that the EPA has been relying on outdated estimates of incidental soil ingestion exposures and the EPA must update these values to ensure that it considers the urban child scenario in its multipathway risk assessment. The risk assessment of exposure to soil contaminants should evaluate both direct exposure, hand-to-mouth, and indirect, object-to-mouth exposure as a study has found a statistically significant positive correlation between the frequency of object or food in mouth activity and blood lead levels, according to the commenter. The commenter added that the 2011 update to the EPA's Exposure Factors Handbook includes more recent studies and estimates of hand-to-mouth behavior, which must be used to assess risks from exposures to contaminated soils.
 EPA must account for the aggregate impact of inhalation and multipathway cancer and chronic non-cancer risk by adding each type of similar risk together for all pollutants. The commenter stated that the purpose of the multipathway assessment is to allow the EPA to look at a person's exposure overall - not just inhalation or other exposure pathways, in isolation. According to the commenter, failing to add up each type of risk in order to come up with a total cancer risk number and a total non-cancer number, and then a cumulative burden metric, makes the EPA's overall risk assessment incomplete. In performing a cumulative risk assessment, the NAS suggests that chemical and nonchemical stressors and how these stressors work in concert to promote adverse health outcomes should be taken into consideration.
      2.2.2-01 Response:  Regarding the commenter's assertion that we did not base the multipathway risk assessment on allowable emissions, we believe it is reasonable for the multipathway risk assessment to be based on actual emissions for this source category, and not the allowable level of emissions that facilities are permitted to emit because there is not a numerical limit for these existing sources. Allowable multipliers for this source category were developed based on the procedures discussed in the Residual Risk Assessment for the Publicly Owned Treatment Works Source Category in Support of the October 2017 Risk and Technology Review Final Rule, Appendix 1 (Emissions Inventory Support Documents) in the docket for this rulemaking. These multipliers were developed using engineering judgement based on readily available information for the source category and result in additional uncertainty compared to our estimates of actual emissions. The conservative assumptions associated with the multipathway screening assessment, along with uncertainties in the allowable emissions estimates, could increase uncertainty in this multipathway risk assessment.
      Naphthalene is not treated as a POM chemical in the multipathway analyses. Naphthalene is listed individually as a HAP under section 112(b) of the CAA. POM also is listed as a HAP under section 112(b) and is defined as organic compounds with more than one benzene ring and a boiling point greater than or equal to 100 degrees Celsius. Under this definition, naphthalene potentially could be considered as part of the POM listing. However, naphthalene is short-lived in environmental media due to its tendency to volatilize and biodegrade and, consequently, will not build up in environmental media over time. It has a moderate affinity for lipids and will undergo short-term bioaccumulation is tissues; however, biochemical processes lead to its biodegradation and elimination. Because it is neither persistent nor bioaccumulative, we do not consider it a PB-HAP, and its inclusion as POM is inappropriate and would result in less accurate and less meaningful estimates of media concentrations and multipathway risk.
      While we acknowledge we do not have screening values for some of the PB-HAP, we do not agree that this results in an inadequate multipathway assessment. In the Air Toxics Risk Assessment Reference Library, we developed the current PB-HAP list considering all of the available information on persistence and bioaccumulation (see http://www2.epa.gov/fera/air-toxics-risk-assessment-reference-library-volumes-1-3), specifically Volume 1 Appendix D). This list considered HAP identified as PB-HAP by other the EPA Program Offices (e.g., the Great Waters Program), as well as information from the persistent, bioaccumulative and toxic (PBT) profiler (see http://www.pbtprofiler.net/). This list was peer-reviewed by the SAB and found to be reasonable for use in the RTR program. Based on these sources and the available information on the persistence and bioaccumulation of other HAP, we do not believe that the potential for multipathway risk from other HAP rises to the level of the PB-HAP currently on the list.
      We have combined risk assessment results to the extent that it is appropriate to do so. We consider the effect of mixtures of carcinogens and use a target organ-specific hazard index (TOSHI) approach for our chronic non-cancer assessments. We do not use a TOSHI approach for our acute analyses nor do we combine the results of our inhalation and multipathway assessments. The multipathway risk assessment conducted for proposal was a screening-level assessment. The screening assessment used highly conservative assumptions designed to ensure that facilities with results below the screening threshold values did not have the potential for multipathway impacts of concern. The screening scenario is a hypothetical scenario, and due to the theoretical construct of the screening model, exceedances of the thresholds are not directly translatable into estimates of risk or hazard quotients for these facilities. In situations where we have previously summed the inhalation and multipathway assessment results (e.g., secondary lead smelters), it was for two refined assessments, and still serves as a conservative overestimate of potential risks given that it is highly unlikely that the same receptor has the maximum results in both assessments.
      Regarding incidental soil contamination, the EPA has estimated risks from both direct and indirect pathways. Direct routes of exposure include direct ingestion of soil and exposure through dermal contact. However, because it has been demonstrated in past analyses that exposure levels associated with dermal contact are but a small fraction of exposure levels associated with ingestion and inhalation pathways, dermal exposures were not assessed for this source category.
2.2.3	Cumulative Risk Assessment
      2.2.3-01 Comment:  Commenter 0061-A1 argued that the EPA must assess the combined impact of multiple pollutants. The commenter stated that this assessment should evaluate the combined impact of each type of risk from multiple pollutants and assess the total cumulative risk burden from all pollutants to make an ample margin of safety determination. The commenter noted that in the POTW risk assessment, the EPA only assesses the combined impact of cancer risk and chronic non-cancer risk that operates on the same target organ, while the commenter argued that the EPA should assess the total and synergistic cancer risk and total chronic non-cancer risk for different pollutants. In addition, the commenter noted that the EPA should apply these same principles to create a mechanism for assessing the total acute risk to chemical mixtures, such as the TOSHI for chronic risk that aggregates the acute impacts on the same organ systems for all pollutants.
      Commenter 0061-A1 asserted that, consistent with NAS recommendations, the EPA must create a metric to assess the total and cumulative risk burden, rather than only looking at each type of risk separately. After first assessing the total cancer, chronic non-cancer, and acute risks, for both inhalation and multipathway exposure, the commenter argued that the EPA also must create a metric to assess the total risk. The EPA must aggregate health risk for each pollutant, and each type of health risk, according to the commenter, to create a cumulative risk determination for the individual "most exposed" to emissions as section 112(f)(2) of the Act requires. The commenter asserted that without performing this cumulative assessment, the EPA has failed to gather the information needed to assess whether the risk to public health is acceptable under section 112(f)(2).
      2.2.3-01 Response:  We have combined risk assessment results to the extent that it is appropriate to do so. We consider the effect of mixtures of carcinogens and use a TOSHI approach for our chronic non-cancer assessments. We do not use a TOSHI approach for our acute analyses nor do we combine the results of our inhalation and multipathway assessments.
            For the subpart VVV source category, the EPA conducted an assessment of the cumulative cancer risks from emitted carcinogens and the cumulative non-cancer hazard indices from all emitted non-carcinogens affecting the same target organ system for both the source category emissions and the facility-wide emissions.
            Concerning comments that we should consider aggregate risks from multiple pollutants and sources, we note that we have done this to the extent it is appropriate to do so. We modeled whole-facility risks for both chronic cancer and non-cancer impacts to understand the risk contribution of the sources within the subpart VVV source category. The individual cancer risks for the source categories were aggregated for all carcinogens. In assessing non-cancer hazard from chronic exposures for pollutants that have similar modes of action or (where this information is absent) that affect the same target organ, we aggregated the hazard quotient. This process creates, for each target organ, a TOSHI, defined as the sum of hazard quotients for individual HAP that affect the same organ or organ system. Whole facility risks were estimated based on the 2011 and 2014 NEI data, 2015 Information Collection Request (ICR) data, and subsequent updates/revisions obtained from facilities, which included emissions from all sources at the POTW, not just subpart VVV wastewater treatment emission sources (e.g., emissions were included for collocated engines, sewage sludge incinerators, boilers, and other equipment which are regulated under separate NESHAP).
            As described in the Residual Risk Assessment for the Publicly Owned Treatment Works Source Category (Docket Item No. EPA-HQ-OAR-2016-0490-0012), we do not sum results of the acute non-cancer inhalation assessment to create a combined acute risk number that would represent the total acute risk for all pollutants that act in a similar way on the same organ system or systems (similar to the chronic TOSHI). The worst-case acute screen is a conservative scenario. That is, the acute screening scenario assumes worst-case meteorology, peak emissions for all emission points occurring concurrently and an individual being located at the site of maximum concentration for an hour. Thus, as noted in Section 2.8.2 of the Residual Risk Assessment for the Publicly Owned Treatment Works Source Category (Docket Item No. EPA-HQ-OAR-2016-0490-0012), "because of the conservative nature of the acute inhalation screening and the variable nature of emissions and potential exposures, acute impacts were screened on an individual pollutant basis, not using the TOSHI approach."
            We did not combine the inhalation and multipathway risk assessment results for each pollutant because it is inappropriate to do so. The multipathway risk assessment conducted for proposal was a screening-level assessment. The screening assessment used highly conservative assumptions designed to ensure that facilities with results below the screening threshold values did not have the potential for multipathway impacts of concern. The screening scenario is a hypothetical scenario, and due to the theoretical construct of the screening model, exceedances of the thresholds are not directly translatable into estimates of risk or hazard quotients for these facilities. For the refined multipathway analysis, it is unlikely that the person with the highest chronic inhalation cancer risk is also the same person with the highest individual multipathway cancer risk.
      2.2.3-02 Comment:  Commenter 0061-A1 stated that the EPA must assess and account for the cumulative impact and risk caused by exposure to multiple source categories' toxic air emissions. The commenter pointed out that the EPA acknowledged the importance of addressing multiple source exposures, but did not do so because of "uncertainties." The commenter asserted that, in addition to performing a cumulative assessment from nearby POTW alone, the EPA must perform a cumulative analysis which aggregates or adds the emissions for the most-exposed communities coming from: (1) the source category (including all individual sources within it); (2) facility-wide risk from collocated sources outside of this category; and (3) all other sources of toxic air pollution in the area. As an example, the commenter pointed to sources in the Hopewell, VA and Macon, GA communities, which are exposed to at least seven and five major sources, respectively. As another example, the commenter pointed to sources in the Houston area that include dozens of major sources, referencing the 2016 Double Jeopardy in Houston report. The commenter noted that the EPA has recognized this need in its recent risk report, yet has failed to propose any changes to the emission standards based on the combined exposure with any other sources. In support of their argument, the commenter also cited recommendations from the SAB and NAS which called for the incorporation of cumulative health risk into its residual risk analysis.,
      Commenter 0061-A1 also noted that the EPA has not used its calculated "facility-wide" risk for collocated sources to set standards, and it has ignored different sources across the street or in close proximity in its Risk Report. In addition, the commenter claimed that the EPA has provided no information on how it reached the "facility-wide" risk number because the EPA provided the numbers in the record without any way for the public to evaluate or comment meaningfully about the "facility-wide" risk assessment, which is a violation of the Clean Air Act's notice and comment requirements. 42 U.S.C. § 7607(d). The commenter also claimed that the EPA should have evaluated facility-wide risk based on "allowable" emissions, and if it did, this would likely increase the risks found.
      Commenter 0061-A1 recommended that the EPA use the risk assessment results available for those source categories for which it has already performed a risk assessment review - such as those covered by the hazardous organic NESHAP and other sources that are frequently located near POTW in its cumulative risk assessment. According to the commenter, the combined risk results for these sources near one another (not just collocated) would likely have higher overall risk than has been estimated for the most-exposed person near a POTW, and therefore stronger standards are needed under section 112(f)(2) for these sources. Finally, the commenter suggested that the EPA consider the existing research regarding health risk from toxic air pollution in urban communities nationwide as well as the OEHHA cumulative assessment approach and apply a similar science-based approach in this residual risk assessment.
      In addition, commenter 0061-A1 noted that the NAS has recommended that the EPA evaluate "background exposures and vulnerability factors," as well as use "epidemiologic and toxicologic evidence" in its risk assessments. Rather than separating an environmental justice analysis and considerations of inequality from the risk assessment, considering these factors as part of the cumulative risk assessment - because of the increased vulnerability created - would be a more effective, meaningful, and scientific approach, according to the commenter. The commenter asserted that, in assessing a source category's emission contributions in affected communities and considering whether these contributions cause the most-exposed people to experience an unacceptable level of public health risk when combined with the existing baseline from past emissions, other HAP emissions, and the community's health status, the EPA can describe and manage uncertainties, similar to many other analyses.
      Commenter 0061-A1 concluded that until the EPA develops a data-driven approach to comprehensively model cumulative risk or impacts from multiple sources, the EPA must incorporate a default or uncertainty factor to adjust the degree to which each individual source category is contributing to the total risk experienced by the most-exposed individuals. For example, according to the commenter, for a source category in an area with up to 10 other HAP-emitting facilities, this default or uncertainty factor should equal at least 10, consistent with the common scientific use of this factor for other kinds of vulnerability. This commenter suggested that wherever there is a history of other exposures or other source categories, the "unacceptable" level of cancer, non-cancer chronic, and acute risk from the source category must be adjusted downward (such that no single source category could constitute all acceptable risk, when the most-exposed person is exposed to many other source categories).
      2.2.3-02 Response:  We disagree with the claim that additional quantitative assessment of risks from sources outside the source category is required under the statute. Section 112(f) requires the EPA to perform a review of whether there is risk remaining from emissions from a source category after promulgation of the technology based MACT standards for that source category. To this end, the EPA conducts a comprehensive assessment of the risks associated with exposure to the HAPs emitted by the source category and supplements that with additional information that is available about other possible concurrent and relevant risks. While the incorporation of additional background concentrations from the environment in our risk assessments (including those from mobile sources and other industrial and area sources) could be technically challenging, they are neither mandated nor barred from our analysis. In developing the decision framework in the Benzene NESHAP currently used for making residual risk decisions, the EPA rejected approaches that would have mandated consideration of background levels of pollution in assessing the acceptability of risk, concluding that comparison of acceptable risk should not be associated with levels in polluted urban air (54 FR 38044, 38061, September 14, 1989). Although the EPA rejected such approaches for considering the acceptable level of risk, the EPA recognized in the Benzene NESHAP that background levels (including natural background) could be considered as part of the EPA's ample margin of safety analysis, as appropriate and as available, along with other factors, such as cost and technical feasibility.
      For the subpart VVV source category, the EPA conducted an assessment of the cumulative cancer risks from emitted carcinogens and the cumulative non-cancer hazard indices from all emitted non-carcinogens affecting the same target organ system for both the source category emissions and the facility-wide emissions. While the emissions for the source category and whole facility emissions have been collected as part of the information data request and reviewed by project engineers and scientists, emissions data for sources outside of POTW are not readily available at the level of detail and quality that is required for a refined risks analysis. Thus, because of uncertainties in this data we do not include the risks from stationary and mobile sources outside of POTW in our facility-wide risk analysis. We also disagree that allowable emissions should be used in the facility-wide risk analysis instead of actuals. The uncertainties associated with allowable emission estimates would make the inhalation risk assessment based on allowable emissions highly uncertain.
      The risk assessment modeling for the subpart VVV MACT accounted for the effects of multiple facilities within the source category that may be in close proximity when estimating concentration and risk impacts at each block centroid. When evaluating the risks associated with a particular source category we combined the impacts of all facilities within the same source category, and assessed chronic exposure and risk for all census blocks with at least one resident (i.e., locations where people may reasonably be assumed to reside rather than receptor points at the fence-line of a facility). The maximum individual risk considers the combined impacts of all sources in the category that may be in close proximity. We do not agree with the idea that we should apply an uncertainty factor related to the number of non-POTW sources near a POTW.
Risk Assessment Results
      2.3-01 Comment:  Commenter 0061-A1 stated that the EPA should decide that the health risks under the existing POTW standards are unacceptable and set residual risk standards to reduce those risks. The commenter noted that the EPA proposed that the health risks it has found are acceptable, even though they are at least 2 times the "aspirational goal" of 1-in-1 million from any given single source category, stated in CAA section 112(f)(2). The commenter also noted that the EPA anticipated approximately 240 people are estimated to have cancer risks greater than 1-in-1 million from inhalation of POTW toxic air pollution alone, which the commenter stated should clearly be unacceptable.
      According to commenter 0061-A1, the EPA should also find the current health risks to be unacceptable for the following reasons, which have been included in more detail elsewhere in this chapter:
 EPA has underestimated the cancer risk from inhalation particularly from early exposure. (Comment 2.2.1-04)
 EPA has underestimated the cancer risk from multipathway exposure. (Section 2.2.2)
 EPA needs to recognize that the combination of cancer and acute risks, together, create unacceptable risk. (Comment 2.2.2-01)
 To account for cumulative impacts of multiple exposures and vulnerabilities, the EPA should reduce its benchmark of what it considers acceptable lifetime cancer risk instead of relying on the outdated upper limit of 100-in-1 million and use a Margin of Exposure ("MOE") framework for non-cancer impacts and adjust the target MOE according to known vulnerability factors. The EPA needs to recognize that the cumulative impacts and multiple source exposure from various sources, including POTW, means that allowing POTW to cause 2-in-1 million cancer risk, plus acute and other health risks, is unacceptable and until the EPA has a specific mechanism for estimating total exposures, a default or uncertainty factor of at least 10X should be used to provide overburdened communities with the protection they need now. (Comment 2.2.3)
 EPA did not evaluate facility-wide risk based on "allowable" emissions, which would likely increase the risks found. (Comment 2.2.3-02)
 It is unjust and inconsistent with the Act's health protection purpose to allow the high health risks caused by POTW to fall disproportionately on communities of color and lower income communities who are least equipped to deal with the resulting health effects. (Comment 2.4)
      The commenter cited California's Office of Environmental Health Hazard Assessment ("OEHHA") Air Toxics Hot Spots Program Guidance Manual (2015), indicating that it addresses most of the scientific developments described above, particularly the explicit consideration of infants and children. The commenter noted that this document applies final scientific technical support documents, and the new manual with support document provide a clear roadmap that the EPA can and should use to close major gaps in its consideration of health risks from air toxics sources. The commenter also attached a table to their comment that was not specifically referenced in the text, but which is associated with these technical support documents, providing a list of all health values that have been approved by OEHHA and the Air Resources Board (ARB) for use in facility health risk assessments conducted for the AB 2588 Air Toxics Hot Spots Program (i.e., inhalation and oral cancer slope factors, non-cancer acute Reference Exposure Levels (RELs), and inhalation and oral non-cancer chronic RELs).
      The commenter stated that the EPA's risk assessment is unlawfully and arbitrarily incomplete, and its determinations under § 7412(f)(2) are unlawful and arbitrary, for reasons discussed above. The commenter also stated that it is unlawful and arbitrary for the EPA to determine in this rule that a section 112(f) assessment will not be necessary in 8 years.
      Further, the commenter contended that under § 7412(f)(2), it would be both unlawful for the EPA to ignore the health risks outlined above, and arbitrary and capricious for the EPA to avoid applying the best available science here.
      Commenter 0061-A1 attached prior comments submitted to the EPA Office of Science Advisor docket in regard to the Request for Information on Cumulative Risk Assessment, EPA-HQ-ORD-2013-0292. (The commenter provided these previously submitted comments with their comments and are identified in the docket as the EPA-HQ-ORD-2016-0490-0061-A2) Commenter contended that these Comments incorporate all of the previously submitted scientific documents on these issues by reference.
      2.3-01 Response:  The EPA disagrees with the commenter. We believe we have adequately estimated risks from these sources and that the risk is acceptable. The EPA is finalizing that the risks are acceptable from this source category. This above compilation of suggestions for improving the perceived deficiencies in our residual risk assessment have been address in other responses in sections 2.2 through 2.4 of this document. Further, it is important to note that the EPA's approach to performing risks assessments in support of residual risk program has been reviewed and supported by the Science Advisory Board (SAB) several times over the past 19 years. First, in 1998 they examined our analytical and policy approach for assessing residual risk from hazardous air pollutants emitted from stationary sources, followed by a second review in 2000 to verify that our application to a specific source category was consistent with the approved approach.  A third SAB consultation in 2006 focused on development of emissions inventories for source categories and updated methods for characterizing human exposure and risks.  Again in 2009, the SAB reviewed and supported our updated and expanded air toxics risk assessment methods, including our multipathway assessment, refinement of acute risk screening, and the methods of assessing potential environmental risk. Recently in 2017, the SAB further reviewed our multipathway and environmental risk assessment methods. We will continue to seek SAB consultation as our risk assessment methods develop and revise our approach as appropriate.
      2.3-02 Comment:  Commenter 0061-A1 states that the EPA must evaluate research performed on health impacts near POTW and that failing to do so is unlawful, arbitrary, and capricious as the EPA must evaluate the best available scientific research documenting any POTW emissions' impact on health threats as part of this rulemaking.
      2.3-02 Response:  The EPA disagrees with the commenter regarding the use of a literature search related to health impacts near POTW. The EPA performs a risk assessment, approved by the SAB, to evaluate human health impacts. This risk assessment was performed using the best available emissions data for the sector. The result of this assessment was that risk was acceptable.
      2.3-03 Comment:  Commenter 0061-A1 contended that, to account for cumulative impacts of multiple exposures and vulnerabilities, the EPA should reduce its benchmark of what it considers acceptable lifetime cancer risk instead of relying on the outdated upper limit of 100-in-1 million. The commenter stated that the EPA based this assumption not on scientific information about cancer risk, but on an unusual 1988 study of people's perceptions of their own risk from 1988, known as the Survey of Societal Risk, to consider various types of health risks at that time. The commenter stated that "the EPA used a comparison of cancer risk to other kinds of hazards Americans then faced in their daily lives, ... effectively choos[ing] a number out of a hat that it would consider acceptable." The commenter opined that the EPA has failed to revisit or update this number for the decades since, even though the science community has made breakthroughs and advances in regard to early-life exposure and children's vulnerability; biomonitoring and other data on adult body burdens of chemicals; the vulnerability of overburdened communities, including socioeconomic disparities; and on ways to analyze and control the impacts of pollutants on human health. The commenter listed landmarks between 1990 and 2016 to demonstrate these breakthroughs and advances by the science community.
2.3-03 Response:  In 1990, Congress codified in section 112(f)(2)(B) of the Clean Air Act the approach we use for our residual risk analyses. Under that approach, the 100-in-1 million cancer risk is not a bright line indicating whether risk is "acceptable."  Rather, we consider this health metric in conjunction with a variety of health factors and their associated uncertainties to determine whether the risk is acceptable. Where we conclude that the risk is not acceptable, we cannot and do not consider costs in requiring controls to bring risks down to an acceptable level. However, the analysis of whether risk is acceptable is not the endpoint. Once we determine that controls are sufficient to ensure that risk is acceptable, we again review the health metrics (e.g., cancer and chronic non-cancer risks) and their associated uncertainties in conjunction with the costs of controls, technical feasibility, and other relevant factors, to determine whether additional controls should be required to provide an ample margin of safety.
      We generally draw no bright lines of acceptability regarding cancer or noncancer risks from source category HAP emissions. It is always important to consider the specific uncertainties of the emissions and health effects information regarding the source category in question when deciding exactly what level of cancer and noncancer risk should be considered acceptable. In addition, the source category-specific decision of what constitutes an acceptable level of risk should be a holistic one; that is, it should simultaneously consider all potential health impacts  -  chronic and acute, cancer and noncancer, and multipathway, -- along with all their uncertainties, when determining the acceptable level of source category risk. The Benzene NESHAP decision framework of 1989 acknowledged this; in today's world, such flexibility is even more imperative, because new information relevant to the question of risk acceptability is being developed all the time, and the accuracy and uncertainty of each piece of information must be considered in a weight-of-evidence approach for each decision. This relevant body of information is growing fast (and it will continue to grow faster and faster), necessitating a flexible weight-of-evidence approach that acknowledges both complexity and uncertainty in the simplest and most transparent way possible. While this challenge is formidable, it is nonetheless the goal of the EPA's RTR decision-making, and it is the goal of the risk assessment to provide the information to support the decision-making process.
      2.3-04 Comment:  Commenter 0061-A1 argued that people living near publicly owned treatment works are exposed to toxic air pollution that harms their health, welfare, and way of life. The commenter pointed out that the EPA's analysis acknowledged that 24 million people live within 50 km of a POTW, and at least 240 people face an extra cancer risk from these facilities, and that the EPA's estimation of a maximum lifetime cancer risk for the most-exposed person (based on emissions the standards allow) is at least 2-in-1 million from inhalation exposure to publicly owned treatment works. The commenter further stated that formaldehyde emissions from the primary clarifier alone account for 50 percent of the cancer incidence, and that the EPA has found high acute health risks from formaldehyde emitted by POTW.
      2.3-04 Response:  The statute requires the EPA to provide the quantitative risk information necessary to inform RTR regulatory decisions, and to this end, the EPA conducted a comprehensive assessment of the risks associated with exposure to the HAP emitted by the source category and supplemented that with additional information that is available about other possible concurrent and relevant risks. The results indicated that, based on actual emissions from the POTW source category, the inhalation cancer risks to the individual most exposed is 0.8-in-1 million. Further, the cancer risks based on allowable emissions from the source category are no greater than approximately 2-in-1 million. Both of these estimates of cancer risk are well below the presumptive limit of acceptability (i.e., 100-in-1 million). In addition, the maximum chronic noncancer TOSHI due to inhalation exposures was less than 1. The evaluation of acute noncancer risk, which was conservative, showed a hazard quotient at or below 1 for all but one POTW facility. For this one facility, a hazard quotient of 2 was estimated based on a CalEPA REL for formaldehyde. CalEPA RELs represent a health-protective level of exposure, with no risk anticipated below those levels, even for repeated exposures; however, the health risk from higher-level exposures is unknown. Therefore, when a CalEPA REL is exceeded and an AEGL-1 or ERPG-1 level is available (i.e., levels at which mild effects are anticipated in the general public for a single exposure), we look to these values as a second comparative measure. For the POTW source category, none of the facilities are estimated to have an AEGL or ERPG greater than 1. Based on the results of the screening analyses for multipathway exposure to and environmental impacts from persistent and bioaccumulative HAP, we also concluded that the cancer risk to the individual most exposed through ingestion is below the level of concern and no ecological benchmarks were exceeded. Considering the above information, we concluded that the risks are acceptable and the requirements in the 2002 POTW NESHAP provide an ample margin of safety to protect public health.
Demographics
      2.4-01 Comment:  Commenter 0061-A1 stated that the EPA must (as required by § 7412(f)(2)) account for increased vulnerability based on demographic differences, as part of the risk assessment. The commenter stated that addressing this issue is particularly important for the EPA because of the need to consider and address environmental justice as mandated by Executive Order 12898 and given that POTW, and thus the EPA's rule regulating them, affect communities that are disproportionately communities of color or lower income. Consistent with NAS recommendations,  the commenter suggested that the EPA should consider the use of socioeconomic factors as part of the EPA's consideration of both vulnerability and variability, as core elements of the risk assessment. According to the commenter, data describing these factors are available from the CDC's Environmental Public Health Tracking Program, the U.S. ATSDR, state and local health agencies, and academic researchers.
      Commenter 0061-A1 suggested that the EPA better account for other types of human variability such as genetics and baseline health status, as recommended by NAS and current science. The commenter pointed to an American Lung Association publication showing that African Americans are at a much higher risk of lung cancer than white Americans. According to the commenter, socioeconomic status has been shown to act as a proxy for other types of human variability to chemical risk that the EPA has not adequately addressed in its Risk Report for the subpart VVV RTR.
      In addition to looking at the demographic census data on race, ethnicity, poverty level, and similar factors, commenter 0061-A1 stated that the EPA must assess the starting point or baseline overall health status of the affected individuals and communities using the best available data at a local and national level, including the baseline cancer levels, respiratory problems, and health problems associated with the toxic chemicals emitted by a source category. The commenter asserted that doing so would be consistent with the 1999 Residual Risk Report and would also follow the EPA's own statements (in the 2014 Second Integrated Urban Air Toxics Report) that more work is needed to reduce excess cancer risks in urban areas that continue to face elevated risks. As an alternative, the commenter suggested that the EPA could use a default factor to account for socioeconomic and other community-based stressors.
      Commenter 0061-A1 also suggested that the EPA better communicate and document the findings of the analysis, as one commenter stated, the EPA has presented environmental justice numbers in the abstract, which makes it difficult for communities to understand the risk assessment and the EPA's findings.
      2.4-01 Response: The EPA continues to evaluate and refine environmental justice analysis, such as the proximity analysis performed for the Definition of Solid Waste. The draft EPA document Technical Guidance for Assessing Environmental Justice in Regulatory Analysis is currently undergoing SAB review. The Office of Air and Radiation is a contributor to this draft document and cites numerous examples of environmental justice (EJ) analysis performed in agency rulemakings. Environment justice considerations are a part of the rulemaking process; however, various factors influence the scope and complexity of an assessment. These factors may include, but are not limited to statutory mandates, data availability, resources and/or timeframe limitations.
      In the Urban Air Toxics Strategy Report to Congress, we acknowledge that national rules and standards can address part of the risk to communities, but because the assessments did not include background risks or contributions to risk from sources outside the facilities more needs to be done at the community level with other tools available within the CAA and within state, local, and other federal programs. The EPA is committed to our efforts to make a difference in communities of concern and developing an integrated strategy focusing work in communities with the most need for the EPA's assistance. This effort to enhance coordination across the EPA programs and with other federal agencies will improve how we support community needs. We will focus on those communities where we think we have opportunities to leverage resources and actions to make a real difference. As we learn lessons on coordinating and focusing our efforts, we will use these lessons to help more communities in the future.
      2.4-02 Comment:  Commenter 0061-A1 stated that the EPA must fully integrate the findings of its environmental justice analysis into this risk assessment and rulemaking and set stronger pollution limits to provide environmental justice.
      2.4-02 Response: Under Executive Order (EO) 12898, the EPA is directed to the greatest extent practicable and permitted by law, to make environmental justice (EJ) part of its mission by identifying and addressing, as appropriate, disproportionately high and adverse human health or environmental effects of its programs, policies, and activities on minority populations and low income populations in the United States. Consistent with EO 12898 and the Presidential Memorandum that accompanies it, the EPA's environmental justice policies promote justice by focusing attention and the EPA efforts on addressing the types of environmental justice harms and risks that are prevalent among minority, low-income, and indigenous populations. EO 12898 and the EPA's environmental justice policies do not mandate particular outcomes from an action, but they demand that decisions involving the action be informed by a consideration of EJ issues. With respect to this rule, the EPA found the overall level of risk from the source categories to be acceptable and to provide an ample margin of safety for all populations in close proximity to these sources, including minority and low-income populations.
--------------------------------------------------------------------------------

Technology review
      3.1-01 Comment: Commenters 0052, 0061-A1, 0067, 0070 provided comments on the technology developments that were considered in the technology review and whether there were additional technologies that should have been considered.
      Two commenters (0052, 0070) contended that there is no technological basis for revising the standard. One commenter (0052) stated that there is no technological basis that requires or permits the EPA to revise the standards because there have been no technology advances since 1998 that warrant a change in the original MACT analysis. One commenter (0070) stated that a pretreatment program cannot be considered a new technology and no new technologies were found by the EPA to be available for emission controls; and therefore, the proposed additional compliance requirements are unnecessary and beyond the scope of the EPA's RTR authority.
      One commenter (0067) provided comments on two specific technologies discussed in the preamble. The commenter disagreed with the EPA's statement that treatment units must be covered for a POTW to use biological treatment as a control for HAP emissions, as this may be unnecessary for a POTW that manages only methanol. The commenter referenced results from a PhRMA Sewer Study which showed low volatilization emissions of methanol from two POTW with high methanol loadings from industrial sources. The commenter also noted that additional controls such as covers are not supported by the EPA's finding that there is no significant risk from POTW emissions. The commenter (0067) also contended that biofilters as a control device are not reliable in the POTW context, as biofilters for air emission stream control are only practicable when they are designed for their operating conditions and the operating conditions are stable. The commenter stated that the EPA should not consider the pilot-study biological treatment system noted in the preamble as a basis for real-world biofilter control efficiencies. In response to a comment solicitation about odor control, a commenter (0067) agreed with the EPA's conclusion that caustic scrubbers and carbon absorbers that are designed for odor control at a POTW have a limited effect on controlling HAP emissions. The commenter (0067) explained that at POTW caustic scrubbers are designed for non-VOHAP and absorbers are designed for a narrow set of organic compounds.
      One commenter (0061-A1) contended that there is a technological basis for revising the standard. The commenter contended that the EPA must set standards that account for all new developments at POTW. Commenter 0061-A1 listed several examples of technologies that they contend must be considered for POTW. The commenter stated that the EPA should consider covers that filter out more of the HAP before they have a chance to reach the air and referred to biodegradation covers as an example of a cover that does not merely partially cover the pretreatment source but also filters the vapors and HAP released by the pretreatment source at the POTW. The commenter referenced an article by Jay R. Witherspoon et al., titled Emissions Control Options for POTW, published May 1993, and included the document as an attachment to their comments. (The attachment is included in the docket and identified as EPA-HQ-OAR-2016-0490-0061-A22.)
      Commenter 0061-A1 also listed biofiltration as a technology that the EPA should consider and stated that this technology is a cost-effective and effective control measure. The commenter noted a study done by the University of Southern California, the County Sanitation Districts of Orange County (CSDOC), and Huntingdon Environmental Engineering, Inc. where biofilters' ability to remove VOC and toxic air emissions from POTW was studied. The commenter contended that the study found that biofiltration reduced HAP as well as hydrogen sulfide and other chemical releases. The commenter referenced an article about this study by Todd S. Webster et al., titled Biofiltration of Odors, Toxics and Volatile Organic Compounds from Publicly Owned Treatment Works, published in Environmental Progress and Sustainable Energy, Fall 1996. The commenter attached this article to their comments. (The attachment is included in the docket and identified as EPA-HQ-OAR-2016-0490-0061-A20.)
      3.1-01 Response: See section IV.B of the preamble to the final rule for response to these comments.
      3.1-02 Comment: A commenter (0061-A1) stated that the EPA must establish emission limits for secondary treatment equipment at POTW, and not to do so violates the CAA. The commenter explained that because the 0.08 HAP fraction standard applies to emission points up to but not including the secondary influent pumping stations and secondary treatment units, the HAP emissions from secondary treatment are uncontrolled. The commenter argued that the EPA is legally obligated to set emission standards for secondary treatment sources for the following reasons.
      The commenter (0061-A1) explained that after publication of the current NESHAP for POTW, the D.C. Circuit in the Nat'l Lime Ass'n F.3d 625, 629 ruled that the EPA has a clear obligation to set emission standards for each listed HAP regardless of whether the best performing sources in the category are using air pollution control technology to limit their emissions. The commenter stated that this legal decision qualifies under §112(d)(6) as a "development" that defines proper pollution controls, practices, and technologies and that makes it necessary to revise the NESHAP for these emission units. The commenter explained that the EPA is legally required to promulgate MACT for secondary treatment units whenever the EPA realizes that it must establish standards for a process for the first time, and must establish the MACT floor even if sources in the category are not currently using pollution control technology. The commenter further pointed out that the EPA's analysis shows that emissions data are available for secondary treatment units at three facilities and for two of these facilities the HAP fraction emitted exceeds the proposed 0.08 standard that would apply for primary treatment units. The commenter stated that the EPA has given no justification for failing to regulate the HAPs (such as chloroform, benzene, toluene, and tetrachloroethylene) that are emitted from secondary treatment units.
	3.1-02 Response: As an initial point, the EPA's obligation in conducting the risk and technology review under CAA 112(d)(6) and (f)(2) is to review the standards already promulgated. The prior standards under review in this rulemaking do not include emission limits for secondary treatment units. Thus, the EPA is not obligated to consider adding emissions limits for secondary treatment units in this rulemaking.
      Second, the commenter has mischaracterized our rationale for not prescribing emission standards for secondary treatment units. We decline to set standards for secondary treatment units at this time because we found no developments in practices, processes or control technology that were not evaluated during development of the original rule in 1999, and because we have concluded that the risk to public health and the environment is acceptable at POTW meeting the current standard.
	At proposal, we requested information on control measures that would further reduce risks from this source category, but our technology review found no new developments in practices, processes, and control technologies that warrant the incorporation of emission standards for secondary treatment units. In addition, the risk assessment conducted for this NESHAP review indicated that today's final rule provides an ample margin of safety to protect public health. The risk assessment was conducted using the total emissions from each POTW, including emissions from both primary and secondary treatment, as well as sludge handling operations. As we stated in the preamble to the proposed rule (81 FR 95372), additional standards are not necessary to bring risk to an acceptable level because cancer risks are well below the presumptive limit of acceptability, and other health risk information indicates there is minimal likelihood of adverse non-cancer (including chronic, acute, and multipathway) health effects due to HAP emissions from this source category. Therefore, based on the data currently available and these reasons, we are not adopting emission controls for secondary treatment units at this time.
	3.1-03 Comment: One commenter (0052) provided corrections for technical information about their POTW: Gulf Coast Waste Disposal Authority (GCA)'s Bayport industrial POTW does not control emissions from tertiary treatment; GCA's Bayport facility collects the headspace air only from its lift station not the collection system; GCA's 40-Acre and Washburn Tunnel Facilities are both major sources of HAP and are subject to subpart VVV although no controls are required for compliance; and GCA's 40-Acre and Washburn Tunnel Facilities' NSR permits do limit VOC and HAP emissions. This commenter questioned the technical basis of the proposed standards given the number of errors for their facilities and potentially for other facilities.
      3.1-03 Response: The EPA has made corrections to our database based on the information provided by GCA for their facilities, and we used the corrected data in the analyses supporting our final decision on the section 112(d)(6) technology review.
--------------------------------------------------------------------------------

Applicability
 General Comments
      4.1-01 Comment: Two commenters (0040, 0069) provided comments regarding applicability. One commenter (0040) stated that the proposed rule does not indicate if the 5 million gallon per day applicability "trigger" is the POTW's average or daily maximum design flow rate. This commenter further stated that the proposed "trigger" does not include discharges from government facilities, which are considered to be industrial users under 40 CFR 403, and that this constitutes a conflict with the water rules.
      One commenter (0069) stated that WWTPs which are a "synthetic minor source" of HAP emissions should not be subject to the POTW NESHAP compliance requirements and requested that the EPA clarify that if a Title V WWTP accepts a federally enforceable emission cap to restrict its potential HAP emissions then that WWTP will not be subject to the POTW NESHAP compliance requirements.
      4.1-01 Response: In today's final rule, we are making no substantive changes to the applicability provisions of §63.1580 and are not finalizing the proposed applicability changes at this time. The only changes to the applicability provisions are editorial changes to improve clarity. One of the conditions for being subject to 40 CFR part 63, subpart VVV is that the POTW must be required under Clean Water Act regulations to develop and implement a pretreatment program as defined by 40 CFR 403.8. A pretreatment program is required under §403.8 only for a POTW with a design flow greater than 5 million gallons per day (MGD) that also meets other conditions. Determining the design flow rate is governed by the long-standing regulations and policies of §403.8, and there should be no confusion about which POTW are required to have a pretreatment program. See section IV.C of the final rule preamble for rationale about why the applicability changes are not being finalized at this time.
      We agree that a POTW that is a synthetic area source is not subject to the rule unless it is a Group 1 POTW (i.e., accepts wastes that is subject to another NESHAP and provides treatment as an agent for the sending facility) which is subject to the rule regardless of whether it is a major source or not. A Group 2 POTW (i.e., a POTW that is not Group 1 but is required to develop and operate a pretreatment program) is subject to the rule only if it is a major source. A Group 2 POTW that is a synthetic area source is not subject to the standard. Under NESHAP policy, to become a synthetic area source for purposes of 40 CFR part 63, the facility must obtain federally enforceable limits to restrict its potential-to-emit (PTE) to below major source status before the first compliance date of the applicable standard ("Potential to Emit for MACT Standards  -  Guidance on Timing Issues," letter from John S. Seitz, Director OAQPS to the EPA Regional Offices, May 16, 1995). Accordingly, for an existing Group 2 POTW to become a synthetic area source under Part 63, the limits on PTE must have been in place before December 25, 1999. For a new Group 2 POTW, the limits on PTE must be in place before the date on which the POTW first begins to accept an industrial waste stream.
      4.1-02 Comment: Commenters 0040, 0052, and 0056 had concerns about the application of the terms "industrial" and "commercial" in the applicability requirements. Commenter 0040 contended that many of the 16,000 POTW in the United States receive "industrial" user discharges and would therefore be subject to the proposed rule. The commenter (0040) stated that under the definition of industrial user in both the CAA and Clean Water Act (CWA), industrial and commercial facilities are considered industrial users and the clear majority of POTW receive industrial user discharges, including commercial discharges. Commenter (0052) contended that the EPA should not add the term "commercial" to the applicability because the term could be interpreted to make small POTW treating "commercial" wastewaters subject to subpart VVV, which is not the intention.
      Commenter 0056 asserted that without clear definitions, more than just six POTW would be subject to the NESHAP. The commenter recommended that the EPA either define an industrial or commercial facility or develop a list of the types of industrial or commercial facilities that would use HAP and have processes that generate wastewaters containing HAP. The commenter recommended that the EPA use this as the basis for a more specific test of whether a POTW may be receiving HAP-containing wastewaters, or as an alternative, revise the applicability to read "a POTW that receives wastewater from large industrial manufacturing or maintenance facilities."
      4.1-02 Response: We are not taking final action at this time on the proposed changes to the applicability language and are keeping the applicability requirements the same as what is currently in the rule, except for a few minor clarifications. We are not defining the terms "industrial" or "commercial" since these terms are not included in the clarifications to the applicability criteria. Details on why the proposed applicability requirements have not been finalized are included section IV.C in the final preamble.
      4.1-03 Comment: Commenters differed on whether the EPA should revise the subcategory names and definitions from industrial and non-industrial to Group 1 and Group 2. One commenter (0050) supported the proposed POTW subcategories and the corresponding changes in the terminology to Group 1 and Group 2 POTW. However, another commenter (0052) disagreed with the proposed changes because Group 1 and Group 2 already have consistent, defined meanings in many other MACT standards. The commenter (0052) believed that classifying POTW as Group 1 or Group 2 will lead to misunderstandings about what POTW are treating.
      4.1-03 Response: As we explained in the proposal preamble (81 FR 95378), we are changing the nomenclature of the subcategories to remove the potential for confusion. The potential for confusion exists because the terms ``industrial'' and ``non-industrial'' have common, everyday meanings that do not exactly align with how those terms are defined in the original rule. We proposed the nomenclature of ``Group 1'' and ``Group 2'' rather than "industrial" and "non-industrial," respectively, rather than creating a new pair of descriptive names because (1) the non-descriptive names ``Group 1'' and ``Group 2'' will alert persons to the fact that they need to examine the specific definitions of the subcategories in the rule, and (2) we could not identify any descriptive names that did not create the potential for confusion similar to the current ``industrial'' and ``non-industrial'' labels. In the proposal, we requested ideas for descriptive names for the two subcategories that would not create a potential for confusion, and we received no such suggestions for alternative names.

 Affected sources
      4.2-01 Comment: Commenters (0050, 0052) provided information about additional POTW that are subject to the POTW NESHAP.
      Commenter 0050 noted that the American Bottoms Regional Wastewater Treatment Facility (ABRTF) is subject to the POTW NESHAP and should be among the facilities that the EPA identified as affected by the proposed rule. The commenter noted that data are available demonstrating that the POTW is a major source of HAP and that the facility should be considered as a Group 2 POTW.
      Commenter 0052 stated that two Gulf Coast Waste Disposal Authority (GCA) facilities are major sources and are subject to the POTW NESHAP: 40-Acre and Washburn Tunnel. The commenter noted that no controls are required for these POTW.
      4.2-01 Response: We acknowledge the information provided by the commenters about these additional major source Group 2 POTW. We have conducted a whole facility risk analysis for these POTW and the results are described in section IV.A of the preamble for this final rule.
      4.2-02 Comment: One commenter (0061-A1) noted that although the EPA has changed the labels for the definitions of industrial and non-industrial POTW to Group 1 and Group 2 to minimize confusion, it is still not clear whether the EPA has identified all existing sources. The commenter declared that the EPA must fulfill all requirements of CAA § 7412(f)(2) and assess the health risks from all POTW that emit HAP. The commenter (0061-A1) contended that there is little or no way for an affected member of the public to evaluate whether their local POTW is covered, without knowing the full list of industrial users and their own waste treatment methods. The commenter (0061-A1) suggested that the EPA collect additional information from all 16,000 POTW to identify any missing major sources.
      The commenter pointed out several POTW that it advocated should be in the EPA's list of covered sources: 40-Acre Facility, Texas City, TX; Washburn Tunnel Facility, Pasadena, TX; Campbell Bayou, Texas City, TX; and Odessa South Facility, Odessa, TX. The commenter (0060-A1) also questioned why the EPA did not evaluate emissions from the Los Angeles Hyperion plant and the DC Blue Plains plant.
      In addition, the commenter recommended that the EPA consider reducing the applicability threshold to a level below 500 MGD. [Editorial note: We conclude that the commenter intended to say 5 MGD.] The commenter claimed that there is no information in the rulemaking record showing that POTW with lower design capacity but that treat industrial waste could not possibly be a major HAP source. The commenter contends that a volume-based definition does not comport with the CAA definition of major source of HAP.
      4.2-02 Response: Based on the information available to us at this time, we have identified 13 facilities that are subject to this rule. To identify potential major sources for this regulatory review, we first searched the regulatory files from the original rulemaking, the 2011 National Emissions Inventory, the EPA Enforcement Compliance History Online (ECHO) database, POTW and state operating permits. Through this process, we identified 18 POTW that were potentially subject to the rule and sent information collection surveys to collect data on emissions to these POTW.
      In response to public comment, we searched state permit files and ECHO for the six POTW that the commenter (0060-A1) designated. From the public comment letters, we identified three additional major sources, and we have included those sources in our analysis. It is possible that a POTW that is less than 5 MGD could emit at the major source level if it receives a high volume of HAP. However, it is likely that pretreatment would be required for high HAP volume discharges, such that HAP emissions at a POTW accepting less than 5 MGD would then be less than major source level. We conclude that it is not practicable nor an efficient use of public and private resources to obtain emissions data from all 16,000 POTW. If a member of the public is concerned about the regulatory status of their local POTW, then they can determine if it is subject to subpart VVV by obtaining a copy of the POTW's operating permit. Any major source should have an operating permit issued under the Title V regulations. Any other POTW will have a minor source operating permit, issued after thorough review by the local permitting agency.
 Major Source Determination
      4.3-01 Comment: Commenter 0069 contended that major source status, and consequently the applicability of the NESHAP, should be based on only the HAP emissions from the wastewater treatment processes and should not include potential HAP emissions from combustion equipment. The commenter stated that HAP emissions from combustion equipment are already regulated under other NESHAP regulations. Commenter 0069 argued that, if the EPA finalizes applicability based on the entire POTW, the EPA should at a minimum revise applicability to be based on actual, not potential, HAP emissions and actual usage of the combustion equipment. The commenter stated that actual usage of each piece of combustion equipment at its full capacity is "extremely rare," and basing applicability on potential emissions leads to a significant overestimation of a POTW's actual emissions, subjecting POTW to costly compliance requirements even though the potential HAP emissions from wastewater treatment processes are low compared to the POTW's Title V Air Permit HAP emission thresholds, and insignificant compared to the actual HAP emissions from their combustion equipment. The commenter explained that POTW are required by their SPDES permit to maintain redundant combustion equipment to avoid non-compliance with the effluent limits of the SPDES permit when combustion equipment must be taken out of service for maintenance or in case of equipment malfunction. The commenter provided an example of two nonindustrial POTW that would be subject to the proposed amendment by virtue of the potential HAP emissions from their combustion equipment, but for which the actual usage rate of the combustion equipment has been about 10% or less of their capacity since 2011. The commenter provided 5 years of data for these POTW.
      4.3-01 Response: The NESHAP general provisions (subpart A of 40 CFR part 63) define "major source" in a manner that is consistent with the definition of major source in section 112(a)(1) of the Clean Air Act (CAA). The CAA gives the EPA the discretion to base major source status on a lesser quantity of emissions but does not authorize the EPA to change the basis from potential-to-emit (PTE) to actual emissions. Nor does the CAA authorize the EPA to subdivide a facility by industrial classification, such as by standard industrial classification (SIC) code. Because the section 112 definition of major source includes no reference to industrial classification, we concluded that Congress intended for the definition of major source of HAP to include the entire plant site. To separate HAP emissions by industrial classification would artificially separate HAP-emitting processes into separate facilities even though all HAP emission sources at the site contribute to public health exposure. Because section 112 contains its own definition of major source, we conclude that Congress did not intend for the EPA to make the section 112 definition identical to the definitions promulgated for other parts of the CAA, such as Title V or new source review, which divide sources by SIC code. Moreover, in the example of low capacity factor boilers described by the commenter, a POTW that only infrequently operates combustion equipment had the opportunity at the time that subpart VVV was published to take enforceable limits to reduce PTE and become a synthetic area source.
      4.3-02 Comment: Several commenters (0050, 0052, 0060, 0062, 0066, 0069, 0070, 0071, 0072) opposed including emissions from collection systems in the determination of whether a POTW is a major source. Commenters 0050, 0052, 0062, 0071, 0072 stated that collection systems/sewers are not always under the jurisdiction of the POTW and are typically owned by another entity.
      Commenters 0060, 0066, 0069, 0070 questioned the legality of requiring POTW to consider collection system emissions when determining rule applicability. Commenters 0060, 0069, 0070 stated that inclusion of collection systems for major source determination is inconsistent with the federal definition of a major source. Commenters 0060, 0069, 0070 stated that POTW collection systems may include hundreds or thousands of miles of sewers and other equipment. Commenters 0060, 0069, 0070 noted that including collection systems in the major source determinations would increase the number of POTW subject to the NESHAP. The commenters stated that the EPA has not fully determined the cost of compliance or impact as a result of the increased number of affected facilities, or determined the environmental benefit of the expanded major source definition. One commenter (0066) stated that expansion of the major source definition to include collection sewers as part of the affected source is not authorized under §112. The commenter also stated that the equipment that collect and convey wastewater to a POTW treatment plant do not reasonably constitute a "building, structure, facility, or installation," are clearly not within a contiguous area under common control, and should not be considered a single source. One commenter (0069) noted that the determination of a major source of HAP emissions should be limited to emission sources within the fence line of each WWTP, which would be consistent with the fact that the compliance emission fraction of the proposed POTW NESHAP is already limited to emissions within the WWTP. Commenter 0070 contended that including collection system emissions in POTW major source determinations is also supported by Alabama Power Co. v. Costle and the EPA's response to that decision.
      Commenters 0056, 0062, 0069, 0070 requested the EPA clarify if the collection system should or should not be considered when a major source determination is made. One commenter (0056) noted that emission data reviewed by the EPA in developing this rule primarily represent the HAP being emitted from the POTW treatment plant only. Two commenters (0056, 0062) stated that collection systems were explicitly listed as exempt from major source determinations in the preamble to the 2002 rule revisions.
      One commenter (0059) stated that the preamble notes "wastewater collection systems, including sewers and other transport systems, may also have significant emissions in cases where the systems transport industrial wastewater.", but the proposed rule does not clarify whether wastewater collection system emissions were included in the RTR modeling study or whether collection systems showed a significant contribution to wastewater HAPs emissions. The commenter requested that the EPA clearly indicate how collection system data were used in the RTR analysis. Commenters 0067, 0071, 0072 disagreed with the EPA's statement in the preamble that collection systems may have significant HAP emissions. Two commenters (0071, 0072) stated that emissions from the collection system are insignificant, and in some cases, are operated under a vacuum for purposes of odor control. Commenter 0067 stated that many soluble HAPs, such as methanol, are not significantly emitted from collection systems as supported by a recent study by the Pharmaceutical Research and Manufacturers of America (PhRMA).
      Commenters 0050, 0060, 0069 stated that it would be extremely difficult (or impossible) for a POTW to accurately estimate and control emissions from a collection system.
      4.3-02 Response: See section IV.D of the final rule preamble for response to these comments.
 Pretreatment
      4.4-01 Comment: Four commenters (0040, 0052, 0067, 0068) objected to the proposal to change the applicability of the rule by removing pretreatment as an applicability determination and making it a requirement. Three commenters (0040, 0052, 0067) stated the revised applicability language was confusing and not needed. One of the commenters (0040) indicated they saw no demonstrated need to redefine applicability and coverage of the rule, and the EPA can always require a pretreatment program for a POTW that needs a NESHAP without making the change. One commenter (0052) stated that the applicability of subpart VVV has been well-defined for over 17 years, and if sources are confused, the EPA has methods to correct any confusion without making rule changes.
      One commenter (0052) opposed changes to the applicability, in particular the EPA's proposal to remove the provision that limits rule coverage to those sources that have, or are required to have, a pretreatment program. The commenter states that those POTW defined in CAA Section 112 and the CWA as 40 CFR 403 are the POTW that the CAA directs the EPA to set standards for. That commenter states that removing pretreatment as an applicability criteria and making it a requirement changes the source category that the EPA intended to control.
      One commenter (0068) stated that the proposed applicability change would cause an additional 12 POTW in their state (Nebraska) to become subject. (The commenter provided a list of the 12 POTW in their comments.) The commenter explained that because in Nebraska the state (not the POTW) implements the National Pollutant Discharge Elimination System (NPDES) pretreatment program, the original rule does not apply to any POTW in Nebraska. Accordingly, the commenter concluded that by proposing to replace the applicability condition in 63.1580(a)(3) that the "POTW is required to develop and implement a pretreatment program" with a condition that the "POTW has a design capacity to treat at least 5 MGD from an industrial or commercial facility," 12 additional POTW in their state could potentially become subject to subpart VVV. The commenter stated that this result conflicts with the EPA's stated goal of not causing additional POTW to be subject to this NESHAP as a result of the proposed changes. The commenter requested that the applicability criteria remain unchanged, or that they be revised in such a way that additional POTW do not become subject to the NESHAP.
      4.4-01 Response: We are not finalizing the proposed applicability changes regarding pretreatment at this time. Pretreatment will remain as an applicability criterion as it exists in the current rule.