4. See responses to comments in the cooking loss adjustment CAA section of this document.
5. The SAB concluded that that the consumption rates and locations for fishing activity for likely highly exposed consumers, i.e., self-caught fish consuming populations modeled in the analysis, are supported by the data presented in the document and are generally reasonable and appropriate given the available data (U.S. EPA-SAB, 2011).
Comment 91: Commenters 18023 and 17807 state that Tetra Tech also performed additional sensitivity analyses using more reasonable assumptions for consumption rates, cooking factor, fish Hg concentration (using mean vs. 75[th] percentile), and EGU-attributable Hg deposition (based on an estimate that CMAQ overestimated EGU-attributable deposition on average by 11 percent provided by the independent consultant, ENVIRON, retained by Southern). ENVIRON at 6. Using these more reasonable assumptions, they found:
"Based on our understanding of past EPA guidance, a conservative risk assessment could consider the 95[th] percentile ingestion rate of a general population such as the 15 to 44-year old female consumer. For 2005 levels of EGU-attributable deposition, and consideration of an HQ threshold of 1.5, only 1 of the 2,366 HUC-12 level watersheds is affected, and no watersheds at 2016 levels of deposition are affected. In comparison, when the 95[th]percentile ingestion rate from the high end female consumer in the Hg Risk TSD is considered, 495 HUC-12 watersheds have an EGU-attributable HQ exceeding 1.5 in 2005, and 48 in 2016."
Response to Comment 91: The EPA does not agree that the analysis by Tetra Tech uses assumptions that are "more reasonable." The SAB agreed that all of the assumptions in the Hg Risk TSD are reasonable and appropriate. The specific assumptions used in Tetra Tech's analysis are not appropriate to identify risks to populations likely to be at greater risk of exposure to Hg levels that exceed the RfD.
Comment 92: Commenter 18023 states that the EPA's data shows U.S. EGU Hg emissions have little influence on fish Hg levels. According to the commenter, there is little improvement in fish Hg concentrations from a 41 ton reduction in U.S. Hg emissions between 2005 and 2016. The commenter notes that the EPA acknowledges that "(t)his means that even substantial reductions in U.S. EGU deposition between the simulation years (2005 and 2016) is unlikely to substantially affect total risk." The commenter provided a plot, prepared by Terra Tech, showing the distribution of fish Hg concentrations in 2005 and projected changed for 2016. The commenter notes that the EPA failed to show similar data depicting the projected results of the proposed rule.
Response to Comment 92: While the commenter is correct in pointing out that eliminating U.S. EGU Hg emissions will not eliminate fish tissue Hg and the associated health risks, the EPA does not agree that there is no improvement in fish Hg concentrations between 2005 and 2016, nor that there will be no further improvement from decreasing U.S. EGU Hg emissions from the baseline in 2016. While total risk from all Hg exposures will remain elevated in much of the U.S., much of that risk is associated with global, non-U.S. Hg emissions. U.S. EGUs remain the largest source of Hg emissions in the U.S., and reductions in those emissions will result in reduced Hg deposition in many highly impacted watersheds. As shown in the revised Hg Risk TSD, average U.S. EGU-attributable fish tissue Hg concentrations is estimated to decrease by 44 percent between 2005 and 2016. Although we did not model risk for the 2005 scenario in the revised Hg Risk TSD, we estimated at proposal that the number of modeled watersheds with populations potentially at-risk from Hg emissions from U.S. EGUs  would decline from 62 percent in 2005 to 28 percent in 2016.
Comment 93: Commenter 18023 states that the EPA's reporting of IQ point loss is erroneous and not relevant to informing policy. The EPA's analysis in the RIA estimates both an average and population-wide accumulation of IQ point loss. According to the commenter, accumulating IQ point loss across population provides no meaningful estimate of an affect. The commenter notes that the analysis included a per-exposed child IQ loss due to all Hg deposition contained in fish but the analysis did not include a projected change after implementation of the rule. According the commenter, the U.S. EGU contribution to these numbers is marginal as evidenced by the null values in Tables 2- 6 and 2-7, Hg TSD, for the 50[th] percentile watershed and therefore the total effect immeasurable.
Response to Comment 93: The EPA disagrees with the commenter's interpretation as to which risk estimates are most relevant for the determination of a hazard to public health. The EPA appropriately focused on populations that frequently consume fish, and watersheds with higher deposition of Hg attributable to U.S. EGUs. Thus the effects at the 50[th] percentile watershed are not useful in determining that there is not a hazard to public health (although certainly if there were a large effect at the 50[th] percentile watershed there would be no doubt that a hazard to public health exists). More important is evaluation of risk in watersheds with high levels of EGU-attributable deposition, and as shown in Tables 2-7, even at the 90[th] percentile of fish consumption, for the 99[th] percentile watershed in terms of EGU deposition, that EGU deposition alone would be enough to result in potential exposures greater than the RfD. Even at the 90[th] percentile watershed in terms of EGU deposition, for the highest fish consumption rates (99[th] percentile), EGU deposition alone is enough to result in potential exposures greater than the RfD.
Furthermore, the EPA disagrees with the commenter regarding the accuracy and relevance of the reported IQ loss in the RIA. The EPA is tasked with providing a national assessment of the benefits of proposed rules. To this end, the estimates provided are national in scope. In fact, the EPA asserts that the estimates presented in the RIA are an underestimate because the EPA was not able to analyze the impacts using the most sensitive endpoints for human health. According to the SAB, "the loss of IQ points is likely to underestimate the impact of reducing methyl Hg in water bodies. The reason is that IQ score has not been the most sensitive indicator of MeHg's neurotoxicity in the populations studied. As noted in the TSD, in the Faroe Islands study the most sensitive indicators were in the domains of language (Boston Naming Test), attention (continuous performance) and memory (California Verbal Learning Test). These two tests are neuropsychological tests that are not subtests of IQ tests and whose relationship with global IQ is not well-characterized. In the Seychelles study, the Psychomotor Development Index was the most sensitive measure and, while this index is a component of the Bailey Scales of Infant Development, it is not highly correlated with cognitive measures (Davidson et al., 2008)[]" (U.S. EPA-SAB, 2011). In addition, the commenter is factually in error regarding the provision of estimates of benefits after rule implementation. See RIA at 5-10.
Comment 94: Commenter 18023 states that the EPA must re-evaluate the risk associated with Hg emissions from utilities by relying on credible assumptions, transparent methodologies, realistic exposure levels, and the EPA's own modeling standards. According to the commenter, the EPA must accurately describe the low health risks posed by utility HAP emissions.
Response to Comment 94: The EPA commissioned a formal peer review of the Hg Risk TSD through the SAB. The overall finding of the panel is that "In summary, based on its review of the draft TSD and additional information provided by EPA representatives during the public meetings, the SAB supports the overall design of and approach to the risk assessment and finds that it should provide an objective, reasonable, and credible determination of the potential for a public health hazard from Hg emitted from U.S. EGUs" (U.S. EPA-SAB, 2011). Furthermore, "The SAB regards the design of the risk assessment as suitable for its intended purpose, to inform decision-making regarding an "appropriate and necessary finding" for regulation of HAP from coal and oil-fired EGUs, provided that our recommendations are fully considered in the revision of the assessment" (U.S. EPA-SAB, 2011).
The primary advice of the SAB was that 1) EPA should "Improve clarity of the Technical Support Document in terms of the methods used in the risk assessment and presentation of results," 2) EPA should "Expand the discussion of sources of variability and uncertainty in the risk assessment," and 3) EPA should "De-emphasize IQ loss as an endpoint in the risk assessment" (U.S. EPA-SAB, 2011). The EPA revised the Hg Risk TSD as part of the final rulemaking and has made that revised TSD available in the rule docket. The revised TSD addresses the comments of the SAB and includes a detailed listing of the specific revisions made to the Hg Risk TSD. Based on the review by the SAB, the EPA accurately described the health risks posed by utility HAP emissions but disagrees with the commenter's statement that those risks are low, as the Hg Risk TSD results show that up to 28% of modeled watersheds have the potential for subsistence level freshwater fish consumers with total Hg exposures exceeding the RfD to have at least 5% of total Hg risk contributed by U.S. EGUs, and up to 12% of modeled watersheds have the potential for subsistence level freshwater fish consumers to have Hg exposures exceeding the RfD due to Hg emissions from U.S. EGUs even before considering Hg exposures due to other sources.
Comment 95: Commenter 18034 states that due mainly to PM controls the EPA's estimates of HQs due to U.S. EGU-attributable emissions of Hg have already decreased significantly between the 2005 and 2016 scenarios. According to the commenter, U.S. EGU-attributable HQs exceeded 1.5 only as a result of combining the highest percentiles of watersheds with the highest fish consumption rates (e.g., 95[th] and 99[th] percentile consumption rates paired with the 95[th] and 99[th] percentile watersheds). According to the commenter, the EPA should characterize HQs for more realistic general recreational angler population.
Response to Comment 95: The EPA disagrees with the commenter's implication that 95[th] and 99[th] percentile consumption rates are not realistic. The Hg Risk TSD is designed to inform the Appropriate and Necessary Finding. As such, the Hg Risk TSD is intended to address the question of whether Hg released from U.S. EGUs contribute to potential exposures associated with increased risk of neurologic health effects. Thus, the Hg Risk TSD is focused on characterizing risk for the group likely to experience the greatest U.S. EGU-attributable Hg risk (i.e., subsistence fishers active at inland freshwater watersheds  -  see revised Hg Risk TSD). Specifically, within that subsistence fisher population, the EPA is interested in those individuals who are most at-risk, which includes those who consume the most fish. For that reason, the EPA included consideration for a range of high-end fish consumption rates including the 99[th] percentile to represent the most highly-exposed individuals. Evidence of these high fish consuming populations can be found in surveys, e.g., Burger et al. (2002), and specialized studies (Burger et al., 1999a,b; California EPA, 1997; Tai, 1999; Corburn, 2002). A search of the literature reveals several studies that identified fishing populations with subsistence or near subsistence consumption rates, including urban fishing populations (including low-income populations), Laotian communities, and Hispanics. The focus on the most highly-exposed individuals is consistent with the appropriate and necessary finding and the treatment of other HAP under CAA section 112. In addition, the SAB concluded that the consumption rates and locations for fishing activity are supported by the data presented in the Hg Risk TSD, and are generally reasonable and appropriate given the available data (U.S. EPA-SAB, 2011).
As stated in the revised Hg Risk TSD, the EPA focused the analysis on those fisher consumers likely to experience the highest levels of individual risk linked to U.S. EGU-attributable Hg. This reflects the goal of determining whether Hg released from U.S. EGUs contribute to potential exposures associated with increased risk of neurologic health effects. Given that focus, it is not necessary to model risk for more generalized fish consuming populations (e.g., recreational anglers) since these populations are "covered" by risk estimates generated for the subsistence fisher populations modeled.
Comment 96: Commenter 11889 submitted, as an addendum to testimony at the Philadelphia hearing, an article for consideration, Stevens et al., 2009.
Response to Comment 96: The EPA appreciates the commenter's identification of this article. The article (Stevens et al., 2009) is focused on assessing whether consumption of fish caught in Montana is "safe" based on comparisons with state consumption guidelines. The regulation of Hg emissions is an issue that is separate from local, state, and federal decisions related to fish consumption advisories. The revised Hg Risk TSD showed that of the watersheds modeled, almost all had potential Hg exposures for subsistence level fish consumers that exceed EPA RfD. As a result, reductions in Hg levels in fish that will result from decreasing Hg emissions from U.S. EGUs will result in reduced risk in most locations for those high fish consuming populations.
Comment 97: Commenter 14115 states that the EPA did not consider key scientific knowledge and many peer reviewed papers that suggest there is no straightforward connection between Hg emissions from power plants, or other man-made sources, to the Hg level in fish. According to the commenter, levels of the biologically active form of Hg, MeHg, are ultimately accumulating in fish tissue depend primarily upon environmental factors, such as sunlight and organic matter, pH, water temperature, and amounts of sulfate, bacteria, and zooplankton present in the ecosystem. MeHg levels in fish do not depend simply on the amount of elemental Hg available for conversion. As a result, according to the commenter, "meaningful management of Hg is likely impossible, because even a total elimination of all industrial emissions, especially those from U.S. coal-fired power plants, will almost certainly not be able to affect trace, or even high, levels of MeHg that have been found in fish tissue over century-long time periods." According to the commenter, a more rational and informed framework for dealing with the relatively low risk of MeHg exposure through fish consumption is required and "EPA's proposed NESHAP may actually be counter-productive to the protection of American public health."
Response to Comment 97: The EPA agrees with the commenter that MeHg levels in fish depend on a complicated set of environmental factors, and the EPA acknowledged this in the revised Hg Risk TSD. Furthermore, the EPA acknowledges that total Hg fish tissue levels are not correlated with levels of total Hg deposition when looking across watersheds because this relationship is highly dependent on the methylation potential at the specific water body, which is affected by pH, sulfate deposition, turbidity, etc. The linearity assumption used in attributing fish tissue MeHg levels to U.S. EGUs is based on the linearity of responses of fish tissue MeHg concentrations within a given water body to changes in Hg deposition, and is not based on correlations between Hg deposition and fish tissue MeHg concentrations between watersheds.
The EPA specifically asked the SAB to evaluate the EPA's assumption of linear proportionality in the relationship between Hg deposition and fish tissue MeHg concentrations, supported by the Hg Maps analysis. The SAB provided the following overall response, which generally supports the EPA's approach:
"The SAB agrees with the Hg Maps approach used in the analysis and has cited additional work that supports a linear relationship between Hg loading and accumulation in aquatic biota. These studies suggest that Hg deposited directly to aquatic ecosystems can become quickly available to biota and accumulated in fish, and reductions in atmospheric Hg deposition should lead to decreases in MeHg concentrations in biota. The SAB notes other modeling tools are available to link deposition to fish concentrations, but does not consider them to be superior for this analysis or recommend their use. The integration of Community Multiscale Air Quality Modeling System (CMAQ) deposition modeling to produce estimates of changes in fish tissue concentrations is considered to be sound. Although the SAB is generally satisfied with the presentation of uncertainties and limitations associated with the application of the Hg Maps approach in qualitative terms, it recommends that the document include quantitative estimates of uncertainty available in the existing literature" (U.S. EPA-SAB, 2011).
The EPA revised the Hg Risk TSD to include additional discussions of uncertainty associated with application of the assumption of linear proportionality in the relationship between Hg deposition and fish tissue Hg levels, and based on the SAB comments, disagree with the commenter's statement that "meaningful management of Hg is likely impossible, because even a total elimination of all industrial emissions, especially those from U.S. coal-fired power plants, will almost certainly not be able to affect trace, or even high, levels of MeHg that have been found in fish tissue over century-long time periods." The EPA provided credible estimates that U.S. EGU-attributable Hg deposition results in up to 29% of total modeled watersheds with populations potententially at-risk.
Comment 98: Commenter 18033 states that the Hg TSD is still based on several unsupported general concerns about Hg levels in the environment ostensibly designed to unearth some demonstrable evidence of "risk to public health." According to the commenter, like the 2000 determination, the EPA has not adequately justified its "appropriate and necessary" determination. The findings that so little health benefit would result from aggressive Hg regulation are unsurprising. The commenter asserts that the modeling supporting CAMR found that EGUs contribute a "relatively small percentage" to fish tissue MeHg levels in the U.S. More importantly, the agency concluded implementation of CAIR would result in a level of Hg emissions that would not cause hazards to public health.
The commenter states that the EPA's findings are similar to the 2000 findings where the EPA found a plausible link between anthropogenic emissions of Hg from sources in the U.S. and MeHg in fish. According to the commenter, "plausible" is very much a euphemism for unproven as the agency further admits that, "...it was not possible to quantify how much of the MeHg in fish consumed by the U.S. population results from U.S. anthropogenic emissions, as compared to other sources of Hg."
Commenter 18033 concludes that to date the EPA has not provided any demonstrable evidence in the rulemaking record to show that anyone in the country has suffered adverse health problems as a result of Hg emissions from coal-fired EGUs. Rather, the EPA is asking the public to accept a higher cost of electricity and job losses based on an attenuated line of reasoning -- EGUs emit Hg; some of that Hg is bound to deposit on the land or in water bodies; some of that deposited Hg in the water bodies can possibly be transformed into MeHg; and some of the MeHg produced in the sediments of those water bodies is consumed by fish where it ultimately enters the food chain.
Response to Comment 98: Based on the review by the SAB, the EPA accurately described the health risks posed by utility HAP emissions and disagrees with the commenter's statement that the EPA has not provided any demonstrable evidence to show that adverse health risks exist. The EPA applied peer reviewed modeling to estimate the deposition of Hg attributable to U.S. EGUs. The EPA also applied an assumption of linear proportionality between changes in deposition and changes in fish tissue Hg levels, which has been supported by the SAB. The EPA established a peer reviewed RfD for Hg which provides a benchmark for evaluating the presence of risks from Hg using the hazard quotient, and which the SAB agrees "is appropriate as the primary means of expressing risk because it is based on an established RfD for MeHg that reflects a range of potential neurobehavioral effects" (U.S. EPA-SAB, 2011). Based on comparisons of total and U.S. EGU attributable Hg exposure to the RfD, the revised Hg Risk TSD reports that up to 29% of total modeled watersheds have the potential for subsistence level freshwater fish consumers with total Hg exposures exceeding the RfD, 24% of modeled watersheds have the potential to exceed the RfD and have at least 5% of total Hg risk contributed by U.S. EGUs, and up to 10% of modeled watersheds have the potential for subsistence level freshwater fish consumers to have Hg exposures exceeding the RfD due to Hg emissions from U.S. EGUs even excluding Hg exposures due to other sources. As explained in the preamble, the EPA believes each of these results independently supports our conclusion that U.S. EGUs pose hazards to public health.

1G - Non-Hg Case Studies
1. Non-Hg case studies emissions.
Commenters: 17621, 17723, 17772, 17775, 17800, 17820
Comment 1: Commenters 17621 and 17775 state that the EPA's use of the arithmetic mean to determine emission factors for a log-normally distributed data set is inappropriate. According to the commenters, geometric mean should be used.
Response to Comment 1: The EPA disagrees with the commenters' assessment of the EPA's use of the arithmetic mean for computing emission factors. The EPA has always relied on the use of arithmetic, not geometric, means for determination of emissions factor estimates. By way of example, the Emission Factor Documentation for AP-42 CAA section 1.1 Bituminous and Subbituminous Coal Combustion document, which was developed in April 1993, describes how emissions factors were developed for the electric utility generating industry.. This document plainly states that "...EPA guidance also prescribes that when averaging emission (sic) factors together in order to obtain an AP-42 factor, the average should be an arithmetic mean..."
Apart from remaining consistent with existing policy, the use of the arithmetic mean for emissions factors provides the single best value for predicting national emissions estimates, as shown in the table below:

                             Emissions (tons/year)
                             Percent of Emissions

                                    Actual
                                   Estimator

                                Arithmetic Mean
                                Geometric Mean
                                    Median
                                Arithmetic Mean
                                Geometric Mean
                                    Median
PM
                                                                         22,945
                                                                         28,204
                                                                         12,303
                                                                         14,288
                                                                            123
                                                                             54
                                                                             62
As
                                                                             13
                                                                            8.8
                                                                            1.7
                                                                            1.3
                                                                             68
                                                                             13
                                                                             10
Cr
                                                                             63
                                                                             56
                                                                            5.3
                                                                            3.5
                                                                             88
                                                                              8
                                                                              6
Ni
                                                                             21
                                                                             20
                                                                            6.1
                                                                            4.7
                                                                             94
                                                                             29
                                                                             22
                                    Average
                                                                           93.3
                                                                             26
                                                                             25
This table was populated with emissions and fuel use data from the ICR. The arithmetic and geometric means, as well as the median, was determined from emissions data, in terms of pounds pollutant per million BTUs. These estimators were then multiplied by each site's average fuel use rate, in terms of millions BTUs per hour, and 8,760 hours per year, then summed to yield an annual emissions estimate. This value was then compared to the sum of each site's actual emissions, obtained from measured emissions and fuel use data. With respect to these data, in each and every instance, use of the arithmetic mean provides emissions estimates closest to actual emissions; in fact, within an average of seven percent of actual emissions. More specifically, use of the geometric mean, as recommended by the commenter, always underpredicts actual emissions by an average of more than seventy percent.
Comment 2: Commenters 17621 and 17775 state that emission factors for Cr were inappropriately calculated. According to the commenters, EPRI's review of the ICR data (Bin 1 -  ESP only) indicates that the data are clearly not normally distributed based on the EPA's own guidelines. Thus, the use of an arithmetic mean is not appropriate, and the use of a geometric mean is more appropriate for a lognormal distribution. According to the commenter, a March 16, 2011 memo by RTI indicated that data sets in the MACT analyses were to be examined for normality by two ratios -- skewness and kurtosis. The 50 sites in Bin 1 (ESP only) were examined for arsenic, Cr, and Ni. The average, standard deviation, skewness, kurtosis (and their error e stimates) for both normal and lognormal transformed values have been calculated and are presented in Table E-2. As stated by RTI, when the ratios of skewness and kurtosis to their error values exceed 2.0, the normal distribution is rejected. By these criteria, arsenic, Cr, and nickel data are clearly not normally distributed. Consequently, the arithmetic average is not appropriate for estimating the bin mean value, and a geometric mean is appropriate for developing emission factors.
Response to Comment 2: See also response to Comment 1. The EPA disagrees with the commenters' assertion that use of an arithmetic mean is fundamentally flawed based on statistical arguments and based on approaches developed for the MACT floor analysis. The purposes of the emissions factors developed for the case study emissions is quite different from the MACT program, which establishes emissions limits using emissions data from the best performing sources in a specific category. Consequently, an emissions factor value should not be expected to replicate a MACT emissions floor as the emissions factor is representative of a national average of all sources within a given category while the MACT floor is representative of the best performing sources within that category. Based on the comments, the EPA revised its methods for developing emissions factors for the case studies to include well-established, robust outlier checks  -  Dixon or Rosner tests, depending on the number of values - when more than three values are evaluated. These tests are the appropriate tests to use for the purpose of developing emission factors from stack test data, rather than the statistical approaches cited by the commenters.
As shown in Figure 1 on page 4 of the Introduction to AP-42 a hierarchy exists for describing emissions. Continuous, site-specific, direct measurement of the pollutants of concern, such as provided by continuous emissions monitoring systems (CEMS) provides the most accurate representation of site emissions. Next, discreet, site-specific measurement of the pollutants of concern, as determined through emissions testing, when combined with process operation knowledge, can provide accurate representation of site emissions, when CEMS data are not available. Emissions factors are the least accurate means for describing site-specific emissions, and there are various emission factor approaches available.
In 1993, the EPA approved the emissions factor approach mentioned by the commenter  -  computing emissions factors by using equations containing filterable PM emissions, fuel metal content, and fuel ash content - for those sources that had the requisite discrete, site-specific data. As noted by EPRI and DOE, the equations they developed were based on between 8 and 38 paired observations for nine metals with correlation coefficients (r[2]) ranging from 0.51 to 0.83. Moreover, the equation developers noted that "...the absolute average emission level varied considerably for a given fuel concentration..." Given the low correlation coefficients, few data pairs, and absence of condensable PM data, the EPA decided as part of the ICR to collect metals and ash content of fuel, filterable and condensable PM emissions, and concurrent metals emissions for nine metals in order to assess the prediction capability of the equations.
The table shown below identifies the emissions factors developed from the ICR data for use in the final rule. All emissions factors are in terms of pounds pollutant per million BTUs.
         Non-Hg metals Emissions Factors from EGU ICR data, lb /mMBTU
                               Non  -  Hg Metal
                        Emissions Factor for Oil Units
             Emissions Factor for Coal Units by Control Device(s)

           (SCCs include 10100401, 10100404, 10100501, and 10102101)
                                   Controls

ESP  -  electrostatic precipitator; FF  -  fabric filter; DS  -  dry scrubber; WS  -  wet scrubber

                                   Antimony
                                   3.30 e-05
                                      ESP
                                   1.45 e-06

                                  FF, DS, WS
                                   4.22 e-07
                                    Arsenic
                                   2.55 e-06
                                      ESP
                                   1.25 e-05

                                      FF
                                   9.72 e-07

                                      DS
                                   1.61 e-06

                                      WS
                                   2.52 e-06
                                   Beryllium
                                   1.62 e-07
                                      ESP
                                   4.16 e-07

                                  FF, DS, WS
                                   1.18 e-07
                                    Cadmium
                                   3.62 e-07
                                      ESP
                                   3.81 e-07

                                  FF, DS, WS
                                   2.20 e-07
                                      Cr
                                   5.70 e-06
                                    ESP, FF
                                   4.89 e-05

                                      DS
                                   1.53 e-06

                                      WS
                                   4.75 e-06
                                    Cobalt
                                   1.71 e-05
                                    ESP, FF
                                   1.58 e-06

                                    DS, WS
                                   5.10 e-07
                                     Lead
                                   1.3 e-05
                                      ESP
                                   6.61 e-06

                                  FF, DS, WS
                                   2.25 e-06
                                   Manganese
                                   9.42 e-06
                                ESP, FF, DS, WS
                                   1.01 e-05
                                      Ni
                                   3.46 e-04
                                  ESP, FF, WS
                                   2.74 e-05

                                      DS
                                   3.41 e-06
Using the ICR data, the EPA conducted regression analyses between metals emissions measured at the site and predicted from the EPRI equations. If the EPRI/DOE equations accepted in AP-42 were good predictors of actual metals emissions, the correlation coefficient (r[2]) would be high, i.e., between 0.85 and 1.00. As indicated in the table below, which shows the individual metals, number of paired observations, and correlation coefficient, the EPRI equations are not good predictors of metals emissions. The EPA concludes that the emission test data is a more accurate predictor of actual emissions than the formulas cited by the contractor, and the EPA has therefore used emission test data and emission factors based on the arithmetic mean rather than the equation-based emission factors.
                                     Metal
                             Pairs of Observations
                                     r[2]
                                   Antimony
                                      66
                                     0.02
                                    Arsenic
                                      112
                                     0.05
                                   Beryllium
                                      104
                                     0.11
                                    Cadmium
                                      78
                                       0
                                      Cr
                                      126
                                       0
                                    Cobalt
                                      134
                                       0
                                     Lead
                                      138
                                     0.15
                                   Manganese
                                      145
                                       0
                                      Ni
                                      149
                                     0.01
Comment 3: Commenters 17621 and 17820 state that EPRI's review of the individual run data in the EPA's data set found seven EGUs with elevated concentrations of Cr, arsenic, nickel, and sometimes manganese. The average Cr concentration from these suspect runs was 5.62E-5 lb/MMBtu, which is more than an order of magnitude higher than the average Cr concentration of 6.2E-6 lb/MMBtu obtained in all the other runs. Two EGUs (Conesville Unit 3, James River Unit 5) had Cr emission factors (EFs) that were statistically significant outliers or extreme values (in this case, defined as the average of the EF data set plus three standard deviations, p < 0.0001). Moreover, in some cases the amount of Cr measured at the stack was greater than the amount entering with the coal (e.g., James River Unit 5, Gallatin Unit 2). Commenters suggest this analysis suggests potential metallic contamination in one or more runs, and data from these seven EGUs should be excluded from any risk analysis.
Response to Comment 3: The EPA disagrees that the data cited are outliers because the EPA employed appropriate statistical outliers tests and has concluded that the data noted by the commenters are in fact not outliers. The identification of sources whose measured emissions do not match the commenter's preconceived notion of emissions behavior is not surprising. There are many possible explanations for these differences. For example, the inconsistency between the test data and the coal analysis could be due to any number of reasons including unrepresentative coal sampling, control device problems, degradation of the refractory, or sampling contamination. The notion that test data should be discarded because it does not match initial expectations is unfounded. In addition, source representatives collected, obtained, and most likely reviewed, all data before certifying their accuracy and submitting them to the EPA. If source representatives or the commenter were concerned about data accuracy, then they should have taken additional steps to explain their concern or improve their results, including qualifying their submissions or conducting additional testing. As the EPA is unaware of such additional test activity, the EPA maintains that the measured, submitted, and certified data are an accurate representation of site emissions. Consistent with that belief, the EPA finds that all relevant data, i.e., those data that are not removed via outlier tests, are suitable for emissions factor development.
Comment 4: Commenter 17621 states that based on its review of the data, metallic contamination was suspected at some of the ICR test sites that showed elevated levels of nickel and in some cases manganese, as well as Cr. Although the Method 29 blank sample train data from these suspect ICR test sites did not typically indicate a problem with sample system or reagent contamination for Cr, nickel, and manganese, the presence of elevated levels for all three of these elements suggests some other source of metallic contamination. Cr data from the ICR data set were evaluated on the basis of ppmw in the stack particulate matter(PM), in an attempt to determine a reasonable range of enrichment factors and to thus develop another tool to identify sites with possible contamination issues. The commenter provided a figure showing all the individual run ICR data for coal-fired units with stack filterable PM plotted versus Cr in the stack particulate (e.g., lb/MMBtu Cr divided by lb/MMBtu FPM, expressed on a ppmw basis) for individual runs. Higher Cr on a ppmw basis is expected at lower filterable PM emissions, due to enrichment effects in the fine particulate. However, there are a significant number of individual test runs that show high Cr levels in the stack particulate at high stack filterable PM emissions, suggesting a problem with these data. The commenter compared this data to an analogous plot of Cr data, from the historical data set used to derive the emission correlations employed in EPRI's 2009 risk modeling. The commenter notes that the plots are generally similar, but the historical data does not show the same issue with outlier data points at higher filterable PM emissions.
Commenter states that the suspect runs for Cr shown in Figure E-1 are associated with the units shown in Table E-3 Those units used by the EPA in the calculation of the Phase II average emission factor for various control class bins are noted. The greatest impact likely occurs for the "-ESP" and "2-FF" bin average EFs, since these groups contain the largest number of sites with potential contamination issues. In some cases, (e.g., James River U5, Gallatin U2, Valley B1, Valley B3, and Craig C1) the amount of Cr measured at the stack was greater than the amount entering with the coal, when coal and stack emission values were compared on a lb/MMBtu basis. This is another indication of possible metallic contamination issues for stack gas measurements at these sites. The commenter provided a summary of Part III individual run ICR coal and stack measurement data from James River Unit 4 and Unit 5. Run 2 at Unit 4 shows both Cr and nickel emissions that are 5 to 10 times higher than Runs 1 and 3, yet the particulate emission rates for all three runs are comparable. Stack emission levels for Run 2 were at or above the inlet coal Cr concentration on a lb/TBtu basis. When expressed on a ppmw basis in the stack particulate, the Run 2 data indicate 18,000 ppmw (nearly 2 wt%) Cr in the PMr. This is inconsistent with other ICR data and historical test data, as shown previously in Figures E-1 and E-2. Likewise, all runs at Unit 5 show elevated Cr levels in the stack PM, as well as stack emission levels that are greater than the inlet coal levels for Runs 1 and 2.
Response to Comment 4: See response to Comment 3.
Comment 5: Commenter 17621 states that annual mass emission rates for each of the EPA case study facilities were developed using revised emission values or revised emission factors for various control class bins. For sites tested in the ICR, revised annual emission values were calculated by omitting the suspect individual run values. If all individual runs for a unit were suspect, a revised average emission factor for the appropriate control class bin was used to estimate emissions. Revised average emission factors for various control class bins were developed using the Phase II data sets presented in the EPA case study spreadsheet supporting data file as the starting point. Runs from units with suspect Cr data sets were then excluded from the Cr and nickel average emission factor calculations for the control configurations that apply to the list of case study plants. In addition, the commenter also developed revised emission factors by coal rank within each applicable control class bin. The resulting final set of revised emission factors used for units listed in the EPA case study spreadsheet are summarized and compared to the original Phase II emission factors calculated by the EPA in that spreadsheet. Note that no adjustments were made to the EPA's Phase II average arsenic emission factors for various control class bins. The commenter provides both the arithmetic average and the geometric mean value for each category. Note that the geometric mean, which may be the better statistic for most cases, is close to the arithmetic mean for the categories from which suspect data have been excluded. The arithmetic mean and geometric mean revised factors are based on the same data sets from which test sites with suspect data have been excluded.
The arithmetic mean values were used by the commenter to estimate actual annual emission for one or more units from the following plants listed in the EPA's case study spreadsheet: Canadys (ORIS 3280), Chesapeake (ORIS 3803), Conesville (ORIS 2840), Cromby (ORIS 3159), Labadie (ORIS 2103), Merrimack (ORIS 2364), Monticello (ORIS 6147), and Muskogee (ORIS 2952). All actual annual emission rates were calculated based on the actual annual heat input values, as presented in the EPA's case study spreadsheet as MMBtu per year.
Response to Comment 5: In regard to commenter's assertion that outlier values should be excluded from emission factor averages, the EPA agrees and has therefore employed appropriate outlier tests, though these tests are different from those used by the commenter. See response to Comment 100 above. In regard to commenter's assertion that the geometric mean may be a better statistic for these purposes, see responses to Comments 1 and 2 above.
Comment 6: Commenter 17621 states that in EPRI's 2009 risk modeling project, emission correlations were developed by EPRI based on historical measurement data for HAP trace elements and then used to estimate emissions from each coal-fired unit in industry. These correlations predict lb/TBtu emission factors for each trace element, based on the following inputs: trace element content of the coal (ppmw), ash content of the coal (ash fraction), and the stack particulate emission rate (lb/MMBtu). These correlations represent modified versions of the correlations adopted by the EPA for estimating emissions from coal-fired units in the "AP-42 Compilation of Air Pollutant Emission Factors." The commenter provides an example of these emission factor correlations for arsenic.
The commenter believes that these correlations provide a more accurate representation of emissions compared to the average emission factor approach used by the EPA for case study sites not measured as part of the ICR. For example, the EPA's case study risk assessment included the four bituminous/ESP units at the Chesapeake Station, but none of these units was tested in the ICR. Therefore, the EPA appears to have used average emission factors derived from ICR measurements for units equipped with ESPs to estimate emissions from Chesapeake. The commenter reviewed the ICR Part II database and found that there were sufficient site-specific measurement data regarding coal composition and stack PM emission rates at Chesapeake to derive emission factors based on the EPRI correlations.
Response to Comment 6: See responses to Comments 1 and 2 above. In addition, while the EPA acknowledges some site-specific measurement data regarding coal composition and stack PM emissions rates at the Dominion Chesapeake Bay Energy Center facility, the EPA concluded based on the analysis described in the response to comment 100 above that the emission factor equations that would be used with the data noted by the commenter would be poor predictors for the emissions rates.
Comment 7: Commenters 17621 and 17775 state that emission factors for Cr were inappropriately calculated. According to the commenters, the emission factors are not differentiated by coal rank. For case study facilities not tested in the ICR, the EPA case study spreadsheet provides an assignment to a specific coal rank and control class. However, for case study facilities with ESPs not tested in the ICR, the EPA apparently used a single average emission factor that is not differentiated by coal rank.
Response to Comment 7: The EPA disagrees that coal rank must be a factor in computing Cr emission factors for use in the case studies. The EPA's analysis has demonstrated that coal rank appears to play no role in metals emissions, despite the EPRI equation developers inability to find meaningful differences in emissions from coal rank, integrating "...the data from the various control technologies and coal types" into generic equations. The EPA's newly revised emissions factor development procedures have the ability to isolate and compare subgroups based on control device type or coal rank; the ICR data were subjected to these tests and no statistical significance was found between coal rank groups.
As shown in the table below, the metals emissions from coals whose rank is less than 8300 BTU/lb lies within the metals emissions from coals whose rank is at least 8300 BTU/lb.

                                    Control
                            Metals Emissions Range
                                     Metal
                                 Configuration
                           by heat input, lb /mmBTU

                               < 8300 BTU/lb
                               >= 8300 BTU /lb
                                      Cr
                             Fabric filter and ESP
                                   1.57E-07
                             1.77e-07 to 8.35e-04

                                 Dry scrubber
                                    -------
                             1.40e-07 to 7.52e-06

                                 Wet scrubber
                                    -------
                             1.36e-06 to 5.69e-05
                                    Arsenic
                                      ESP
                                    -------
                             1.73e-07 to 2.75e-04

                                 Fabric filter
                                   1.65E-06
                             1.64e-07 to 4.11e-06

                                 Dry scrubber
                                   1.00E-07
                             6.08e-08 to 2.33e-05

                                 Wet scrubber
                                    -------
                             2.34e-08 to 2.31e-05
Comment 8: Commenters 17621 and 17775 state that the ICR test EGUs were omitted from the 1-ESP bin used by the EPA to calculate the Phase II average emission factors. According to the commenters, the Sunbury, boiler 4, a coal-fired unit with ESP controls, should be included in the 1-ESP bin calculations. The commenters request that the EPA check the ICR data set to be sure all test units have been properly assigned to a control class bin for the emission factor calculations.
Response to Comment 8: The EPA agrees with the commenter that the unit mentioned - WPS Energy Services Sunbury Generating Unit 4 - was not included in the calculation of emission factors for the proposed rule. This unit was included in the ICR as one of the fifty additional coal-fired electric utility steam generating units not otherwise chosen for emissions testing as a best performing unit.

Minimum and maximum values from similar units (coal-fired with ESPs) found during the emissions factor development for the final rule bracket Sunbury Unit 4's reported emissions:
                                   Pollutant
                          Emissions Factor, lb/mmbtu

                    Minimum value from ICR test data subset
                   Average from Sunbury Unit 4 ICR test data
                       Average from ICR test data subset
                    Maximum value from ICR test data subset
                                    Arsenic
                                    1.73e-7
                                    6.46e-6
                                    1.25e-5
                                    2.75e-4
                                      Cr
                                    1.77e-7
                                    5.85e-6
                                    4.89e-5
                                    8.35e-5
                                      Ni
                                    1.54e-7
                                    6.10e-6
                                    2.74e-5
                                    3.73e-4
For the final rule, the EPA did not include the test data for Sunbury Unit 4 in its analysis. However, since the reported values from Sunbury Unit 4 are a fraction of the average from the ICR data (arsenic: 52%, Cr: 12%, Ni: 22%), and since there is already a large sample size for the data the EPA did use for the average emission factors, the impact of these data would be negligible to the results of the case studies. Furthermore, the coal emission factors for the bin associated with this unit (metals bin 103 "bituminous coal, conventional boiler, with ESP") was not used at most of the case studies showing risk > 1/million. The emission factors that would have been impacted by these data were used for 3% of the Cr (risk driver) emissions at the Conesville facility and just 0.01% of the emissions at Yorktown. Though the factor was used for 100% of the emissions at the Dominion Chesapeake Bay Energy Center facility, any minimal impact of additional test data given the large sample sizes already used would not have changed the results of the final case studies.
Comment 9: Commenters 17621 and 17775 state that EPRI found several errors in the stack parameters (e.g., number of stacks, stack flow, velocity) used by the EPA for several case study EGUs. These errors would likely have implications for calculated emissions, as well as for the overall risk assessment.
Response to Comment 9: The EPA agrees that stack parameters impact estimated risks. The EPA modeled each coal unit as a separate emission source in AERMOD (with the exception of Spruance and Yorktown). For units that share a common stack, the units were given the same stack parameters and location but different source identifiers. This was done to facilitate the processing of emissions that would be input into AERMOD. The number of modeled stacks is not incorrect as the commenter stated. Regarding the comment about incorrect stack parameters, The EPA used the stack parameter data collected from facilities and submitted by the commenter in the modeling of the case study facilities for the final rule.
Comment 10: Commenter 17723 states that only Cr VI was found to pose non-cancer risks to the maximally exposed individual of greater than one in a million. According to the commenter, considering the analytical difficulties in measuring Cr in general and Cr (VI) in particular this finding has to be taken with a "grain of sodium chloride." The commenter notes that their testing performed in response to the ICR indicated that in some test runs, the unit was emitting vastly more Cr than was originally present in the coal. The commenter states that the EPA did not follow conventional data rejection standards, concluded that transmutation of elements within a coal-fired boiler environment must be chemically plausible, and included questionable results into their exposure risk models. The commenter notes that any regulation of non-Hg metals should be restricted to Cr (VI), and then only following a rigorous quality review of the emissions data collected during the ICR.
Response to Comment 10: See response to Comment 3. The EPA disagrees with the commenter's assertion that test data used in calculating emission factors for the case studies is flawed. However, to further strengthen the EPA's analysis in response to this and other comments, the EPA applied statistical outlier tools to the Cr and other metal source test data in developing emissions rates to use for the final case study analysis. The EPA asserts that the sample sizes and approaches used for the case study Cr emission factors have followed a rigorous quality review.
Further, the EPA disagrees with the commenter's assertion that Cr is the only non-Hg HAP that should be regulated. Source categories listed for regulation under CAA section 112(c) must be regulated under CAA section 112(d), and the D.C. Circuit Court has stated that EPA has a "clear statutory obligation to set emission standards for each listed HAP." See Sierra Club v. EPA, 479 F.3d 875, 883 (D.C. Cir. 2007), quoting National Lime Association v. EPA, 233 F.3d 625, 634 (D.C. Cir. 2000). Therefore, even if EPA concluded that CAA section 112(n)(1) authorized a different approach for regulating HAP emissions from U.S. EGUs, the chosen course (i.e.,listing under CAA section 112(c)) requires the Agency to regulate under CAA section 112(d) consistent with the statute and case law interpreting that provision. In any case, the EPA disputes that Cr (VI) is the only non-Hg metal HAP that poses a hazard to public health and the environment. The EPA acknowledges that Cr was the primary cancer risk driver, but arsenic and nickel also pose significant risk in the case studies. Further, the EPA has not evaluated the additional risk posed from the non-Hg metal HAP from other sources nearby EGUs, and the EPA maintains that the uncertainty associated with that potential additional risk is further support for the agency's finding.
Comment 11: Commenter 17772 states that none of the 4 out of 16 coal-fired units that posed a risk greater than one in a million was actually tested for Cr(VI). Instead, these four facilities were tested for Cr compounds and a previous study that included four coal-fired boilers was used to make the unsupported assumption that 12% of the Cr will be Cr(VI) and the remaining 88% will be trivalent Cr or Cr(III) for every coal-fired unit. According to the commenter, the EPA failed to recognize that Cr(VI) is highly water-soluble and is easily reduced to Cr +3 in the presence of SO2 in a low pH environment. The resulting Cr(III) would be expected to precipitate out in a FGD. The actual amount of Cr(VI) that would be present in the emissions from an EGU with a wet scrubber is likely to be far lower than the 12% estimate made by the EPA.
Response to Comment 11: The EPA disagrees with the commenter's assertion that any impact of scrubbers will impact the case study analyses. In the EPA's final case study analysis, six facilities have risk greater than one in one million, and of these, four facilities have Cr as the risk driver (James River, Conesville, TVA Gallatin, and Dominion  -  Chesapeake Bay). For these facilities, none of the units contributing the bulk of the Cr emissions have scrubbers according to the data provided to the EPA by those facilities, so scrubber impacts on Cr speciation is not relevant to the EPA's conclusions based on the non-Hg case studies.
In any case, the EPA disagrees with the commenter's conclusions about the impacts of scrubbers on Cr speciation. There have been several studies that have attempted to quantify the amount of Cr(VI) in the PM resulting from the combustion of coal. These studies have typically shown that Cr(VI) can range from <1% of the total Cr to up to 20%.[,][,] The specific amount is likely a function of the complex flue gas chemistry, the specific coal type, the combustion conditions, and site-specific configuration of the post-combustion control equipment. The EPA has seen, in some cases, an increase in leachable (i.e., water soluble) Cr in coal combustion residuals (fly ash, scrubber sludge) for units that have selective catalytic reduction (SCR) units for NOx control. Since Cr(VI) was not measured during the 2010 Utility ICR, an assumption of 12% Cr(VI) seems conservative, but very reasonable.
Regarding the comment that "EPA apparently failed to recognize that Cr(VI) is highly water-soluble." The EPA agrees that some Cr(VI) compounds are highly water soluble. The Cr(VI) oxide (CrO3) is water soluble and some chromates  -  NaCrO4, K2CrO4, etc. are water soluble. However, there are other Cr(VI) compounds, for example calcium chromate (CaCrO4), that are not very water soluble. The water solubility will only enhance the control of Cr(VI) compounds over Cr(III) compounds in an FGD scrubber if the Cr(VI) compounds are in a gaseous state, which is unlikely. Control of sub-micron Cr particulate matter in an FGD scrubber will be limited by mass transfer, not by solubility. As a result, there is no reason to assume that Cr(VI) particulate matter would have enhanced control over that of Cr(III) compounds in a typical FGD scrubber. Given these considerations, EPA maintains that an assumption that 12% of the Cr emitted is Cr(VI) seems reasonable even for units with wet scrubbers.
The technology referenced - that Cr(VI) " is easily reduced to Cr(III) in the presence of SO2 in a low pH environment" - refers to a water treatment technology for reducing Cr(VI) to Cr(III) in solution - often for treating waste streams from plating operations. In the FGD environment, a Cr(VI) compound that is in solution has already been captured. The presence of SO2 and local low pH environments (and the fact that Cr(VI) is easily reduced) should result in some Cr(VI) reduction. However, again, that does not reduce air emissions of Cr(VI)...since that Cr(VI) was already captured. In any case, this is not entirely effective since the bulk pH of the scrubber solution is usually held at about a pH of 6 and the efficiency of the reduction reaction is highly dependent on pH with most waste water treatment processes operated between pH 2.0 and 3.0. Soluble forms of Cr have been found in FGD scrubber effluents and leached from coal combustion solid residuals (fly ash, scrubber sludge, etc.)
Comment 12: Commenter 17800 states that two of the OG&E plants, Muskogee and AmerenUE-Labadie, were never sampled as part of the ICR Part III. However, the EPA stated that emission estimates are from the 2010 ICR utility data and that "Where test data were not available for a specific unit, emission factors were derived from similarly configured units..." According to the commenter, the EPA gives no detailed description of how emissions for these plants were developed and thus modeling results from these units should be considered suspect. Since the AmerenUE-Labadie plant burns a variety of subbituminous coals, the actual non-Hg emissions determined in the EPA's analysis may not be representative.
Response to Comment 12: The EPA disagrees with the commenter that the EPA gave no detailed description of how emissions for these plants were developed. These data were provided in an Excel spreadsheet and PDF file to the docket for this rule on 05/05/2011. The EPA agrees with the commenter that Muskogee and Ameren UE-Labadie facilities were not sampled, but this fact does not change the outcome of the case studies because neither of these facilities showed risk > 1/million in the EPA's final analysis. The EPA agrees that site-specific test data are a better source of emissions information when it is available, but use of emission factors is an appropriate option when no better data are available. The EPA used test data for all of the case studies where it was available.
2. General comments on non-Hg Risk Case Studies
Commenters: 17383, 17621, 17689, 17716, 17723, 17760, 17772, 17774, 17808, 17820, 17877, 17885, 18025, 18831, 18500, 17871, 10943, 6543, 19536/19537/19538, 18023
Comment 13: Several commenters (19536, 19537, 19538) state that the EPA's 16 case study analysis reaffirms the need to regulate HAP emitted by both coal and oil-fired EGUs. The commenters note that over 40% of the case studies conducted by the EPA to quantify health hazards associated with the inhalation of non-Hg HAP indicated a cancer risk greater than or equal to the one in one million threshold level threshold required to delist a source as a category regulated under section 112 of the CAA. The case study examining cancer risk from an oil-fired EGU indicated that the greatest cancer risk estimate quantified in the assessment, ten in one million, is associated with this source. The commenters note that studies of acid gases were not included due to uncertainties in their emission rates, and that potential overlapping impacts from different EGUs and other pollutant sources likely compound the cancer risks estimated in the case studies. The commenters agree with the EPA's decision to only peer review the speciation of Cr and Ni in the analysis of the health risks posed by non-Hg EGU emissions. The AERMOD modeling system methodology applied in the EPA's non-Hg HAP chronic inhalation test cases is well-established and has undergone numerous evaluations. For example, one recent comparative study finds that AERMOD produces the most reliable exposure risk simulation results among four different common exposure assessment methods.
Response to Comment 13: None needed.
Comment 14: Commenter 18023 states that the EPA's 16 plant assessment may be flawed by the use of "beta" tests versions of the processor software and cannot be relied upon to draw conclusions. According to the commenter, the EPA processed the meteorological data used in these assessments with beta (i.e., test) versions of meteorological processors AERMET and AERMINUTE. The commenter obtained from the EPA the meteorological data used for the EPA's assessment of the Conesville facility and processed these data with the EPA's current regulatory versions of these processors, which differ from the beta version. A comparison of the hourly wind speed and hourly wind direction data produced by the beta processor and by current EPA processors revealed numerous and often substantial disparities.
Response to Comment 14: The EPA remodeled the case study facilities using the current versions of AERMINUTE (version 11059), AERMET (version 11059), and AERMOD (version 11103). While there were differences in the number of calm and missing winds in the current AERMINUTE/AERMET output compared to the beta version, the resulting risks differed by less than 2%, on average. For Conesville, which had the largest difference in calms between the beta and current versions of AERMINUTE/AERMET, the risks differed by 3%. For the final rule, the case study facilities have been modeled with the current available versions of AERMINUTE, AERMET, and AERMOD.
Comment 15: Commenter 18023 states that the EPA's finding that only three coal-fired facilities and one oil-fired facility out of roughly 440 coal-fired facilities and 97 oil-fired facilities in the U.S. indicated risk greater than one in a million supports a finding that it "appropriate" to regulate those four and not the other 537.
Response to Comment 15: The EPA disagrees. The 16 facilities the EPA selected as case studies for assessment may not represent the highest-emitting or highest-risk sources. Although case study facility selection criteria included high estimated cancer and non-cancer risks using the 2005 NEI data, high throughput, and minimal emission control, another necessary criterion was the availability of ICR data for the EGUs at those facilities (or for similar EGUs at other facilities). Because the ICR data were collected for the purpose of developing the MACT standards, the ICR was targeted towards better performing sources, with a smaller set of random recipients. Therefore, facilities for which ICR data were available may not represent the highest-emitting sources. The EPA's assessment of the case study facilities for the proposed rule concluded that three coal-fired facilities and one oil-fired facility had estimated lifetime cancer risks greater than one in a million. For the final rule, revisions were made to the 16 case studies based on comments received, and the results indicate that five coal-fired facilities and one oil-fired facility had estimated lifetime cancer risks greater than one in a million. The EPA maintains that its finding that more than 30% of the case study facilities had a cancer risk greater than one in one million is sufficient to support the appropriate finding. Furthermore, the EPA did not base the appropriate finding on just the case study analysis as explained in the preamble to the proposed rule.
Comment 16: Commenter 18023 states that the EPA's discussion in the preamble to the proposed rule misleads the reader into believing that non-Hg HAP emissions from U.S. EGUs are associated with serious human health effects. According to the commenter, the EPA's discussion of the medical impacts associated with excessive exposure to an individual HAP would lead the reader to believe that those harms flow directly and inevitably from EGU emissions because EGU emissions have trace amounts of non-Hg HAP. For example, this CAA section begins with a description of the HAP measured in the ICR of EGUs and suddenly notes, "Exposure to high levels of the various non-Hg HAP emitted by EGUs is associated with a variety of adverse health effects. These adverse health effects include chronic (long-term) health disorders (e.g., effects on the central nervous system, damage to the kidneys, and irritation of the lung, skin, and mucus (sic) membranes); and acute health disorders (e.g., effects on the kidney and central nervous system, alimentary effects such as nausea and vomiting, and lung irritation and congestion)." The commenter notes that the reader will infer that the health effects described are associated with EGUs despite the fact that the impacts described are exposure effects at high levels. EGUs do not expose individuals to high levels of non-Hg HAP.
The EPA states HCl is a corrosive gas that can cause irritation of the mucous membranes of the nose, throat, and respiratory tract. Brief exposure to 35 ppm causes throat irritation, and levels of 50 to 100 ppm are barely tolerable for 1 hour. The 35 ppm, 50 ppm, and 100 ppm exposures referenced in the EPA's discussion represent concentrations of 50,000, 75,000, and 150,000 μg/m[3], respectively. The EPRI has shown that there is no concentration from a utility unit greater than 630 μg/m[3], which is approximately 100 to 250 times lower than the exposure levels described by the EPA. The inhalation risk assessment from EPRI assessed the short-term (1-hour) concentrations of HCl and other HAP emitted by EGUs and found the hazard index to be below 0.3. Therefore, at a minimum (i.e., assuming all risk is from HCl), there was no concentration above 630 μg/m[3]. The EPA's implication that the public can experience such exposures and the implication that this rule will serve to preclude such exposures are the antithesis of transparency. The EPA did not report any analyses of acute exposure, but this result is consistent with the EPA's chronic hazard index range (based on annual averages) of 0.05 to 0.005 for the 16 "high risk" plants assessed for health risk.
The commenter state that the discussion of effects without the context of actual exposure was not isolated to HCl but included a list of HAP. See 76 FR 25,003 - 05.
Response to Comment 16: The EPA disagrees with the commenter's assertion that the health effects associated with exposures to non-Hg HAP emissions from U.S. EGUs are mischaracterized in the preamble to the proposed rule. The discussion of the health effects of non-Hg HAP provided in the preamble includes general information on the potential health effects associated with a broad range of exposure concentrations (from low to high levels) of the various non-Hg HAP (some of which have been determined to be carcinogenic to humans) based on peer reviewed scientific information extracted from priority sources such as IRIS, Cal EPA and ATSDR health effects assessments. The preamble CAA section referred to by the commenter does not include a quantitative analysis of HCl (or other non-Hg HAP) exposures to the public.
Comment 17: Commenters 17760 and 18831 state that in the Utility Study, the EPA found that only 11 of the 137 oil-fired EGUs potentially posed inhalation cancer maximum individual risk greater than one in a million in 1990. The new scientific evidence, the fuel mix of several of the 11 plants identified as high risk by the EPA changed significantly since 1990, such that, based on new data, there likely would be fewer units posing one in a million cancer risk even using the rest of the EPA's assumptions. According to the commenters, the EPA failed to address this in the Non-Hg Risk Assessment, instead deciding to rely on emissions from only one oil-fired EGU. Non-HG Risk Assessment at 12-13.
Response to Comment 17: The EPA disagrees that addressing the fuel changes over the suite of all EGUs modeled in the past is relevant to the case study modeling performed for the MATS rule. The fuel mix used for the case studies considered for the MATS rule is based on current data provided by the facilities in response to the ICR for the rule, which identifies the HECO Waiau facility as completely oil-fired, as well as one unit at the Dominion, Yorktown facility. The EPA agrees that changes in fuel mix away from oil will change the risks at such a unit. The EPA cannot base decisions for the appropriate and necessary analysis on "likely" changes to units, but rather has selected case studies that demonstrate risks greater than one in one million for several facilities, which have fuel mixes of coal only, coal and oil, and oil only.
Comment 18: Commenter 17760 states that with the assumptions in the Utility Study, both in terms of conservative scientific estimates and overestimated amounts of oil burned by these units, the EPA concluded that the risks from oil-fired units would result in only one new cancer case every five years. See Utility Study at p. 6-50, Table 6-23. The commenter does not believe that this level of risk, standing alone, warrants regulation under CAA section 112(n)(1)(A) of the CAA. The agency should rescind the 2000 Regulatory Determination with respect to oil-fired EGUs until such time as the agency develops an appropriate factual record for regulation.
Several commenters (17383, 17689, 17877, 17885) state that even if the additional studies the EPA performed were taken as accurate representation they hardly demonstrate that it's necessary and appropriate to regulate HAP emissions from coal-fired U.S. EGUs under CAA section 112 because three sites nationwide show risks greater that one in one million with the highest at eight in one million.
Response to Comment 18: The EPA disagrees with the commenter's characterization of the Utility Study. The Utility Study represented the highest-quality factual record of information available at the time regarding EGU emissions and risks. Further, the EPA's recent risk assessments of 16 EGU case studies, performed with more recent data and refined scientific methods, indicate that there are still six EGU facilities that pose estimated inhalation cancer risks greater than one in a million. The EPA maintains that the findings of the case studies are one element that independently supports the EPA's determination that it remains appropriate and necessary to regulate EGUs under CAA section 112.
Comment 19: Commenter 17774 states that the highest cancer risk estimated for coal-fired EGUs is still within the acceptable range used by the EPA in other programs and is also far less than the background exposure risks the average person experiences. The background risk of developing cancer in a lifetime is approximately 1 in 3 (0.33). According to the EPA's own data, the predicted added cancer risk of exposure to HAP from U.S. EGUs would change the background risk from 0.33 to 0.330001. This level of change is so minimal that it could not be observed in any health effects study that might be conducted.
Response to Comment 19: As explained in the preamble to the proposed rule, the EPA reasonably looked to the cancer risk threshold established under CAA section 112(c)(9)(B)(1) for delisting a source category as an indicator of the level of cancer risk that was appropriate to regulate under CAA section 112. Commenter's comparison of the cancer risk from U.S. EGUs as compared with the risk of contracting cancer from unknown sources is not the standard Congress established for evaluating HAP emission risk and the commenter has provided no support for its contention that the agency should evaluate risk in that manner. The EPA maintains that the analysis was reasonable.
Comment 20: Commenter 17885 states that the EPA conducted a health risk assessment on a limited number of facilities and found a "few" facilities that have estimated maximum cancer risks in excess of one in a million for Ni or hexavalent Cr. According to the commenter, the Northern Star's Cambria Cogen was one of the plants included in the assessment and had a calculated maximum cancer risk of 0.5 per million for hexavalent Cr. None of the facilities selected had a non-cancer impact exceeding a hazard index of 1 for any HAP. Cambria Cogen had a maximum hazard index of 0.003 for Ni. Based on this limited health risk assessment, the EPA apparently decided that they were justified to regulate all non-Hg HAP for all sources in this category. For Cambria Cogen, and other similar waste coal power plants, this means the imposition of potentially costly emission controls or facilities that do not have a significant public health risk according to the EPA criteria.
Response to Comment 20: The facilities the EPA selected as case studies for assessment may not represent the highest-emitting (and highest-risk) sources. Although case study facility selection criteria included high estimated cancer and non-cancer risks using the 2005 NEI data, high throughput, and minimal emission control, another necessary criterion was the availability of ICR data for the EGUs at those facilities (or for similar EGUs at other facilities). Because the ICR data were collected for the purpose of developing the MACT standards, the ICR was targeted towards better performing sources for non-Hg metal HAP, acid gas HAP, and organic HAP, with a smaller set of random recipients. Therefore, facilities for which ICR data were available may not represent the highest-emitting sources. The EPA agrees with the commenter that the estimates of chronic inhalation risks for Northern Star's Cambria Cogen are below levels of concern. In addition, the EPA does not agree with the commenter's implication that the EPA must make a facility-specific finding for each HAP for each source and then only regulate individual EGU facilities for the individual HAP that identified as causing an identified hazard to public health or the environment. That approach is not required under CAA section 112(n)(1) or anywhere under CAA section 112, and it would be virtually impossible to undertake such an effort. For these reasons, the EPA does not agree with the commenter and maintains that the Appropriate and Necessary Finding is reasonably supported by the record and consistent with the statute for all the reasons set forth in the preambles to the proposed rule and this final action.
Comment 21: Several commenters (17621, 17820, and 18023) state that the EPA's assumption that implies that a person stays exactly at the center of a census tract for 70 years and that a unit will operate in exactly the same manner for 70 years is unrealistic. The commenters suggest that Tier 3 risk assessment is warranted or a lifetime exposure adjustment is needed.
Response to Comment 21: The EPA disagrees that an exposure adjustment is needed because it runs counter to the long-standing approach that the EPA took to estimate the maximum individual risk, or MIR. The MIR is defined by the EPA's Benzene NESHAP regulation of 1989 and codified by CAA 112(f) as the lifetime risk for a person located at the site of maximum exposure 24 hours a day, 365 days a year for 70 years (e.g., census block centroids). The MIR is the metric associated with the determination of whether or not a source category may be delisted from regulatory consideration under CAA section 112 (112(c)(9)). The MIR is the risk metric used to characterize the inhalation cancer risks associated with the case study facilities. The EPA used the annual average ambient air concentration of each HAP at each census block centroid as a surrogate for the lifetime inhalation exposure concentration of all the people who reside in the census block. The EPA used this approach to estimate MIR values in all of its risk assessments to support risk-based rulemakings under CAA section 112 of the CAA to date.
Comment 22: Commenter 18023 asserts that the EPA explains in its preamble that the agency "focus[ed] in this rulemaking on exposure to MeHg through ingestion of fish [because] potential health risks do not likely result from Hg inhalation exposures associated with Hg emissions from utilities." Moreover, the EPA identifies the driving health metric as the RfD establish by NAS of 0.1 micrograms/kg-day. Likewise, the non-Hg HAP health impacts are not associated with acute concentrations. Instead, they are addressed in terms of total chronic exposure. The EPA analyzed "the MIR for each facility [in the 16-plant study] as the cancer risk associated with a continuous lifetime (24 hours per day, 7 days per week, and 52 weeks per year for a 70-year period)." Because the alleged health benefits are derived from total exposure (for example through bioaccumulation of Hg, or through continuous lifetime exposure to Cr(VI)), the EPA should explain how its numerical emission limit units, which would not directly restrict total exposure if heat inputs increase, redress this health concern. In its preamble, the EPA simply notes that its emission limit units are consistent with, and allow for simple comparison to, other regulations.
Response to Comment 22: The EPA disagrees with the commenter's assertion that the numerical emission limits being promulgated in today's final rule must be justified on their ability to redress the health concerns that were identified as the basis for regulating EGUs. The emission limits in today's rule are technology-based, as prescribed under CAA section 112, and do not need to be justified on the basis of their ability to protect public health. Regarding potential health concerns, the EPA has up to 8 years after the promulgation of the technology-based emission limits for EGUs to determine whether the regulations protect public health with an ample margin of safety. If the regulations do not, the CAA directs the EPA to promulgate additional more stringent standards (within the prescribed 8 years) to achieve the appropriate level of public health protection.
Comment 23: Commenter 17772 claims that prior studies provide no support for establishing standards for non-Hg HAP metals. The "Utility Study" concluded that "Hg from coal-fired utilities is the HAP of greatest potential concern and merits additional research and monitoring." It also identified other HAP of "potential concern," but explicitly stated that "the remaining HAP evaluated in the Utility Study did not appear to be a public health concern." Congress clearly intended that the EPA was to determine the "emissions which may warrant regulation under this [112(n)(1)(A)] CAA section." In 1990, after analysis and review of the Utility Study - even with the assumed increase in emissions and exaggerated modeling data, the EPA determined that Hg was the only HAP emission that warranted regulation.
Response to Comment 23: The EPA does not agree with the commenter's characterization of the 2000 listing or the proposed rule for the reasons set forth in the preamble to the proposed rule. The commenter also characterizes the Utility Study, and the EPA maintains that document speaks for itself. The EPA notes that the commenter makes much of the direction in CAA section 112(n)(1)(A) that the EPA develop and describe alternative control strategies for HAP "emissions which may warrant regulation under [CAA section 112]." Commenter then stated that the EPA determined that only Hg emissions warranted regulation. However, in the Utility Study, the EPA developed alternative control strategies for all HAP, so it is clear that at the time the study was issued the EPA considered all HAP emitted from U.S. EGUs as potentially warranting regulation.
Comment 24: Commenter 18500 requests that the agency remove non-Hg HAP from the rule. Commenter 18422 stated that the EGU MACT should not include acid gases or metal HAP other than Hg and Ni because the agency has not provided adequate evidence of risk nor made a showing that regulation of other HAP and acid gases is necessary and appropriate. Commenter 17911 stated that while EPA studies have demonstrated health concerns associated with methyl-Hg and bio-accumulations, health impacts were not identified for acid gases and PM2.5, which will be covered by updated rules for ozone, regional haze, and National Ambient Air Quality Standards. The commenter asserted legal disconnect with CAA section 112 of the CAA, and the rule should be re-proposed and only cover methyl-Hg emissions. The commenter adds that while addressing HAP may have the collateral benefit of controlling criteria pollutants, the focus should be on HAP health impacts.
Response to Comment 24: We do not agree with the commenter's characterization of the law or the facts as set forth in the preamble to the proposed rule. While the EPA may not have identified health concerns associated with each and every HAP emitted by EGUs, which is not what the CAA requires, the EPA has, in fact, identified health concerns associated with HAP emissions from U.S. EGUs emissions, and has used those health concerns to justify that it is appropriate and necessary to regulate EGUs under CAA section 112. Once this determination has been made, it is the EPA's obligation to address all HAP emitted by EGUs in any subsequent technology-based or risk-based regulations.
Comment 25: Several commenters (17777, 17871, 10943, 6543) state that they are concerned that significant errors were made in the risk calculations reported by the EPA, but no specific errors have been identified.
Response to Comment 25: The EPA disagrees with the commenters that the risk calculations contain unspecified errors. Both risk assessments have successfully undergone peer review.
Comment 26: Commenter 18436 submitted a report emphasizing that technology-based emission limitations for specific industrial categories have been established for HAP. Although this regulatory system has undoubtedly reduced the emission of toxic air pollutants in Alabama, the commenter claimed that the present regulatory system is not sufficient to reduce ambient concentrations of all toxic air pollutants below levels that pose an unacceptable risk to human health. The commenter states that HAP are known to cause damage to the eyes, skin, breathing passages, kidneys, lungs, and nervous system.
Response to Comment 26: No response needed.
3. Nickel risk.
Commenters: 19622, 17760, 17870, 17621, 18025, 18031, 12380
Comment 27: Commenter 19622 states that the May [sic] 16[th] memorandum on nickel cancer risk [Non-Hg Case Study Chronic Inhalation Risk Assessment] was based on 1) assumptions about the composition of the Ni emissions, 2) lack of consideration of differences in carcinogenic potency among Ni compounds and 3) assumptions about the linearity of the dose‐response for Ni and respiratory cancer effects. According to the commenter, for all three aspects the Memorandum chose a very conservative position leading to a conclusion that is likely to overstate the risks. The commenter urges the EPA to reconsider these three elements and weigh them in a more realistic way.
Comment 28: Commenter 19622 states that different forms of Ni have shown clear differences in their potency to induce respiratory tumors. Ni subsulfide and complex oxides containing Ni and copper are considered to be the more potent Ni compounds at inducing respiratory tumors. This information comes from results of epidemiological (e.g., ICNCM, 1990) and animal studies (NTP 1996a,b,c, Sunderman et al., 1987). In contrast, other Ni oxides such as Ni monoxide and silicate oxides are expected to have lower potency based on human and animal studies (e.g., Goldberg et al., 1987; 1992; 1994; NTP 1996c). For example, high calcining temperature NiO had a 7‐fold lower potency to induce respiratory tumors in animal inhalation studies than Ni subsulfide (NTP 1996c, Danish EPA, 2008). Water-soluble Ni compounds do not induce tumors in rats via inhalation or oral routes (NTP 1996a; Heim et al., 2007). Epidemiological evidence does indicate that soluble Ni exposures can increase cancer risks in sulfidic ore refinery workers. Soluble Ni compounds are suspected of not inducing tumors on their own but enhancing respiratory tumor induction when inhaled at levels above the threshold for respiratory toxicity (Goodman et al., 2011[,]; Oller et al., 2002[,]). For these reasons, a unit risk for soluble Ni has never been derived. Recently, the SCOEL (2011) concluded that if soluble Ni exposures to workers were kept below 10 μg Ni/m[3], respiratory cancer risks would be prevented. Even after adjusting for exposure conditions of the general public (24 h/day, 7 days/week, 52 weeks/year, 70 years), the resulting adjusted value would be several fold higher than the value corresponding to an excess risk of one in one million calculated in the May [sic] 16[th] memorandum. Metallic Ni has not been shown to increase respiratory risks in epidemiological studies and was not a respiratory carcinogen in rat inhalation studies (ICNCM, 1990; Oller et al., 2008).
According to the commenter, assigning the same carcinogenic potency of Ni subsulfide to other forms of Ni is overly conservative and inconsistent with the best available evidence. This is particularly true, since the unit risk estimate (URE) of 4.8 x 10[‐][4] per μg/m[3] that the EPA assigned to Ni subsulfide is an artificial value derived by doubling the URE that the EPA calculated for Ni refinery dust  -  on the assumption that Ni subsulfide constituted roughly 50% of the total Ni present in Ni refinery dust but was responsible for 100% of the cancer risk.
Comment 29: Commenter 17760 states that one conservative assumption by the EPA was that the Ni emitted from oil-fired plants is 50% as carcinogenic as Ni subsulfide. The EPA admitted in the Utility Study that the limited data available indicated that less than 10% of the Ni emitted from oil-fired EGUs is Ni subsulfide. This demonstrates that the low-level risk estimated by the EPA has been greatly overstated. According to the commenter, the EPA should obtain more Ni speciation data using updated techniques, and should, in light of such information, reevaluate whether it is appropriate and necessary to regulate oil-fired EGUs.
Comment 30: Commenter 17760 states that nothing in the preamble to the proposed rule refutes that 2005 Finding where the EPA acknowledged the flaws in the Utility Study. The agency concluded that "[b]ecause EPA could not have reasonably found that it was appropriate to regulate Ni emissions from oil-fired Utility Units based on the record before it at the time of the 2000 Regulatory Determination, it should not have made a finding that it was necessary to regulate such emissions." According to the commenter, the EPA rejected the 2005 Finding for reasons unrelated to public health risks associated with Ni emissions.
Comment 31: Commenter 17760 states that the Utility Study and Non-Hg Risk Assessment provide insufficient bases for regulating oil-fired EGUs under CAA section 112. Both studies raised substantial uncertainties regarding the species of Ni being emitted and the risk of such emissions from oil-fired EGUs. This lack of data made it impossible for the EPA to give an accurate assessment of the risk to human health from Ni emissions from oil-fired EGUs. In the face of such uncertainty, the EPA made ultraconservative assumptions aimed at overestimating the risk. According to the commenter, while this strategy may have been appropriate for the Utility Study, it should not have formed the basis for determining whether to regulate oil-fired units under CAA section 112(n).
Comment 32: Commenter 17760 states that they support the analysis of the Non-Hg Risk Assessment completed by Edward J. Zillioux on behalf of Florida Power & Light Company: "Comment on EPA's Ni Risk Assessment used to support the National Emission Standards for HAP (NESHAP)" (June 26, 2011)
Comment 33: Commenter 17760 states that the EPA acknowledged that the characterization of the chemical speciation for Ni emissions in the Non-Hg Risk Assessment should be subject to peer review and has stated that it will publish the result of the peer review and any EPA response to it before the final EGU MACT rule. The commenter supports this process and urges the EPA to withhold any ultimate determination until the results of that peer review and the EPA's response can be made publicly available and be subjected to public review.
Comment 34: Commenter 17870 states that the Non-Hg Case Study Chronic Inhalation Risk Assessment for the Utility MACT Appropriate and Necessary Analysis fails to take into consideration studies demonstrating that Ni sulfate alone has no evidence of carcinogenicity (NTP, 1996a; Dunnick et al., 1995).[,]
Other papers have compared various studies including epidemiologic evidence of worker inhalation exposures to Ni refinery dust containing soluble Ni compounds. Oller (2002), for example, concluded, "Overall, the weight of evidence indicates that inhalation exposure to soluble Ni alone will not cause cancer; moreover, if exposures are kept below levels that cause chronic respiratory toxicity, any possible tumor-enhancing effects (particularly in smokers) would be avoided."
Comment 35: Commenter 17870 states that in the Non-Hg Case Study Chronic Inhalation Risk Assessment, the EPA relies on two agencies that "have determined that Ni sulfate, specifically, and Ni compounds, in general, are carcinogenic." According to the commenter, this reliance is problematic because these agencies relied on worker exposure studies that often suffer from poor quality of existing exposure data, no consistent dose response with increasing concentrations of soluble Ni, inconsistent results across cohorts, and presence of mixed exposures to water-insoluble Ni compounds and other confounders with known or suspected carcinogenic potential (e.g., soluble cobalt compounds, arsenic, acid mists, PAHs, cigarette smoke, etc.). The Danish EPA reported that the Technical Committee for Classification and Labeling (TCC&L), European Chemicals Bureau, "has agreed to classify Ni sulphates as Care. Cat. l; R49 (May cause cancer by inhalation), as there is no concern for carcinogenic potential with other routes of administration."
Comment 36: Commenter 17870 states that a focused assessment of the potential for carcinogenicity from inhaled Ni soluble salts was conducted by TERA (Toxicology Excellence for Risk Assessment) and others (Haber et al., 2000) under contract to the Metal Finishing Association of Southern California, Inc., the U.S. EPA, and Health Canada. Conclusions of the assessment are (1) "the role of soluble Ni alone in carcinogenicity to humans cannot be determined from the epidemiologic studies" (2) "the carcinogenic activity of insoluble Ni compounds should not be used to predict the carcinogenic potential of water-soluble Ni salts," and (3) "under the U.S. The EPA's 1996 proposed Guidelines for Carcinogen Risk Assessment, inhaled soluble Ni compounds would be classified as `cannot be determined,' because the existing evidence is composed of conflicting data" (e.g., co-exposure of populations to soluble and insoluble forms of Ni and limitations in exposure measurements). The final EPA Guidelines for Carcinogen Risk Assessment (2005) employ different descriptors than the 1996 proposed guidelines; the comparable descriptor used for conflicting evidence in the final guidelines is inadequate information to assess carcinogenic potential.
Comment 37: Commenter 17870 states the NTP 1996 series of inhalation studies of Ni species also included the results of 2-year studies of Ni subsulfide and Ni oxide. The conclusions of the studies with Ni subsulfide were: (1) clear evidence of carcinogenic activity of Ni subsulfide in male and female F344/N rats and (2) no evidence of carcinogenic activity of Ni oxide in male or female B6C3F1 mice. Conclusions of studies with Ni oxide were: (1) some evidence of carcinogenic activity of Ni oxide in male and female F344/ N rats, (2) no evidence of carcinogenic activity of Ni oxide male B6C3F1, mice, and (3) equivocal evidence of carcinogenic activity of Ni oxide in female B6C31F, mice (NTP, 1996c). Together with the NTP 2-year inhalation studies of Ni sulfate that showed no evidence of carcinogenic activity in either male or female F344/N rats, or in male or female B6C3F1 mice, it is clear that differences exist in carcinogenic potential between various Ni species.
Comment 38: Commenter 17870 states that extensive literature exists indicating that only selected compounds of Ni may be regarded as carcinogenic or potentially carcinogenic in humans, with many papers reporting on postulated mechanisms that drive the carcinogenic process among Ni species. This is the subject of an extensive review by Teaf et al. (2004), which also developed RfCs for Ni sulfate and Ni oxide using the benchmark dose approach in conjunction with NTP data for Ni species. The Memorandum cites NTP (2005), which noted that "The combined results of epidemiological studies, mechanistic studies and carcinogenesis studies in rodents support the concept that Ni compounds generate Ni ions in target cells at sites critical for carcinogenesis, thus allowing consideration and evaluation of these compounds as a single group." The fact that individual Ni compounds have been shown to display a wide range of efficiency with respect to the delivery of the Ni(II) ion to the target site has been ignored by this treatment and, thus, has not recognized the large variation in carcinogenic potential shown by the experimental evidence. For example, the Teaf et al. review cites evidence that soluble Ni does not readily enter mammalian cells, is rapidly cleared from the lung, and does not appear to be sufficiently bioavailable at nuclear target sites to induce tumors. In addition, the delivery of Ni(II) from high temperature Ni oxide to the target site appears to be much less efficient than for Ni subsulfide (Sunderman et al., 1987). The degree of phagocytosis between different forms of crystalline species may be a factor in carcinogenic potential (e.g., 2-3% for Ni oxide vs. >22% for Ni subsulfide), and this process may be mediated by differences in surface charges between the crystalline species and between crystalline and non-crystalline Ni species (Cost and Heck, 1982; Heck and Costa, 1983). Such mechanistic differences help explain the range in experimental findings of carcinogenic activity from no evidence for NiSO4::6H2O, to equivocal evidence for Ni oxide, to clear evidence for Ni subsulfide. A recent review of mechanisms in metal carcinogenesis, including Ni, included the following caveat:
"The toxicity and carcinogenicity of Ni(II) depends on its intracellular dose that, in turn, is a function of physicochemical properties of particular Ni compounds, their ability to enter the cell and/ or to dissolve within the cell. Because of a fast clearance from the exposed tissues, which limits cellular uptake, water-soluble Ni(II) compounds possess lower toxic and carcinogenic potential as compared to semi-soluble compounds such as Ni subsulfide."
Comment 39: Commenter 17870 states that the EPA study on Ni did not take into account the evidence that no crystalline sulfidic Ni compounds, the only Ni compounds that clearly have been established as carcinogenic or potentially carcinogenic in humans, have been found in studies of residual oil fly ash samples (Galbreath, 2000;. Galbreath, 2005; Galbreath, 2004; Huggins, 2011).
Comment 40: Commenter 17870 notes that the EPA had available a report from the Energy & Environment Research Center of the University of North Dakota to the Electric Power Research Institute, which was entered into the rulemaking docket and noted in footnote #9 on p.l3 of the Memorandum. This was referred to in the Memorandum only as "Recent data from industry." The footnote noted that the insoluble Ni is primarily in a spinel form and that this spinel form "is not in the insoluble crystalline form." This was a mistake by the authors of the Memorandum; the spinel is the insoluble crystalline form. The footnote also stated that the report "does not provide us with a better means for characterizing the risks" since there was no attempt to characterize the toxicity of the spinel form. It is generally recognized that metals in spinel forms are tightly bound in lattice structures and thus essentially lose their chemical, physical, and physiological properties. Citing studies with the spinel compounds chromite (FeCr2O4) and magnetite (Fe304), Heaney and Banfield (1993) concluded "Spinels appear to be relatively inert in biological systems." In addition, there is a large and readily available literature, associated with the pigment chemical industry, on the insolubility and lack of bioavailability of heavy metal compounds absorbed by spinel lattices.
Comment 41: Commenter 17870 states that direct speciation measurements by Galbreath et al. indicated that >95% of the total Ni in residual oil PM was present as a mixture of NiSO4::xH2O and a Ni oxide spinel compound, similar in composition to NiFe2O4 (Huggins et al., 2011; Heaney, 1993).
According to the commenter, each of these studies, however, looked at Ni speciation in fly ash sampled from no more than two EGUs. This has prompted the question of whether the results were applicable to oil-fired EGUs in general in the U.S. Huggins et al. included emission studies of eight EGUs at three utility companies from Florida, New York, and Hawaii and is more broadly applicable. The data analyses of the oil used by these three companies are representative of residual oil use in the oil-fired electric generating industry. The commenter notes that approximately two-thirds of the residual oil power generation in the U.S. is supplied by the three companies involved in this testing - Florida Power and Light Company (FPL), Hawaiian Electric Company, Inc. (HECO), and National Grid. Huggins et al. (2011) was recently published and has been entered into the docket of the NESHAP proposed rule. The paper summarizes Ni speciation determined by Ni XAfS spectroscopy, which is the best available method for directly and nondestructively determining the speciation in such emissions. The Ni speciation of all samples investigated was found to be dominated by Ni sulfate in the form of NiSO4::6H20, with lesser amounts of Ni oxides, either (Ni, Mg)O and/or NiFe2O4. Importantly, the potentially carcinogenic Ni sulfide compounds are absent within the detection limits of the method (+-2% of the total Ni).
Comment 42: Commenter 17870 states that in consideration of the lack of carcinogenicity of Ni sulfate alone, the equivocal evidence for carcinogenicity of Ni oxides along with mechanistic limitations in the delivery of the Ni+2 ion to the target site from Ni oxide exposures, the reported lack of bioavailability of spinel compounds, and the absence of sulfidic Ni species found in Ni speciation studies of oil-fired EGUs, they urge the EPA to re-evaluate the conclusions in the preamble to the proposed rule on the carcinogenicity of emissions from oil-fired EGUs.
Comment 43: Commenter 19622 states that the application of a linear dose-response approach to estimate the cancer risk of Ni in EGU emissions using a URE based on refinery dust exposure that does not match the composition of total Ni in EGU emissions represents an overly conservative approach to estimating increased cancer risk in the general population. According to the commenter, there have been some recent movements to consider some of the metal compounds as genotoxic carcinogens with a "practical threshold" for the purpose of risk assessment and setting of Occupational Exposure Levels (Bolt and Huici-Montagud, 2008; De Flora, 2000). The majority of the genotoxic effects that have thresholds can be explained by indirect effects through the generation of oxygen radicals or the inhibition of DNA repair.
In the case of epigenetic effects, the Ni (II) ion has been shown to compete with Mg (II) ion for binding to histones and triggering histone modification, DNA methylation, and changes in chromatin conformation and gene expression. Again, these effects have thresholds. The inferred theoretical presence of thresholds for tumors induced by Ni manifests in the practical threshold actually observed in some animal and human studies.
   *    The oral carcinogenicity study in rats with blood Ni levels approximately 300-fold above background did not show any systemic tumors (Heim et al., 2007).
   *    The inhalation studies in rats exposed to Ni sulfate and in rats exposed to Ni metal indicated that these compounds did not induce any respiratory tumors. For Ni metal this occurred at blood Ni levels 4 to 6-fold above background and lung Ni levels 3 to 4-fold above background (NTP, 1996a; Oller et al., 2008).
   *    In the case of Ni oxide, a threshold for tumor induction was clearly observed in the rat study (NTP, 1996c).
   *    None of the Ni compounds induced significant tumors in mice even at higher exposure levels than in rats (NTP, 1996a,b,c).
   *    Many epidemiological cohorts did not show excess respiratory cancer risks even though workers were exposed to high levels of Ni. For example ICNCM 1990; Shannon et al., 1984, 1991; Egedahl et al., 2001; Cornell, 1983; Cornell and Landis, 1983; Cox et al.,1981; Enterline and March 1982; Jakobsson et al.,1997; Moulin et al.,1993; Sorahan, 2004; Arena et al., 1998, Cragle et al.,1984; Godbold and Tompkins, 1979; etc.
More specifically, the presence of thresholds for the carcinogenicity of Ni was discussed at a 2010 TERA workshop on Ni ion bioavailability (http://www.tera.org/Peer/NiBioavailability/). This concept was recently accepted by the SCOEL in the derivation of an indicative inhalable OEL of 0.01 mg Ni/m[3] for Ni compounds based on carcinogenicity data in epidemiological studies (SCOEL, 2011).The approach followed in the May [sic] 16[th] Memorandum is not supported by the most recent data and understandings of Ni-related carcinogenicity. The commenter, therefore, urges the EPA to reconsider its risk analysis for Ni emissions from U.S. EGUs and develop a more realistic estimate of the increased risk.
Comment 44: Commenter 17621 states that the EPA assumed that 65% of Ni emissions from liquid-oil-fired EGUs are in the form of insoluble, crystalline species that are as carcinogenic as Ni subsulfide (Ni3S2). According to the commenter, this assumption is overly conservative because recent measurements by EPRI and others found that Ni emissions from residual-oil combustion are primarily soluble Ni sulfate, with lesser amounts of Ni/magnesium oxide and Ni ferrite. No regulatory agency, including the EPA, currently provides a cancer unit risk or other dose-response value for Ni sulfate or other soluble Ni compounds for use in risk assessment. The commenter notes the following studies:
   *    Huggins et al., 2011  -  As study based on 21 PM samples from eight residual oil-fired EGUs determined, using X-ray diffraction (XRD) and X-ray absorption fine structure spectroscopy (XAFS), that Ni in the PM samples was primarily Ni sulfate (NiSO4 :: 6H2O), with lesser amounts of Ni/magnesium oxide [(Ni, Mg)O] and/or Ni ferrite (NiFe2O4). Potentially carcinogenic Ni sulfide compounds were absent, within the detection limits of the methods (+- 3% of total Ni).
   *    EPRI1999  -  Work by the University of Louisville indicated that 3 - 26% of the total Ni emissions were composed of sulfidic forms of Ni. However, it could not be determined whether Ni subsulfide was present due to the limitations of the indirect (i.e., operationally defined) speciation method employed, sequential extraction.
Comment 45: Commenter 17621 states that, to date, soluble Ni compounds, including Ni sulfate, have not demonstrated the ability to induce cancer in either animal bioassays or epidemiological studies (Goodman, 2009; NTP 1996a, TERA, 1999, ). Limited evidence suggests that soluble Ni compounds may promote the carcinogenicity of insoluble Ni compounds as found in Ni refining exposure scenarios (presence of substantial Ni subsulfide). However, the California EPA Office of Environmental Health Hazard Assessment (OEHHA) derived cancer risk estimates for all Ni compounds (soluble and insoluble), but based on evidence from insoluble Ni (subsulfide, Ni refinery exposures) (CalEPA, 2009).
Comment 46: Commenter 17760 states that to determine the real risk from Ni emitted by oil-fired units, it is critical to know what species of Ni are emitted. Ni subsulfide (Ni3S2) is considered the most carcinogenic Ni species. In contrast, inhalation exposure to water soluble Ni salts has not been shown to cause cancer. According to the commenter, the data the EPA had available that showed that 3 to 26% of the Ni species emitted from oil-fired units was sulfidic. Utility Study at 6-7. However, the EPA conservatively assumed in the Utility Study that the Ni emissions from oil-fired units were 50% as carcinogenic as Ni subsulfide.
Comment 47: Commenter 17760 states that the EPA relied on an invalid method of Ni speciation known as "sequential Ni extraction" and therefore the data is not reliable (Galbreath et al., 2003).
Comment 48: Commenter 17760 states that to provide additional data on speciation of Ni, the commenter hired the Energy and Environmental Research Center (EERC) at the University of North Dakota to conduct a fly ash speciation study to better understand the species of Ni emitted by oil-fired EGUs. The EERC study, "Ni Species Emissions Inventory for Oil-Fired Boilers," was submitted to the EPA in the docket for the 2004 proposed NESHAP for EGUs (OAR-2002-0056-0018). The EERC study detected no Ni sulfide or Ni subsulfide in the emissions from the two tested oil-fired units. The detected Ni species were Ni sulfate, Ni oxide and Ni in the form of spinel. Ni sulfate is not a carcinogen (see footnotes 2 and 3). Ni in a spinel form is tightly bound in an iron complex and likely is not bioavailable. According to the commenter, this study strongly suggests that the EPA's assumption regarding the carcinogenicity of the Ni emitted by oil-fired EGUs is incorrect and that the inhalation cancer risks posed by oil-fired units are far closer to zero.
Comment 49: Commenter 17760 states that the Hawaiian Electric Company, Florida Power and Light Company, and National Grid conducted Ni carcinogenicity testing at their respective units. The companies took a total of 21 samples from eight units that combust residual oil. The test results indicated that Ni subsulfide may be present in concentrations ranging from 0 to less than 3%. The results of the studies were peer reviewed and published in Environmental Science & Technology on June 28, 2011.
Comment 50: Commenter 17760 states that the EPA did not conduct its own characterization of the actual speciation data and ignored the available data, instead assuming all insoluble Ni is crystalline and that the upper risk estimate for Ni subsulfide should be applied. According to the commenter, this is unreasonable. The EPA layered assumption upon assumption to develop a risk estimate that has no basis in the actual data.
Comment 51: Commenter 18025 states that the EPA's assumption that 50% of Ni emitted from oil-fired EGUs is carcinogenic greatly overestimates the Ni inhalation cancer risk from oil-fired utilities. Updated studies, including the DOE's final report entitled Ni Species Emission Inventory For Oil-Fired Boilers (2004), have been published evaluating the Ni species that are emitted by residual oil-fired EGUs.
Comment 52: Commenter 18831 states that the EPA's overestimation of the risks posed by oil-fired EGUs, particularly from Ni emissions, was the result of using outdated information. According to the commenter, the EPA received more recent and realistic data regarding the risks posed by Ni emissions from oil-fired units on two occasions: (1) in 2004, industry groups submitted data on Ni speciation in response to the EPA's initial proposal to establish MACT standards for EGUs; and (2) in 2011, industry members submitted data on Ni speciation after completing testing required by the EPA's 2010 ICR. The EPA should rely on this data and if they do not it will result in the imposition of burdensome and unnecessary regulation on EGUs.
Comment 53: Commenter 19622 states that the May [sic] 16 Memorandum's assumption that 65% of total Ni in power plant emissions is present as crystalline Ni subsulfide is overly conservative and not supported by current data. According to the commenter, there is information available on the chemical forms of Ni that are present in power plant emissions and in ambient air (e.g., Huggins et al., 2011; Galbreath et al., 2005; 2003; 2000). In general, two forms of Ni predominate: a water soluble Ni compound (Ni sulfate hexahydrate) and a water insoluble, oxidic, Ni compound (complex Ni oxide containing various amounts of other elements such as Fe and Mg). Importantly, neither Ni subsulfide nor complex oxides containing Ni and Cu are significantly present in power plant emissions. In fact, the most recent and carefully done analysis found that less than 3% of total Ni in particulate samples from oil-fired utility steam-generating units was present as sulfide or subsulfide (Huggins et al., 2011).
Comment 54: Commenter 19622 states that based on data from Germany, Ni subsulfide would at most constitute 8.5% of urban air and 4.5% of air near a steel mill (Füchtjohann et al., 2000). The EU 4[th] Ambient Air Ni Directive (CSTEE, 2001) found that Ni subsulfide would not constitute more than 10% of urban or "hotspot" air. The Directive states: "Also, there are considerable differences in carcinogenic potency among the different Ni species in ambient air, with the most potent sulfidic Ni only constituting up to 10 percent of the sum of Ni species in air as judged from the limited amount of data available." Commenter also notes that in the final version of the Texas Commission on Environmental Quality Development Support Document for Ni and Inorganic Ni Compounds (TCEQ, 2011), the report notes that Ni subsulfide emissions are mainly associated with Ni refining and mining operations. According to ATSDR (2005), there are no Ni refining or mining operations in the U.S. The TCEQ (2011) report further states:"Available information from the 2005 TRI indicates that Texas Ni emissions would predominantly be metallic (e.g., railroad equipment, steel foundries, aircraft engines, metal forging, oil/gas field machinery, plate work), along with soluble Ni (e.g., electric utilities) and Ni oxides (e.g., electric utilities, steel foundries and works, aircraft engines) (personal communications with Dr. Adrianna Oller (Ni Institute), Richard Wilds (Union Tank Car), and Randy Hamilton (TCEQ) 2008)." The report concludes: "Therefore, based on TRI data, Texas Ni emissions are expected to be low in (or per HAP devoid of) sulfidic Ni."
Comment 55: Commenter 12380 states that the absence of Ni sulfides in PM samples from the various commercial oil-burning power plants investigated in this study is significant because sulfidic Ni compounds are generally considered to be the most highly carcinogenic Ni compounds (U.S. EPA, 1998; Sunderam, 1987). According to the commenter, the assumption made by the EPA that the Ni compound mixture emitted from U.S. oil-fired power plants is 50% as carcinogenic as Ni3S2 would appear overly conservative with respect to the findings of this study and should be re-assessed.
Comment 56: Commenter 18020 disagrees with the EPA's assumption that 50% of the Ni emissions from EGUs are in the form of Ni subsulfide, the most carcinogenic species. Current scientific studies show that the actual percentage of emissions in the Ni subsulfide species is essentially zero. Almost all Ni emissions have been shown to be in forms of Ni that basically pose zero inhalation cancer risk; therefore, commenter recommends that the EPA exclude oil-fired units from the rule.
Response to Comments 27 - 56: The EPA disagrees with the commenters' assertion that it is impossible to give an accurate assessment of the risks to human health from Ni emissions from U.S. EGUs, and maintains that its assessment of the potential inhalation risks from EGU emissions of Ni compounds is scientifically valid, reasonable, and based on the best-available current scientific understanding. To that end, in July 2011, the EPA completed an external peer review (using three independent expert reviewers) of the methods used to evaluate the risks from Ni and Cr compounds emitted by EGUs in a report titled, "Methods to Develop Inhalation Cancer Risk Estimates for Cr and Ni Compounds." There were two charge questions relating to Ni in that review. First, do the EPA's judgments related to speciated Ni emissions adequately take into account available speciation data, including recent industry spectrometry studies? Second, based on the speciation information available and what is known about the health effects of Ni and compounds, and taking into account the existing URE values (i.e., values derived by the Integrated Risk Information System (IRIS, 1991) California Department of Health Services (CDHS, 1991); and the Texas Commission on Environmental Quality (TCEQ, Development Support Document, 2011)), which of the following approaches to derive unit risk estimates would result in a more accurate and defensible characterization of risks from exposure to Ni and compounds?
   1. To continue using the same approach as that developed for use in the 2000 NATA, which consists of using the IRIS URE for Ni subsulfide and assuming that Ni subsulfide constitutes 65% of the mass emissions of all Ni compounds.
   2. To consider a more health-protective approach, based on the consistent views of the most authoritative scientific bodies (i.e., NTP in their 12[th] ROC, IARC, and other international agencies) that consider Ni compounds to be carcinogenic as a group.
   3. To make the same assumptions as in option 2, but considering alternative UREs derived by the CDHS or TCEQ
In responding to these peer review questions, two of the reviewers agreed with the views of the most authoritative scientific bodies, which consider Ni compounds carcinogenic as a group. These reviewers, therefore, did not focus on the availability of Ni speciation profile data. The third reviewer recommended that the EPA review several manuscripts on Ni speciation profiles showing that sulfidic Ni compounds (which the reviewer considered as the most potent carcinogens) are present at low levels in emissions from U.S. EGUs.
Ni and Ni compounds have been classified as human carcinogens by national and international scientific bodies including the IARC (1990), the World Health Organization (WHO, 1991), and the European Union's Scientific Committee on Health and Environmental Risks (SCHER, 2006). In their 12th Report of the Carcinogens, the NTP has classified Ni compounds as known to be human carcinogens based on sufficient evidence of carcinogenicity from studies in humans showing associations between exposure to Ni compounds and cancer, and supporting animal and mechanistic data. More specifically, this classification is based on consistent findings of increased risk of cancer in exposed workers, and supporting evidence from experimental animals that shows that exposure to an assortment of Ni compounds by multiple routes causes malignant tumors at various organ sites and in multiple species. The 12[th] Report of the Carcinogens states that the "combined results of epidemiological studies, mechanistic studies, and carcinogenesis studies in rodents support the concept that Ni compounds generate Ni ions in target cells at sites critical for carcinogenesis, thus allowing consideration and evaluation of these compounds as a single group." Although the precise Ni compound (or compounds) responsible for the carcinogenic effects in humans is not always clear, studies indicate that Ni sulfate and the combinations of Ni sulfides and oxides encountered in the Ni refining industries cause cancer in humans. There have been different views on whether or not Ni compounds, as a group, should be considered as carcinogenic to humans. Some authors believe that water soluble Ni, such as Ni sulfate, should not be considered a human carcinogen, based primarily on a negative Ni sulfate 2-year NTP rodent bioassay (which is different than the positive 2-year NTP bioassay for Ni subsulfide).(Oller, 2002; Heller et al., 2011; Goodman et al., 2011) Although these authors agree that the epidemiological data clearly supports an association between Ni and increased cancer risk, they sustain that the data are weakest regarding water soluble Ni. A recent review by Grimsrud and Andersen (2010) highlights the robustness and consistency of the epidemiological evidence across several decades showing associations between exposure to Ni and Ni compounds (including Ni sulfate) and cancer.
Based on the views of the major scientific bodies mentioned above, and those of expert peer reviewers that commented on the EPA's approaches to risk characterization of Ni compounds, the EPA considers all Ni compounds to be carcinogenic as a group and does not consider Ni speciation or Ni solubility to be strong determinants of Ni carcinogenicity. With regard to non-cancer effects, comparative quantitative analysis across Ni compounds indicates that Ni sulfate is as toxic or more toxic than Ni subsulfide or Ni oxide (Haber, 1998; NTP, 1996a).
Regarding the second charge question, two of the reviewers suggested using the URE derived by TCEQ for all Ni compounds as a group, rather than the one derived by IRIS specifically for Ni subsulfide. The third reviewer did not comment on alternative approaches. The EPA decided to continue using 100% of the current IRIS URE for Ni subsulfide because IRIS values are at the top of the hierarchy with respect to the dose response information used in the EPA's risk characterizations, and because of the concerns about the potential carcinogenicity of all forms of Ni raised by the major national and international scientific bodies. Nevertheless, taking into account that there are potential differences in toxicity and/or carcinogenic potential across the different Ni compounds, and given that there have been two URE values derived for exposure to mixtures of Ni compounds that are 2-3 fold lower than the IRIS URE for Ni subsulfide, the EPA also considers it reasonable to use a value that is 50% of the IRIS URE for Ni subsulfide for providing an estimate of the lower end of a plausible range of cancer potency values for different mixtures of Ni compounds.
4. Cr risk.
Commenters: 17774, 17383, 17689, 17877, 17885, 17772 17885
Comment 57: Commenter 17774 states that Cr was the HAP that the EPA identified as exceeding a one in a million cancer risk from 3 out of the 16 facilities in the EPA study. According to the commenter, there are several problems with the EPA's analysis related to the fact that Cr emissions were evaluated as being entirely hexavalent Cr(VI), the carcinogenic form of the heavy metal. While hexavalent Cr is the oxidized form of Cr that is likely to be emitted from coal-fired EGUs, not all of the emitted Cr will remain in the hexavalent form by the time it reaches the target population. Some may be converted to the much less toxic (and noncarcinogenic) trivalent species. The EPA apparently acknowledges the problems of treating all Cr as if it were of the hexavalent species by stating that this approach is being evaluated through a peer review process. Moreover, the level of Cr exposure being contemplated in the EPA's risk assessment is far below that which occurred in the occupational setting. The cancer estimate the EPA derives should, therefore, be looked on with some skepticism due to the uncertainty in extrapolating doses downward to such an extent.
Comment 58: Several commenters (17383, 17689, 17877 and 17885) state that validity concerns with the chronic inhalation study by the EPA included (1) the use of surrogate speciated Cr emissions data instead of actual emissions data, (2) the assumption that units were run 100% of the time which is impossible, (3) dispersion modeling was used that is biased towards over-predicting downwind impacts, and (4) estimated ambient concentrations were utilized as substitutes for real exposure concentrations for all people within a census block.
Comment 59: Commenter 17772 states that none of the 4 out of 16 coal-fired units that posed a risk greater than one in a million were actually tested for Cr(VI). Instead, these four facilities were tested for Cr compounds and a previous study that included four coal-fired boilers was used to make the unsupported assumption that 12% of the Cr will be Cr(VI) and the remaining 88% will be trivalent Cr or Cr(III) for every coal-fired unit. According to the commenter, the EPA failed to recognize that CR(VI) is highly water soluble and is easily reduced to Cr(III) in the presence of SO2 in a low pH environment. The resulting Cr(III)would be expected to precipitate out in a FGD. The actual amount of Cr(VI) that would be present in the emissions from an EGU with a wet scrubber is likely to be far lower than the 12% estimate made by the EPA.
Comment 60: Commenter 17855 states that the EPA conducted a health risk assessment on a limited number of facilities and found a "few" facilities that have estimated maximum cancer risks in excess of one in a million for Ni or hexavalent Cr. According to the commenter, the Northern Star's Cambria Cogen was one of the plants included in the assessment and had a calculated maximum cancer risk of 0.5 per million for hexavalent Cr. None of the facilities selected had a non-cancer impact exceeding a hazard index of 1 for any HAP. Cambria Cogen had a maximum hazard index of 0.003 for Ni. Based on this limited health risk assessment, EPA apparently decided that they were justified to regulate all non-Hg HAP for all sources in this category. For Cambria Cogen and other similar waste coal power plants, this means the imposition of potentially costly emission controls or facilities that do not have a significant public health risk according to the EPA criteria.