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## Supplement to the Non**- Hg Case Study Chronic Inhalation Risk Assessment**  **for the Utility MACT “Appropriate and Necessary” Analysis**

**Office of Air Quality Planning and Standards U.S. Environmental Protection Agency**  **Research Triangle Park, NC 27711** 

**November 1, 2011**

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Introduction A previous document 1 

### discussed the methods and results of the chronic inhalation risk assessment of hazardous air pollutants (HAPs) other than mercury from coal- and oil- fired electric utility

steam generating units (EGUs) at s ixteen case study facilities, which was performed in support of the “appropriate and necessary” finding for coal- and oil- fired EGUs . Several changes were made to the emissions estimates, dispersion modeling, and risk characterization of these facilities in response to public comments on the proposed rule , and this report documents those changes and their impact on the estimated risks from the case study facilities. 1. Emissions In response to comments on the proposed rule, the emissions data used in the case studies were updated for several facilities in two ways. First, in response to comments that EPA’s methodology

was not sufficiently refined, EPA us ed year- specific heat input for the modeled ye ars 2005 through 2009, rather than the average 2007 -2009 heat input for all years. Second, in response to comments that EPA’s approach to emission factor development should use outlier tests, EPA revised its c alculations for emission factors to apply to those units that had not been tested in the ICR. Only the arsenic, chromium, and nickel emissions were recomputed for use in modeling because these pollutants were the key risk drivers for the case studies. Both of these updates were made only to the case study facilities that had estimated cancer risks near 1 in a million at proposal . The subsections below provide more information on these updates. In addition, the detailed calculations for the case study emissions at the unit level are provided in the spreadsheet “Case_Study _Emis_MATS_Final.xlsx , ” which is included in the docket (EPAHQ - OAR-2009 - 0234 -2939 ) . 1.1 Unit- Level Annual H eat Input The preferred source of unit- level annual heat input data was EPA’s Clean Air Markets continuous emission monitoring (CEM) program. Unit- level annual heat input data for calendar ye ars 2002 -2010 were obtained for all units that report these data to EPA. Heat input data are important because emissions are proportional to heat input. The only facility without CEM data was the HECO Waiau facility (ORIS 766). This facility was contacted directly

to obtain actual unit- specific annual heat input data. The year- specific heat input data used for the final rule are an improvement over the approach used at proposal, which used a multi -ye ar average heat input for each modeled ye ar. Table 1 provides the total facility- level heat input for each ye ar, as well as the average value. While the average value was not used for any calculations, it is provided for comparison to the value used at proposal. For three of the case study facilities remodeled for the final rule, the revised heat input is higher (Amerenue - Labadie, 0.3%; James River, 2.5%; and Conesville, 24%). For the rest of the facilities, the heat input is lower (Dominion

– Yorktown, 12%; Chesapeake Energy

Center, 8.8%, Heco Waiau, 2.5%; OG &E

– Muskogee, 8.6%; PSHNH

– 1 Non-Hg Case Study Chronic Inhalation Risk Assessment for the Utility MACT “Appropriate and Necessary” Analysis , March 16, 2011. Docket ID No. EPA-HQ - OAR-2009 - 0234 -2939. Available at www.regulations.gov.

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Merrimack, 16%; and TVA Gallatin, 3.2%). While these facility- level changes give some indication of the impact on risk, because each unit at a facility can contribute differently to the risk, the unit- level heat input changes can give a somewhat different view of the changes. These unit- level changes are available in the case study emissions spreadsheet discuss ed above . **Table 1: Final case study heat input (MMBtu) compared to heat input used at proposal .**  **Facility 2005**  **2006 2007**  **2008 2009**  **Average Propos**  **ed Rule**  Amerenue Labadie 168,514,660 170,157,435 182,401,603 165,591,139 166,226,274 170,578,222 171,126,775 City Utilities of Springfield - James River 16,452,496 15,943,500 13,610,535 15,181,310 11,968,020 14,631,172 14,997,208 Conesville 96,719,546 92,193,174 108,230,769 100,770,581 66,087,859 92,800,386 115,092,253 Dominion - Yorktown 40,366,974 21,700,400 29,638,959 22,409,846 19,286,905 26,680,617 23,447,200 Dominion Chesapeake Energy Center 41,070,023 37,711,371 40,777,823 36,222,677 35,255,050 38,207,389 34,853,246 Heco Waiau 14,673,660 14,397,785 14,935,405 13,320,107 14,884,983 14,442,388 14,080,684 OG&E - Muskogee 106,454,236 104,916,428 87,737,665 104,566,459 92,434,936 99,221,945 90,739,465 PSHNH - Merrimack 34,045,565 34,410,607 36,317,955 30,332,534 25,319,652 32,085,263 26,821,184 TVA Gallatin 73,113,053 74,908,225 77,474,644 79,699,781 64,123,359 73,863,812 71,515,151 

### 1.2 Development of Emission Factors For several of the case study facilities, emission factors were used as the best available alternative source of emissions information because appropriate facility- specific stack test data were not available to compute emissions. The case study facilities using emission factors that were not based on site- specific stack test data are Conesville (3% of the risk driver emissions), PSHNH

– Merrimack (35%), and all risk driver emissions at Chesapeake Bay Energy Center, Dominion

– Yorktown, OG&E

– Muskogee, and Amerenue - Labadie. The risk driver emissions are those emissions that contributed the most to the total facility risk. The emission f

actors used in these cases were recalculated based on revised methods that had not been used at the time of proposal , including the use of well- established, robust outlier checks (Dixon or Rosner tests) , depending on the number of values and when more than three values were evaluated. The complete documentation for the arsenic, chromium, and nickel emission factors is available in the docket in separate documents: Coal_Fired_Utility _Boiler_Arsenic.pdf

, Coal_Fired_Utility

_Boiler_Chromium.pdf

, and Coal_Fired_Utility

_Boiler_Nickel.pdf

. The same hexavalent chromium percentages of total chromium used at proposal were used for the final rule analysis ( 12% for coal units and 18% for oil units) .

### 4

1.3 Emissions Estimates Tables 2 through 4 give the estimated emissions for the facilities remodeled. These emissions estimates reflect the changes in heat inputs and emission factors described above. While the average values shown were not used in the modeling (the year- specific values were used), they

are provided for comparison to the emissions values used at proposal. The detailed calculations and unit- level emissions are available in the case study emissions spreadsheet . **Table 2: Final**  **case study arsenic emissions (tons/year) compared to emissions used at proposal** **. Facility**  **2005 2006**  **2007 2008**  **2009 Average**  **Proposed Rule**  Amerenue - Labadie 1.05E+00 1.06E+00 1.14E+00 1.03E+00 1.04E+00 1.07E+00 1.72E+00 City Utilities of Springfield

-James River 1.96E - 02 1.90E - 02 1.63E - 02 1.82E - 02 1.43E - 02 1.75E - 02 1.78E -02 Conesville 1.65E - 01 1.46E - 01 1.76E - 01 1.76E - 01 1.13E - 01 1.55E - 01 3.26E -01 Dominion - Yorktown 2.29E - 01 1.32E - 01 1.73E - 01 1.35E - 01 1.17E - 01 1.57E - 01 2.09E -01 Dominion Chesapeake Energy Center 2.57E - 01 2.36E - 01 2.55E - 01 2.26E - 01 2.20E - 01 2.39E - 01 3.46E -01 Heco Waiau 2.53E - 02 2.50E - 02 2.56E - 02 2.30E - 02 2.57E - 02 2.49E - 02 2.46E -02 OG&E - Muskogee 6.65E - 01 6.56E - 01 5.48E - 01 6.54E - 01 5.78E - 01 6.20E - 01 9.11E -01 PSHNH - Merrimack 2.76E - 01 2.79E - 01 2.94E - 01 2.46E - 01 2.05E - 01 2.60E - 01 2.33E -01 TVA Gallatin 1.45E - 02 1.49E - 02 1.54E - 02 1.58E - 02 1.27E - 02 1.47E - 02 1.42E -02 

### Table 3: Final case study hexavalent chromium emissions (tons/year) compared to **emissions used at proposal .**  **Facility 2005**  **2006 2007**  **2008 2009**  **Average Proposed**  **Rule** Amerenue - Labadie 4.94E - 01 4.99E - 01 5.35E - 01 4.86E - 01 4.88E - 01 5.00E - 01 5.77E -01 City Utilities of Springfield

-James River 5.55E - 01 5.42E - 01 4.66E - 01 5.24E - 01 4.13E - 01 5.00E - 01 4.99E -01 Conesville 4.06E - 01 2.85E - 01 3.77E - 01 4.53E - 01 2.74E - 01 3.59E - 01 6.74E -01 Dominion - Yorktown 1.51E+00 2.84E - 01 7.78E - 01 3.67E - 01 2.51E - 01 6.37E - 01 4.25E -01 Dominion Chesapeake Energy Center 1.20E - 01 1.11E - 01 1.20E - 01 1.06E - 01 1.03E - 01 1.12E - 01 1.27E -01 Heco Waiau 2.86E - 03 2.89E - 03 2.86E - 03 2.60E - 03 2.91E - 03 2.82E - 03 2.87E -03 OG&E - Muskogee 3.12E - 01 3.08E - 01 2.57E - 01 3.07E - 01 2.71E - 01 2.91E - 01 3.06E -01 PSHNH - Merrimack 3.69E - 02 3.73E - 02 3.94E - 02 3.29E - 02 2.75E - 02 3.48E - 02 4.77E -02 TVA Gallatin 1.16E+00 1.19E+00 1.23E+00 1.27E+00 1.02E+00 1.17E+00 1.14E+00

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**Table 4: Final case study nickel emissions (tons/year) compared to emissions used at proposal** **. Facility**  **2005 2006**  **2007 2008**  **2009 Average**  **Proposed Rule**  Amerenue - Labadie 2.31E+00 2.33E+00 2.50E+00 2.27E+00 2.28E+00 2.34E+00 4.21E+00 City Utilities of Springfield

-James River 3.36E+00 3.27E+00 2.80E+00 3.15E+00 2.48E+00 3.01E+00 3.03E+00 Conesville 3.26E+00 2.59E+00 3.25E+00 3.55E+00 2.21E+00 2.97E+00 3.95E+00 Dominion - Yorktown 7.26E+01 1.18E+01 3.63E+01 1.59E+01 1.04E+01 2.94E+01 1.84E+01 Dominion Chesapeake Energy Center 5.63E - 01 5.17E - 01 5.59E - 01 4.96E - 01 4.83E - 01 5.23E - 01 8.89E -01 Heco Waiau 3.96E+00 3.93E+00 4.01E+00 3.60E+00 4.02E+00 3.90E+00 3.87E+00 OG&E - Muskogee 1.46E+00 1.44E+00 1.20E+00 1.43E+00 1.27E+00 1.36E+00 2.23E+00 PSHNH - Merrimack 1.55E - 01 1.56E - 01 1.65E - 01 1.38E - 01 1.15E - 01 1.46E - 01 2.85E -01 TVA Gallatin 5.48E+00 5.61E+00 5.80E+00 5.97E+00 4.80E+00 5.53E+00 5.35E+00 

### Annual emissions estimates for all case study facilities are given in Table 5, including estimates for facilities that have been revised as discussed above, and the same estimates used at the time of proposal for facilities without revised emissions estimates .

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**Table 5. Case s** **tudy a** **verage a** **nnual e**  **missions (2005** **- 2009)**  **.**

**Facility Location**  **Unit Type Unit ID**  **As (TPY) Cr** **+6** 

### (TPY) **Ni (TPY)** Xcel Bayfront Ashland, WI 1 coal 5 Cambria Cogen Ebensburg, PA 2 coal B1 1.00E -03 3.60E -02 2.20E -01 B2 1.10E -03 7.80E -03 7.20E -02 SC&E Canadys Canadys, SC 3 coal CAN001 5.10E -02 1.90E -02 1.30E -01 CAN002 4.90E -02 1.80E -02 1.30E -01 CAN003 2.20E -02 2.40E -03 9.60E -02 Dominion Chesapeake Energy Center* Chesapeake, VA 4 coal Unit 1 4.1E -02 1.9E -02 8.9E -02 Unit 2 4.4E -02 2.1E -02 9.6E -02 Unit 3 6.5E -02 3.0E -02 1.4E -01 Unit 4 9.0E -02 4.2E -02 2.0E -01 Conesville* Conesville, OH 4 coal 3 4.6E -02 3.3E -01 1.8E+00 4 4.7E -02 1.1E -02 5.1E -01 5 3.2E -02 7.2E -03 3.5E -01 6 3.0E -02 6.9E -03 3.3E -01 Exelon Cromby Generating Station Phoenixville, PA 1 coal Unit 1 6.60E -02 3.00E -03 1.80E -02 1 oil Unit 2 2.40E -03 6.00E -04 3.40E -01 TVA Gallatin* Gallatin, TN 4 coal 1 3.5E -03 2.8E -01 1.3E+00 2 3.4E -03 2.8E -01 1.3E+00 3 3.9E -03 3.2E -01 1.5E+00 4 3.8E -03 3.1E -01 1.4E+00 City Utilities of Springfield -James River* Springfield, MO 3 coal 3 3.9E -03 1.0E -01 6.3E -01 4 4.2E -03 3.8E -02 4.1E -01 5 9.4E -03 3.6E -01 2.0E+00 Amerenue - Labadie* Labadie, MO 4 coal 1 2.4E -01 1.1E -01 5.4E -01 2 2.7E -01 1.3E -01 5.9E -01 3 2.7E -01 1.3E -01 6.0E -01 4 2.8E -01 1.3E -01 6.1E -01 PSHNH – Merrimack* Bow, NH 2 coal 1 7.8E -02 1.0E -02 4.4E -02 2 1.8E -01 2.4E -02 1.0E -01 Monticello Steam Electric Plant Mount Pleasant, TX 3 coal 1 6.10E -02 1.16E -01 4.10E -01 2 6.20E -02 1.17E -01 4.10E -01

### 7 **Facility Location**  **Unit Type Unit ID**  **As (TPY) Cr** **+6** 

### (TPY) **Ni (TPY)** 3 1.10E -01 1.98E -02 1.70E -01 OG&E – Muskogee* Fort Gibson, OK 3 coal 4 2.0E -01 9.5E -02 4.4E -01 5 2.0E -01 9.3E -02 4.4E -01 6 2.2E -01 1.0E -01 4.8E -01 Spruance Genco Richmond, VA 8 coal GEN1 8.40E -04 3.10E -04 2.40E -03 GEN2 9.00E -04 3.20E -04 8.30E -03 GEN3 3.50E -03 5.60E -04 6.20E -03 GEN4 2.40E -03 3.60E -04 4.10E -03 PSI Energy – Wabash River West Terre Haute, IN 1 coal -gas PG7221FA 1.30E -03 7.50E -04 5.00E -03 2 coal 4 1.10E -01 4.50E -03 4.10E -02

6 3.30E -01 1.40E -02 1.20E -01

Heco Waiau* Waiau, HI 6 oil W3 2.0E -03 2.1E -04 3.2E -01 W4 2.0E -03 2.1E -04 3.0E -01 W5 2.8E -03 2.9E -04 4.3E -01 W6 2.1E -03 1.2E -04 3.2E -01 W7 8.5E -03 1.2E -03 1.4E+00 W8 7.5E -03 7.9E -04 1.2E+00 Dominion – Yorktown* Yorktown, VA 2 coal Units 1&2 1.2E -01 5.6E -02 2.6E -01 1 oil Unit 3 3.9E -02 5.8E -01 2.9E+01 

### * Facility was remodeled for the final rule. Facilities not remodeled for the final rule have the same annual emissions estimate for each year.

### 8

2 . Dispersion Modeling The methodology

used for dispersion modeling of the case study facilities was discussed in more detail in the previous document. 2 

### The modeling was done using AERMOD , EPA’s preferred model for near- field dispersion. Table 6 provides the model scenario information used for the case study facilities . This information is unchanged from the proposed rule . Table 7 provides the stack parameters used for the final rule modeling. **Table 6**  **. Model s**  **cenario i** **nformation** . **Facility Downwash**  **Urban/rural (population)**  **Surface station Upper air station**  Xcel Bayfront No Rural Ashland Kennedy Memorial Airport, WI Minneapolis, MN Cambria Cogen Yes Rural Johnstown Cambria County Airport, PA Pittsburgh, PA SC&E Canadys No Rural Charleston Intl. Airport, SC Charleston Intl.

Airport, SC Dominion Chesapeake Energy Center * No Urban (200,000) Norfolk Intl. Airport, VA Washington Dulles,

VA Conesville * No Rural Zanesville Municipal Airport, OH Wilmington, OH Exelon Cromby Generating Station No Rural Philadelphia Intl. Airport, PA Washington Dulles, VA TVA Gallatin * No Rural Nashville Intl. Airport, TN Nashville Intl.

Airport, TN City Utilities of Springfield -James River * No Rural Springfield Regional Airport, MO Springfield Regional

Airport, MO Amerenue - Labadie * No Rural St. Louis Lambert Intl. Airport, MO Lincoln, IL PSHNH – Merrimack * No Rural Concord Municipal Airport, NH Albany, NY Monticello Steam Electric Plant No Rural Tyler Pounds Field, TX Shreveport, LA OG&E – Muskogee * No Rural Muskogee Davis Field, OK Norman, OK Spruance Genco No Urban (200,000) Richmond Intl. Airport, VA Washington Dulles,

VA PSI Energy – Wabash River No Rural Terre Haute Hulman Regional Airport ,IN Wilmington, OH Heco Waiau * Yes Urban (300,000) Honolulu Intl Airport, HI Lihue, HI Dominion – Yorktown * Yes Rural Newport News Intl. Airport, VA Washington Dulles, VA 

### * Facility was remodeled for the final rule. 2 Non-Hg Case Study Chronic Inhalation Risk Assessment for the Utility MACT “Appropriate and Necessary” Analysis , March 16, 2011. Docket ID No. EPA-HQ - OAR-2009 - 0234 -2939. Available at www.regulations.gov.

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**Table 7. Stack p**  **arameter d**  **ata.**

**Facility Location**  **Unit Type Unit ID**  **Lat Long**  **Stack Height (m)**  **Stack**

**Temperature (K)**  **Stack**

**Velocity (m/s)**  **Stack**

**Diameter (m)**  Xcel Bayfront Ashland, WI 1 coal 5 46.5872 - 90.9018 59.44 371.48 13.05 1.86 Cambria Cogen Ebensburg, PA 2 coal B1 40.4748 - 78.703 70.10 466.48 27.83 2.29 B2 40.4748 - 78.703 70.10 466.48 27.83 2.29 SC&E Canadys Canadys, SC 3 coal CAN001 33.0646 - 80.6235 60.96 415.37 11.00 4.88 CAN002 33.0653 - 80.6232 60.96 412.04 12.62 4.88 CAN003 33.065 - 80.6218 60.96 413.71 19.93 4.88 Dominion Chesapeake Energy Center* Chesapeake, VA 4 coal Unit 1 36.7705 - 76.3012 53.34 430.35 17.37 3.97 Unit 2 36.7706 - 76.3011 53.34 429.25 17.37 3.97 Unit 3 36.7709 - 76.3009 60.96 407.05 17.98 3.97 Unit 4 36.7712 - 76.3008 60.96 427.05 21.34 4.27 Conesville* Conesville, OH 4 coal 3 40.1648 - 81.9044 137.16 416.48 10.31 5.33 4 40.1862 - 81.8787 243.84 416.48 25.30 7.93 5 40.1856 - 81.8798 243.84 324.82 23.90 7.93 6 40.1856 - 81.8798 243.84 324.82 23.90 7.93 Exelon Cromby Generating Station Phoenixville, PA 1 coal Unit 1 40.1524 - 75.5303 91.44 388.71 17.92 4.27 1 oil Unit 2 40.152 - 75.5304 91.44 388.71 17.11 4.27 TVA Gallatin* Gallatin, TN 4 coal 1 36.3156 - 86.4005 152.70 406.48 17.07 7.62 2 36.3156 - 86.4005 152.70 406.48 17.07 7.62 3 36.3151 - 86.4009 153.01 395.37 18.90 7.62 4 36.3151 - 86.4009 153.01 395.37 18.90 7.62 City Utilities of Springfield - James River* Springfield, MO 3 coal 3 37.1084 - 93.2602 60.96 427.59 9.45 3.65 4 37.1084 - 93.2598 60.96 427.59 10.06 3.65 5 37.1084 - 93.2605 106.68 433.15 27.70 3.12 Amerenue Labadie* Labadie, MO 4 coal 1 38.5626 - 90.8381 213.36 436.21 32.66 6.25 2 38.5621 - 90.8377 213.36 424.21 30.32 6.25 3 38.5614 - 90.8371 213.36 413.54 31.96 6.25 4 38.5614 - 90.8371 213.40 446.93 34.83 6.25 PSHNH – Merrimack* Bow, NH 2 coal 1 43.142 - 71.4685 68.58 391.48 41.98 2.62 2 43.1418 - 71.4682 96.62 422.04 36.92 4.42

### 10 **Facility Location**  **Unit Type Unit ID**  **Lat Long**  **Stack Height (m)**  **Stack**

**Temperature (K)**  **Stack**

**Velocity (m/s)**  **Stack**

**Diameter (m)**  Monticello Steam Electric Plant Mount Pleasant,

TX 3 coal 1 33.0907 - 95.0375 121.92 453.15 24.69 6.55 2 33.0914 - 95.038 121.92 453.15 24.69 6.55 3 33.0923 - 95.0378 140.21 354.26 26.52 2.44 OG&E – Muskogee* Fort Gibson, OK 3 coal 4 35.7618 - 95.2886 106.68 402.04 14.02 7.31 5 35.7619 - 95.288 106.68 402.04 14.02 7.31 6 35.7621 - 95.2872 152.40 402.04 25.13 6.55 Spruance Genco Richmond, VA 8 coal GEN1 37.4552 - 77.4312 76.20 355.37 17.03 2.62 GEN2 37.4555 - 77.4309 76.20 355.37 17.03 2.62 GEN3 37.4557 - 77.4307 76.20 355.37 17.03 2.62 GEN4 37.4559 - 77.4304 76.20 355.37 17.03 2.62 PSI Energy – Wabash River West Terre

Haute, IN 1 coal -gas PG7221FA 39.5303 - 87.4256 68.58 452.59 19.17 5.49

2 coal 4 39.5274 - 87.4232 137.16 410.93 34.26 7.62

6 39.5274 - 87.4232 137.16 410.93 34.26 7.62

Heco Waiau* Waiau, HI 6 oil W3 21.3891 - 157.9615 42.09 469.26 12.25 3.05 W4 21.389 - 157.9613 42.09 469.26 12.25 3.05 W5 21.3888 - 157.9612 41.91 414.26 12.25 2.74 W6 21.3887 - 157.961 41.91 414.26 12.25 2.74 W7 21.3885 - 157.9606 41.91 392.04 16.12 3.20 W8 21.3884 - 157.9603 41.91 392.04 16.12 3.20 Dominion – Yorktown* Yorktown, VA 2 coal Units 1&2 37.2154 - 76.4622 98.80 417.35 22.60 4.90 1 oil Unit 3 37.2152 - 76.4612 149.05 415.93 33.52 6.86 

### * Facility was remodeled for the final rule.

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The list below discusses the inputs used in the modeling of the case study facilities for the final rule, and notes where there were differences compared to the proposed rule . 1. Each boiler or combination of boilers was modeled as an individual emission point in AERMOD , unchanged from the proposed rule analysis . 2. Hourly

emissions for 2005 -2009 were modeled explicitly for each emission point for arsenic, chromium (VI) , and nickel. Five -ye ar average concentrations were calculated within AERMOD. For the propos ed rule analys is, a unit emission rate ( 1 gram per second ) was used, and the resulting hourly concentrations were scaled using hourly heat input values to derive pollutant- specific 5 -ye ar average conc entrations calculated outside of AERMOD. This methodology difference does not change the concentration estimates. 3. Building parameterization and surface characteristics were unchanged from the propos ed rule analys is . 4. Some stack parameters changed bec ause of new data received during the public comment period. 5 . Current versions of AERMI NUTE (11059) and AERMET (11059) were used, and the meteorological data used for the proposed rule analysis were reprocessed using the se versions . B eta versions of AERMINUTE and AERMET were used for the proposed rule analys is . 6 . Receptor locations (Census blocks within 20 km of the source) were unchanged from the proposed rule analys is . The current version of AERMAP (11103) was used to calculate source and receptor elevations , whereas version 09040 was used for the proposed rule analys is . 7 . The current version of AERMOD (11103) was used . A beta version of AERMOD was used for the proposed rule analys is . As noted above, updated versions of AERMAP, AERMI NUTE, AERMET, and AERMOD were used in the modeling of the case study facilities for the final rule . The changes between versions 09040 and 11103 of AERMAP resulted in no differences in elevations of sources and receptors. The meteorological data used for the propos ed rule were reprocessed using versions 11059 of AERMINUTE and AERMET , and processed along with the proposal emission inputs in version 11103 of AERMOD to compare differences due to AERMET and AERMOD changes . The differences in the modeled concentrations were insignificant between the beta and current versions of AERMET and AERMOD. 3 . Chronic Inhalation Risk Assessment F or chronic inhalation exposures, we used the 5 -year average ambient concentrations of HAP estimated from the refined dispersion modeling. The estimated ambient concentration at each nearby census block centroid was used as a surrogate for the chronic inhalation exposure concentration for all the people who reside in that census block. We assessed non- cancer health effects from chronic exposures by comparing the chronic inhalation exposure concentration to the Reference Concentration values. We calculated the maximum individual risk, or MIR, for each facility

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 -ye ar period) exposure to the maximum concentration at the centroid of an inhabited census block. Individual cancer risks were calculated by multiplying

### 12

the estimated lifetime exposure to the ambient concentration of each HAP (in micrograms per cubic meter) by its cancer unit risk estimate (URE), which is an upper bound estimate of an individual's probability

of contracting cancer over a lifetime of exposure to a concentration of 1 microgram of the pollutant per cubic meter of air. We used URE values for arsenic and hexavalent chromium from EPA’s Integrated Risk Information System (IRI S), which is a human health assessment program that evaluates quantitative and qualitative risk information on effects that may result from exposure to environmental contaminants. Unit risk estimates in IRIS have undergone both internal and external peer review. In the preamble to the proposed rule , we discussed the reasons for using 65% of the IRIS URE for nickel subsulfide for all nickel compounds. InJuly 2011, we completed an external peer review (using three independent expert reviewers) of the methods used to evaluate the risks from nickel compounds emitted by EGUs in a report titled, “Methods to Develop Inhalation Cancer Risk Estimates for Chromium and Nickel Compounds . ” 3 

### Based on the views of major scientific bodies such as the International Agency for Research on Cancer (IARC) , the World Health Organization (WHO), and the European Union’s Scientific Committee on Health and Environmental Risks (SCHER), and those of the expert peer reviewers who commented on our approaches to risk characterization of nickel compounds, we consider all nickel compounds to be carcinogenic as a group and do not consider nickel speciation or nickel solubility to be strong determinants of nickel carcinogenicity. Based on this review, we decided to use 100 percent of the current IRIS URE for nickel subsulfide, rather than assuming that 65 percent of the total mass of emitted nickel might be nickel subsulfide, as used in previous analys es. We used the IRIS URE value because IRIS values are ty

pically preferred for use in HAP risk assessments performed in support of air toxics regulations under the Clean Air Act . 4 

### The IRIS values are preferred because they are developed in accordance with EPA risk assessment guidelines and because of the level of peer review IRIS values receive. We used 100 percent of the IRIS value because of the concerns about the potential carcinogenicity

of all forms of nickel raised by the major national and international scientific bodies. Nevertheless, taking into account that there are p otential differences in toxicity and/or carcinogenic potential across the different nickel compounds, and given that there have been two URE values derived for exposure to mixtures of nickel compounds that are 2 - 3 fold lower than the IRIS URE for nickel su bsulfide 5 

### , the EPA also considers it reasonable to use a value that is 50 percent of the IRIS URE for nickel subsulfide for providing an estimate of the lower end of a plausible range of cancer potency values for different mixtures of nickel compounds . The health reference values used in the assessment are given in Table 8 . **Table 8**  **. Health r** **eference v** **alues u**  **sed in the a** **ssessment.** 3 Mercury and Air Toxics Standards Rule Docket, ID No. EPA-HQ - OAR-2009 - 0234. Available at www .regulations.gov. 4 http://www.epa.gov/ttn/atw/toxsource/chronicpriority.html 5 Two UREs (other than the current IRIS values) have been derived for nickel compounds: one developed by the California Department of Health Services (http://www.arb.ca.gov/toxic s/id/summary/nickel_tech_b.pdf ) and the other by the Texas Commission on Environmental Quality (http://www.epa.gov/ttn/atw/nata1999/99pdfs/healtheffectsinfo.pdf ).

### 13

**Pollutant CAS Number**  **URE (1/μg/m3)**  **Source RfC**  **(mg/m 3**  

### ) **Source** Arsenic 7440382 4.3E -03 IRIS 0.000015 CalEPA Chromium (VI) 18540299 0.012 IRIS 0.0001 IRIS Nickel 7440020 0.00048 IRIS 0.00009 CalEPA HCl 7647010 0.02 IRIS 

### 3. Results . The results of the assessment are given in Table 9 . Based on estimated actual emissions, the highest estimated lifetime cancer risk from any of the sixteen case study facilities was 20 in a million, driven by

nickel emissions from the one case study facility with only oil- fired EGUs. For the facilities with coal- fired EGUs, there were five with maximum cancer risks greater than 1 in a million (the highest was five in a million), four driven by hexavalent chromium, and one driven by nickel from an oil- fired EGU . There were also two facilities with coal- fired EGUs with cancer risks at 1 in a million. All of the facilities had non- cancer target- organ- specific hazard index (HI) values less than one, with a maximum HI value of 0.4 (also driven by nickel emissions from the one case study facility with only oil- fired EGUs). The cancer risk estimates from this assessment indicate that the EGU source category would not be eligible for delisting under section 112(c)(9)(B)(i) of the CAA, which specifies that a category

may be delisted only

when the Administrator determines “... that no source in the category (or group of sources in the case of area sources) emits such hazardous air pollutants in quantities which may

cause a lifetime risk of cancer greater than one in one million to the individual in the population who is most exposed to emissions of such pollutants from the source....” We note that, since these case studies do not cover all facilities in the category, and since our assessment does not include the potential for impacts from different EGU facilities to overlap one another (i.e., these case studies only look at facilities in isolation), the maximum risk estimates from the case studies may underestimate true maximum risks.

### 14

**Table 9**  **. Chronic**  **i nhalation**  **r isk**  **a ssessment**  **r esults.**  **Facility Proposed Rule Assessment**  **Final Rule Assessment**

**Max Risk**  **Risk Driver Max HI**  **HI Driver**  **Max**

**risk Risk Driver**  **Max HI**  **HI Driver**  Xcel Bayfront 4.0x10 - 9 Formaldehyde 0.005 HCl Not Remodeled Cambria Cogen 5.0x10 - 7 Chromium VI 0.003 Nickel Not Remodeled SC&E Canadys 6.0x10 - 7 Arsenic 0.009 HCl Not Remodeled Dominion Chesapeake Energy Center 3.0x10 - 6 Chromium VI 0.05 HCl 2x10 - 6 Chromium VI 0.0 5 a HCl a Conesville 3.0x10 - 6 Chromium VI 0.01 Nickel 2x10 - 6 Chromium VI 0.008 Nickel Exelon Cromby Generating Station 3.0x10 - 7 Arsenic 0.008 Nickel Not Remodeled TVA Gallatin 1.0x10 - 6 Chromium VI 0.006 Nickel 2x10 - 6 Chromium VI 0.007 Nickel City Utilities of Springfield - James River 8.0x10 - 6 Chromium VI 0.04 Nickel 5x10 - 6 Chromium VI 0.03 Nickel Amerenue Labadie 8.0x10 - 7 Arsenic 0.006 Arsenic 7x10 - 7 Chromium VI 0.004 Arsenic PSHNH - Merrimack 1.0x10 - 6 Arsenic 0.01 Arsenic 1x10 - 6 Arsenic 0.01 Arsenic Monticello Steam Electric Plant 6.0x10 - 7 Chromium VI 0.003 Arsenic Not Remodeled OG&E - Muskogee 1.0x10 - 6 Arsenic 0.01 Arsenic 1x10 - 6 Chromium VI 0.008 Arsenic Spruance Genco 8.0x10 - 8 Arsenic 0.007 HCl Not Remodeled PSI Energy – Wabash River 1.0x10 - 7 Arsenic 0.001 Arsenic Not Remodeled Heco Waiau 1.0x10 - 5 Nickel 0.4 Nickel 2x10 - 5 b Nickel 0.4 Nickel Dominion - Yorktown 1.0x10 - 6 Chromium VI 0.02 Nickel 2x10 - 6 b Nickel 0.03 Nickel a Although HCl was not included in the remodeling of this facility, HCl was the HI driver pollutant at proposal, and this is carried through for the final rule assessment . b Based on considering the emitted nickel to be 100% as potent a carcinogen as pure nickel subsulfide ; if we consider the emitted nickel to be 50% as potent a carcinogen as nickel subsulfide (see text), estimated risks would be 1x10 - 5 for Heco Waiau and 1x10 - 6 for Dominion - Yorktown .