# Appendix 11.2

Holcomb Class I Visibility Modeling Report

## Visibility Impact Modeling Results

Holcomb Station Expansion

prepared for:

Sunflower Electric Power Corporation

Hays, Kansas

for submission to: Kansas Department of Health & Environment

prepared by:

HDR Engineering, Inc. 701 Xenia Ave. South, Suite 600 Minneapolis, MN 55416 (763)-591-5452

Attn: Ed Liebsch

Ed.Liebsch@hdrinc.com

June 8, 2007Holcomb Station Expn., Visibility Results 1 June 8, 2007 

### Visibility Impact Modeling Results Holcomb Station Expansion

1.0 INTRODUCTION

This report briefly summarizes the results of Class I area dispersion modeling for the proposed expansion of Holcomb Station, located in western Ka nsas, west of Garden City. The proposed expansion would consist of two nominal 700 MW elect ric generating units and support equipment. Holcomb Station currently has one nomin al 360 MW electric generating unit, with air emission controls consisting of lo-NO X burners for nitrogen oxide (NO X ) control, a lime spray dryer (dry scrubber) for sulfur dioxide (SO 2 ) control and a fabric filter (baghouse) for parti culate matter control. The proposed new units at the site would use state-of-the-art emission controls to

minimize NO X , SO 2 and other acid gases, particulate matter, and merc ury.

The analysis presented in this report was requested by the Kansas Department of Health & Environment (KDHE), which is the agency responsible for issuance of a construction (Prevention of Significant Deterioration) air permit, in consul tation with US Environmental Protection Agency (EPA) Region 7 staff, and US Fish & Wildlife Service (FWS) staff.

EPA’s New Source Review (NSR) guidance (DRAFT, Octo ber 1990 New Source Review Workshop Manual) states that Class I impact analysi s are necessary for major sources locating within 100 km of a Class I area. While the propose d project, which will be a major modification of the facility, is located much farther away from any Class I area, the EPA NSR guidance states

that sources more distant than 100 km should be con sidered for analysis if they are large and considered to have a potential for adverse impact a t Class I areas. At the request of FSW and KDHE, Sunflower Electric has completed a Class I vi sibility impact analysis with the assistance of HDR Engineering, Inc.

The proposed project is quite distant from the near est Class I areas, at nearly 400 km from Great Sand Dunes National Monument in Colorado, and sligh tly over 400 km from Wichita Mountains National Wildlife Refuge in south-central Oklahoma. While the Wichita Mountains area is slightly farther away from the plant site than the Great Sand Dunes, Wichita Mountains is in a more predominant wind direction. This analysis foc uses primary on Wichita Mountains because of higher expected impacts than at Great Sand Dunes , but the impacts at both areas are summarized in this report.

2.0 METHODOLOGY

The atmospheric dispersion and atmospheric chemistr y modeling for estimating visibility impacts was accomplished with the current regulatory versio ns of the CALPUFF modeling system, which is an EPA-guideline approach for estimating visibil ity impacts at distances beyond 50 km and up

to a few hundred km from a Class I area. CALPUFF h as generally been recognized as being applicable up to 300 km downwind, and is considered to become over-conservative (high) in its impact predictions beyond 300 km. Given that the C lass I areas analyzed here are nearly 400 km away, the CALPUFF visibility impacts presented here are considered to be overestimates of the impacts that should be expected from the proposed f acility.Holcomb Station Expn., Visibility Results 2 June 8, 2007

The methodology for estimating impacts with the CAL PUFF system (CALMET meteorological preprocessor, CALPUFF model, POSTUTIL postprocessor and CALPOST postprocessor) is detailed in the attached, final modeling protocol. This protocol was the subject of two review cycles over the past months with staff from KDHE, E PA Region 7, and FWS providing comment on the protocol. Changes recommended by these agen cies have been incorporated into the final protocol, which included as Attachment 1 of this re port.

3.0 RESULTS

3.1 Model Input and Results Summary

The results of the CALPUFF visibility analysis are presented in this section. This analysis is

based on the emissions factors and rates shown in T able 1 as input to CALPUFF. These emission rates are based on a maximum heat input rate, for b oth units combined, of 13,002 mmBtu/hour.

Table 1. Emission Rates Input to CALPUFF Visibilit y Analysis

Pollutant Emission Factor (lb/mmBtu) Emission Rate (lb/hr, both units)

Sulfur dioxide 0.101 1313.2 Nitrogen oxides (as NO2) 0.05 650.1

Coarse Particulate Matter 0.00384 49.9

Fine Particulate Matter 0.0103 129.2

Elemental Carbon PM 0.000382 5.0

Tables 2 and 3 present the CALPUFF (actually CALPOS T postprocessor) results for visibility impact at the Great Sand Dunes and Wichita Mountain s Class I areas, respectively.

At Great Sand Dunes, there are three episodes (days ) when modeled light extinction exceeded the Federal Land Managers’ (FLMs) de-minimis threshold of 5%. This would normally be grounds for triggering a more refined analysis. Meteorolog ical data for these days at the nearest weather site, Alamosa, Colorado, were reviewed to determine conditions in the area on these days. The numbers in parentheses next to the listed values ov er 5% represent the Julian Day number of the subject episode. For all three of the days over 5% visibility modeled impact, the weather conditions were generally clear at the Alamosa obse rving station.

While the FLMs’ guidance for visibility modeling ha s for the past few years specified light extinction as the metric for assessing visibility i mpact, they are drafting guidance to soon change this to a deciview metric, based on a 98 th percentile impact. This would be consistent with EPA’s recommended visibility metric for Best Available Re trofit Technology (BART) analyses. In general, states and EPA have been using a 0.5 deciv iew impact level (98 th percentile, for a refined analysis) as a basis for assessing whether a source is exempt from BART retrofits. At the request of the FWS, the “Method 6” results in the above tab le are presented for comparison with the anticipated new FLM metric. The results in Table 2 show that for Great Sand Dunes, the 98 th
percentile impacts would be well below the 0.5 deci view threshold.

Thus, there appears little potential for adverse im pact at Great Sand Dunes, especially when considering the more statistically robust 98 th percentile deciview metric, and there does notHolcomb Station Expn., Visibility Results 3 June 8, 2007

appear to be a need for refined analysis. Also, co nsidering that CALPUFF likely significantly overestimates the impacts, there does not appear to be cause for concern at Great Sand Dunes.

Table 2. Summary of Great Sand Dunes Visibility Im pact Results, in Percent Light

Extinction Increase, and in Deciview Increase

Great Sand Dunes Background Visibility Method Rank 2001 2002 2003

1 2.60 11.17 (307) 8.27 (311)

2 1.60 8.12 (296) 4.08

3 1.40 4.00 3.59

4 1.11 3.18 2.90

5 0.78 2.92 1.59

6 0.67 2.76 1.40

7 0.56 2.66 1.20 Method 2 (all values in % light extinction)

8 0.49 2.62 1.10

1 0.171 0.549 0.572

2 0.153 0.404 0.361

3 0.146 0.234 0.261

4 0.096 0.216 0.200

5 0.093 0.212 0.118

6 0.062 0.203 0.093

7 0.057 0.190 0.092 Method 6 (all values in deciviews)

8 0.048 0.138 0.091

At Wichita Mountains, the model predicted higher ex ceedances of the FLMs’ 5% light extinction de-minimis threshold, especially for 2001 meteorolo gy. A review of meteorology at Lawton, Oklahoma, for the episodes (days) of these predicte d impacts (Julian Day in parentheses), shows that all three days were affected by very high humi dity, fog and precipitation. These conditions would not only make it difficult to see great dista nces, but there is concern in the scientific community that the calculations of visibility impac ts on such days are not accurate.

For the 2002 and 2003 episodes that are over 5% lig ht extinction (more marginally than for 2001), there was less precipitation than for the 20 01 episodes, and two of the episodes in 2002 and 2003 had no reported precipitation at Lawton on the subject days.

Using the newer metric of deciviews, assessed on a 98 th percentile basis (see “Method 6” results above), the impacts at Wichita Mountains are all be low the 0.5 deciview threshold commonly being used to determine a potentially adverse visib ility impact in BART analyses nationwide.

The 98 th percentile impacts at Wichita Mountains are higher than at Great Sand Dunes, which is expected, given the greater predominance of winds f rom Holcomb Station toward Wichita Mountains. However, even at Wichita Mountains, the 98 th percentile deciview values for each year are significantly lower than the 0.5 deciview BART threshold. As explained above, the tendency of CALPUFF to overestimate impacts beyond 300 km means that there is little potential for adverse visibility impact from the proposed fac ility at the Wichita Mountains.Holcomb Station Expn., Visibility Results 4 June 8, 2007

Table 3. Summary of Wichita Mountains Visibility I mpact Results, in Percent Light

Extinction Increase, and in Deciview Increase

Wichita Mountains Background Visibility Method Rank 2001 2002 2003

1 30.58 (47) 7.20 (19) 6.36 (62)

2 18.36 (46) 5.99 (38) 5.43 (61)

3 13.48 (347) 5.71 (270) 4.78

4 4.76 5.01 (342) 4.43

5 4.48 3.83 3.63

6 3.77 3.43 3.54

7 2.45 3.07 3.39 Method 2 (all values in % light extinction)

8 2.26 2.93 3.32

1 1.107 0.487 0.614

2 0.921 0.486 0.524

3 0.517 0.468 0.312

4 0.369 0.427 0.299

5 0.229 0.418 0.268

6 0.216 0.366 0.229

7 0.212 0.363 0.222 Method 6 (all values in deciviews)

8 0.212 0.331 0.213

3.2 Analysis of Worst-Case Modeled Episodes

At the request of the FWS, this section of the repo rt presents the results of an analysis to estimate impacts at receptors intermediate between Holcomb S tation and Wichita Mountains, on the two days (Julian Days 46 & 47, or February 15 & 16, 200 1) that generated the maximum impacts. For this analysis, receptors were placed ever 25 km from 250 km downwind to the nearest point of the Wichita Mountains Class I area, just over 40 0 km downwind. Table 4 presents the results of this analysis for both days.

The two sets of results in Table 4 are somewhat dif ferent for these episodes, although they are both reasonable based on the CALPUFF model design, depending on atmospheric chemistry and dispersion. For Day 46, the impacts decrease unifo rmly with downwind distance. This is not unusual with dispersion models not including any ch emistry interactions and this pattern can typically be attributed simply to increasing disper sion with distance. For Day 47, modeled impacts increase up to 325 km downwind, and then be gin decreasing uniformly. Such a pattern could be caused by multiple effects simulated by th e model, including:

1) meandering plume with transport downwind, 2) simple dispersion of an elevated, stable, plume dow n to the ground, thus peaking the impact at 325 km, with increasing dispersion therea fter, 3) chemistry & dispersion interactions, wherein chemic al conversion using background constituents is “exhausted” at 325 km, and then dis persion takes over, or 4) elevation changes with distance.Holcomb Station Expn., Visibility Results 5 June 8, 2007

Any of these factors could affect predicted concent ration patterns with downwind distance. However, it is clear that the impact data in Table 4 are consistent with the reported worst-case impacts at Wichita Mountains.

Table 4. Visibility Impacts in 2001 at Intermediat e Receptors Located Between Holcomb

Station and Wichita Mountains

Day 46 Day 47

Bkgd. Light Ext. (1/10 6 m) => 18.495 19.185
Receptor Location

Distance Elevation Total Ext. Total Ext.
Receptor ID (km) (m) 1/mega-m  Ext. (%) 1/mega-m  Ext. (%)

1235 250 643 26.900 45.44 24.832 29.43

1236 275 564 26.409 42.79 25.465 32.73

1237 300 522 25.558 38.19 25.828 34.63

1238 325 546 24.648 33.27 25.965 35.34

1239 350 500 23.779 28.57 25.913 35.07

1240 375 433 22.891 23.77 25.658 33.74

Wichita Max. 400+ 606 21.891 18.36 25.052 30.58

4.0 CONCLUSIONS

Modeled visibility impacts at both the Great Sand D unes National Monument in Colorado, and the Wichita Mountains National Wildlife Refuge in O klahoma areas, assessed according to the

98 th percentile deciview metric, are below the threshol d of 0.5 deciviews. This threshold is now being used in regulatory reviews of existing source s to determine if they are potentially subject to

retrofit emissions controls. The FWS and other FLM s are expected to soon begin using a similar approach to Class I analysis for purposes of PSD/Ne w Source Review permits.

This analysis of Class I area visibility impacts ha s demonstrated that the proposed Holcomb Station expansion is not expected to adversely affe ct visibility at the Great Sand Dunes National Monument in Colorado, or the Wichita Mountains Nati onal Wildlife Refuge in Oklahoma.