Final Modeling Protocol

Best available Retrofit Technology (BART)

Dispersion Modeling Protocol for Selected Nebraska Utilities

prepared for:

City of Grand Island

Hastings Utilities

Nebraska Public Power District

Omaha Public Power District

prepared by:

HDR Engineering, Inc.

6190 Golden Hills Drive

Minneapolis, MN 55416

(763)-591-5452

Attn: Ed Liebsch

Ed.Liebsch@hdrinc.com

October 31, 2006
Final Modeling Protocol

Best available Retrofit Technology (BART)

Dispersion Modeling Protocol for Selected Nebraska Utilities

1.0 INTRODUCTION

1.1 Objectives & Approach

This dispersion modeling protocol describes the procedures proposed for use in applying the

CALMET/CALPUFF modeling system (Earth Tech 2000) to certain Nebraska utility plants

subject to Regional Haze rules. This protocol proposes the use of the following model,

preprocessor and postprocessor versions for the facilities listed herein:

SMERGE: Version 5.61 (060309)

CTGPROC: Version 2.66 (060202)

TERREL: Version 3.681 (060202)

MAKEGEO: Version 2.26 (041230)

CALMET: Version 5.53a (Level 040716)

CALPUFF: Version 5.754 (Level 060202)

POSTUTIL: Version 1.52, Level 060412

CALPOST: Version 5.6393 (Level 060202)

The purpose of the Regional Haze rules is to help remedy any existing impairment of visibility in

Class I designated National Parks, Wilderness Areas, and Wildlife Refuges, in an attempt to bring

visibility back to its presumed level in prehistoric times. The procedures herein are consistent

with EPA’s Regional Haze guidance provided under 40 CFR 51, Appendix Y, and with CENRAP

BART Modeling Guidelines (Dec. 15, 2005).

The primary objective of this analysis is to determine whether several Nebraska facilities which

are “eligible” for Best Available Retrofit Technology (BART) emission controls, are also BARTsubject, meaning they would need to undergo a BART technology analysis to help establish

whether and what type of emissions controls are needed to meet Regional Haze requirements.

This protocol is being submitted to the Nebraska Department of Environmental Quality (NDEQ)

for its review and approval, for use in determining which BART-eligible sources are BARTsubject. Also, if approved by the NDEQ, this protocol will be used to estimate the relative Class I

area visibility improvements associated with various candidate emission control options for any

BART-subject sources addressed in this protocol.

In general, the technical approach used here is consistent with the CENRAP BART Modeling

Guidelines. To the extent that important technical options differ from the CENRAPrecommended defaults, such differences will be addressed in this protocol. To the extent that this

protocol is silent on specific model input settings, one can assume that the parameter setting will

either be consistent with CENRAP defaults (see tables in Appendices B, C, and D of CENRAP
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BART Modeling Guidelines), is not relevant to this particular modeling exercise, or has no effect

on modeled predictions (e.g., certain model diagnostic output settings).

1.2 Identification of Sources and Relevant Class I Areas

The sources (and operators) covered by this protocol, along with their general locations, include

the following:

• Gerald Gentleman Station, Units 1 & 2 (Nebraska Public Power District), near North

Platte,

• Sheldon Station, Unit 1 (Nebraska Public Power District), near Hallam,

• Nebraska City Station Unit 1 (Omaha Public Power District), near Nebraska City,

• North Omaha Station Units 4 & 5 (Omaha Public Power District), in Omaha,

• C.W. Burdick Station Units 3 & 4 (City of Grand Island), in Grand Island, and

• North Denver Station Unit 5 (Hastings Utilities), in Hastings.

The relevant Class I areas selected for this analysis include the nearest Class I areas in several

general directions from the facilities. None of these Class I areas are in Nebraska. The selected

Class I areas are located at distances of 300 to 600 kilometers or more from the above sources,

and are within the CENRAP-prepared meteorological grid representing the central CENRAP

region. Many more Class I areas lie at greater distances from the sources of interest, but it is not

expected that the more distant Class I areas would be areas of worst-case impact. The Class I

areas selected for this analysis include:

• Wind Cave National Park, in western South Dakota,

• Badlands National Monument, in western South Dakota,

• Hercules-Glades Wilderness, in southern Missouri,

• Mingo National Wildlife Refuge, in southern Missouri,

• Wichita Mountains National Wildlife Refuge, in southern Oklahoma,

• Great Sand Dunes National Monument, in south-central Colorado, and

• Rocky Mountain National Park, in north-central Colorado.

Shown in Figure 1 is a graphic depicting the locations of the sources and Class I areas proposed

to be addressed in this analysis. The rectangular box covering this region shows the boundaries

of the modeling domain for the proposed analysis, over which puffs will be transported,

dispersed, and chemically converted, as calculated by the CALPUFF model and post-processors.

1.3 Source Impact Evaluation Criteria

As directed by the NDEQ, the evaluation criteria for determining whether individual facilities

contribute to adverse impacts are consistent with suggested levels in EPA guidance (40 CFR 51,

Appendix Y). An impact level of 1.0 deciview or more by BART-eligible units (collectively) at a

single facility means that the affected source by itself is causing adverse visibility impact. An

impact level of 0.5 deciviews or more by BART-eligible units (collectively) at a single facility

means that the affected source is reasonably anticipated to contribute to adverse visibility impact.

In accordance with Appendix Y, the 98

th

percentile of the daily deciview impacts, within each

year of meteorology modeled, evaluated separately at each Class I area, will be the criteria to

establish a contribution to adverse visibility impact. For a year of 365 days, this means that any

exceedances over 0.02*365 = 7.3 are over the allowable threshold. Thus, seven (7) 24-hour
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Figure 1. Modeling Domain for BART Analyses
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periods in a year exceeding 0.5 deciviews are acceptable to exempt a source from BART, while

eight 24-hour periods exceeding 0.5 deciviews mean a source is BART-subject.

One additional specification is that an exceedance of the 0.5 deciviews threshold can occur at any

receptor point within a given Class I area, to count as a day over the 0.5 threshold for that Class I

area. This is consistent with modeling guidance developed by the VISTAS Regional Planning

Organization, which covers states in the southeastern US (VISTAS 2006).

1.4 Modeling Study Participants

As listed above, the modeling study participants include four public utilities in Nebraska (NPPD,

OPPD, City of Grand Island, and Hastings Utilities), with a total of six facilities containing

BART-eligible emission units. The modeling study will be completed by HDR, Inc.

1.5 Protocol Review Process

The protocol review process will begin upon submittal of this proposed protocol to the NDEQ,

which will distribute it for comment to appropriate agencies, including EPA Region VII and

various Federal Land Managers. Protocol review and approval are expected to be expedited due

to the fact that this protocol relies heavily on the CENRAP-recommended modeling protocol,

which has already undergone review by many interested agencies. Upon approval of this

protocol, with any needed revisions, HDR will apply it to the subject sources and provide a report

documenting model results for NDEQ review and approval, to determine which facilities are

BART-subject.

2.0 SOURCE DESCRIPTION

2.1 Unit-Specific Source Data

In general, the emission rates to be used for this analysis will be representative of 24-hour

(calendar day) maximum emission rates for the baseline period of 2001-2003. However, there are

some exceptions. For emission units that can routinely operate on more than one fuel (fuels used

for start-up are not considered), the worst-case fuel will be assumed for emissions input purposes,

even if it was not used during the 24-hour maximum facility operating rate (in million Btu/hr, or

MMBtu/hr). This is consistent with recommendations in the CENRAP modeling guidance.

For example, C.W. Burdick Station used only natural gas during the baseline period. However,

because the affected units at this facility can also burn No. 6 fuel oil, the modeled emissions for

this facility will represent 24-hour maximum load for the period, with calculated emissions as if

that load was achieved using No. 6 fuel oil, and fuel sulfur and heating value specifications of the

on-hand fuel. Because the maximum combined (Units 2 & 3) load for Burdick Station was

achieved with only Unit 3 in operation, only Unit 3 will be modeled for this study.

Also, because North Denver Station #5 (Hastings Utilities) was used only very sparingly in the

baseline period (2001-2003), its 24-hour maximum emissions for the baseline/modeled period

would be minimal. However, at Hasting Utilities’ request, to conservatively assess potential

impacts, it will be modeled at its maximum potential load condition, using the current worst-case

fuel, which is No. 2 fuel oil with a maximum allowable sulfur content of 0.5%.
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The SO2 and NOx baseline emission rate inputs for the affected coal-fired units are determined

from Continuous Emission Monitor (CEM) data. These CEMs are used for monitoring of

emissions as required under the Acid Rain program. The PM emission rates for these units are

based on the maximum 24-hour estimated heat input rate over the 2001-2003 period, together

with an emission factor (lb/MMBtu) determined from the latest stack testing. For oil and gasfired units, the emission rates will be calculated based on either AP-42 emission factors (NOx and

PM) or sulfur mass-balance (SO2), based on fuel sulfur specifications and measured fuel flows.

For facilities with multiple, BART-eligible emission units (Gerald Gentleman, North Omaha,

Burdick), the combined maximum 24-hour emissions from the BART-eligible units at the facility

will be used to determine modeled emission rates. Because stack heights for the multiple units at

these facilities are identical or nearly so, and other stack parameters do not vary greatly,

emissions for the multiple stacks at a facility will be summed and modeled as coming from one

stack, the one that would generate slightly lower plume rise, to conservatively estimate Class I

area impacts while minimizing computer time for CALPUFF runs. For stacks that are only a few

meters apart, the separation of a few meters would have negligible effects on predicted impacts

when those impacts are occurring several hundred kilometers away. A sensitivity analysis for

one facility will be provided along with final modeling to substantiate that combining stacks does

not have an appreciable effect on dispersion, compared with modeling the stacks separately.

Estimated particulate matter (PM) emissions will be allocated into PM-coarse (PMC, particles

from 2.5 to 10 microns in diameter) and PM-fine (PMF, particles below 2.5 microns in diameter)

portions, based on size distribution data for filterable PM as provided in the latest sections of AP42 (USEPA, 1998a). Also, condensable PM emissions will be estimated from AP-42 emission

factors, and all of the condensable emissions will be assumed to form particles in the PMF size

range. While some condensable emissions may form particles larger than 2.5 microns in

diameter, or may agglomerate onto particles already larger than 2.5 microns in diameter, it is

conservative to assume all the condensable material forms the smaller particles, which are more

important in generation of regional haze. In any case, for power plant sources at significant

distances from Class I areas, the direct PM emissions are typically responsible for a very small

portion of the total modeled visibility impacts, based on prior CALPUFF modeling experience in

other states. Thus, speciation and size distribution of PM emissions is not considered to be a

significant issue in driving model results.

Emissions of other potential visibility-impairing pollutants, namely volatile organic compounds

(VOCs) and ammonia (NH3), will not be considered as emitted for this analysis, due to their

negligible importance for the types of sources (utility boilers) to be modeled. Also, minor

emissions from intermittent sources (auxiliary boilers, emergency generators, minor PM sources,

including fugitives) will not be assessed in this study, given that these types of sources will emit

little, if any, emissions of visibility-impairing pollutants in comparison to the primary electric

generating units being modeled for this study.

Stack parameters that vary with time (i.e., exit velocity and temperature) will be based on

measurements corresponding with maximum 24-hour emissions determined from CEM data, or

where no CEM data exist, will be based on either measured flows and temperatures from stack

testing, or lastly in priority, from design maximum values.

Attachment 1 is an Excel spreadsheet that provides a listing of emissions and other stack data to

be used for each listed BART-eligible source.
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2.2 Nearby Sources Affecting Same Class I Areas

Because the BART-eligible emission units included in this analysis will be analyzed facility-byfacility with respect to the 0.5 deciview threshold, to determine if they “reasonably contribute” to

Class I area visibility impairment, the presence or lack of nearby sources is not especially relevant

to this analysis. However, Nebraska may need to consider this issue in preparing its State

Implementation Plan submittal to evaluate whether the collective emission reductions proposed

will be effective in improving visibility at Class I areas.

3.0 OTHER MODEL & PROCESSOR INPUT DATA

3.1 Modeling Domain

The modeling domain proposed for this analysis (see Figure 1) covers a large portion of the

CENRAP central region, as described previously. The modeling domain will extend from 50-80

km or more beyond the farthest extent of each Class I area to be analyzed, in accordance with

recommendations provided in the Interagency Workgroup on Air Quality Modeling (IWAQM)

Phase 2 Summary Report and Recommendations for Modeling Long Range Transport Impacts,

U.S. Environmental Protection Agency, EPA–454/R–98–019, December 1998 (USEPA, 1998b).

Given that the BART-eligible sources in Nebraska are relatively well centered within the

meteorological and computational domains, these domains are expected to provide a good

representation of emissions transport between sources and receptors.

3.2 Terrain and Land Use

Terrain data files were obtained through Bowman Environmental, and represent 30-meter

resolution Digital Elevation Model (DEM) US Geological Survey data. Land use data files with

30-meter resolution were downloaded from the National Land Cover Dataset (NCLD) files

available from the US Geological Survey at http://edcsgs9.cr.usgs.gov/pub/data/landcover/states/.

3.3 Meteorological Data Processing

The meteorological data base proposed for this study includes the same CALMM5 database of

2001, 2002, and 2003 data used by CENRAP for producing its meteorological databases with

CALMET. However, in producing its meteorological database CENRAP used the NOOBS=2

option in CALMET, which does not re-introduce meteorological observations into the MM5 data

fields. For the proposed BART analyses of Nebraska sources, HDR will use the NOOBS=1

option. This means that the CALMET runs will re-introduce surface observations, which will

tend to bias the MM5 meteorological grids in favor of individual station data for grid nodes

nearer the station observation points. The re-introduction of surface observation is intended to

compensate for an apparent underestimate of total cloud cover in the MM5 model output, among

other concerns expressed by Region 7 EPA.

For precipitation, the MM5 data fields will be used as they are, without re-introducing

observations. Thus, the CALMET input parameter NPSTA will be set to -1.
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In producing its databases, CENRAP prepared three separate data sets with CALMET, covering

three prospective modeling domains: a north-central domain, a central domain, and a southcentral domain. The “central domain” MM5 (CALMM5 format) meteorological data obtained

from Alpine Geophysics (which processed the original meteorological data fields for CENRAP)

will be used, together with the re-introduced observations, for this study.

A total of fifty (50) surface stations will be used for CALMET meteorological data processing.

These stations are well distributed across the entire modeling domain and are listed in Table 1.

Table 1. Surface Meteorological Stations

Station # WMO# Elev. (m) Anem. (ft) Abbrev. Location Lat. Long.

23047 723630 1093.0 32.8 AMA Amarillo, TX 35.23 -101.7

3935 723489 102.4 ** CGI Cape Girardeau, MO 37.233 -89.567

24017 725636 1011.3 33.0 CDR Chadron, NE 42.833 -103.1

24018 725640 1863.9 32.8 CYS Cheyenne, WY 41.15 -104.8

93037 724660 1884.0 32.8 COS Colorado Springs, CO 38.817 -104.683

3945 724450 272.2 32.8 COU Columbia, MO 38.817 -92.217

13984 724580 447.8 32.8 CNK Concordia, KS 39.55 -97.65

3017 725650 1650.2 32.8 DEN Denver (Intl. Airport), CO 39.833 -104.65

14933 725460 291.7 32.8 DSM Des Moines, IA 41.533 -93.65

13985 724510 787.0 26.0 DDC Dodge City, KS 37.767 -99.967

13964 723440 136.9 32.8 FSM Fort Smith, AR 35.333 -94.367

13975 723527 667.8 33.0 GAG Gage, OK 36.3 -99.676

23065 724650 1114.3 32.8 GLD Goodland, KS 39.367 -101.7

14935 725520 560.8 32.8 GRI Grand Island, NE 40.967 -98.317

14936 726540 390.1 32.8 HON Huron, SD 44.4 -98.217

3947 724460 306.3 32.8 MCI Kansas City (Int'l Airport), MO 39.3 -94.733

14938 724455 294.4 33.0 IRK Kirksville, MO 40.1 -92.55

14920 726430 198.7 32.8 LSE La Crosse, WI 43.883 -91.25

3013 724636 1129.0 ** LAA Lamar, CO 38.067 -102.683

3950 723575 325.8 33.0 LAW Lawton, OK 34.567 -98.417

23020 724516 875.7 33.0 LBL Liberal, KS 37.05 -100.967

93010 724665 1695.3 33.0 LIC Limon, CO 39.183 -103.717

14939 725510 356.6 32.8 LNK Lincoln, NE 40.833 -96.767

14837 726410 264.0 32.8 MSN Madison, WI 43.133 -89.35

14940 725485 373.4 33.0 MCW Mason City, IA 43.15 -93.333

13893 723340 77.4 32.8 MEM Memphis (Intl. Airport), TN 35.05 -89.983

14923 725440 180.4 32.8 MLI Moline, IL 41.467 -90.517

53918 723439 282.9 ** BPK Mountain Home, AR 36.367 -92.467

14941 725560 472.4 32.8 OFK Norfolk, NE 41.983 -97.433

24023 725620 846.7 32.8 LBF North Platte, NE 41.117 -100.667

13967 723530 391.7 26.0 OKC Oklahoma City, OK 35.838 -97.6

14942 725500 299.3 32.8 OMA Omaha (Eppley Airport), NE 41.317 -95.9

14842 725320 198.1 32.8 PIA Peoria, IL 40.667 -89.683

24025 726686 531.0 33.0 PIR Pierre, SD 44.383 -100.283

24090 726620 963.2 32.8 RAP Rapid City (airport), SD 44.05 -103.05

14925 726440 397.5 32.8 RST Rochester, MN 43.9 -92.5

94822 725430 222.5 32.8 RFD Rockford, IL 42.2 -89.1

93997 724585 566.3 33.0 RSL Russell, KS 38.883 -98.817
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24028 725660 1202.4 32.8 BFF Scottsbluff, NE 41.867 -103.6

14943 725570 333.8 32.8 SUX Sioux City, IA 42.383 -96.383

14944 726510 435.3 32.8 FSD Sioux Falls, SD 43.583 -96.733

93822 724390 181.1 32.8 SPI Springfield, IL 39.85 -89.683

13995 724400 383.7 32.8 SGF Springfield, MO 37.233 -93.4

13994 724340 161.8 32.8 STL St. Louis (Lambert), MO 38.75 -90.367

13996 724560 268.5 32.8 TOP Topeka, KS 39.067 -95.633

23070 724645 1749.9 ** TAD Trinidad, CO 37.267 -104.333

13968 723560 198.1 32.8 TUL Tulsa, OK 36.2 -95.883

24032 725670 789.4 32.8 VTN Valentine, NE 42.883 -100.55

94910 725480 264.6 32.8 ALO Waterloo, IA 42.55 -92.4

3928 724500 402.6 32.8 ICT Wichita, KS 37.65 -97.45

**Anemometer height not listed for these stations. Height of 32.8 meters is assumed.

For this analysis, surface station meteorological data (for the re-introduction option) were

obtained from the National Climatic Data Center, and were provided to HDR by Bowman

Environmental. The MM5 meteorological fields were obtained from Alpine Geophysics in

CALMM5 format, covering the same “central region” grid defined in the CENRAP modeling

guidance.

3.4 Air Quality Data Base

The background air quality data proposed for use in this study are the CENRAP-recommended

values for monthly ozone, ammonia, and peroxide concentrations.

3.5 Receptor Data

The receptors proposed for this analysis are those in each identified Class I area (see Section 1.2

above) as downloaded from the National Park Service Class I receptor database, accessed at the

following web site: http://www2.nature.nps.gov/air/Maps/Receptors/index.cfm.

3.6 Relative Humidity Function [f(RH)]

The relativity humidity function, f(RH) is a parameter that relates to the hygroscopic growth of

particles. As relativity humidity increases, certain particles such as sulfates and nitrates begin to

agglomerate liquid water at relative humidity below 100%, thus greatly increasing the haziness of

the atmosphere. Monthly values of f(RH) have been tabulated by EPA for all the Class I areas

where visibility is considered an important value. The EPA-tabulated f(RH) values found in

Appendix A, Table A-3, of Guidance for Estimating Natural Visibility Conditions Under the

Regional Haze Rule, Publication EPA-454/B-03-005, September 2003, will be used for this

study, specific to each Class I area. This means that in post-processing the model results with

CALPOST, each individual Class I area will be processed separately, since the f(RH) values are

input in the CALPOST processing step.

3.7 Natural Conditions at Class I Areas

Natural background visibility at Class I areas is a very important determinant in assessing the

level of impact in deciviews from a given source. If the natural background visibility is very
Final Modeling Protocol

good, due perhaps to lower average humidity and other geographic and climate factors, it will not

take as large a fine particle concentration to create a 0.5 deciview impact, as in an area that is

naturally hazier. Also, in any given area, the haziness will vary considerably from day-to-day,

depending on season and synoptic meteorological patterns. It is therefore necessary to describe

the background visibility conditions within which a given facility impact will be assessed. For

purposes of this protocol, the CENRAP-recommended default values will be used to describe

background visibilities for the “east” and “west” Class I areas, as appropriate. For this purpose,

“east” and “west” are divided by the eastern edge of the state boundaries of the Dakotas,

Nebraska, Kansas, Oklahoma, and Texas.

The CENRAP-recommended defaults for CALPOST processing reflect the use of “average

background visibility” conditions. Thus, average background visibility will represent the

atmosphere within which the perceptibility of plumes is analyzed using the procedures in this

protocol.

4.0 BART CONTROL MODELING RESULTS

Any sources determined to be BART-subject need to be re-modeled to assess the relative

visibility improvements that could be attained with each prospective control option. The

modeling protocol described in this document will be used for such analysis, unless another

protocol is provided to NDEQ and approved for such use.

5.0 REPORTING

A combined BART-subject modeling report will be prepared to concisely summarize model

results for all of the facilities covered by this protocol, and will be submitted to NDEQ for review

and approval. The modeling report will be accompanied by a compact disk (or disks) containing

CALPUFF, POSTUTIL, and CALPOST input and output files. One exception is the CALMM5

meteorological data base, which is too large to efficiently place on CD, but which is available

separately from CENRAP. Also, the processed CALMET output meteorological fields are too

large to transmit on CD, but can be copied to an external hard-drive upon request, if the drive is

supplied to HDR.

6.0 REFERENCES

CENRAP, 2005. CENRAP BART Modeling Guidelines, Dec. 15, 2005.

Earth Tech, 2000. A User’s Guide to the CALPUFF Dispersion Model (Version 5), January

2000.

National Park Service, 2006. Class I area receptor information, accessed at

http://www2.nature.nps.gov/air/Maps/Receptors/index.cfm.

USEPA, 1998a. Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and

Area Sources. Publication AP 42, Fifth Edition, Volume I, Chapter 1: External Combustion

Sources. Available on-line at: http://www.epa.gov/ttn/chief/ap42/ch01/index.html.
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USEPA, 1998b. Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary

Report and Recommendations for Modeling Long Range Transport Impacts, U.S. Environmental

Protection Agency, EPA–454/R–98–019, December 1998.

USEPA, 2003. Guidance for Estimating Natural Visibility Conditions Under the Regional Haze

Rule, Publication EPA-454/B-03-005, September.

VISTAS, 2006. Protocol for the Application of the CALPUFF Model for Analyses of Best

Available Retrofit Technology (BART). Visibility Improvement State and Tribal Association

of the Southeast (VISTAS) December 22, 2005 (Revision 2 – 3/9/06).