UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

RESEARCH TRIANGLE PARK, NC 27711 

MAY 1 5 2009 

OFFICE OF 

AIR QUALITY PLANNING 

MEMORANDUM AND STANDARDS 

SUBJECT:	 Model Clearinghouse Review ofCALPUFF Modeling Protocol for BART 

FROM:	 Tyler Fox, Leader "-;T'+ 

Air Quality Modeling Group (C4a~01)' , 

TO:	 Kevin Golden, Lead Regional Modeler 

Air Permitting, Monitoring, and Modeling Unit (8P-A) 

Carl Daly, Chief
 

Air Permitting, Monitoring, and Modeling Unit (8P-A)
 

INTRODUCTION 

In response to your memorandum ofFebruary 24,2009, the Model Clearinghouse has reviewed 

the proposed position and resolution ofthe issues presented in order to develop a suitable air 

quality analysis for visibility for the Otter Tail Power Big Stone Unit I located in Eastern South 

Dakota. The purpose ofthis analysis is to detemrine ifthis source is subject to Best Available 

Retrofit Technology (BART) requirements under EPA's Region Haze Program regulations. 

Guidelines for detennining how to identify sources "subject to BART" are provided in section III 

ofEPA's Guidelinesfor BARTDetermination Under the Regional Haze Rule, which is located in 

Appendix Y to Part 51 ofTitle 40 ofthe Code ofFederal Regulations. Section III.A.3.(Option 

I) ofAppendix Y, allows the use ofCALPUFF model to predict the visibility impacts from a 

single source at a Class I area and states that CALPUFF is the best regulatory model currently 

available for this application. Furthermore, with respect to the use of CALPUFF for regulatory 

applications, footnote 8 in this section of Appendix Y references EPA's Guideline on Air Quality 

Models (GAQM), published in AppendixW ofPart 51. Section 6 ofthe GAQM includes 

recommendations regarding application ofCALPUFF for visibility assessments and for long 

range transport (LRT) applications in general (nominally beyond about 50 kilometers), indicating 

that such applications ''will require significant consultation with the appropriate reviewing 

authority (paragraph 3.0(b) [ofAppendix W]) and the affected FLM(s) [Federal Land 

Managers]". Appendix Y also recommends developing a modeling protocol and following the 

guidance contained within the Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 

2 Summary Report and Recommendations for Modeling Long Range Transport Impacts 

(USEPA, 1998). The IWAQM Phase 2 summary report is also referenced by the GAQM: Thus, 

when CALPUFF is used in this context, it is our understanding that EPA Regional Offices have 

Internet Address (URLj • http://www.epa.gov
 

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encouraged following both the IWAQM Phase 2 report and the GAQM when conducting 

modeling for the BART program.	 . 

Recently the FLMs have made us aware that a number ofthe issues identified in the Region's 

memorandum regarding this BART application arso exist for Prevention of Significant 

Deterioration (PSD) modeling conducted for assessing impacts in mandatory Class I areas. 

While Appendix Y and the GAQMboth offer some flexibility in models and procedures for 

visibility assessments, deviations from the use ofpreferred models or modifications ofpreferred 

models under PSD is discussed in Section 3 oftheGAQM and requires Regional Office approval , I 

in all cases. See also, 40 C.F.R. § 51.,I 66(1)(2). Given the impottanf:e ofthe issues that the 

Region has identified and their similarity to issues identified by the FLMs in recent PSD 

applications, the Model Clearinghouse believes it appropriate to.evaluate the protocol proposed 

'by Otter Tail power for its scientific merit. 

The Model Clearmghousereview has focused upon the primary issues identified in the Region's 

memorandum, but also identified several other issues that the Region may wish, to consider in its 

ongoing negot~ations. In summary, 

1)	 We coincur with Region 8's position that the use of a 1 kIn grid resolution in 

CALMET/CALPUFF .isnot adequately justified given the geographical characteristics of 

the domain ofinterest and the 

,	 limitations ofthe modeling system . 

2)	 We concur with Region 8's view based on EPA guidelines that ''blending'' National 

Weather Service (NWS) observations with prognostic model data is the most technicallysound approach to developing meteorological fields for application ofthe CALPUFF 

model when prognostic model data are incotporated. This approach should be used 

unless adequate documentation is provided demonstrating that an alternative approach 

has equal technical merit. Absent pertinent evaluations, we' are unable to endorse use of 

the NOOBS =1 option recommended in the Otter TaZl Protocol at this time 

] . 

3)	 We defer the decision on the appropriateness ofthe proposed concentration postprocessing procedures to the Regional Office and the FLMs. 

, In addition, we are proposing revisions to the IWAQM phase 2 recommendations that are 

responsive to the issues and concerns'raised in this'memorandum. A more complete discussion 

is provided in the draft document Reassessment ofthe Interagency Workgroup on Air Quality 

Modeling (IWAQM) Phase 2 Summary Report: Revisions to Phase 2 Recommendations (USEPA, 

2009) available for review on EPA's Support Center for Regulatory Atmospheric Modeling 

(SCRAM) website. 

The remainder ofthis memorandum provides background on'the Region 8 request and a more 

detailed explanation for each ofthe above recommendations. ' 

- 2
 
BACKGROUND 

EPA Region 8, in conjunction the US Fish and Wildlife Service, National Park Service, and the 

state ofSouth Dakota, has worked to develop an adequate CALPUFF modeling protocol for the 

Best Available Retrofit Technology (BART) analysis for the Otter Tail Power Big Stone Unit I 

electrical generating unit in eastern South Dakota. Big Stone Unit I is a large uncontrolled coalfired facility that is approximately 400 km qom the nearest Class I areas in Minnesota and South 

Dakota. 

The facility's consultant completed a CALpUFF modeling analysis in September 2008. This 

, analysis was conducted in the absence ofa protocol ~pproved by the aforementioned parties. In 

this submittal, the Big Stone Unit I had, an impact of 0.489 delta-deciview (d-dv) on the 

Boundary Waters (BOWA) Class I area Other modeling ofthis facility produced vastly 

different results, raising concerns that the methods used in the September 2008 analysis may 

have resulted in the lower modeled impacts. For example, CAMx source apportionment 

modeling conducted in 2007 by EPA Region 7 on the Big Stone Unit I yielded a maximum 

change of 1.87 d-dv at BOWA, with ten days exceeding a 0.5 d-dv change. 

') 

In January 2009, the facility's consultant submitted the Otter Tail Protocol (TRC, 2009) toEPA 

Region and the FLMsoutlining proposed procedures for a revised c;ALPUFF analysis. The 

Otter Tail Protocol proposed specific changes to the Western Regional Air Partnership (WRAP) 

BART modeling protocol (WRAP, 2006) including grid resolution, radius ofinfluence values for '­

CALMET, and the CALMET NOOBS options that are not 'EPA-approved. Additionally, the 

Otter Tail Protocol proposed the use of alternative procedures for post-processing nitrate 

concentrations that are not consistent with the WRAP BART modeling procedures. Both EPA 

Region 8 and the FLMs objected to the proposed deviations, but subsequent negotiations with 

the facility have not yielded any changes to the proposed Otter Tail Protocol. 

:'	 In February 2009 EPA Region 8 referred the Otter Tail Protocol to the EPA Model 

Clearinghouse for review ofthe Region's position on grid resolution, non-default CALMET 

options, andCALPUFF post-processing options. This Clearinghouse memorandum will address 

the specific deviations from the WRAP protocoIidentified by the Region's Modeling 

Clearinghouse request. ' 

CALMET/CALPUFF GRID RESOLUTION 

'The Otter Tail Pro'tocol called for the use ofthree'separate CALMET/CALPUFF modeling 

domains covering mandatory Class I areas in South Dakota, North Dakota, and Minhesota, 

"[O]wing to the high spatial resolution and the large extent ofthe area ofinterest". Each ofthe 

proposed modeling ddmains utilize a horizontal grid resolution of I kilometer, deviating from the 

4 km horizontal grid resolution recommended by the WRAP protocol. The Otter Tail Protocol 

specifically states that the 

" ...complex terrain is best resolved with a 1 km grid. Additionally, the coastline ofLake 

Superior, close to Boundary Water Canoe Area WA, and ofother smaller lakes on the 

trajectories to thev~ious Class I areas, is also best resolved at Han resolution." 

3
 
An argument for the use offiner resolution CALMET wind fields ~hould address two 

components. The first is that the,prognostic meteorological data sets from NWP models lack 

sufficient resolution to ,capture meteorological features ofinterest which would be responsible 

for transport of airborne contaminants from the source to the Class I area(s) ofinterest. The 

secon~ component ofthe argument is that the diagnostic wind model (DWM), CALMET, can 

enhance the NWP data used as the first-guess wind field (IPROG=14) sufficiently to adequately 

replicate the key meteorological features ofinterest. 

Model Clearinghouse Recommendation on Grid Resolution 

Based upon a review ofthe Otter Tail Protocol and relevant scientific literature, the Model 

Clearinghouse offers the following conclusions. First, the Otter Tail Protocol presents no 

scientific evidence to support the claim that I km CALMET resolution jncreases the objective 

,accuracy ofthe final wind field, especially in areas ofrelatively modest topographic relief, such 

as for each ofthe three domains proposed. The preponderance ofscientific literature is 

'- consistent in the conclusion that there is a limitation to the benefit ofhigher resolution gridded 

meteorological data, whether from NWP or DWM models, especially for areas ofmodest 

topographic relief Higher,resolution data does not necessarily improve model performance, but 

may in fact degrade model performance for some predicted meteorological parameters. Second, 

CALMET has limited ability to independently capture the full three-dimensional structure of 

complex flows. Without the benefit of high resolution NWP data or a high density of 

representative observational data, the ability oftheDWM to accurately simulateJhese conditions 

is limited. Several studies have documented the inherent limitations ofDWM diagnostic 

algorithms (e.g., Earth Tech, Inc. (2001), Scire (2P08), and Scire (2009)) 

, Therefore, we concur with the Region's position that the use ofa 1 km grid resolution'in 

CALMET/CALPUFF is not adequately justified given the geographical characteristics ofthe 

domain ofinterest and the limitations ofthe modeling system. Furthermore, as indicated in our 

Introduction, the Otter Tail Protocotlinks the limited geographic extent ofthe three proposed 

modeling domains to the use ofhigh (1 km) spatial resolution, implying a trade-offin 

computational resources between grid resolution and spatial coverage. We do not feel that such 

a trade-off is justified, and are concerned that the proposed domains may not adequately simulate 

the potential for plume recirculation. Based on a review,ofthe relevant scientific literature and a 

review 0 f the CALMET capabilities, we also see no evidence to support the use 0 fa 4 km grid 

resolution for CALMET/CALPUFF in this case, as recommended in the WRAP BART protocol. 

Note that the WRAP protoc;ol addresses BART evaluations a~ross a wide domain encompassing 

the most rugged terrain in the U. S.', and this assessment regarding the applicability of4 km grid 

resolution for the Otter Tail analysis is not intended to suggest that grid resolutions higher than 

the 36 km MM5 data are not justified for other areas within WRAP. 

Based on our review ofthis issue and given the limitations ofthe CALMET DWM" our view is 

that the candidate NWP data used should appropriately characterize the key meteorological 

features that govern source-receptor relations for the specific application. We also see no clear 

basis for, or benefit from, extending the CALMET/CALPUFF grid resolution much beyond the 

resolution ofthe prognostic model used to specify the first.guess wind field. Since the Model 

4
 
Clearinghouse recommendation is to maintain the original horizontal grid resolution ofthe NWP 

data in most situations, it would ,be inappropriate to apply CALMET with any diagnostic 

adjustments, unless a sufficiently dense and representative network ofobserved data are 

available, and the improved perfurrpance ofthe CALMET wind fields can be objectively 

demonstrated. When properly applied with adequately resolved NWP <lata, the CALMET firstguess fi.eld likely already reflects the relevant meteorological features ofinterest at that 

resolution. 

The Mod,el Clearinghouse recomme~dation,gtrictly implies that thtt candidate NWP data .used 

should appropriately characterize the key meteorological features that govern source-receptor 

relations for the specific application. This places a higher emphasis on ensuring that the 

candidate NWP dataset is at the appropriate horizontal grid resolution and that the dataset 

captures the key meteorological features for the specific application. Therefore, the 

recommendation for establishing the suitability ofNWP dataset under Section8.3(d),ofthe 

GAQM is a critical component for planning asu,ccessful LRT model application. In light of 

these, concerns, the appropriateness and adequacy ofthe CALMET/CALPUFF grid resolution,as 

well as any prognostic model data used as input to CALMET, should be adequately justified 

based on ~h~ specific. ne~s ofthe a~plicat.ion, and me~sures should b~ taken )to .objectively ~sess

the resultmg meteorologICal fields, mcludmgboth hOflzontal and vertIcal vetOCIty fields, pnor to 

their acceptance for use in CALPUFF. ,In accordance with Section 8.3(d) of the GAQlvJ, we must 

emphasize that acceptance ofa prognostic data set is·contingent upon concurrence from the 

appropriate reviewing autHority. Therefore, at a ~nimum, any protocol should include an 

evaluation oftne performance ofthe candidate NWP datasetprior to acceptance by the reviewing 

authority. Model performance evaluation procedures should be based on appropriate and 

acceptable metries and methods. Further, ifthe intent is to apply CALMET at resolutions much 

higher than the original NWP dataset, the suitability,ofthe resultant datasets should aJso Qe 

examined through the appropriate statistical analysis. 

A more complete discussion ofthis issue is provided in the draft document Reassessment o/tlte 

Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary Report: Revisions 

to Phase 2 Recommendations (USEPA, 2009) available for review on EPA's Support Center for 

Regulatory Atmospheric Modeling (SCRAM) website. This draft report also provides a detailed 

discussion ofmodel e.valuation methods and prQcedures appropriate for these applications, 

including procedures for evaluation ofdiagnostic meteorological fields. 

CALMET NON-DEFAULT SETTINGS 

As background, when the CALPUFF modeling -system was promulgated mApril 2003 as the 

preferred model for LRT regulatory applications under the GAQM, the "hybrid" approach 

referred to in Section 8.3 of the GAQM (formerly Section 9.3 prior to 2005) called for both'NWS 

surface and upper air 4ata. Shortly after its promulgation, the EPA-approved version ofthe 

CALMET/CALPUFF modeling system included new options which eliminated the need for 

surface and upper air observations, relying totally upon prognostic data as the sole· 

meteorological input into CALMET. This approach is most conunonly referred to as the 

''NOOBS'' approach, and is invoked by selecting the NOOBS = 1 or 2 option in CALMET. The 

Otter Tail Protocol specifically recommends the use ofthe NOOBS = 1 option ofCALMET, 

5
 
, \ 

, 

which uses NWP data in lieu oftwice daily upper air soundings normally ~ployed in the 

construction of GALMET wind fields, but incorporates surface observations. The NOOBS = 2 

option uses no observed surface or upper air data, relying solely on the NWPdata. The Otter 

Tail Protocol contends that using upper air observations directly into CALMET is likely to 

degrade the quality .ofthe wind field~ as cOmpared to the use of gridded MM5 data, although no 

further rationale or objective evidence for this claim is offered. 

As discussed in the IWAQM reassessment report (USEPA, 2009), there is a clear body of 

evidence to suggest that higher spatial and temporal frequency ofNWP data used in LRT 

modeling generally results in better LRT model verification statistics. Therefore, in theory, the 

NOOBS approach in CALMET could offer the opportunity to t~e advantage ofhigher 

temporally and spatially resolved initial guess wind fields from NWP data than could otherwise 

be achieved through the exclusive use dftwice-daily RAOB soundings. However, it is important 

to note that eALMET does not merely pass through the majority ofthe information from the 

NWP model to C~PUFF. Much ofthe original NWP data (e.g., planetary boundary layer 

(PBt) heights and scaling parameters) IS recomputed within CALMET. Therefore, careful 

consideration must be given to how thesere-diagnostic procedures are implemented within 

CALMET. As also noted in the IWAQM reassessment report (USEPA, 2009), CALMET does 

not fully utilize the 3-dimensional temperature fields when applying diagnostic adjustments to 

the wind fields under the regulatory default option, although the full temperature field is passed 

to CALPUFF (along with the vertical velocities) ifthe LCALGRD option is selected. Aside 

from the documented limitations ofthe modeling system to properly utilize the full benefits of 

current state-of-the-practice prognostic modeling capabilities, there are few, if any, objective 

evaluations ofmodel performance on which to base acceptance ofthese NOOBS options. 

Model Clearinghouse Recommendation for Non-default. CALMET Settings 

, While the Otter Tail Prot~col only proposes the use ofthe NOOBS=1 option ofCALMET, our 

experiences from the assessment ofthe VISTA's version (USEPA, 2008) and the200l 

Philadelphia study (Anderson, 2006) suggest that careful consideration ofthe underlying science 

and its implementation must be taken when using the more advanced features ofCALMET. A 

literature search conducted by the Model Clearinghouse on subsequent evaluations ofthe 

"CALMET model used in both the traditional "hybrid" approach and the newer ''NOOBS'' 

approach yielded no significant information regarding the performance ofthe ''NOOBS'' 

approach as compared to the traditional "hybrid" approach, other than the references listed in 

Appendix A-4 ofthe descriptiop. ofthe CALPUFF modeling system delineated in the GAQM. 

Given the documented limitations ofthe modeling system described above, and lacking any 

relevant evaluations ofthe NOOBS=l approach, we would not be able to endorse its use at this 

time without a thorough inspection ofits implementation and evaluation ofmodel performance. 

The Model Clearinghouse also concurs with Region 8's view based on existing EPA guidance 

that "blending" ofNWP data with observations is the most technically-sound approach to 

developing meteorological fields for application ofthe CALPUFF model. This ~pproach should 

be used absent information showing that an alternative approach has equal technical merit. 

Section 8.3.1.2(d).ofthe GAQM states that these mesoscale meteorological fields should be used 

in conjunction with available standard NWS or comparable meteorological observations within 

6
 
and near the modeling domain. While the traditional method for this approach has been 

accomplished through the use ofCALMET in its "hybrid" mode, Section 8.3.1.2(d) does not 

preclude the use ofother methods to "blend" observational data into NWP data. It is EPA's view' 

that t~e use ofprognostic data from an NWP model using four-dimensional data assimilation 

(FDDA) is consistent with this recorruhendation for ''blending''. A more complete discussion of 

this issue is provided in the draft IWAQM reassessment report (USEPA, 2009), including, 

proposed revisions to the IWAQM Phase 2 recommendations that are responsive to the issues 

and concerns raised in this memorandum. We also anticipate that new guidance and additional 

regulatory clarifications on the use ofNWP and observational data in LRT modeling will be 

developed in the future as the modeling community expands its use ofNWP data in dispersion 

modeling. " 

" 

CONCENTRATION POST-PROCESSING ISSUES 

The Otter Tail Protocol proposes the use ofthe Ammonia Limiting Method (ALM) which 

utilizes time-varying background values ofsulfate, nitrate, and total ammonia. Monthly 

background averages are der,ived from 2002 CMAQ modeling results from the WRAP for each 

ofthe Class I areas under review. The Otter Tail Protocol contends that the ,full ALM approach 

is consistent with the MNITRATE=1 approach that the FLMs have previously accepted in,Class 

I visibility analyses. Both Region 8 and the<FLMs object to the use ofthe full ALM, and would 

prefer a constant ammonia background and the application ofMNITRATE=1. 

Under Section 6.2.i(e) ofthe GAQM, CALPUFF may be applied for haze attribution 

assessments when larger domains ~e involved than can normally be handled by the VISCREEN 

model. No specific guidelines exist within the GAQM, which covers the application of 

CALpUFF for the post-processing ofchemical species. General guidance on the application of 

CALfUFF for such analyses can be found in the IWAQM Phase 2 report (USEPA, 1998) and 

Federal Land Managers FLAG 2000 guidance (NPS, 2000). According to Section 6.2.1 (e) of 

the GAQM, specific procedures and analyses for CALPUFF should be determined in 

consultation with the appropriate reviewing authority and the affected FLMs. Since EPA Region 

8 is the reviewing authority ofrecord for this analysis, the Model Cle,aringhouse defers to the 

Region's judgment as to the best analytical procedures for post-processing 0 f concentrations for \ 

visibility calculations. 

ADDITIONAL OBSERVATIONS FOR CONSIDERATION 

The Model Clearinghouse would also like to highlight several other observations that the Region 

should consider in its evaluation ofthe Otter Tail Protocol as it pertains to grid resolution. As' 

noted above, the proposed use ofa I km grid resolution in CALMET/CALPUFF is linked in the 

Otter Tail Protocol with the specification oftlfree separate modeling domains of limited extent, 

ostensibly to balance the computational demandsofthe high resolution grid. The emission unit 

under ,review is located atthe extreme eastern edge ofthe proposed modeling domains for both 

the southwestern and northwestern domains. Since during significant periods ofthe year the 

synoptic scale winds will flow' zonally from west to east over the high plaID~ ofthe north central 

United States, it is reasonable to expect that the emissions fromthe unit being modeled will 

rapidly flow offofthe computational domain. Ifrecirculation ofthe emissions is possible, the , I 

7 
proposed grid configuration creates the potential fot artificial elimination of emissions from the 

computational domain. Therefore, we recommend that the Region consider expanding the 

domains both east and south to prevent the possibility of artificial elimination ofemissions from 

the computational grid. Also, given our response to the issue regarding grid resolution, there 

does not appear to be any technical or practical issues that would necessitate the use ofmultiple 

domains for this application. 

,The stack parameter information listed in'Table 2-1 ofthe Otter Tail Protocol appears 

inconsistent with stack data reported on the WRAP website and utilized in the 2007 CAMx 

PSAT analysis previously cited. Region 8 should verify that the information contained irrthe 

Otter Tail Protocol is correct. 

SUMMARY 

The Model Clearinghouse has reviewed the BART modeling protocol for the Otter Tail Power 

Big Stone Unit I in South Oak:~ta and Region 8's positions regarding the proposed 

CALMET/CALPUFF grid resolution, non-default CALMET settings, and concentration postprocessing options. Based upon our review ofthe supporting information contained within the 

Otter Tail Protoeo/and available literature regarding the use ofNWP data in DWM's, the Model, 

gearinghouse concurs with Region 8's position on grid resolution and the use ofnon-default 

options. We defer the final issue regarding post-processing to the Region and the I1LMs for 

appropriate resolution. Ifyou have any further questions Of comments, please contact me at 

(919) 541-5562. 

cc:	 Roger Brode, C439-01 

Richard Wayland, C304-02 

Bifl Harnett, C504-01 

Raj Rao, C504-01 

Tim Allen, USFWS 

John Notar, NPS . 

I 

John Vimpnt, NPS 

Rick Graw, USFS 

EPA Regional Modeling Contacts, Regions I-VII, IX-X 

8
 
REFERENCES 

Anderson, B.A., 2006: Use ofPrognostic Met~rological Model Output in Air Quality Models: 

The Good, the Bad, and the Ugly. Presentation at the 2006 EPA Regiona~ State, and Local 

Modeler's Meeting, San Diego, CA, May 16-18, 2006. 

http://www.c1eanairinfo.com/regionalstatelocalmodelingworkshop/old/2006/documents/RSLIPR 

ESENTAnON.pdf 

Earth Tech, 2001: CALPUFF/MM5 Study Report: Final Report. Tech Rep. Earth Tech, Inc., 

Concord, MA 40 pp. www.dec.state.ak.us/air/ap/docs/finrep.pdf \ 

NPS, 2000: Phase I Report ofthe Federal Land Managers' Air Quality Related Values 

Workgroup (FLAG). National Par:\{ Service, Air Resources Division; U.S. Forest Service, Air 

Quality Program;. U.S. Fish and Wildlife Service, Air Quality Branch. 

http://www.nature.nps.gov/air/Pubsfpdfiflag/FlagFinaLpdf 

Scire, 1.S., 2008: Development, Maintenance and Evaluation ofCALPUFF. Presentation at 9th 

Conference on Air Quality Modeling, Research Triangle Park, NC, October 9 -10, 2008. 

http://www.epa.gov/scramOOJ/9thmodconf/scire calpuffpdf 

___,2009: Modeling in a Complex Terrain Environment at H:igh Latitudes. Presentation at 

the The Latest Developments in Air Modeling Specialty Cpnference ofthe Air & Waste 

Management Association, Toronto, Ontario, Canada, January 19-22, 2009. 

http://www.awma.org/proceedings/CDNairmodeling2009:html 

TRC Environmental Corporation, 2009: Modeling Protocol for a BART Assessment ofthe Big 

Stone I Coal-Fired Power Plant, Big Stone City, South Dakota. Prepared fur Otter Tail Power 

Company, Big Stone' City, SD, 39 pp. 

USEPA, 1998: Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary 

Report and Recommendations for Modeling Long Range Transport Impacts. Tech Rep., EPA454/R-98-009, Research Triangle Park, NC, 160 pp. ., 

http://www.epa.gov/scramOOll7thconf/calpufflphase2.pdf 

__-,,2008: Assessment ofthe "VISTA's Version ofthe CALPUFF Modeling System. Tech 

Rep., EPA-4541R-08-007, Research Triangle Park, NC, 32 pp. 

http://www.epa.gov/ttn/scram/reports/calpuffvistas assessment report finaLpdf 

__---'---" 2009: Reassessment ofthe Interagency Workgroup on Air Quality Modeling 

(IWAQM) Phase 2 Summary Report: Revision.s to Phase 2 Recommendations (Draft). EPAEPA-4541B-09-XXX, Research Triangle Park, NC, XX pp. 

WRAP, 2006: CALMET/CALPUFF Protocol for BART Exemption Screening for Class I Areas 

in the Western United States. WRAP Air Quality Modeling Forum, Regional Modeling Center, 

43 pp. . 

9 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
 

REGION 8
 

1595 Wynkoop Street 

DENVER,CO 80202-1129 

Phone 800-227-8917 

http;/lwww.epa.gov/region08 

FEB 2 2009 Ref: 8P-AR 

MEMORANDUM 

SUBJECT: CalpuffVisibility Modeling Protocol for Regulatory Analysis 

FROM: Kevin Golden, Lead I\egional Modeler , ./ 1 . I 

/ / , LI7U)~ /". / A

/'>-t. '''l -,...., .../:;- . ~,,-.~

Carl DalYJChiefA)permitting• Monitoring, and Modeling Unit 

C@"j Dw/ "r\:.> 

TO: Tyler Fox, Leader 

Air Quality Modeling Group, OAQPS 

This memo seeks your concurrence with Region 8's intent to reject certain aspects of a BART 

analysis proposed by Otter Tail Power for the Big Stone Unit I EGU in eastern South Dakota. 

The Calmet-related issues with Big Stone have also been raised by commenter's at recent 

EPA/State/Local modeling workshops and in the technical literature. A long term fix of the 

interface between Caimet/MM5/Cal puff needs to be developed to provide consistency and 

accuracy in Calpuff applications. In the interim, EPA guidance is needed on how to address these 

issues in regulatory applications. In the absence ofa refined model evaluation data set that 

would allow a definitive resolution to these issues, Region 8 is seeking an approach that will 

provide a reasonably conservative estimate of Big Stone's impact on visibility in Class 1 areas. 

BACKGROUND 

Region 8 has been working with the Federal Land Managers ,md South Dakota to develop an 

acceptable Calpuff modeling demonstration to determine whether the Big Stone Unit I power 

plant in eastem South Dakota is subject-to-BART. Big Stone Unit I is a large uncontrolled coalfired facility that is approximately 400 km from the nearest Class 1 areas in MN. We have 

attempted to develop a modeling protocol with the companyIFLMs/SD, however the company's 

consultant (Otter Tail Power's consultant is 'fRC) has not been responsive to Region 8's, SD's, 

and the FLM's comments. We are concerned about the continuing delay in resolving this issue 

since the December 2007 regulatory deadline for States to submit Regional Haze SIPs has passed 

and EPA has issued a finding of failure to submit to SD. In addition, the company has proposed 

another unit at the Big Stone facility that would rely, in part, on S02 and NOx emission 

reductions from the existing Unit I to avoid the PSD process for the new unit. There has been 

considerable interest in the media, at the political level, and in the environmental community on 
the Big Stone nev·" unit issue. 

Big Stone I has previously been modeled for BART visibility impacts by Region 7 as part of 

work being conducted for Nebraska using the particulate source apportiorunent (PSAT) 

capability ofCAMx. That "screening" analysis showed impacts exceeding 0.5dv at Class I parks 

in both SO and !\1N. In addition, 'IRC applied the Cal puff model in their September 2008 

submittal in the absence ofan approved protocol. That analysis showed an impact of 0.489 dv on 

the Boundary Waters Class 1 area. 

SPECIFIC ISSUES AND REGION 8 POSITION 

Modeling grid 

TRC has proposed to use three CALMET modeling domains developed with 1 km resolution and 

an overlaying 36 km MM5 grid (see Figure 3-1 in TRC attachment). Region 8 has accepted I km 

and smaller grids in modeling applications in Colorado and Montana where complex terrain is in 

close proximity to the source because we believe that the higher resolution at these distances will 

better characterize terrain effects and local scale meteorology. However, at a distance of 400 km 

in relatively tlat terrain it does not seem reasonable that, in the absence of additional data, a I km 

resolution would provide a more accurate estimate of source impacts. This is particularly true 

when the M~v15 data is only at a 36 km resolution. We are concerned that the proposed I km grid 

resolution in Calpuff/Calmet will not necessarily enhance and may even degrade model 

perforn1ance. We are not aware ofa model evaluation data base that would aJlow us to test 

model performance at these distances using various grid resolutions. Region 8 believes that a 4 

km resolution in Calmet I Calpuff would likely provide a conservative estimate of impacts in this 

application. 

Calmet Non-default settings 

TRC is proposing to use the non-default "no-obs" setting in Calmet, which would make this a 

non-guideline modeling demonstration. TRC argues that inclusion of the upper air data directly 

into Calmet is likely to degrade the quality of the wind fields, and that these observations are not 

dense enough, thus they propose to use model settings noobs=l and itwprog=2. These switches 

remove the need for upper air observations both with regard to winds and temperature. TRC's 

arguments are not supported by data showing degraded wind fields. Appendix W (paragraph 

8.3.1.2(d» requires that mesoscale meteorological fields be used in conjunction with NWS or 

comparable observations, not in place of such observations. Region 8 believes that upper air 

observations and temperature profiles should use the default settings. (noobs-O and itwprog=O). 

Ammonia issues 

Initially TRC would assume a constant background ammonia concentration of 1 parts per billion 

(ppb) as recommended in the 2006 WRAP Protocol, However, TRC proposes to use data from a 

CMAQ 2002 modeling application in the ammonia limiting method (ALM) analysis. This would 

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result in ammonia concentrations lower than values that have recently been measured in the MN 

Class I areas, and significantly lower than those measured in southwestern MN closer to the 

location of the Big Stone facility (Caughey, 2008). Region 8 has more confidence in the 

measured ammonia levels which suggest that a value of at least I ppb is appropriate for use in 

Calpuff and any ammonia limiting analysis. 

In their September 2008 submittal TRC utilized a specific version of ammonia limiting (referred 

to as ALM) during the POSTUI'IL step that was specifically developed as part of the VISTAS 

BART process and was reviewed and rejected by FWSfNPS. VISTAS subsequently did not 

pursue or incorporate that method further into VISTAS work. In that case, EarthTech (now 

TRC) was the consultant for VISTAS. However, FWSfNPS has accepted a similar anunonia 

limiting process through the use of POSTUTIL's "MNITRATE=I" switch. Region 8 proposes to 

accept this approach, which is consistent with the VISTAS RPO process. 

Source Emissions 

In response to our previous request, TRe's latest protocol documents the emissions that would 

be used in the modeling. TRC proposes to model only S02, NOx, and PM2.5 emissions from the 

facility. In visibility modeling Region 8 has required sources to provide more detailed speciation 

of particulates and condensable particulate emissions in Calpuff BART applicability modeling. 

This should include primary S04, SOA (organic carbon particles), elemental carbon (EC), PM 

fine, and PM coarse particulates as per NPS recommendations. 

Reference: 

Caughey, M.,el ai, April 30,2008 Ambient Gaseous Ammonia Monitoring at the Femberg, MN 

Air Monitoring Site Using Passive Diffusion Monitoring. Illinois State Water Survey, University 

of Illinois 

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