UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

RESEARCH TRIANGLE PARK, NC 27711 

MAY 1 5 2009 

MEMORANDUM 

OFFICE OF 

AIR QUALITY PLANNING 

AND STANDARDS 

SUBJECT: Model Clearinghouse Review ofCALPUFF Modeling Protocol for BART 

FROM: TylerFox,Leader 

Air Quality Modeling 

~+ Group (C4£h~ol)' ~ ' 

TO: Kevin Golden, Lead Regional Modeler 

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

Carl Daly, Chief 

Air Permitting, Monitoring, and Modeling Unit (SP-A) 

INTRODUCTION 

In response to your memorandum of February 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 detemrineifthis 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 Ill 

ofEPA's Guidelines for BART Determination Under the Regional Haze Rule, which is located in 

Appendix Y to Part 51 of Title 40 of the Code of Federal Regulations. Section III.A.3.(0ption 

1) of Appendix 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 ofCALPUFF for regulatory 

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

Models (GAQM), published in Appendix W of Part 51. Section 6 of the 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) [of Appendix 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 (URL) • 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 of the issues identified in the Region's 

memorandum regarding this BART application afso 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 of preferred models or modifications of preferred 

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

in all cases. See also, 40 C.P.R.§ 51..166(1)(2). Given the impottanr,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 km grid resolution in 

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

the domain of interest 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 of the CALPUFF 

model when prognostic model data are incorporated. 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 TaZI Protocol at this time 

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

' In addition, we are proposing revisions to the IW AQM J.>hase 2 recommendations that are 

responsive to the issues and concems'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 of this memorandum provides background on'the Region 8 request and a more 

detailed explanation for each of the above recommendations. · 

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BACKGROUND 

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

state of South 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 arialysis in September 2008. This 

· analysis was conducted in the absence of a protocol ~pproved by the aforementioned parties. In 

this submittal, the Big Stone Unit I had. an impact of0.489 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 ori 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. 

'1 

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

Region ~and the FLMs outlining proposed procedures for a revised G;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 of influence 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 of the Region's position on grid resolution, non-default CALMET 

options, and CALPUFF post-processing options. This Clearinghouse memorandum will address 

the specific deviations from the WRAP proto co I identified by the Region's Modeling 

Clearinghouse request. · 

CALMET/CALPUFF GRID RESOLUTION 

'fhe Otter Tail Pro.tocol called for the use of three· 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 of the area of interest". Each of the 

proposed modeling ddmains utilize a horizontal grid resolution of 1 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 of Lake 

Superior, close to Boundary Water Canoe Area W A, and of other smaller lakes on the 

trajectories to the v~ious Class I areas, is also best resolved at llan resolution." 

3 
An argument for the use of finer 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) of interest. The 

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

enhance the NWP data used as the first-guess wind field (IPROG=l4) sufficiently to adequately 

replicate the key meteorological features of interest. 

Model Clearinghouse Recommendation on Grid Resolution 

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

Clearinghouse of:Iers the following conclusions. First, the Otter Tail Protocol presents no 

scientific evidence to support the claim that 1 km CALMET resolution increases the objective 

.accuracy of the final wind field, especially in areas of relatively modest topographic relief, such 

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

" consistent in the conclusion that there is a limitation to the benefit of higher resolution gridded 

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

topographic relie£ 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 ofthe.DWM to accurately simulate ,these conditions 

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

algorithms (e.g., Earth Tech, Inc. (2001), Scire (2f>08), and Scire (2009)) 

. Therefore, we concur with the Region's position that the use of a I km grid resolution·in 

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

domain of interest and the limitations of the modeling system. Furthermore, as indicated in our 

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

modeling domains to the use of high (1 km) spatial resolution, implying a trade-off in 

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 of the CAL MET capabilities, we also see no evidence to support the use of a 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 of 4 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 of this issue and given the limitations of the 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 of the prognostic model used to specify the first-guess wind field. Since the Model 

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

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

adjustments, unless a sufficiently dense and representative network of observed data are 

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

demonstrated. When properly applied with adequately resolved NWP qata, the CALMET firstguess field likely already reflects the relevant meteorological features of interest at that 

resolution. 

The Mo<lel Clearinghouse recomme~dation Btrictly 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 Section 8.3(d),ofthe 

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

these, concerns, the appropriateness and adequacy of the 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 of the a~plicat.ion, and me~sures should b~ taken )to .objectively ~sess 

the resultmg meteorologiCal fields, mcludmg both honzontal and vertical vdocity fields, pnor to 

their acceptance for use in CALPUFF. ·In accordance with Section 8.3(d) of the GAQlvf, 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 of the candidate NWP datasetprior to acceptance by the reviewing 

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

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

higher than the original NWP dataset, the suitabilityofthe resultant datasets should aJso qe 

examined through the appropriate statistical analysis. 

A more complete discussion of this issue is provided in the draft document Reassessment oftlte 

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 of model e.valuation methods and prqcedures appropriate for these applications, 

including procedures for evaluation of diagnostic meteorological fields. 

CALMET NON-DEFAULT SETTINGS 

As background, when the CALPUFF modeling .system was promulgated m April 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 of the 

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 co111rnonly 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 of the NOOBS = 1 option ofCALMET, 

5 
'\ 

' which uses NWP data in lieu of twice 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 NWP data. The Otter 

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

degrade the quality .of the wind field~ as c.Ompared 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 of higher 

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 CALMET does not merely pass through the majority of the information from the 

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

(PBL) heights and scaling parameters) Is recomputed within CALMET. Therefore, careful 

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

CALMET. As also noted in the IW AQM reassessment report (USEP A, 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) if the LCALGRD option is selected. Aside 

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

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

evaluations of model performance on which to base acceptance of these NOOBS options. 

Model Clearinghouse Recommendation for Non-defauli CALMET Settings 

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

experiences from the assessment of the VISTA's version (USEPA, 2008) and the 2001 

Philadelphia study (Anderson, 2006) suggest that careful consideration of the 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 of the 

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

approach yielded no significant information regarding the performance of the ''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 of the NOOBS=l approach, we would not be able to endorse its use at this 

time without a thorough inspection of its implementation and evaluation of model 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 of the CALPUFF model. This approach 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 of other methods to "blend" observational data into NWP data. It is EPA's view 

that t~e use of prognostic 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 IW AQM reassessment report (USEPA, 2009), including_ 

proposed revisions to the IWAQM Phase 2 recommendations that areresponsive 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 oft.he Ammonia Limiting Method (ALM) which 

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

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

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

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

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

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

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

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

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

CALPUFF for the post-processing of chemical species. General guidance on the application of 

CALfUFF for such analyses can be found in the IW AQM Phase 2 report (US EPA, 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 of record for this analysis, the Model Cle,aringhouse defers to the 

Region's judgment as to the best analytical procedures for post-processing of 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 of the Otter Tail Protocol as it pertains to grid resolution. As' 

noted above, the proposed use of a 1 km grid resolution in CALMET/CALPUFF is linked in the 

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

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

under ,review is located at the extreme eastern edge of the proposed modeling domains for both 

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

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

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

rapidly flow offofthe computational domain. If recirculation 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 of emissions 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 of multiple 

domains for this application . 

. The stack parameter information listed in' Table 2-1 of the 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 Dak:~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 Protocol and available literature regarding the use ofNWP data in DWM's, the Model , 

9earinghouse concurs with Region 8's position on grid resolution and the use of non-default 

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

appropriate resolution. If you have any further questions ot comments, please contact me at 

(919) 541-5562. 

cc: Roger Brode, C439-01 

Richard Wayland, C304-02 

Bifl Harnett1 C504-01 

Raj Rao, C504-0l 

Tim Allen, USFWS I 

John Notar, NPS . 

John Vimpnt, NPS 

Rick Graw, USPS 

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.cleanairinfo.com/regionalstatelocalmodelingworkshop/old/2006/documents/RSLlPR 

ESENT A TION.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 of the 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/Pubsfpd fiflag/FlagFinal.pdf 

Scire, J.S., 2008: Development, Maintenance and Evaluation ofCALPUFF. Presentation at 91

h 

Conference on Air Quality Modeling, Research Triangle Park, NC, October 9 -1 0, 2008. 

http://www.epa.gov/scramOOJ/9thmodconf/scire calpuff.pdf 

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

the The Latest Developments in Air Modeling Specialty Conference of the 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 of the 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/scramOO l/7thconf/calpufflphase2. pdf 

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

Rep., EPA-454/R-08-007, Research Triangle Park, NC, 32 pp. 

http://www.epa.gov/ttn/scram/reports/calpuff vistas assessment report final.pdf 

-.----'---'' 2009: Reassessment of the Interagency Workgroup on Air Quality Modeling 

(IWAQM) Phase 2 SummaryReport: Revision.s to Phase 2 Recommendations (Draft). EPAEPA-454/B-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 

Ref: 8P-AR 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

REGION 8 

1595 Wynkoop Street 

DENVER.CO 80202-1129 

Phone 800-227-8917 

http:llwww.epa.gov/region08 

FEB 2 ~ 2009 

MEMORANDUM 

SUBJECT: CalpuffVisibility Modeling Protocol for Regulatory Analysis 

FROM: 

TO: 

Kevin Golden, Lead f\egional Modeler 

/ ' / . Ll?u' /'' / )~· A /'>-(,. ·"l __ .._., . ./':/ - . ~"- ·~ 

Carl DalyJChief A)Pcrmitting. Monitoring, and Modeling Unit 

c@.__/ J Ct/ "r\:.> 

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 Calmet/MM5/Cal puff needs to be developed to provide consistency and 

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

issues in regulatory applications. In the absence of a 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 Cal puff modeling demonstration to determine whether the Big Stone Unit l power 

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

attempted to develop a modeling protocol with the company/FLMs/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 arc 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. ln 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·.r 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 (PSA T) 

capability ofCAMx. That "screening'' analysis showed impacts exceeding 0.5dv at Class 1 parks 

in both SO and .t\1N. In addition, TRC applied the Calpuffmodel in their September 2008 

submittal in the absence of an approved protocol. That analysis showed an impact of0.489 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 I km resolution and 

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

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

perforn1ance. We are not aware of a model evaluation data base that would allow us to test 

model perforn1ance at these distances using various grid resolutions. Region 8 believes that a 4 

km resolution in Cahnet I Cal puff 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 Ca!Inet 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 1\WS 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-0 and itwprog=O). 

Ammonia issues 

Initially TRC would assume a constant background ammonia concentration of I 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 

2 
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 

Cal puff and any ammonia limiting analysis. 

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

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

BART process and was reviewed and rejected by FWS/NPS. VISTAS subsequently did not 

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

TRC) was the consultant for VISTAS. However, FWS/NPS has accepted a similar anunonia 

limiting process through the use of POSTUTIL's "MNITRA TE=l" switch. Region 8 proposes to 

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

Source Emissions 

In response to our previous request, TRC'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 Cal puff 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 al, 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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