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)

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

INTRODUCTION

In response to your memorandum ofFebruary 24, 2009, the Model Clearinghouse has reviewed the proposed position and resolution oftheissues presented in orderto develop a suitable air quality analysis for visibility for the OtterTail 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 Programregulations.

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

### Ill ofEPA's Guidelines forBARTDetermination Under the RegionalHaze Rule, 

### which is located in Appendix Y to Part 51 ofTitle 40 ofthe Code ofFederal Regulations. Section III.A.3.(0ption 1) 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, withrespect to theuse ofCALPUFF for regulatory applications, footnote 8 in this section ofAppendix Y references EPA's Guideline onAir Quality Models (GAQM), 

### published in Appendix W ofPart 51. Section 6 ofthe GAQM

### includes recommendations regarding application ofCALPUFF for visibility assessments and for long range transport (LRT) applications in general (nominallybeyond about 50kilometers), indicating that such applications ''will

### require significant consultation withthe 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 theInteragency Workgroup onAir QualityModeling (IWAQM) Phase 2 Summary Report andRecommendations forModelingLongRange TransportImpacts 

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

### Thus, when CALPUFF is used in this context, it is ourunderstanding that EPA Regional Offices have

Internet Address (URL) • http://www.epa.gov Recycled/Recycl•ble • PrlnledwHh Vegetable 011 Based Inks on Recycled Paper (Minimum 25% Postconsumer)I. encouraged following boththe IWAQM Phase 2 report and the GAQMwhen conducting modeling for the BART program. · Recently the FLMs have made us awarethat a number ofthe issues identified in the Region's memorandumregarding this BART application afso existfor Prevention ofSignificant 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 ofthe GAQMand 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 bythe FLMs in recent PSD applications, theModel Clearinghouse believes it appropriate to.evaluate the protocolproposed 'by OtterTail 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'sposition that the use ofa 1 kmgrid resolution in CALMET/CALPUFF.isnot adequatelyjustified given the geographical characteristics of the domain ofinterest and the limitations ofthe modeling system



### . . 2) We concur with Region 8's view based onEPA guidelines that ''blending" National Weather Service (NWS) observations withprognostic model datais the most technicallysound approach to developing meteorological fields for application ofthe CALPUFF model when prognostic model data are incorporated. This approach should be used unless adequate documentation is provided demonstrating that an alternative approach has equaltechnical merit. Absent pertinent evaluations, we' are unable to endorse use of the NOOBS =1 option recommended in the Otter TaZIProtocol 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 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 documentReassessment oftheInteragency Workgroup onAir Quality Modeling (IWAQM) Phase 2 SummaryReport: Revisions to Phase 2Recommendations (USEPA, 2009) available for review onEPA'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. ·



### - 2BACKGROUND

EPARegion 8, in conjunctionthe 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 OtterTail Power Big Stone Unit I electrical generating unit in eastern South Dakota. Big Stone Unit I is a large uncontrolled coalfired facility that is approximately400 km qomthe 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 inthe absence ofa protocol**~pproved** bythe aforementioned parties. In

this submittal, the Big Stone Unit I had. an impact of0.489 delta-deciview (d-dv) onthe Boundary Waters (BOWA) Class I area Othermodeling 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 orithe 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 submittedthe Otter Tail Protocol (TRC, 2009) toEPA Region**~and** the FLMs outlining proposed procedures for a revised G;ALPUFF analysis. The Otter Tail Protocolproposed 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 ofalternative procedures for post-processing nitrate concentrations that are not consistentwiththe WRAP BART modeling procedures. BothEPA 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 Protocolto the EPAModel Clearinghouse for review ofthe Region's position on grid resolution, non-default CALMET options, and CALPUFF post-processing options. This Clearinghouse memorandumwill address the specific deviations from the WRAP protocoIidentified by the Region's Modeling Clearinghouse request. ·
CALMET/CALPUFF GRID RESOLUTION

'fhe 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 highspatial resolution and the large extent ofthe area ofinterest". Each ofthe proposed modeling ddmains utilize a horizontal grid resolution of 1kilometer, deviating from the 4 km horizontal grid resolution recommendedbythe 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 BoundaryWater Canoe Area WA, and ofother smaller lakes onthe trajectories to the**v~ious** Class I areas, is also best resolved at 

### llanresolution."

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 beresponsible for transport ofairborne contaminants from the sourceto the Class I area(s) ofinterest. The**secon~** component ofthe argument is that the diagnostic wind model (DWM), CALMET, can enhance theNWP data used as the first-guess wind field (IPROG=l4) sufficiently to adequately replicate the keymeteorological features ofinterest.

Model ClearinghouseRecommendation on GridResolution

Based upon a review ofthe Otter Tail Protocol and relevant scientific literature, the Model Clearinghouse of:Iers the following conclusions. First, the Otter Tail Protocolpresents no scientific evidenceto support the claim that 1km CALMET resolution increases the objective .accuracy ofthe final wind field, especially in areas ofrelatively modest topographic relief, such
as for eachofthethree 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 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 capturethe full three-dimensional structureof complex flows. Without the benefit ofhighresolutionNWP data or a high density of representative observational data, the ability ofthe.DWMto accurately simulate,these conditions is limited. Several studies have documented the inherent limitations ofDWM diagnostic algorithms (e.g., EarthTech, Inc. (2001), Scire (2f>08), and Scire (2009))

. Therefore, weconcur with the Region's position that the use ofa I km grid resolution·in

CALMET/CALPUFF is not adequatelyjustified given the geographical characteristics ofthe domain ofinterest and the limitations ofthe modeling system. Furthermore, as indicated in our Introduction, the Otter TailProtocotlinks 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-offisjustified, and are concerned that the proposed domains maynot adequately simulate the potential for plume recirculation. Based on a review,ofthe relevant scientific literature and a review ofthe CALMET capabilities, we also see no evidence to supportthe use ofa 4 kmgrid 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 higherthan the 36 kmMM5 data are notjustified for other areas within WRAP.

Based on ourreview ofthis issue and given the limitations ofthe CALMET DWM,.ourview is that the candidate NWP data used should appropriately characterize the keymeteorological features that govern source-receptorrelations for the specific application. We also see no clear basis for, orbenefit 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



### 4Clearinghouse 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 sufficientlydense and representative networkofobserved data are available, and the improved perfurrpance ofthe CALMET wind fields can be objectively demonstrated. When properly applied with adequatelyresolved NWP qata, the CALMET firstguess field likely already reflects the relevant meteorological features ofinterest at that resolution.

The Mo<lel Clearinghouse**recomme~dation**Btrictly implies that thtt candidateNWP 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 candidateNWP dataset 

### is at the appropriate horizontal grid resolution andthat 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 GAQMis a critical component for planning a su,ccessful LRT model application. In light of these, concerns, the appropriateness and adequacy ofthe CALMET/CALPUFF grid resolution, as well as anyprognostic model dataused as input to CALMET, should be adequatelyjustified based on**~h~** specific.**ne~s** ofthe**a~plicat.ion,** and**me~sures** should**b~** taken)to.objectively**~sess** the resultmg meteorologiCal fields, mcludmgbothhonzontal and vertical vdocity fields, pnorto their acceptance for use in CALPUFF. ·In accordance with Section 8.3(d) ofthe GAQlvf, we must emphasize that acceptance ofaprognostic data set is·contingent upon concurrence from the appropriate reviewing autHority. Therefore,

# at a

### ~nimum, anyprotocol should include an evaluation oftneperformance ofthe candidateNWP datasetpriorto acceptance bythe reviewing authority. Model performance evaluationprocedures should bebased on appropriate and acceptable metrics and methods. Further, ifthe intent is to apply CALMET at resolutions much higher than the original NWP dataset, the suitabilityoftheresultant datasets should aJso qe examined through the appropriate statistical analysis.

A more complete discussion ofthis issue is provided in thedraft document Reassessmentoftlte Interagency Workgroup onAir QualityModeling (IWAQM) Phase 2 SummaryReport: Revisions to Phase 2 Recommendations (USEPA, 2009) available for review onEPA's Support Center for Regulatory AtmosphericModeling (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.



### CALMETNON-DEFAULT SETTINGS

Asbackground, 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 ofthe GAQM(formerly Section 9.3 priorto 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 totallyupon 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 ofthe NOOBS = 1 option ofCALMET,



### 5'\ ' which uses NWP data in lieu oftwice daily upper air soundings normally**~ployed** in the construction ofGALMET wind fields, but incorporates surface observations. TheNOOBS = 2 option uses no observed surface orupper 

### air data, relying solely ontheNWP data. The 

### Otter TailProtocol contends that using upper air observations directly into CALMET is likely to degrade the quality.ofthe wind**field~** as c.Ompared to the use ofgridded MM5 data, although no further rationale orobjective evidence for this claim is offered.

As discussed in the IWAQM reassessment report (USEPA, 2009), there is a clear bodyof evidence to suggest that higher spatial and temporal frequency ofNWP dataused in LRT modeling generally results in better LRT model verification statistics. Therefore, in theory, the NOOBS approach in CALMET could offer the opportunityto**t~e** advantage ofhigher temporally and spatially resolved initial guess wind fields from NWP datathan could otherwise be achieved through the exclusive use dftwice-daily RAOB soundings. However, it is important to notethat CALMET does not merelypass through the majority ofthe information from the NWP model to**C~PUFF.** Much ofthe original NWP data (e.g., planetaryboundary layer (PBL) heights and scaling parameters) Is recomputed within CALMET. Therefore, careful consideration must be givento how these re-diagnostic procedures are implemented within CALMET. As also noted in theIW AQM reassessment report (USEPA, 2009), CALMET does not fully utilize the 3-dimensionaltemperature 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 properlyutilize the full benefits of current state-of-the-practice prognostic modeling capabilities, there are few, ifany, objective evaluations ofmodel performance onwhichto base acceptance ofthese NOOBS options.



### Model ClearinghouseRecommendation forNon-defauli CALMETSettings

, While the 

### Otter Tail

### Prot~col onlyproposes the use ofthe NOOBS=l option ofCALMET, our

experiences from the assessment ofthe VISTA's version (USEPA, 2008) and the 2001 Philadelphia study (Anderson, 2006) suggest that careful consideration ofthe underlying science and its implementation must betaken whenusing the more advanced features ofCALMET. A literature search conductedby the Model Clearinghouse onsubsequent evaluations ofthe

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

approach yielded no significant information regarding theperformance ofthe ''NOOBS" approach as compared to the traditional "hybrid" approach, other than the references listed in Appendix A-4 ofthedescriptiop. ofthe CALPUFF modeling system delineated in .the 

### GAQM. Given the documented limitations ofthe modeling system described above, and lacking any relevant evaluations oftheNOOBS=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 approach should be used absent information showing that an alternative approach has equal technical merit. Section 8.3.1.2(d).ofthe 

### GAQMstates that these mesoscale meteorological fields should be used in conjunction with available standard NWS or comparable meteorological observations within

6and near the modeling domain. While the traditional method for this approachhas 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 modelusing four-dimensional data assimilation (FDDA) is consistent withthis recorruhendation for ''blending". A more complete discussion of this issue is provided in the draft IW AQMreassessment 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 anticipatethat new guidance and additional regulatory clarifications onthe 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 TailProtocolproposes theuse oft.he AmmoniaLimiting 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 TailProtocol contends that the,full ALM approach is consistent with the MNITRATE=l approachthat the FLMs have previously accepted in,Class I visibility analyses. BothRegion 8 and the<FLMs object to the use ofthe full ALM, and would prefer a constant ammoniabackground and the application ofMNITRATE=l.

Under Section 6.2.i(e) ofthe GAQM, CALPUFF maybe applied for haze attribution assessments when largerdomains**~e** involved than cannormallybe handled bythe VISCREEN model. No specific guidelines exist within the GAQM, which covers the application of CALPUFF for thepost-processing ofchemical species. General guidance onthe application of CALfUFF for such analyses canbe found in the IW AQM Phase 2report (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 consultationwiththe 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'sjudgment as to the best analytical procedures for post-processing ofconcentrations for\ visibilitycalculations.



### 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 TailProtocol as it pertains to grid resolution. As' noted above, the proposed use ofa 1 km grid resolution in CALMET/CALPUFF is linked in the Otter TailProtocol with the specification ofthree separate modeling domains oflimited extent, ostensiblyto balance the computational demands ofthe high resolution grid. Theemission 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 overthe high**plam~** ofthenorth 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

7proposed grid configuration creates the potential fotartificial elimination ofemissions from the computational domain. Therefore, werecommend that the Region consider expanding the domains both east and southto prevent the possibility ofartificial elimination ofemissions from the computational grid. Also, given ourresponse to the issue regarding grid resolution, there does not appearto be any technical orpractical issues that would necessitate the use ofmultiple domains for this application

.

. The stack parameterinformation listed in'Table 2-1 ofthe Otter Tail Protocol appears inconsistent with stack datareported onthe WRAP website and utilized in the 2007 CAMx PSAT analysis previouslycited. Region 8 should verify that the information contained irrthe Otter Tail Protocolis correct.



### SUMMARY

The Model Clearinghouse has reviewed the BART modeling protocol for the OtterTail 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 ourreview ofthe supporting information contained within the Otter Tail Protocoland available literature regarding the use ofNWP datain DWM's,the Model , 9earinghouse concurs withRegion 8'sposition on grid resolution and theuse ofnon-default options. We defer the final issue regarding post-processing to the Region and the FLMs for appropriate resolution. Ifyou have any further questions 

### otcomments, 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 ESENTATION.pdf

Earth Tech, 2001: CALPUFF/MM5 StudyReport: Final Report. Tech Rep. EarthTech, Inc., Concord, MA40pp. 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/FlagFinal.pdf
Scire, J.S., 2008: Development, Maintenance and Evaluation ofCALPUFF. Presentation at 91 h Conference onAir 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 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 onAir QualityModeling (IWAQM) Phase 2 Summary Report and Recommendations for Modeling Long Range Transport Impacts. Tech Rep., EPA454/R-98-009, Research Triangle Park, NC, 160pp. "' http://www.epa.gov/scramOOl/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 ofthe Interagency Workgroup onAir 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, RegionalModeling Center, 43 pp.

.



### 9Ref: 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 DalyJChiefA)Pcrmitting. Monitoring, and Modeling Unit



# c@.__/ 

# JCt/ "r\:.> Tyler Fox, Leader Air Quality Modeling Group, OAQPS

This memo seeks your concurrence with Region 8's intent to reject certain aspects ofa 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 ofthe interface between Calmet/MM5/Calpuffneeds to be developed to provide consistency and accuracy in Calpuffapplications. 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 ofBig 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 Calpuffmodeling 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 offailure 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 (PSAT) capability ofCAMx. That "screening'' analysis showed impacts exceeding 0.5dv at Class 1parks in both SO and .t\1N. In addition, TRC applied the Calpuffmodel in their September 2008 submittal in the absence ofan approved protocol. That analysis showed an impact of0.489 dv on the Boundary Waters Class 1area.

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 of400 km 

### in relatively tlat terrain it does not seem reasonable that, in the absence ofadditional data, a I km resolution would provide a more accurate estimate ofsource impacts. This is particularly true when the**M~v15** 

### data is only at a 36 km 

### resolution. We are concerned that the proposed 1km 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 allow us to test model perforn1ance at these distances using various grid resolutions. Region 8 believes that a 4 km resolution in Cahnet I 

### Calpuffwould likely provide a conservative estimate ofimpacts 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 ofthe upper air data directly into Ca!Inet is likely to degrade the quality ofthe 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 ofsuch 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
2result 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 ofthe Big Stone facility (Caughey, 2008). Region 8 has more confidence in the measured ammonia levels which suggest that a value ofat least I ppb is appropriate for use in Calpuffand any ammonia limiting analysis.

In their September 2008 submittal TRC utilized a specific version ofammonia limiting (referred to as ALM) during the POSTUT'IL step that was specifically developed as part ofthe 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, EarthTech (now TRC) was the consultant for VISTAS. However, FWS/NPS has accepted a similar anunonia limiting process through the use ofPOSTUTIL's "MNITRATE=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 ofparticulates 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 al, April 30, 2008 Ambient Gaseous Ammonia Monitoring at the Femberg, MN Air Monitoring Site Using Passive Diffusion Monitoring. Illinois State Water Survey, University ofIllinois



### 3