### June 15,2011 Memorandum to theNorthDakotaRegional Haze SIP File DocketID# EPA-R08-0AR-2010-0406 Subject: August 3, 2010 Correspondence from theNorthDakotaDepartmentof Health (SupplementNo.1 to the North Dakota SIP for Regional Haze)
From: Gail Fallon, EnvironmentalEngineer Environmental Protection Agency, Region 8

This isto documentthat EPA replaced pages inthe original SIP submittal as requested perthe subject correspondence. Attached to this memorandum is the onepage containing errors which were removed. A copy ofthe subjectcorrespondence and correctedpages is includedin the docket.future emissions inventory was modified to reflect the control technology for each candidate source (AVS I EGU, AVS 2 EGU, Coyote EGU, and Tioga Gas Plant), and modeling was conducted using the revised future inventory for one source at a time. The reasonable progress goals in 40 CFR 51.308(d)(1) requires improvement in the most impaired days. The most impaired days are defined in 40 CFR 51.301 as the average visibility impainnent for the twenty percent days with the highest amount ofvisibility impainnent. Therefore, modeling addressed the 20% worst days for both TRNP and L W A Class I areas. The results for each candidate source were compared with the results using the unmodified future emissions inventory (Table 8.11) to detennine the additional visibility improvementdue to the tested control technology. Modeled visibility improvement, for each candidate source/technology, is provided inTable 9.9. The single source controlledemissions (modeledtons peryear) and annualized cost effectiveness (dollars per deciview) are also reported in the table. Reported visibility improvement (in deciviews) reflects the higher value for either TRNP or L WA. Note that visibility improvement reported for Coyote represents the total for both S02 and NOx control technologies, and the improvement reported for the Tioga Gas Plant represents the total for all 1920 and 2350 horsepower engines. As shown in the table, predicted visibility improvement is very marginal for all candidate sources/technologies, and consequentlycostperdeciview is very high.

Table 9.9 Visibility Improvement and CostEffectiveness Visibility Visibility Improvement Improvement Cost Source Pollutant Control Technolo2Y Emissions (TPy) (dv)* (0/ 0 *** Effectiveness (S/dv)** TRNP LWA**TR.~P** LWA AVS1 NO. LNB+SNCR 2358 0.005 

### om 0.03 0.05 1,124,000,000 AVS2 NO. LNB+SNCR 2,144 0.005 

### om 0.Q3 0.05 1,124,000,000 Coyote S02 NO. Wet Scrubber ASOFA+SNCR 1,924 5,871 0.02 0.04 0.11 0.20 1,113,000,000 TiogaG.P. 1920 BHp Engines NO. LEC Retrofit 268 0 0.5 0 0.26 21,200,000 2350 BHp Engines NO. SCR 33 *The less efficienttechnologies evaluated wouldprovide less improvement. **Based on the maximum visibility improvement (per source) at any Class I area in North Dakota. ***Improvement 

### (%) from baseline conditions. 

### Time Necessary for Compliance Up to 6.5 years after SIP approval is necessary to achieve compliance (see EC/R report in Appendix 

### I.l). Additional time maybe necessaryifnonnal maintenance outages do not coincide with the projected schedule. It is anticipated that all required changes could be implemented by 2018 depending on the date of approval of this SIP. 

### It is not anticipated that any of the remaining sources will beretiredpriorto 2018.

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