From: McWilliams, Douglas A. [mailto:douglas.mcwilliams@squirepb.com]  

Sent: Monday, July 20, 2015 1:29 PM

To: Greenberg, Alan (ENRD)

Subject: Updated Tilden SO2 Annual Emission Estimate [I‐AMS.FID1382176]

Alan Greenberg,  

EPA requested certain information from Cliffs Natural Resources related to actual SO2 emissions from Tilden Unit 1 to be used to support

EPA’s determination that additional controls for SO2 did not meet the cost‐effectiveness criterion for Best Available Retrofit Technology

(BART) for Tilden Unit 1.  Specifically, EPA requested an updated estimate of the actual annual SO2 emission rate for Tilden Unit 1.  According

to 40 CFR Part 51, Appendix Y (“App. Y”), the baseline emission rate for the BART cost effectiveness calculation “should represent a realistic

depiction of anticipated annual emissions for the source.  In general, for the existing sources subject to BART, you will estimate the

anticipated annual emissions based upon actual emissions from a baseline period.”  See App. Y, Step 4.  In its original cost effectiveness

calculation, Tilden used 1,153 tpy SO2 as the anticipated annual SO2 emissions based on limited stack test data to demonstrate that add‐on

SO2 controls were not cost effective for Tilden Unit 1.   This cost effectiveness analysis continues to be a valid basis for determining that SO2

controls are not BART for Tilden Unit 1.  However, Tilden recently installed continuous emission monitors (CEMs) for SO2, which generated

sufficient valid SO2 data to develop an updated realistic depiction of anticipated annual SO2 emissions from Tilden Unit 1.  We are providing

this updated analysis in response to EPA’s request with the understanding that it provides additional support for EPA’s determination that

SO2 BART does not include add‐on emission control systems for Tilden Unit 1.    

  

As we have discussed, SO2 emissions at Tilden Unit 1 vary considerably depending upon the sulfur content of the fuels burned and the sulfur

content of the ore.  Therefore, we examined CEMs data to determine whether they reflect anticipated ore and fuel conditions for this

source.  The CEMs data when burning natural gas were used to assess the range of actual SO2 emissions attributed to the sulfur in the ore

during this time period.  The updated analysis starts with the realistic upper bound of SO2 emissions from the ore and then adds the

anticipated SO2 contribution from solid fuel when burning 100% coal.  This calculation established 845 tons per year as the upper range of a

realistic depiction of anticipated annual SO2 emissions.   In arriving at this estimate, Cliffs does not assume that future operating parameters

will differ from past practice and, therefore, enforceable restrictions are not required to support this baseline emission rate for cost

effectiveness calculations.  See App. Y at Step 4, subpart (d).

                                                                                                                                                             

This estimate of annual emissions is independent of the calculation used to support short‐term emission limits.  The CEMs data from

September 2014 shared with EPA previously indicated that maximum short‐term SO2 emissions are expected to be 500 lbs/hr on a 30‐day

rolling average basis when high sulfur ore and solid fuel usage occur simultaneously for 30 days or more.  This snapshot of CEMS data

remains an appropriate basis for establishing the interim 500 lb/hr short‐term SO2 limit in the settlement agreement.  However, looking at all

available information, it is not realistic to assume that SO2 will be emitted at 500 lbs/hr for an entire year.  Therefore, the calculation

provided above to support a realistic depiction of anticipated annual SO2 emissions at 845 tons per year is entirely consistent with a source

with the potential to generate 500 lbs/hr SO2 during a single 30‐day period under maximum short‐term conditions.     

Please let me know if you need additional information to support EPA’s BART determination.  

The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. Douglas A. McWilliams 

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