Minnkota Power ~PQ C 0 0 P E R A T I V E , I N C • Your Touchstone Energy® Partner ~ 

1822 Mill Road• P.O. Box 13200 •Grand Forks, ND 58208-3200 •Phone (701) 795-4000 

June 6, 2012 

Mr. Terry O'Clair 

Director, Division of Air Quality 

North Dakota Department of Health 

918 East Divide Avenue, 2nd Floor 

Bismarck, ND 58501-1947 

Subject: Proposed Revision to the North Dakota State Implementation Plan 

Dear Mr. O'Clair: 

Minnkota Power Cooperative, Inc. (Minnkota), has the following comments and 

concerns relating to the proposed revisions to the State Implementation Plan (SIP) and 

EPA's comments dated April 20, 2012. 

The proposed revisions to Section 8.3.2 of the SIP would restrict the Milton R. Young 

Station's Unit 1 to a "ten-minute average" PM emission limit of 0.062 lb/106 BTU to 

·ensure compliance with the applicable 20% opacity limit under NDAC 33-15-03.01.2. 

On April 20, 2012, the Department received comments on the proposed revision to the 

SIP from EPA, who requested the ten-minute PM emission limit be reduced by a safety 

margin of 10% percent to 0.0523 lb/106 BTU. 

Minnkota has installed and is operating certified continuous particulate monitors (PM 

CEMS) on both Unit 1 and Unit 2 at the Milton R. Young Station. The PM CEMS was 

installed on Unit 2 as a requirement of the Consent Decree dated July 27, 2006. The 

PM CEMS was installed on Unit 1 as a result of the addition of a "wet" flue gas 

desulfurization unit (FGD). Because both units now employ "wet" systems, water vapor 

and entrained water droplets in the flue gas preclude the accurate measurement of 

opacity. 

In a letter dated February 16, 2010, Minnkota requested approval of an alternative 

monitoring method for the required continuous opacity monitors. On December 23, 

2010, the request was granted by the EPA. The request was approved with conditions, 

which Minnkota accepted by letter on January 31, 2011. Because opacity limits at 40 

CFR 60.42(b) are independently enforceable limits, EPA allowed Minnkota to 

demonstrate compliance using visible emissions readings in accordance with 40 CFR 

Part 60, Appendix A, Method 9. 

-
MPC requests the SIP revision be changed to the alternative monitoring method 

approved by EPA in their December 23, 2010, correspondence for the following 

reasons: 

1. The Department references the compliance assurance monitoring (CAM) plan 

to determine the ten-minute PM emission limit. This value (as listed in the 

CAM plan and submitted by Minnkota) was determined in accordance with 

40 CFR Part 60, Appendix A, Method 17. To maintain the isokinetic sampling 

required by Method 17, all test runs were in excess of one hour. It would not 

be possible to certify a PM CEMS with ten-minute measurement since it is not 

allowed under PS11. Although Minnkota has proven the PM CEMS to be 

very accurate on an hourly basis, it is very doubtful that a ten-minute emission 

period is representative of the actual emission exiting the stack. Due to the 

presence of water droplets in the flue gas the PM testing is currently 

conducted under Method 58. A 10 minute test run is not allowed in Method 

58 either. 

2. As was previously discussed with the Department the PM CEMS has the 

ability to sample in ten minute intervals. Minnkota has tried to reduce the 

sample time to ten minute periods on the PM CEMS and has found that it 

results in poor data. It is our belief the sample collected on the filter in the PM 

CEMS is an extremely small quantity and is therefore difficult for the monitor 

to accurately measure. 

Should you have any questions concerning the above, please contact me at 701-795-

4221, or at jgraves@minnkota.com. 

Sincerely, 

MINNKOTA POWER COOPERATIVE, INC. 

John T. Graves, P.E. 

Environmental Manager 

CC: Craig Bleth 

Kevin Thomas