# MinnkotaPower**~PQ** C 0 0 P E R A T I V E , I N C • YourTouchstoneEnergy® Partner

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1822 Mill Road• P.O. Box 13200•Grand Forks, ND 58208-3200 •Phone (701) 795-4000 June6, 2012

Mr. Terry O'Clair Director, Division ofAir Quality North Dakota Department ofHealth 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), hasthefollowing 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 ofthe SIPwould restrictthe Milton R. Young Station's Unit 1to a "ten-minute average" PM emission limit of0.062 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% percentto 0.0523 lb/106 BTU.

Minnkota has installed and is operating certified continuous particulate monitors (PM CEMS) on both Unit 1 and Unit2 atthe Milton R. Young Station. The PM CEMS was installed on Unit 2 as a requirement ofthe Consent Decree dated July 27, 2006. The PM CEMS was installed on Unit 1as a result ofthe addition ofa "wet" flue gas desulfurization unit (FGD). Because both units now employ "wet" systems, watervapor and entrained water droplets in the flue gas precludethe accurate measurement of opacity.
In a letterdated February 16, 2010, Minnkota requested approval ofan alternative monitoring method for the required continuous opacity monitors. On December23, 2010, the requestwas granted by the EPA. The request was approved with conditions, which Minnkota accepted by letter on January 31, 2011. Because opacity limits at40 CFR60.42(b) are independently enforceable limits, EPA allowed Minnkota to demonstrate compliance using visible emissions readings in accordancewith 40 CFR Part 60, AppendixA, Method 9. 

# -MPC requests the SIP revision be changed to the alternative monitoring method approved by EPA in their December23, 2010, correspondence forthe following reasons: 1. The Department references the compliance assurance monitoring (CAM) plan to determinethe 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, AppendixA, Method 17. To maintain the isokinetic sampling required by Method 17, all test runs were in excess ofone hour. Itwould not be possibleto 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 doubtfulthat aten-minute emission period is representative ofthe actual emission exiting the stack. Due to the presence ofwaterdroplets 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 timeto ten minute periods on the PM CEMS and has found that it results in poordata. It is ourbeliefthe sample collected on the filter in the PM CEMS is an extremely small quantityand is therefore difficultforthe monitor to accurately measure.

Should you have any questions concerning the above, please contact me at 701-795- 4221, oratjgraves@minnkota.com.
Sincerely, MINNKOTA POWER COOPERATIVE, INC.

John T. Graves, P.E. Environmental Manager CC: Craig Bleth Kevin Thomas