~: , .

215 South Cascade Street

PO Box 496

Fergus Falls, Minnesota 56538-0496

218739-8200

www.otpco.com (web site)

May 21,1998

Mr. Brian Gustafson

Natural Resources Engineer

Air Quality Program

South Dakota Department ofEnvironment

and Natural Resources _ _.~ -

Joe Foss Building

523 East Capitol

Pierre, SD 57501-3Un

Dear Mr. Gustafson:

Power Company

SUBJECT: BIG STONE PLANT - PERMIT NUMBER 28.0801-29

This letter is in response to your May 9, 1997 letter of approval for installation of an over-fire

air system at Big Stone Plant. The following is a list ofDENR requirements for the project

and the corresponding Otter Tail Power Company responses: '.

1. . Otter Tail Power Company shall notify.the department, in writing, within 5 days of

the initial start-up date ofthe over-fire air system;

OTP Response: Notification ofsystem startup was provided via letter of October 9, 1997.

2. Otter Tail Power Company shall evaluate the affects ofthe over-fire air system on the

air emission from the cyclone-fired boiler;

OTP Response: Baseline emission tests were conducted prior to installation ofthe over-fire

air system. Emission tests were also conducted while using the over-fire system. Those test

results are documented in the enclosed data sheet. Please note that during the tests, NOx

emissions were reduced from approximately 1.28 Ibs/mmBtu to approximately 0.73

Ib/mmBtu, which is a reduction of approximately 43%. Also note that the emissions ofthe

other regulated air pollutants are not materially affected by operation ofthe over-fire air

system.

3. Otter Tail Power Company shall submit the proper documentation for revising the

Title V air quality operating and acid rain permit within one year ofthe initial start-up ofthe

over-fire air system. The documentation shall identify ifthere were any increases or

decreases i.n emissions, quantify the increase or decrease for each pollutant, if applicable, and

identify the appropriate permit revisioIl process; and . ," " " . , , ...., .

OTP Response: It is Otter Tail's opinion that installation ofthe over-fire air system is

consistent with the Phase II NOx Compliance Plan that was filed with the Department of

An Equal Opportunity Employer
Mr. Brian Gustafson

May 21, 1998

Page 2

Environment and Natural Resources on October 29, 1997. Based on that plan, Big Stone

Plant must meet an annual average NOx emission rate ofO.86lbs/mmBtu beginning with

calendar year 2000. It is our understanding that the DENR will have to reopen the Title V

permit by January 1, 1999, to incorporate the Phase II NOx Compliance Plan. No additional

permit revisions are necessary for the project.

4. Otter Tail Power Company shall at all times during the use ofthe over-fire air system,

comply with its existing air quality operating permit and acid rain permit.

OTP Response: The only purpose for installation ofthe over-fire air system is for

compliance with regulatory requirements. In absence ofthe Phase II NOx reduction

requirements, the project would not likely have been completed.

Should you have any questions on our responses or on the project, please contact me at 218-

739-8407.

~~Terry Graumann

Manager, Environmental Engineering

Enclosure

---.- ---