May 26, 2015

Memorandum to the North Dakota SIP File

Docket ID # EPA-R08-OAR-2015-0026

Subject: Minnkota Alternative Monitoring Plan State Implementation Plan (SIP)

From: Gail Fallon, Environmental Engineer, Air Pro gram Environmental Protection Agency Region 8

Purpose:

This memorandum is to document correspondence and d iscussions both internal to EPA and between EPA and the State of North Dakota during th e period of January through October 2012 that supported the development of the alternative m onitoring plan for Minnkota’s Milton R. Young Station (MRYS) Unit 1. The work involved Gail Fallon (EPA Region 8, Air Program), Michael Owens (EPA Region 8, Air Program), Jonah St aller (EPA Region 8 Office of Regional Counsel), Hans Buenning (EPA Region 8 Enforcement), Josh Ricard (EPA Region 8 Enforcement), Barrett Parker (EPA OAQPS) and Tom Ba chman (North Dakota Department of Health).

Background:

In 2006, Minnkota entered into a consent decree wit h North Dakota and EPA to settle allegations of noncompliance under the Prevention of Significan t Deterioration (PSD) Program. As part of this settlement, Minnkota was required to control s ulfur dioxide emissions from MRYS Units 1 and 2. After installing wet scrubbers to comply wit h the consent decree, monitoring opacity via continuous opacity monitoring systems (COMS) became infeasible. This was due to the large amount of moisture from the scrubbers. Minnkota req uested approval for alternative monitoring

for MRYS Units 1 and 2 from EPA’s Technical Enforce ment Program. EPA granted Minnkota’s request in a December 23, 2010 letter. Unit 1 is su bject to PSD requirements in 40 CFR 51 which requires the alternative monitoring plan be incorpo rated into the SIP. North Dakota submitted a SIP revision covering the alternative monitoring pl an for Unit 1 on April 8, 2013. Unit 2 is subject to new source performance standards (NSPS) of 40 CFR 60 so a SIP revision for alternative monitoring at Unit 2 is not required.

Our review of the draft SIP revision for alternativ e monitoring at MRYS Unit 1 focused primarily on the proposed particulate matter (PM) c ontinuous emissions monitoring system (CEMS) emission limits in the alternative monitorin g plan and the correlation with data provided in a Minnkota Compliance Assurance Monitoring (CAM) Plan for MRYS dated February 1, 2010. We requested that North Dakota provide clarif ication on several points including state rules governing opacity and various aspects of the CAM Plan. Further discussion below describes the information that the State provided.2

North Dakota’s Clarifying Information for State Rul es and the MRYS CAM Plan:

The applicable state rule for the opacity limit is 33-15-03-01.2 which cross references 33-15-03- 02 (i.e. 20% opacity with one six-minute period up to 40%). For many years (including when the monitoring requirement was incorporated into the SI P) the applicable rule was 33-15-03-01 (i.e. 40% opacity with one six-minute period up to 60%). North Dakota interprets the 33-15-03-02 rule to specify a six-minute averaging period for the 20% opacity standard.

The averaging time for the mass PM emission measure ments in the CAM Plan is unclear in the plan itself. The State determined that the CAM Plan was developed from nine test runs for PM (with at least a one-hour sampling period per test run). Three runs were done at normal operations (low opacity), three runs at slightly de tuned electrostatic precipitator (ESP) operation (mid-point opacity), and three runs at higher detun ing of the ESP (high opacity). The PM measurements were done by EPA reference method not PM CEMS. The State confirmed that no scrubber was installed on Unit 1 during the PM test ing and that the PM CEMS manufacturer is MSI, model BetaGuard PM.

The averaging time for the opacity measurements in the CAM Plan is also unclear in the plan itself. The State determined that the nine opacity readings for the CAM Plan graph were based on the average for the duration of the PM test run (one-hour average).

In the CAM Plan, the nine PM emission rates were pl otted against the nine average opacity readings during the PM test run. By conducting nine test runs (three at each desired opacity reading), the PM and opacity readings essentially b ecome three-hour averages when fitting the

curve to the data.

EPA’s Review of CAM Plan:

EPA provided our assessment of the draft SIP revisi on for the subject alternative monitoring plan in our April 20, 2012 comment letter to North Dakot a. Minnkota expressed some concerns regarding EPA’s April 2012 comments in a June 6, 20 12 letter to North Dakota.

North Dakota originally proposed a PM emission limi t of 0.062 lb/MMBtu (ten-minute average). After reviewing the CAM Plan data, EPA was concerne d that this limit would not allow an adequate compliance safety margin. In our April 201 2 letter, we suggested a 10% safety margin was warranted and that this would correspond to a P M limit of 0.052 lb/MMBtu. Minnkota’s concerns in its June 2012 letter were primarily rel ated to the averaging time for the PM emission

limit. Minnkota noted that since test runs in the C AM Plan were in excess of one hour, it would not be possible to certify a PM CEMS with a ten-min ute measurement. Minnkota also noted that sample collection on the PM CEMS filter is in such small quantity that ten-minute sample periods are insufficient to obtain accurate measure ment. The State and Minnkota ultimately agreed to the 0.052 limit as long as the limit woul d be based on a three-hour averaging time. Minnkota requested the three-hour averaging time to allow for operational variations as well as for reasons of convenience since the monitoring sys tem is set up to record three-hour averages

for the PM limit. North Dakota noted that there wou ld be little chance that Minnkota would3

exceed the opacity limit since its PM limit is 0.03 0 lb/MMBtu (three-hour average). It would exceed its PM limit before exceeding its opacity li mit.

OAQPS checked that the PM CEMS equipment installed at MRYS Unit 1 is accurate enough to read the 0.052 lb/MMBtu limit. OAQPS used the ligni te Fd factor of 9860, providing the

correlation for the limits shown in Table 1 and con firming that the mg/m3 values are well above the detection level for a beta gauge PM CEMS (such as the BetaGuard).

Table 1, EPA OAQPS Review of BetaGuard CEMS Accurac y

Fd, ft3/MMBtu Emissions limit, lb/MMBtu mg/m3

9860 0.05 81.2

9860 0.052 84.5

Conclusions:

North Dakota’s opinion is that the 0.052 lb/MMBtu l imit essentially lowers Minnkota’s allowable opacity limit to less than 20% and elimin ates the one six-minute period at 40%. It was not our intent to make the opacity limit more strin gent. Our position is that the lower PM limit than the State originally proposed will ensure equi valency of monitoring methods and compliance with the opacity limit as required by EP A’s regulations.