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 Program 

 Environmental Protection Agency Region 8 

Purpose: 

This memorandum is to document correspondence and discussions both internal to EPA and 

between EPA and the State of North Dakota during the period of January through October 2012 

that supported the development of the alternative monitoring 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 Staller (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 Bachman (North Dakota Department of 

Health). 

Background: 

In 2006, Minnkota entered into a consent decree with North Dakota and EPA to settle allegations 

of noncompliance under the Prevention of Significant Deterioration (PSD) Program. As part of 

this settlement, Minnkota was required to control sulfur dioxide emissions from MRYS Units 1 

and 2. After installing wet scrubbers to comply with 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 requested approval for alternative monitoring 

for MRYS Units 1 and 2 from EPA’s Technical Enforcement Program. EPA granted Minnkota’s 

request in a December 23, 2010 letter. Unit 1 is subject to PSD requirements in 40 CFR 51 which 

requires the alternative monitoring plan be incorporated into the SIP. North Dakota submitted a 

SIP revision covering the alternative monitoring plan 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 alternative monitoring at MRYS Unit 1 focused 

primarily on the proposed particulate matter (PM) continuous emissions monitoring system 

(CEMS) emission limits in the alternative monitoring 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 clarification 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. 
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North Dakota’s Clarifying Information for State Rules 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 SIP) 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 measurements 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 detuned electrostatic precipitator (ESP) operation 

(mid-point opacity), and three runs at higher detuning 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 testing 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 plotted 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 become three-hour averages when fitting the 

curve to the data. 

EPA’s Review of CAM Plan: 

EPA provided our assessment of the draft SIP revision for the subject alternative monitoring plan 

in our April 20, 2012 comment letter to North Dakota. Minnkota expressed some concerns 

regarding EPA’s April 2012 comments in a June 6, 2012 letter to North Dakota. 

North Dakota originally proposed a PM emission limit of 0.062 lb/MMBtu (ten-minute average). 

After reviewing the CAM Plan data, EPA was concerned that this limit would not allow an 

adequate compliance safety margin. In our April 2012 letter, we suggested a 10% safety margin 

was warranted and that this would correspond to a PM limit of 0.052 lb/MMBtu. Minnkota’s 

concerns in its June 2012 letter were primarily related to the averaging time for the PM emission 

limit. Minnkota noted that since test runs in the CAM Plan were in excess of one hour, it would 

not be possible to certify a PM CEMS with a ten-minute 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 measurement. The State and Minnkota ultimately 

agreed to the 0.052 limit as long as the limit would 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 system is set up to record three-hour averages 

for the PM limit. North Dakota noted that there would be little chance that Minnkota would 
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exceed the opacity limit since its PM limit is 0.030 lb/MMBtu (three-hour average). It would 

exceed its PM limit before exceeding its opacity limit. 

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 lignite Fd factor of 9860, providing the 

correlation for the limits shown in Table 1 and confirming 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 Accuracy 

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 limit essentially lowers Minnkota’s 

allowable opacity limit to less than 20% and eliminates the one six-minute period at 40%. It was 

not our intent to make the opacity limit more stringent. Our position is that the lower PM limit 

than the State originally proposed will ensure equivalency of monitoring methods and 

compliance with the opacity limit as required by EPA’s regulations.