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Taconite BART FIP UPL Equations 

March 7, 2016 

EPA has proposed to eliminate UPL Equation 2 from the proposed Taconite BART FIP 

rule citing an error. Petitioners ArcelorMittal and Cliffs have not agreed to this change. During 

subsequent discussions EPA espoused an interpretation of the term “data point” in the 

nonparametric equation (UPL Equation 3) that was different from the use of the term “data 

point” in UPL Equations 1 and 2. While we agree that the term “data point” means individual 

hourly values for the remaining UPL Equation 1, EPA is proposing that the term “data point” 

means a 720-hour average value for UPL Equation 3. Petitioners see nothing in the settlement 

language or proposed rule language that supports EPA’s departure from the common use of the 

term “data point.” 

Petitioners offer the following as additional support from EPA’s own rulemakings that the 

data points to be used in UPL equations should be individual hourly values, not averages of 

multiple data points reflecting the averaging period to be used for demonstrating compliance. 

1) USEPA responded to the D.C. Circuit Court’s remand of the record for the Major 

Source Boiler MACT rule by submitting a July 14, 2014 Memorandum from Stephen 

D. Page, Director of USEPA’s Office of Air Quality Planning and Standards to explain 

the use of the UPL when setting emission standards under the MACT provisions of 

Clean Air Act 112(d) (the “Page Memo”). This Memo states: 

The most important parameters in the UPL calculation are the mean 

(average) performance of the unit or units, the distribution of the dataset, 

the variance in the measured emission values (that is, the individual data 

points), and the sample size. 

Page Memo at p. 4 of 15, emphasis added. The Page Memo further clarifies that the 

variability component of the UPL equation is based on individual hourly data points, 

not the set of 3-run averages. Page Memo at p. 10 of 15. The compliance 

demonstration continues to be based on stack testing using the average over 3 onehour test runs, but it is the individual run values that are the data points used to 

assess variability in the UPL equations. UPL equations use individual hourly data 

points, not a data set of average values reflecting the averaging period that will be 

used to demonstrate compliance. 

 

EPA-R09-OAR-2015-

0165-0035 - Use of U

2) The term “data point” has also been used in rulemakings that use a “percentile” 

approach to establishing a limit. The nonparametric Equation 3 uses this “percentile” 

approach, where values are ranked from lowest to highest and the 95th percentile in 

that data set becomes the limit. USEPA used this approach in its final rulemaking for 

the stripped resin limits in the PVC MACT where it had a larger data set collected 

over four years “between 523 and 5,165 data points total for the calculation of each 
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limit.” 77 Fed. Reg. at 22872 (April 17, 2012). The attached floor memo for the PVC 

rule goes on to explain “Percentiles are based on the distribution of the available 

emission observations (e.g., test runs), and do not embody a predictive aspect that a 

prediction interval does.” ERG Floor Memo at p. 4 (February 8, 2012). For stripped 

resins, the data were comprised of individual samples or composited samples for 

each HAP compound collected from the best performers. See id. at 43-44. The data 

points from the top performers were then ordered and ranked and the 99.9th

percentile established the emission limit. Even with a 99.9 percentile limit, 

commenters expressed concern with spikes during startup that could exceed the 

emission limit. EPA explained, “We believe the 24-hour averaging time and 8-hour 

sampling frequency will allow sources to demonstrate compliance with the stripped 

resin limits.” See 77 Fed. Reg. at 22882 (April 17, 2012). The percentile approach 

sets limits based on the rank of individual data points and the averaging used to 

demonstrate compliance assures a pathway to full compliance. 

 

EPA-HQ-OAR-2002-0

037-0193 floor memo

2012-6421.pdf

As EPA has used both the UPL and the Percentile approaches to set limits, the “data 

points” used as inputs are the individual grab samples or individual test runs. The 

data points are used to establish the limit that is achievable under the full range of 

operating conditions. The averaging period for the compliance demonstration is 

necessary to avoid noncompliance 55 of the time for a limit set at the 95th percentile 

of the ranked nonparametric data set.