Re: Hg data 

12/08/2011 01:10 PM 

From: Bill Maxwell/RTP/USEPA/US 

 

To: "Higgins, Cortney" <Cortney_Higgins@omb.eop.gov> 

 

Cc: RobertJ Wayland/RTP/USEPA/US@EPA 

Cortney -- 

Attached is your spreadsheet with information added to the "notes" field 

that identifies the units selected for mercury testing. Some of the 

units noted are included because they share a stack with a unit that was 

selected. 

To ensure data quality, the we performed three levels of outlier analyses 

on the submitted data averages before they were considered for the 

floors. The first level was a visual plotting of the data via a scatter 

plot to identify obvious outliers that warranted removal from the data 

set pending further investigation. Once these data were removed, the 

remaining data were then sorted by emission average (low to high) and the 

MACT floor sets of averages were chosen. In addition to the initial 

scatter plot analysis, another outlier analysis was performed once the 

data were entered into the UPL spreadsheet. This outlier analysis (to 

identify gross outliers) determined if the maximum test average in a 

unit’s set of test averages was two orders of magnitude greater than the 

minimum value for the given unit. Such gross outliers were removed from 

floor consideration. The third and final level of outlier analyses was 

the use of Tukey's Exploratory Data Analysis Model. 

Only four test averages were excluded from the data sets based on the 

second outlier analysis and no test averages were excluded based on the 

third outlier analyses. The four removed test averages were all 

associated with Hg emissions tests and were not used to calculate the Hg 

floors for Subcategory 1. All of these data were from Part II stack 

tests; two of the four excluded data points were submitted with no runlevel data. Without run-level data, it was not possible to further 

evaluate the validity of these outliers. The two remaining averages 

reflect non-detect values from a Method 29 test on two units sharing a 

common stack. These units also submitted Method 30B run-level data under 

Part III with emission rates above the detection limit. Because the 

outlier was due to limitation of the sampling method, these test averages 

were removed from further analysis. The emission data averages excluded 

from each respective spreadsheet using the “two orders of magnitude” 

check and Tukey's Model are shown in Row 42 of their respective UPL 

spreadsheet’s columns. 

Thank you. 

partii_iii_hg_EPA_120811.xls 
Deliberative Document -- FOIA Exempt 

Bill Maxwell 

Energy Strategies Group 

Sector Policies and Programs Division 

U.S. EPA Mail Code D243-01 

109 T.W. Alexander Drive 

Research Triangle Park, NC 27711 

Phone: 919-541-5430 

FAX: 919-541-5450 

From: "Higgins, Cortney" <Cortney_Higgins@omb.eop.gov> 

To: RobertJ Wayland/RTP/USEPA/US@EPA 

Cc: Bill Maxwell/RTP/USEPA/US@EPA 

Date: 12/07/2011 03:48 PM 

Subject: Hg data 

Hi Bob, 

 

Is there a field in the attached spreadsheet that indicates if a unit was 

part of the best performing 15% or one of the randomly selected units 

from 

the ICR? If not, do you have a list of those facilities (preferably 

including the Facility ID)? 

 

Also, the sheet for the existing not-low BTU Hg coal floor indicates that 

4 units were considered outliers for setting the floors. What were the 4 

outliers? How were they selected? – it’s difficult to understand the 

Gross Outlier test in the floor spreadsheet (which it seems is based on 

the maximum value for the floors being 100 times great than the minimum 

value, but I’m not sure). 

 

 

Regards, 

Cortney 

 [attachment "partii_iii_hg.xls" deleted by Bill Maxwell/RTP/USEPA/US]