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 stacktests; 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.xlsDeliberative 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]