1 TSRIA Document 2.3:

ATTACHMENT B INVALIDATION OF ELEV ATED COBURN ROAD SO 2 POINTS USING NEW EPA STANDARDS 1

1.0 INTRODUCTION
On February 27, 2014, EPA provided TSRIA w ith a handout outlining a new “weight of evidence” standard from 40 C.F.R. Part 58, pr omulgated in early 2013, and a portion of the SO 2 Data Validation Template found in Appendix D of Volume II of EPA’s Quality Assurance Handbook for Air Pollution Measurement Systems, issued in May 2013 (EPA Handout). The validation template lists validation criteria, with two falling into the “Critical Criteria” category: 1) “One Point QC Check” – commonly referred to as a precision check – must be performed every two weeks, and the analyzer response s hould not differ from the known concentration by more than ± 10%. 2) Zero/span check – must also be performed ever y two weeks. The allowable error for the span point is ± 10%, while the zer o point must be in error by no more than ± 1.5 ppb. According to the EPA Handout, “observations that do not meet each and every criterion on the critical criteria table should be invalidated unless there are compelling reason and justification for not doing so.”

2.0 RE-EVALUATION OF ELEVATED COBURN ROAD SO 2 POINTS Based on the EPA Handout, TSRIA asked Bison Engineering to conduct a new review of the elevated Coburn Road SO 2 data points for 2009-2013, using only failure to satisfy the Critical Criteria from the EPA Handout as a basis for invalidation. Based on this review, Bison Engineering identifie d a total of five data points that must be considered invalid based on the EPA Handout, as shown in Table 1: Table 1 – Summary of Invalid Coburn Road Data Points

Date SO 2 Conc. (ppb) Reason(s) for Invalidation Feb 10, 2010 91 Error for preceding zero check on 2/9/10 was + 3 ppb Error for following zero check on 2/17/10 was + 2 ppb July 8, 2010 111 Error for preceding zero check on 6/28/10 was + 7 ppb Error for following zero check on 7/12/10 was + 5 ppb July 9, 2010 92 Error for preceding zero check on 6/28/10 was + 7 ppb Error for following zero check on 7/12/10 was + 5 ppb Oct 22, 2010 89 Interval between preceding (10/4/10) and following (10/25/10) zero/span/precision checks was 3 weeks

1 Steve Heck, Bison Engineering Inc. March 7, 2014.2 Jan 16, 2013 51 Error for following zero check on 1/18/13 was + 1.6 ppb

Of particular note is that these data points include four of the five highest daily maximum concentrations measured in 2010.

3.0 IMPLICATIONS Exclusion of the above data poi nts significantly affects the 99 th -percentile daily maximum value in 2010, since four of the five highest daily maximum concentrations measured in 2010 are invalid. In descending order, the f our highest values in 2010 now become: Dec 24: 101 ppb Oct 3: 87 ppb Dec 21: 86 ppb Sep 28: 83 ppb Thus, exclusion of the four 2010 data points in Table 1 reduces the 99 th -percentile value from 91 ppb to 83 ppb. This also has a significant effect on the three-year design va lue calculations used by EPA to justify a proposed Non-Attainme nt designation, whether based on a 2009-2011 or 2010-2012 evaluation period: 1) Design value for 2009-2011 using all data: 79.00 ppb 2) Design value for 2009-2011 excludi ng four 2010 data points: 76.33 ppb 3) Design value for 2010-2012 using all data: 78.33 ppb 4) Design value for 2010-2012 excludi ng four 2010 data points: 75.67 ppb
The results summarized above show that th e distinction between the 2009-2011 and 2010-2012 design value periods is significant. Originall y, EPA allowed use of data from 2012, but chose to base the Designation on 2009-2011 b ecause it claimed that use of 2012 (as part of a 2010-2012 calculation) made no differe nce to the designation. See EPA RTC at 52. Based on analysis using the New Standards, invalida tion of data that do not meet Critical Criteria results in a 2010-2012 design valu e that is technically only 0.18 ppb above the 75 ppb standard (because a value of 75.49 ppb would be rounded down to 75 under EPA’s rules). This difference is well below the 1 ppb resolu tion specification of the SO 2 analyzer used to make the Coburn Road measurements.
A lesser effect on the 99 th -percentile value is noted for 2013: when the single value of 51 ppb is invalidated, the 99th-percentile va lue changes from 48 ppb to 46 ppb.

4.0 ADDITIONAL DATA QUALITY CONCERNS
Based on the EPA Handout and the ZSP Check problems identified above, the “Weight of Evidence” standard suggests that relevant air quality data behavior and tren ds that relate to the validity of data with quality assurance concerns must be examined.3 After reviewing the raw AQS data downloa d files for 2009-2012, Bison Engineering has identified three additional data points that should be considered suspect because 1) they occurred in hours immediately preceding or following an Au tomated Zero/Span (AZS) check; and 2) they are inconsistent with surrounding ambient data. They are summari zed in Table 2, and discussed below. Table 2: Summary of Suspect Coburn Road Data Values September 22, 2009 March 11, 2012 September 13, 2012
Hour SO 2 ppb Hour SO 2 ppb Hour SO 2 ppb

06 30 06 9 01 7
07 24 07 3 02 12
08 18 08 8 03 7
09 107 09 27 04 41
10 AZS 10 93 05 AZS
11 2 11 AZS 06 129

12 0 07 35
08 16

AZS checks are automated analyzer calibration check s that normally occur with no site operator present. They are normally performed every 25 hours and are to be accomplished within one discrete hour. The AZS routine is programmed into the site’s datalogger; it instructs the analyzer to stop sampling ambient air, and instead sample calibration gas and zero air generated by the site’s calibration system. After the AZS is completed, the analyzer is instructed to resume sampling ambient air. This is accomplished by opening and clos ing solenoid valves controlling different analyzer sampling ports. On occasion th ese solenoid valves can leak, or may fail to open or close entirely. It is statistically odd th at three of the seven highest daily maximum one-hour concentrations from 2009 – 2012 (or 42.9%) occurred in hours immediat ely preceding or following an AZS check, whereas only ~10% of all hours i mmediately precede or follow such a check. Because the time of occurrence of AZS checks advances by one hour per day to eliminate temporal data bias effects, only ~10% of these seven values (perhaps one value) should fall in an hour adjacent to an AZS based on random chance. While the seeming preference of high values to occur at hours adjacent to AZS checks may be purely coincidental, the data tr ends themselves are also conc erning, and raise at least the possibility of a leaking or ineffective solenoid – or a timing error – so that some portion of the high-concentration calib ration gas may have been introduced into the ambient air sampling pathway, thereby affecting a reported data value:

 On September 22, 2009 the concentrations for hours 6 through 8 were between 18 and 30 ppb. In hour 9 - the hour preceding the AZS – the concentration suddenly jumped to 107 ppb. Yet in hour 11 the concentration was only 2 ppb.4  On March 11, 2012 the concentration duri ng hours 6 through 9 ranged between 9 and 27 ppb. In hour 10 – the hour preceding the AZ S – the concentration suddenly jumped to 93 ppb. Yet, in hour 11 the c oncentration had dropped to zero.

 On September 13, 2012 concentrations from hours 1 through 3 ranged from 7 to 12 ppb. In hour 4 – immediately preceding the AZS – the concentration suddenly jumped to 41 ppb. In hour 6 the recorded concen tration jumped to 129 ppb, and then dropped sharply to 35 ppb in the following hour. The concentration at hour 6 is a remarkable outlier because it is so much higher than other values observed during similar upwind emissions. It is highly improbable that su ch a value would occur in the fashion described above. Effect on Design Value Calculations Exclusion of any one of these inconsistent SO 2 values, in addition to the clearly invalid data points discussed in Sections 2.0 and 3.0, further re duces the calculated de sign values as shown below:

 If only the September 22, 2009 value of 107 ppb is excluded, the 99 th -percentile value for 2009 drops from 72 ppb to 69 ppb. The 2009-2011 design value correspondingly drops from 76.33 ppb to 75.33 ppb – showing compliance.

 If only the March 11, 2012 value of 93 ppb is excluded, the 99 th -percentile value for 2012 drops from 70 ppb to 55 ppb. Accordi ngly, the 2010-2012 design value drops from 75.67 ppb to 70.67 ppb – well below the 75 ppb standard.

 If only the September 13, 2012 value of 129 ppb is excluded, the 99 th -percentile value for 2012 also drops from 70 ppb to 55 ppb and the design value again becomes 70.67 ppb.

 If both of the anomalous 2012 values are excluded, the 99 th -percentile value for 2012 drops to 54 ppb and the design value drops to 70.33 ppb. Excluding both the 2009 and 2012 values discusse d above has no cumulative effect, since both of those years cannot be part of the same 3-year design value calculation.