Appendix F

Background Concentration Determination for Non

- A ttainment Area January 23, 2015

U.S.EPA issued the “ Guidan ce for 1

- Hour SO 2 Nonattainment Area SIP Submissions”

on April 23, 2014. In Appendix A of the guidance

, several approaches for determining the SO 2 background concentrations are suggested. In this appendix

, Ohio EPA , working with the Kentucky DAQ, has applied the methods suggested in U.S. EPA’s guidance to identify the po tential SO 2 background concentration in the Campbell County KY

- OH

, nonattainment area for the 1

- hour SO 2 National Ambient Air Quality Standard (NAAQS).

According to the guidance, a “ f irst t ier” approach uses a uniform monitored background contribution based on the overall highest hourly backgro und SO 2 concentration from a representative monitor. However, t his approach is identified as “... conservative in many cases and may also be prone to reflecting source

- oriented impacts, increasing the potential for double

- cou nting of monitored contribution

. ” Therefore, U.S.EPA recommends a less conservation “first tier” method based on the monitored design values for the latest 3

- year period. F rom the design value report ( See Appendix A

- 2 of the Redesignation Request and Maintenance Plan ) at Monitor 21

- 037

- 3002 for 2012

- 2014 , the 3

- year design value is 7 2 ppb, which is slightly less than the 2010 1

- hour SO 2 NAAQS

. Thus, both of the “first tier” methods are overly conservative and are not appropriate for determining the background concentration of this area

. As discussed in U.S. EPA’s guidance, Section 8.2.2 .b of Appendix W provid es another option :

“ U se air quality data in the vicinity of the source to determine the background concentration for the averaging times of concern . Determine the mean background concentration at each monitor by excluding concentrations when the source in question is impacting the monitor...For shorter time periods, the
mete o rological conditions accompanying concentrations fo r concern should be identified. Conce n trations for meteorological conditions of concern, at monitors, not impacted by the source in question, should be averaged for separate averaging time to determine the average background value. Monitoring sites inside a 90 degree sector downwind of the source may be used to determine the area of impact. ”

The Kentucky monitor 21

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- 3002 is the only monitor located in the vicinity of our study area suitable for this analysis. T wo major SO 2 emission sources , Duke Energy’s W.C. Beckjord (Beckjord) and W. H. Zimmer (Zimmer) facilities were considered as a part of this analysis and concentrations were excluded when these sources in question were impacting the monitor.

Google Earth tools were used to determine a n arc of 90 degrees when the se two sources in question are impacting the monitor , and the hourly meteorological data (WBAN: 93814) was downloaded via ftp://ftp.ncdc.noaa.gov/pub/data/noaa/isd

- l ite

. As can be seen in the Figure 1 below, these two sources would impact the monitor whenthe wind blows from 74.81° to 164.81° . Therefore, the hourly monitoring data with the

recorded wind directions within the range were eliminated

. Figure 1

T he average SO 2 concentration was then calculated for each year in the 2010

- 2014 dataset which was retrieved from U.S. EPA’s Air Quality System (AQS)

. Data for 2014 was only available through August 31, 2014 at the time of this analysis. In addition, to be more conservative, the annual average SO2 concentrations for non

- zero values

w ere calculated

. The results show t he highest value , 4.4 0 ppb, is the background concentration for this area using this approach ( see Table 1).

Table 1

Year Background Concentration (all data)

(unit: ppb) Background Concentration (non

zero) (unit: ppb) 2010 3.82 4.36 2011 2.12 4.1 0 2012 1.16 3.91 2013 1.01 4.40 2014 1 1.86 2.89

1 Through August 31, 2014Because it has been determined that Beckjord is the only source impacting this monitor

,

and given their proximity to the monitor and the predominant wind directions potentially impacting the monitor , the same analysis was also conducted and concentrations were excluded only when Beckjord was impacting the monitor

. Again, Google Earth tools

w ere used to determine an arc of wind directions to exclude from the background determination. In this instance, a reduced arc of 45 degrees was used instead of 90 degrees. It was determined that an exclusion arc of 90 degrees relative to the monitor woul d potentially eliminate any potential contributions of Zimmer emissions to monitor values. The reduced arc allows for the exclusion of Beckjord emission impacts, the inclusion of Zimmer impacts, and provides an additional measure of conservatism to the ba ckground determination. T he hourly meteorological data (WBAN: 93814) was downloaded via ftp://ftp.ncdc.noaa.gov/pub/data/noaa/isd

- lite

. As can be seen in the Figure 2 below, Beckjord would impact the monitor when the wind blows from 81 ° to 126 ° . Therefore, the hourly monitoring data with the recorded wind directions within the
range were eliminated. Figure 2

The average SO 2 concentration was then calculated for each year in the 20 10

- 2014 dataset. Again , to be more conservative, the annual average SO 2 concentrations for

non

- zero values w ere calculated

. The results show t he highest value, 4.76 ppb, is the background concentration for this area using this approach (see Table 2 ).Table 2

Year Background Concentration (all data)

(unit: ppb) Background Concentration (non

zero) (unit: ppb) 2010 3.82 4.49 2011 1.94 4.28 2012 1.03 4.29 2013 0.8 4.76 2014 2 1.66 2.91

In sum mary , the background concentration for this area can be conservatively estimated at 4.76 ppb without double

- counting emissions from Beckjord based on the above analysis

. To preserve conservatism in the background and to demonstrate further that the shutdown of the Walter C. Beckjord facilities provides for attainment, Ohio EPA conducted an ana lysis of hourly SO 2 concentrations recorded at monitor 21

- 037

- 3002, wind direction data from the Cincinnati weather station located at the Cincinnati Northern Kentucky Airport, and emissions fro m both the Walter C. Beckjord and William H. Zimmer facilities for years 2012 through February 28, 2015. The full analysis is presented in detail in Appendix K of the redesignation request. Briefly, Ohio EPA compiled 2,939 non

- zero monitor values for whi ch SO 2 emissions from the Walter C. Beckjord facility were zero. The 99 th percentile value of these hourly data is the 29 th highest hourly value, or 11 ppb. Note that 11 ppb represents the 99 th percentile of all hours, not of maximum daily values and is t herefore more conservative than an actual design value for this period. Additionally, by not attempting to account for plume travel time from the Walter C. Beckjord facility to the monitor, it is likely that some hours in this dataset represent impacts of emissions from the Walter C. Beckjord facility, and therefore carry an additional measure of conservatism. As noted in Appendix K of the redesignation request, no exceedances of the standard were recorded at any hour for which emissions from Walter C. Be ckjord were zero.

2 Through August 31, 2014