Enclosure

EPA Response to Petition for Reconsideration

from the Texas Commission on Environmental Quality

By letter dated July 18, 2012, the Texas Commission on Environmental Quality (TCEQ) petitioned the EPA to reconsider the final area designation for Wise County in the Dallas-Fort Worth (DFW area. For the reasons discussed below, the EPA is denying the Petition. TCEQ also reque sted that the EPA stay

the effective date of the desi gnation for Wise County. Because the EPA is denying Petitioner’s reconsideration request, the EPA is also denying the stay request. Fo r the sake of clarity, we have organized this response according to th e structure of the July 18, 2012 Petition.

I. Analysis of TCEQ’s Sou rce Apportionment Modeling:

Issue: The EPA erred in failing to follow its own guidance. The guidance requires th e agency to use the Source Apportionment Modeling (SAM) re sults in a relative way using a relative respons e factor (RRF) and anchor the analysis on the base year Design Value (DV) at the m onitor, rather than using modeled future-year concentrations dire ctly in a deterministic approa ch (using direct model outputs). The EPA ignored the TCEQ SAM relative res ponse-based predictions and instead cherry-picked direct predictions from TCEQ's SAM (not anchored to any measurements) to declare that Wise County's contribution to the Eagle Mountain Lake monitor's design value wa s significant. The same principles apply where

ozone concentrations at a monitor location are allo cated to a specified set of emission sources, an approach the EPA followed in the modeling conducted for the Cross Stat e Air Pollution Rule (CSAPR).

Response: The EPA fully described the reasons it we ighed some of the model outputs provided by Texas more than others and why we evaluated Te xas’s SAM results using additional metrics. Thus, we do not

believe this issue warrants reconsideration. We note that in Texas’s February 29, 2012 comment letter attachment they included SAM resu lts using the absolute values from the model (average and maximum contributions) and also results using an RRF technique . So the EPA did not cher ry pick the results but used information provided by Texas and further evaluated Texas’s SAM results. 1 In fact, TCEQ had six different figures with the absolute values and only one figure with relative values for the DFW SAM

comments.

As discussed in greater detail in the Technical Support Document (TSD ) and in other Responses in this Petition response, we had concerns with model performance and that the episode was not reflective of the complete suite of conditions that result in ozone exceedances in the DF W area. Because of our concerns we indicated that we were putting more we ight on the day specific (absolute values) and not the average values. The RRF approach averages the impacts over all exceedances , and with a limited set of modeled days we believe this could give a potentia lly misleading assessment. Even in an analysis of the entire ozone season, we would still want to ev aluate the day-specific impacts in addition to the averaged and relative imp acts to determine if imp acts occur often enough from a specific meteorological regime that transports emissions from an area that is not transported toward the monitor in other regimes, which would potentially limit an area’s ability to reach attainment. 2 For example if a regime occurs on average only 20% of the time but drives the overall area’s design value (DV), it could have

1 See Enclosure to Texas’s February 29, 2012 comment letter. Abso lute values SAM analysis included Pages 10-14, Figures 7, 8, 9, 10, 11, 12 for the DFW area and Pages 18-27, Figures 17-32 for the Housto n/Galveston/Brazoria area.

2 In the case of Wise County and DFW we discuss in the TSD and elsewhere that the meteorological regime of Light and

Variable winds with some recirculation of air masses is one of the classic worst-case regime s that often impacts the DFW design value.significant implications for attainment. Because the RRF approach averages the impacts of all the meteorological regimes, it masks to some degree the im pact of the meteorological regime that drives the highest levels. This is of pa rticular concern in evaluati ng SAM for a determination of inclusion/exclusion of a county unde r only one meteorological regime. No te that if the EPA had used a relative reduction factor approach to estimate the day-specific impact s from the TCEQ SAM, we believe the modeled impacts from Wise County would likely have been larger. 3

SAM is a technique to look at culp ability of individual areas or s ource groups on specific area(s) of concern, and it is common to use both direct mode l results and relative modeling results. The EPA’s SAM analysis is consistent with many past SAM analyses that have been conducted by the EPA, RPOs, states, and other researchers. The EPA has never i ssued specific guidance on how SAM analysis should be performed, therefore our analys is does not conflict with the EP A guidance. The EPA has issued guidance for attainment demonstrations indicating thatmodeling should be analyz ed in a relative sense using the RRF technique for determining whether the emissions reduction measures in an adopted plan will achieve overall attainment/nonattainment, but the EPA has not issued guidance on how SAM should be evaluated or more specif ically how SAM should be performe d when evaluating the impact of a county on a violating monitor in the context of an attainment/nona ttainment designation decision. We

further note that to the extent that the EPA has guidance on m odeling, guidance documents are not binding rules and thus cannot “requir e” any specific action by the EPA, states or any other party. As noted, the EPA fully explained how it interpreted the SAM results in the re cord for this action.

The EPA has used SAM to support national rulemakings such as the CSAPR to assess a state’s impact on downwind receptors of concern (the EPA defined nonattainment or maintena nce receptors). In the context of this designation action, TCEQ submitted and the EPA used SAM to evaluate impacts of a single county’s emissions contribution to a downwind receptor in an adjacent nonattainment area. This is fundamentally a finer scoping of SAM compared to analyses in the EPA’s national rulemakings that

are on the scale of state-to-state impacts, so there is no direct co mparison. As discussed further in addressing other specific issues rais ed in the petition, we think there we re concerns and differences that we documented in our Final TSD that supported our c onsideration of impacts on a daily basis, and we therefore focused on the higher and maximum impact s than on the average impacts that would result from a RRF based analysis. 4 We note, however, that contrary to the suggestion by the Petitioner, when we have used SAM in national rulemakings the EPA has used absolute values as well as relative values.

Issue: TCEQ’s RRF analysis results for Wise County i ndicated the impact from Wise County emissions at the Eagle Mountain Lake monitor was 0.41 parts per billion (ppb). This value is below the EPA’s 1% threshold, therefore Wise County should not have been included in the DFW nonattainment area.

Response: As also discussed elsewhere, the EPA does not have specific guidance on evaluating SAM results nor how to evaluate the impact of emissions from a county on a nearby violating monitor in the context of a designation decision. Th e EPA evaluates each submission of SAM on a case-by-case basis, carefully assessing a number of issues including how the modeling was conducted, model performance, and available data from the analysis in order to derive appropriate conclusi ons from the results.

The EPA used a 1% of the National Ambient Air Quality Standards (NAAQS) (0.75 ppb) cutpoint in evaluating SAM results to identify days with a non- trivial impact. We did not imply that 1% of the NAAQS was a criteria threshold po int for inclusion or exclusion. O ur basis for identifying days with a

3 Electronic SAM files provided by TCEQ included a file “Hood-Wise_Dvf_Contribution_wPies.xls” that included both the absolute values and the RRF based calculated value. The absolute 2012 impacts from Wise County on the Eagle Mountain Lake monitor is 0.58 ppb (mean of 10 days used in the RRF) and the RRF based approach has a value of 0.64 ppb.

4 Final TSD SAM discussion on pages 15-20 and HYSPLIT discussion pages 14-15.non-trivial impact is discussed on page 17 of the TS D where we explained, “[o]ften in attainment demonstration modeling, controlling of sources is ev aluated and results in onl y a few tenths of a ppb change, therefore we used a 1% of the standard thre shold for the days where we would consider Hood or Wise County’s emissions to be significant.” We also note that modeling from TCEQ in a 2007 8-hour Ozone Attainment Demonstration for DFW included multip le analyses of individual control strategies and the resultant impacts on monitors in DFW area, where Texas had chosen c ontrols that provided changes of a few tenths of a ppb. In addition, we considered the recent Cross State Air Pollution Rule, which used a one percent threshold in the source apportionment modeling to determine if a state’s emissions significantly impacted a downwind state’ s nonattainment or mainte nance area. Thus we determined that an impact of 0.75 ppb, or one percen t of the 2008 ozone standa rd, which is higher than that used by the state in determin ing emissions strategies for the DF W area, would be appropriate as a metric to identify days with a nontrivial impact.

It is important to note that the number of days w ith an impact of 0.75 ppb or more is only one of the

metrics evaluated from the SAM results. In the DFW Final TSD and in supporting files, we discussed all

of the metrics used in our assessment of the SAM resu lts, and the unique factors that we weighed in our analysis of SAM results for DFW. Given the detailed daily information available for analyzing SAM for the DFW and Houston areas designations, we evalua ted the average impact, maximum impact, and an additional metric, the number of days where imp acts may be high enough that reductions might be beneficial in development of an attainment demonstration.

Issue: The EPA appears to conclude in the Final TSD that TCEQ’s SAM was not adequate because it

was not inclusive of an entire ozone season in ad dition to underestimating exceedances on many days by underpredicting peak values. To compensate for th ese concerns, the EPA relied on absolute modeled maximum concentrations to predict the potenti al contribution from Wi se County to the DFW nonattainment area. The use of photochemical modeli ng that supports a DFW attainment demonstration is appropriate and relevant eviden ce to determining the potential dow nwind contribution of Wise County to the DFW nonattainment area; it is the best eviden ce possible. It was irrational for the EPA to fail to utilize this evidence, particularly since the EPA had ample opportunity to notify TCEQ of any concerns.

The EPA's rationale for not utilizi ng the TCEQ SAM because it did not include an entire ozone season is based on the fact that the TCEQ SAM should have included days from the August-September period, which typically show higher ozone concentrations th an the June period modele d. This reason ignores the specific facts of the actual monitoring data for 2006, which the EPA does not explain. The EPA also ignored the basis and support prov ided for the June 2006 episode da ys, instead of an entire ozone

season.

TCEQ referred to the Modeling Protocol for the 2011 DFW Ozone Attainment Demonstration, provided to the EPA on October 5, 2010, noted that the 2006 base year was chosen largely because it represents an exceptionally rich set of air quality and mete orological measurements, which satisfies one of the criteria listed in the modeling guid ance for selecting episodes. The prot ocol also explai ned that in 2006, June had the most high- ozone da ys of any month (more than Augus t/September), and that all the meteorological conditions linked to formation of hi gh ozone concentrations were represented, also consistent with the guidance. TC EQ continued that th e EPA modeling guidance recommends relatively long time periods covering multiple synoptic cycles and does not require a full ozone season, so using the May 31 - July 2, 2006 period is entir ely consistent with the guidance. The EPA's explanation does not address why an ep isode based on an entire ozone season would be necessary, given that the more specific period of Ma y 31 - July 2, 2006 had the most high-ozone days of any month in 2006. The EPA's evaluation of the TCEQ SAM ignored both the factual monitoring datafor 2006 and its own guidance to use modeling in a rela tive sense, without explai ning why this deviation from established guidance was appropriate in this case.

Response: The EPA did consider the SAM results pr ovided by TCEQ and our concerns with the SAM are documented on pages15-20 of our Final TSD. 5 The EPA took these concer ns into account in our interpretation of the SAM results for purposes of designations. The EPA recognizes that model episode selection is always a balance of ma ny factors including the availability of data and the time available for completion in addition to considerations as to whet her all important meteorological regimes have been addressed. We would agree that the 2006 episode is a great improve ment over the previous 10- day episode for Dallas from 1999. Because these factors ha ve to be balanced, no model episode is perfect

and the limitations have to be considered. In this case the modeling does not include all of the meteorological regimes that can lead to high ozone and the mode l has an under prediction bias. We also noted that TCEQ’s own DFW conceptual m odel analyses, that has been included in TCEQ’s 2011 DFW Ozone Attainment Demonstration SIP and past Attainment Demonstrations SIPs, also indicated a roughly bimodal distribution of ozone exceedances with highest values in mid- to late-summer (JulySeptember), and that this latter summer period had so me different meteorological regimes than the early summer period that TCEQ included in their modeling. Based on our analysis of HYSPLIT results, the worst days for some of the DFW area monitors that set the Design Value are in the later summer. Later summer is also when the frequency of weak frontal passages are higher where we could see influence from Wise County emissions on DFW nonattainment monitors more often. The fact that not all meteorological regimes are addressed led us to wei gh day-specific impacts and maximum impacts more than average impacts. It is important to note th at since violations of the ozone NAAQS cannot be separated from exceedances, 6 looking at day specific impacts w ould be reasonable even if the model

covered a full ozone season. The fact th at the model has an under-predicti on bias led us to consider that the model was not predicting all of the exceedan ces that had occurred during the episode. We note that

the current 2011 DFW Ozone Attain ment Demonstration modeling of 2012 projected levels indicated

that the DFW area would be well under the 1997 8- hour standard, but based on 2008-10 data at the time and more recent 2011 (DV of 90 ppb) and 2012 prelimin ary data (DV of 87 ppb), the area is still well above the levels projected by the model (2012 DV of 78 ppb). This confirmed our concerns about modeling underprediction bias.

5 EPA Final TSD pp. 15-20 and including this quote on pp. 16, “[e]valuations of the conceptual model for high ozone in DFW by TCEQ, EPA and others indicates that high ozone in DFW is roughly a bimodal distribution with lower peaks in early summer (May-June) and the highest va lues in mid to late-summer (July-September) and that the mid to late summer has some different meteorological/transport regimes than the earl y summer episodes. Th erefore, TCEQ’s SAM does not include a large number of days and does not include all of the meteorology regimes conducive for ozone events in DFW and is missing the events that happen in mid to late-s ummer that often set the DFW area’s DV.”

6 In analyzing possible contributions from emissions in surrounding counties using the SAM tool, the EPA only evaluated and considered the amount of modeled impact from Wise County emissions on monitors that were violating the 2008 ozone standard according to the 2008-2 010 data. We focused our assessment on monito rs violating the standa rd and, in doing so, examined contributions on days when there were exceedances at those violating monitors. As a factual matter, it is not possible to separate “actual viola tions” from the “exceedances” that result in th e violation. Based on the form of the ozone standard, an area is determined to be violating the standard if the three consecutive year averag e of the annual fourth highest daily maximum 8-hour average ambient air quality ozone concentra tion is greater than the standa rd (0.075 ppm). Therefore, all daily maximum 8-hour averages that exceed 0.075 ppm at a violating monitor (i.e., “exceedances”) are relevant for purposes of determining whether emissions contribute to a violation at that monitor. Accordingly, we restricted our review of available modeling impact results to days with modeled exceedan ces at violating monitors. As part of this analysis, we evaluated the monitoring data during the episode modeled to determine if exceedances had actua lly occurred at the monitoron that specific day. The use of modeled exceedance days for estimating ozone using photochemical grid models is a longestablished practice for modeled attainment demonstrations. This approach is recommended by the EPA in “Guidance on the Use of Models and Other Analyses for Demonstrating Attainme nt of Air Quality Goals for Ozone, PM2.5, and Regional Haze” (EPA-454/B-07-002), and used by th e EPA to support Federal rules such as the Cross-State Air Pollution Rule.We also note that while weak frontal passages are one of the conceptual m odel meteorological regimes

for the DFW area for the 1997 8-Hour st andard and would also be expected to be one of the key regimes for the 2008 8-Hour Ozone standard, and there were not many of these in later summer 2006 compared to what occurred in other years. There were a numb er of these specific regimes in 2007 and other years, including one in August 2007 th at resulted in the highest 8-hour read ings monitored in DFW in the last 15 years (121 ppb at two monitors). The EPA’s mode ling guidance is premised upon trying to model the meteorology/emissions of past ozone exceedances such that a modeling system can be developed to accurately assess potential impacts of emission changes and predic t if an area will reach attainment by the required date. Based upon the many competing fact ors, including the amount of time it takes to run computer models and develop modeling that is pe rforming accurately enough for the task at hand the EPA’s guidance is to weigh the mitigating factor s and model enough days to develop a sufficient modeling system. The EPA’s guidance does indicate that at a minimum, areas should model enough days to capture multiple synoptic periods and many areas have been modeling complete ozone seasons to help capture enough days and meteorology combinati ons that perform adequately for use in predicting

future attainment/nonattainment levels. 7

Issue: The EPA also justified its use of the ab solute modeled maximum concentration because the TCEQ modeling under-predicted the peak 8-hour contributions in 2006. The RRF concept was developed precisely to correct fo r situations where the model over- or under-predicts the baseline

concentrations. The EPA failed to explain why the RRF concept, developed by the EPA to address both the possibility of under- and over-pre diction of photochemical models, was not applied for the purpose of evaluating the possible c ontribution of Wise County to the DFW nonattainment area.

The EPA appears to argue that the TCEQ SAM was not adequate because the TCEQ SAM used spatially averaged baseline and future ozone concen trations instead of maxima. However, since the EPA didn't actually use the RRF-based contribution to 2012 future de sign values, this argu ment is irrelevant. The primary reason the EPA guidance was developed supporting the use of the maximum value "near" a

monitor is to allow the RRF calculation to account for possible migration of ozone plumes due to implementing controls in an area. Instead of considering an RRF-ba sed approach, the EPA relied on the 2012 daily modeled absolute contributions. 8

Similarly, there is no rational basis for the EPA's use of a 70 ppb threshol d for selecting days to analyze

since the EPA did not use those da ys to calculate an RRF as per the EPA guidance. Instead, the EPA selected days using a 70 ppb threshold from the 2006 baseline and used corres ponding days in 2012 to look for Wise County contributions above 0.75 ppb. On many of those days in 2012, the predicted eighthour ozone concentrations were le ss than 75 or 70 ppb. The EPA should have selected days using a 75 ppb threshold from the future year modeling, but in any event, did not provide a rational basis for its

7 The EPA’s 2007 Modeling Guidance pp.122-23, “Due to increased computer speeds, it is now prudent to recommend modeling relatively long time periods. For 8-hour ozone and 24-hour PM2.5, at a minimum , (emphasis added) modeling episodes which cover full synoptic cycles is desirable. Depending on the area and the time of year, a synoptic cycle may be anywhere from 5-15 days. Modeling even longer time periods of up to a full season may simplify the episode selection process and provide a rich database with which to apply the modeled attainment test.”; pp. 140 “With the advancement in computer technology over the past decade, computer speed and storage issues are no longer an impediment to modeling long time periods. In fact, many groups have recently modeled entire summers and/or full years for ozone, PM2.5, and regional haze (Baker, 2004a) (U.S. EPA, 2005b)”

8 The TCEQ used averages instead of ma xima for its calculation of the future DV contributions because the APCA software reports averages, but notes that using averages does not necessa rily introduce bias in the RRF calculation. In fact, the total DV calculated using the APCA average-based RRF only differed from that calculated using the maximum-based RRF by 0.2 ppb (77.86 ppb vs. 78.06 ppb), so it is extremely unlikely that using spatial maxima would have made any perceptible difference in Wise County's modeled 2012 DV contribution.selection. For example, the EPA notes in the DFW TSD that "This analysis indicated Wise County emissions had even larger impacts of up to 5 ppb on the Eagle Mountain Lake monitor." The EPA refers to the 2012 contribution from Wise County to Eagl e Mountain Lake of 5.03 ppb on June 13th. While in the 2006 baseline modeling the eight-hour ozone maxi mum concentration in the 3x3 grid cell array around the Eagle Mountain Lake monitor on Ju ne 13 was 72.91 ppb, in the 2012 modeling the eighthour ozone maximum concentration in the 3x3 grid cell array around the Eagle Mountain Lake monitor was only 59.74 ppb. Although Wise County may have contributed 5.03 ppb to the 2012 modeled concentration of 59.74 ppb, the to tal 2012 predicted ozone was much less than the 2008 eight-hour ozone standard of 75 ppb. The EPA thus erred in thei r analysis by selecting days to analyze based on comparing the 2006 baseline ozone concentrations to a 70 or 75 ppb threshold. The comparison should have been made to 2012 future year ozone predicted concentrations. Furthermore, the EPA's choice to analyze days with ozone concentrations as low as 70 ppb, was erroneous, since such days could not reasonably be expected to contribute to nonattainment of the 2008 ozone NAAQS.

Response: TCEQ’s comments included both the maxi mum and average impact values for Wise County emissions based on using the absolute SAM result s for 2012 (not using the RRF technique). The RRF calculation approach for DFW was provided in one Table, in add ition to the 6 figures presenting absolute results from direct model output data (w ithout any RRF analysis). As noted above, the EPA placed less weight on the average impact, which in cludes both the average of the days, and the RRF approach which is another way to average the information over all the days above a threshold. The EPA explained our reasoning for considering modeled impact on days with values of less than 75 ppb. In the TSD (page 16) we indicated:

“Therefore, TCEQ’s SAM does not include a large number of days and does not include all of the meteorology regimes conducive for ozone events in DF W and is missing the even ts that happen in mid

to late-summer that often set the DFW area’s DV. As a result, it may be appropriate to place more weight on the maximum estimated impact and the num ber of days with sizeable impacts on violating monitors as compared to averag e impact. Another obser vation is that the evaluation used modeled exceedances for contribution and the modeling is underestimating exceedances on many days and therefore is underestimating the num ber of days of potential contribu tion. Modeling is significantly under predicting peaks by 5-20 ppb at cr itical monitors; therefore we also looked at contribution at lower modeled values (70 ppb).”

We also noted that the RRF approach indicates that a threshold lower th an the standard can be used and

should be used if there are not e nough days with modeling values above the standard in the base (2006 in this case). The EPA’s attainment demonstratio n guidance for the 1997 8-hour standard recommended using thresholds as low as 15 ppb below the standard to obtain e nough days for evaluation, especially when weighing that the base modeling is underestim ating compared to the monitoring data. For the 1997 8-hour ozone standard (84 ppb), our guidance allows basecase (2006 here) modeling days as low as 70 ppb to be used for the RRF evaluation. This supports the use of modeled days w ith thresholds of 70 and 75 ppb in the basecase 2006 modeling instead of onl y evaluating days with modeled exceedances in 2012. Although we have not revised our guidance for the 2008 8-hour ozone standard, we can try applying the same logic to the 75 ppb standard, whic h could result in values as low as 59 ppb to be allowed in RRF calculations. We also note that TCEQ’s own RRF analysis used days with values below 70 ppb and even below 60 ppb in the 2012 model projectio ns and only had 3 days out of 10 with values above 75 ppb in the RRF calculations for the Eagle Mountain Lake monitor. The use of this lower threshold in the guidance is a direct result of taking into account poten tial issues with model underprediction, etc., so the logic to use a threshold of 65 or 70 ppb is within the logic and guidance currently used for RRF analyses in our guidance. Therefore we disagr ee with TCEQ assertion that wehave not validated using a modeling threshold of 70 ppb period, when their own RRF based comments included values as low as 58 ppb in 2012.

TCEQ’s 2012 ozone modeling projecti ons using the RRF technique indica te only four monitors in the DFW area would be above the 75 ppb standard, w ith the highest value of 78.06 ppb at the Eagle Mountain Lake monitor. In contrast, the ac tual 2009-2011 DV was 83 ppb and the preliminary 2010- 2012 DV at Eagle Mountain Lake is 82 ppb. Furthermor e, 80% of the monitors in DFW are exceeding the 75 ppb standard (16 of the 20 mo nitors) and have preliminary 2012 4 th High values above 75 ppb (data ranges from 76 to 92 ppb). The DFW ar ea 2009-2011 DV was 90 ppb and the preliminary 2010- 2012 DV of 87 ppb is still 10 ppb above the standard. The monitoring data demonstrates that the 2006 model predicted levels are below current monitore d values and the modele d 2012 DV projections are underestimated by more than 10 ppb at some monitors. Therefore the 2006 levels seem more appropriate to compare to actual 2011 and preliminary 2012 monitored data.

In photochemical grid modeling the modeling domain is broken up into 4 km x 4 km squares that we call grid cells. In this case when we obtain the mode l value for further evaluation we look at the value for the grid cell the monitor is in and all grid cells immediately touc hing the grid cell with the monitor (similar to a Tic Tac Toe box with the monitor in the center). The EP A guidance is to use the maximum value from the 9 values to represent the model es timate for the monitor and TCEQ used the average value in some of their analysis. TCEQ indicates, based on one example calculation, that the difference between using the average or maximum modeled valu es in the grid cells around a monitor would not result in a perceptible difference in arguing that th eir use of the average value was acceptable. TCEQ’s example calculation was for a Future Design Value calcu lation (based on all emissions in the model) and not for a source apportionment calcu lation (which uses the model estimate for only the emissions from Wise County in this case). We note the EPA’s gui dance recommends using the maximum value of the grid cells in the grid cel l array around a monitor. From one of th e files from TCEQ we were able to evaluate what the differences are when we used the maximum vs. the average value and we did note some differences in source apportionment results. If the SAM had been evaluated using the maximum value, as EPA guidance recommends, th e values may have been larger.

II. Analysis of HYSPLIT Model Results:

Issue: The Petitioner claims that the EPA failed to quantify the number of traj ectories transecting Wise County before crossing either the Ea gle Mountain Lake or the Keller m onitor and also failed to quantify the number of trajectories that passed over other counties before pa ssing through Wise County. In each case those percentages were extremely low for the tr ajectories passing over Wise County. Furthermore, the EPA failed to provide a rationa le for how trajectorie s traversing Wise Count y indicate contribution from Wise County. Since ozone readings at a monito r are cumulative of the su m of the ozone and the ozone precursors along the trajectory path, the EPA’ s failure to quantify th e number of trajectories through other counties was irrational and in error. Furthermore, the EPA failed to explain how much ozone if any would result from the VOCs from Wise County.

Response: The EPA conducted HYSPLIT analysis of several monitors in DF W for purposes of the Preliminary Technical Support Document or TSD (December 2011) and the Final TSD (April 2012). In

the Final TSD we noted that “The HYSPLIT model yields an estimate of the path an air mass has traveled before reaching a monitor at a specific lo cation and time. Specificall y, the model provides the centerline of the probable path. By knowing where an air mass has traveled before reaching a monitor where an exceedance has occurred, one can consider what potential areas and emission sources could

have contributed to the exceedance.” The EPA include d trajectory plot maps for the Keller and EagleMountain Lake monitors in both the Preliminary a nd Final TSDs and also made the individual back trajectory files available for review during the comment period. While the EPA did not specifically state the number of trajectories that tran sect Wise County in text in the TS D, the plots in the TSDs indicate that 3 trajectory ‘centerlines’ di rectly traversed Wise County for th e Keller monitor, and at least 7 trajectory ‘centerlines’ traversed Wise County for th e Eagle Mountain Lake monitor. In addition, some other back trajectories th at did not directly traverse Wise Coun ty had centerlines near enough to Wise County to suggest a path of upwind infl uence involving Wise County emissions.

We note that a review of the individu al trajectory files shows that seve ral of the days that trajectories passed through Wise County were also days that made up the 1st to 4th highest monitored values, which are the values used in establishing the Design Valu e at the Eagle Mountain Lake and Keller monitors during the periods evaluated; these individual trajectory files were incl uded in the supporting materials for the EPA’s intended and final designations. 9

We also considered the amount of emissions in Wise County and the proximity to violating monitors. TCEQ has well established the record that the DFW area ozone levels are NOx limited and we based our analysis on the amount of Wise County NOx emissi ons and their ozone gene ration potential. In the SAM results for Wise County emissions and commen ts that TCEQ provided, there was a specific analysis that indicated that almost all of the ozone increases at mon itors were due to Wise County NOx

emissions. 10 In general the VOCs from Wise County were not considered to contribute to ozone levels very much.

III. Significance of Contribution of Oil and Gas Activity:

Issue: The Petitioner stated that current oil and gas activity levels in Wise County are unlikely to be contributing significantly to nonattainment in the DF W nonattainment area. The Petitioner noted that oil and gas production and drilling in Wise County is star ting to decline and stated that there is no evidence of a correlation between the growth in Barnett Sh ale gas production develo pment activity and ozone production in the DFW area. The Petitioner expressed concerns that the EPA may have inadvertently

9 We note that all this data is available in the record. For th e Eagle Mountain Lake Monitor, the following days were the 1st thru 4th High values that set the monitor’s DV. Highlighted in BOLD is the days that EPA’s HYSPLIT analysis indicates potential contribution from Wise County emissions. 2006 (6/14 – 107 ppb, 6/9 – 106 ppb, 6/28 – 98 ppb, 7/18 – 98 ppb); 2007 ( 8/14 – 121 ppb , 8/15 – 101 ppb, 10/04 – 86 ppb, 9/22 – 84 ppb , 7/25 – 84 ppb); 2008 (8/04 – 98 ppb, 6/18 – 92 ppb

, 6/23 – 86 ppb, 6/19 – 85 ppb); 2009 ( 6/25 – 100 ppb , 6/5 – 92 ppb, 6/26 – 92 ppb, 8/26 – 91 ppb

, 7/2 – 91 ppb ); 2010 (6/4 – 94 ppb, 8/27 – 91 ppb, 8/28 – 83 ppb, 5/29 – 81 ppb). When there was a tie for the fourth high value we looked at trajectories for both days.

10 Governor Perry’s comment letter dated February 29, 2012, pages 13, “[a]t the Weatherford (Parker County) ozone monitor NOx emissions from Hood and Wise Counties created 97-99% of the contributed ozone from these counties, while VOC emissions were only responsible for 1-3% of the contributed ozone from these counties.” See Final TSD, pages 6-8; Houston Final TSD, pages 5-7; RTC pages 52-56, including “...the VOC emissions resulting from oil & gas production activities are relatively nonreactive in the photochemical gene ration of ground-level ozone and that additionally the DFW area is NOx-limited such that VOC emissions in general do not contribute as much as NOx emissions to the generation of ground-level ozone.” And “EPA has since reviewed the updated emissions data reported by the TCEQ and notes that the revised numbers do not affect the ranking of the counties for VOC emissions. EPA’s analysis i ndicates that even with the reduced 2009 VOC emissions data, the emissions from Wise County still contribute to measured violations of the 2008 ozone NAAQS at monitors in neighboring counties. In making our final decision, we considered the reduced emissions and the reduction in drilling activity since 2009.” The Governor Perry’s comment letter dated February 29, 2012, pages 17-21, also referred to other TCEQ documents that further support that DFW area is a NOx limited regime and changes to VOC levels do not result in much impact in ozone levels: TCEQ 2011 DFW 1997 8-hour Ozone Attainment Demonstration SIP – “APPENDIX E: Protocol for the Eight-Hour Ozone Modeling of the Dallas-Fort Worth Area,” and “APPENDIX D: Conceptual Model For The DFW Attainment Demonstration SIP Revision For The 1997 Eight-Hour Ozone Standard.”“double-counted” emissions by summing the emi ssions data from the 2008 National Emissions Inventory with that of TCEQ’s 2009 Speci al Inventory for the Barnett Shale.

Response: This comment was raised during the comment period. While we did not specifically respond to this comment for the DFW area, the comment was considered by the EPA. T hus it is not appropriate for reconsideration. In the final DFW TSD, the EPA provides two emissions inventories (EIs) of nitrogen oxides (NOx) and volatile organic compounds (VOCs), which are ozone precursors (pages 7- 8). The two EIs are: 1) a 2008 EI of all Wise Count y sources and 2) a TCEQ 2009 Barnett Shale special inventory. The 2008 EI included revisions to the EI submitted by TCEQ in October 2011 which updated oil and gas sector pneumatic emi ssions (pages 6-7). The EPA did not add emissions from the Barnett Shale special inventory to the 2008 EI.

The central issue is whether emission s from Wise County contribute to oz one violations in nearby areas. As the record indicates, monitors in the Dallas CS A are violating the ozone standard and the EPA is required to designate areas as nonattainment if they vi olate the standard or cont ribute to a violation in a nearby area. As discussed in the RTC and TSD, so me of the highest days during the 2006-2010 period included transport of Wise County em issions (including any Barnett Shal e-related emissions) to some of the highest ozone exceedances at the Eagle Mountain Lake and Keller monitors, which are two of the DFW area’s monitors with the highest ozone levels. The TCEQ’s SAM also shows that emissions from Wise County (which would include Barnett Shale-re lated emissions) are transported to the violating

monitors and that the amount of c ontribution could be as high as 50% of the total impact on certain days with high ozone levels. 11 TCEQ’s SAM submitted by the Petitioner included the combination of meteorology and emissions from Wise County (i ncluding emissions from oil and gas production activity), and the resultant modeling indicated co ntributions to multiple exceedances of the ozone

standard at several monitor sites.

Design values and design value trends are a product of a number of variables, not simply the emissions of one or more types of emissions sources, whic h is why we perform a five-factor analysis in determining whether an area contributes to a violati on of the standard in a nearby area. Decreases in design values over time can occur due to many va riables, including decrea ses in ozone precursor emissions (such as in the DFW Nonattainment area due to federal measures and measures implemented by TCEQ in past ozone attainment de monstration SIPs). The fact that th e design value is lower (i.e., that ozone has not “increased”) does not preclude a determination that emissions from Wise County

contribute to exceedances at violatin g monitors in the DFW CSA.

11 See the TCEQ source apportionment modeling files, including the Excel Spreadsheet th at was placed in the record during the final action. (Hood-Wise_DVf_Contribution_wPies.xls)