Greg Nudd <GNUDD@tceq.state.tx.us>

02/15/2007 04:48 PM To Erik Snyder/R6/USEPA/US@EPA

cc tim@den.nps.gov, Joe Kordzi/R6/USEPA/US@EPA, Bret Anderson/ARTD/R7/USEPA/US@EPA, j logan@fs.fed.us,

meredith

_ bond@fws.gov, Tim

_ Allen@fws.gov, Bruce bcc

Subject Re: Concerns on CALPUFF BART analyses and future analyses.
History: This message has been forwarded.

Erik,

Thanks again for putting the concerns in writing, it greatly helps our decision making process. The TCEQ Regional Haze Team has discussed your concerns internally and with the appropriate management.

We have been swayed by your arguments that the 98th percentile is not sufficiently conservative and will revise the CAMx BART modeling guidance to indicate that the High-1st-High and the

0.5 deciview threshold should be used to determine whether or not a source has screened out using the CAMx modeling platform.

However, our technical opinion is that, especially with the move away from the 98th percentile, the use of one year of meteorological data is sufficiently conservative for demonstrating that a source does not contribute to visibility impairment at a Class 1 area.

We acknowledge your concerns regarding the screening modeling that has already occurred. We don't necessarily agree with them, but we understand your position. We do agree that these

decisions have been made and it is too late to reconsider them.

We will continue to seek your input on similar issues as this progresses because we appreciate your perspective and insight and because we want to keep the TCEQ, EPA and FLMs on the same page as much as possible.

If you have any further questions or unresolved concerns about these issues, p lease let us know.

Greg Nudd, P.E. Technical Specialist Air Quality Division TCEQ

512-239-1247

>>> <Snyder.Erik@epamail.epa.gov> 2/13/2007 9:56 AM >>> Hi Greg and others,

I apologize for the long email, but wanted to cover the details and I've included excerpts from the citations as an attachment.EPA wishes to work through some issues that have recently arisen due to further review of techniques that TCEQ has utilized in the group screening analysis with CAMx and the draft model plant Addendums (I and II). We understand time is in short demand and further progress has to be taken quickly. We had a detailed conference call on February 8, 2007 with representatives of TCEQ, representatives of EPA, and representatives of the Federal Land Managers.

To provide a synopsis of our concerns, these are the abbreviated topics discussed in detail in the text below: · The Guideline on Air Quality Models (40 CFR Part 51 App. W) and CALPUFF promulgations both give technical reasons justifying the requirement of a minimum of 3 years of meteorology data (MM5 type data) be used to capture year-to-year meteorological variability. (The CALPUFF promulgation citations are included and the same citations exist in the GAQM but were not included) · The choice of the use of the 98% (High-8th High) was selected for the BART analysis (FR promulgating BART procedures 7/6/2005) based upon the level of model predictions that CALPUFF generates because of limited (conservative) chemistry. CAMx uses a more robust chemistry

p ackage and comparisons between the two models indicate that CAMx is less conservative in predicting high values for visibility impairment. · The original draft protocol indicated that the CAMx work would use groups of at least 11 or 12 sources in the screening of groups. Later TCEQ work looked at smaller groups (as small as 5-6 sources) that reduced the level of conservatism of the analysis.

In our recent discussions last week we discussed these three areas of concern that affect our expectations for how additional screening modeling is conducted for the 49 sources that have not been screened out at this point. We are not requesting that TCEQ re-evaluate the sources that have been previously screened out from BART, but want to rectify these concerns in the path forward. For the sources that have been screened out with the group runs with CAMx, and the draft model plants, we are not requesting a re-screening be completed with another value than the High-8th High value. We are requesting that additional documentation of the distribution of model predictions be shared that shows the High-1st High through the High-8th High value for each of the groups that were evaluated. We are also requesting that the model plants that are tied to the High-8th High value not be allowed to be used to screen out any more sources than currently documented in the Addendums I and II. We are considering the Texas work to date as reviewed to be acceptable with the High-8th High as long as no future screening work will use this value (unless theanalysis is conducted with 3 years of MM5 data with observations and the CALPUFF modeling system in an approved protocol).

Further detailed discussion of our concerns

The two areas of concern are the length of meteorological period being modeled in comparison to EPA’s Guideline on Air Quality Models (GAQM) included in Appendix W of 40 CFR Part 51. The other area of concern deals with the use of the 98th percentile (High-8th High value). The BART rule indicates that the 98th percentile was chosen based on the use of the CALPUFF modeling system that includes certain limitations in chemistry and analysis that the overall CALPUFF system yields a certain level of conservatism to the analysis. Because of these two issues our position is that for further CAMx modeling (small group or single source analyses) that the protocols (that EPA and FLMs will review concurrently with TCEQ) only use the High-1st High and that this value has to be below 0.5 deciview to allow a

source to be screened out of BART.

Issue #1: As further detailed and highlighted in the attached citations from the Federal Register notice approving CALPUFF (April 15, 2003), EPA approved the use of three years of prognostic meteorological data (MM5 data) in lieu of using 5 years worth of NWS data. EPA spent considerable time in reviewing the issues and choosing a minimum of three years for prognostic meteorological data to be used in CALPUFF long range transport modeling analyses. As is documented in the highlighted citations, a minimum of five years is recommended to capture the year-to-year variability of longer periods and yield a stable distribution of model predictions when compared to a much longer period that fully encompass the year-to-year variability {GAQM 9.1.3.1(a)}. In weighing the minimum distribution to capture year-to year variability in meteorological conditions and also make the burden of using a more sophisticated data set from a

p rognostic meteorological model reasonable, EPA determined a minimum of three years of prognostic meteorological modeling should be used. TCEQ’s group screening modeling with CAMx utilizes only one-year worth of meteorological data in comparison to CALPUFF modeling conducted for BART screening that is required to use a minimum of three years. Since TCEQ’s CAMx modeling only uses one year worth of meteorology, the year-to-year variability issue is not being addressed in this analysis, and another year could yield a more conservative list and result with less sources being screened out of BART. In our review of year-to-year variability of modeling included in permitting applications for impacts the High-2nd-High can vary on the order of 20% in value from year-to-year in three to five year

p eriods. Furthermore a detailed review of High-8th-High would alsoshow a year-to-year variability of similar levels. Therefore, TCEQ’s use of the High-8th-High is not as conservative a test as using three years worth of MM5 data, nor is it an approved technique in accordance with the requirements of the Guideline on Air Quality Models 9.1.3.2(d).

Issue #2: The other technical and regulatory issue of concern is the use of the High-8th-High based on a 98% that was set in the BART regulations included in the July 6, 2005 Federal Register. As discussed in detail on pages 39121-39124, the use of the 98th

p ercentile was chosen based on the use and technical knowledge of the level of conservatism that the CALPUFF modeling system was know to generate. In the notice EPA indicated that there are other features of our recommended modeling approach (using the CALPUFF system) that are likely to overstate the actual visibility effects of an individual source. Most important, the simplified chemistry in the model (CALPUFF) tends to magnify the actual visibility effects of

that source. Because of these features and the uncertainties associated with the model, EPA believed it was appropriate to use the 98th percentile for CALPUFF. Elsewhere in the notice ( p age 39123-4),

EPA discussed the conservatism and the level of over- p rediction of visibility impairment that CALPUFF would yield due to CALPUFF’s simple chemistry. EPA also discussed that states may wish to evaluate other models such as regional photochemical models, but the chemistry in these models is more sophisticated and would be less conservative in yielding visibility impairment estimates than the use of the CALPUFF modeling system. Some technical analyses have been

p rovided that also document that the absolute maximum predicted by CALPUFF is significantly greater than values predicted with a

p hotochemical model (see evaluations/ p resentations of CALPUFF vs. CAMx predictions for LADCO sources presented by Environ/LADCO). For these technical and regulatory basis reasons, we do not think it is appropriate for further analyses with CAMx to utilize the High-8th-High value.

Issue #3: Originally the work that TCEQ undertook was understood (as outlined and discussed in teleconferences on the draft modeling

p rotocol) to be utilizing only groups of 11 or more sources and not smaller groups (as small as 5-6) as was done in subsequent work. The switch to smaller groups took away some of the conservatism that we originally considered in evaluating the draft modeling protocol.

Issue#4: In other non-guideline techniques and techniques not as conservative as the EPA recommended technique, we have agreed to allow areas to use the High-1st-High in their BART screening analyses. Examples of areas that have used the High-1st-High are theCENRAP BART CALPUFF protocol for CALPUFF without the incorporation of observations (GAQM requires prognostic meteorological analyses to incorporate observations), CAMx modeling conducted for Nebraska, and other states including Texas that have used the CENRAP protocol with ‘no-obs’. Based on previous precedent for less conservative modeling that was conducted in a non-guideline technique, we do not believe that TCEQ should allow the current work using the High-8th-High to be used for any further screening analyses (including model plants based on previous work and documented in Addendums I and II) than has currently been completed and reviewed by EPA and the FLMs. EPA and FLMs have agreed that we will not request additional analyses with alternate cut point levels than the High-8th-High for the sources

that were screened out to result in the 49 Texas sources still in the BART screening process at this time. We believe that TCEQ should agree to use the High-1st-High value in comparison against a 0.5 deciview value in future screening (group or individual sources) work with CAMx, as TCEQ has agreed in the CALPUFF w/o observations

p rotocol. TCEQ should also submit the distribution of values from the High-1st-High to the High-8th-High for each of the source groups included in modeling conducted to this point.

If time allowed, p otentially an analysis could be conducted in the two primary areas of concern to come up with estimates for adjustment factors. To address the issue from the impact of year-to-year variability (1-year vs. 3-years of met), an adjustment factor

p otentially could be created based on either evaluations of numerous modeling outputs, or running CAMx for 3 years of meteorology as mentioned by TCEQ last week. An analysis to attempt to estimate the

difference in conservatism between CALPUFF and CAMx could also be

p otentially be done. In previous teleconferences, FLMs and EPA have requested any documentation that is available that would include comparisons of CALPUFF to CAMx results. If one or both of these type analyses were conducted, p otentially the analyses would support consideration of using a value other that the High-1st High for future screening. If TCEQ wishes to discuss these potential options further, EPA and the FLMs would be happy to discuss potential options and analysis work that could be done.

In conclusion, at this point in time TCEQ has narrowed the BART eligible sources that have not been previously screened out to 49 sources. For the 49 sources left they have the option of conducting additional modeling with CAMx, CALPUFF with incorporation of observations, or CALPUFF w/o observations or moving directly to the ‘factor analysis’ in the BART determination process. For both additional CAMx work and CALPUFF with observations, a modeling

p rotocol would have to be submitted to TCEQ and also EPA and the FLMsfor concurrent review and comment prior to finalizing the protocol and conducting modeling. EPA is recommending that TCEQ modify the

p rotocol document provided for further CAMx modeling to reflect that the High-1st-High must be used, not the High-8th-High.

Thanks for the opportunity to work these issues out and work out an equitable solution that does not require the need to address previous decisions, but will result in future analyses that take into consideration technical and regulatory concerns that were raised. If you have questions, p lease contact me to discuss further.

-Erik Snyder

Regional Air Quality Modeler EPA Region 6

Phone: 214-665-7305

Fax: 214-665-7263 email: snyder.erik@epa.gov

(See attached file: Excerpts from FR-CFRs.doc)