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, jlogan@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, please 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

 package 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 the
 analysis 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

 prognostic 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

 periods. Furthermore a detailed review of High-8th-High would also
 show 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

 percentile 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 (page 39123-4),

 EPA discussed the conservatism and the level of over-prediction 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

 provided that also document that the absolute maximum predicted by

 CALPUFF is significantly greater than values predicted with a

 photochemical model (see evaluations/presentations 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

 protocol) 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 the
 CENRAP 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

 protocol. 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, potentially 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

 potentially 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

 potentially 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, potentially 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

 protocol would have to be submitted to TCEQ and also EPA and the FLMs
 for concurrent review and comment prior to finalizing the protocol

 and conducting modeling. EPA is recommending that TCEQ modify the

 protocol 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, please 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)