### Attachment A: EPA Region 9 Comments on the May 13, 2010 Supplemental N02 Air Quality ImpactAnalysis for the Avenal EnergyProject

Comment 1: Avenal's May 13, 2010 I-hourN02 

### submittal did not include necessary information indicatingwhich, ifany, nearby sources were modeled orthe process used to determine which nearby sources should be included. A full impact analysis should include modeling ofnearby

sources as well as monitored background values. The recommendations for modeling for nearby

sources are discussed in EPA's Guideline onAir QualityModels 

### (40 CFRPart51, Appendix W) Subsection 8.2.3, and relevant excerpts are quoted below. All sources expected to cause a significant concentration gradientin thevicinity ofthe source orsources underconsideration for emission Iimit(s) should be explicitly modeled. Please provide a description ofthe process used for determiningwhich nearby sources should be included in the modeling, as well as the modeling analysis for any such sources.
8.2 Background Concentrations

8.2.3 Reconlmendations (Multi-Source Areas)

a. In multi-source areas, two components ofbackground should be determined: contributions from nearby sources and contributions from other sources.
b. Nearby Sources: All sources expected to cause a significant concentration gradient in the vicinity ofthe source or sources under consideration for emission limit(s) should be explicitly modeled. The number ofsuch sources is expectedto be small except in unusual situations. Owing to both the uniqueness ofeach modeling situation and the large number ofvariables involved in identifying nearby sources, no attempt is made here to comprehensively define this term. Rather, identification ofnearby sources calls for the exercise ofprofessionaljudgementby the appropriate reviewing authority (paragraph 3.0(b)). This guidance is not intended to alter the exercise ofthatjudgement orto comprehensively define which sources are nearby sources.

c. For compliance with the short-term and annual ambient standards, the nearby sources
as well as the primary source(s) should be evaluated using an appropriate Appendix A model with the emission input data shown in Table 8-1 or 8-2.



### Comment 2: Avenal's May 13, 2010 I-hourN02 

### submittal did not include necessary information concerning the source emission inputdata. Existing NOx emission inventories used to support modeling for compliancewith the annual N02 

### standard may not be adequate for use in assessing compliancewith the new hourly standard, since maximum ground-level concentrations for an hourly standard may be more sensitive to operating levels than for the annual standard, and maximum allowable hourly emission rates for nearby sources needed for modeling hourly impacts may be higherthan emission rates that may have been used for the annual standard. The source emission inventory discussion should include an analysis ofmodel load as discussed in 40 CFRPart 51, Appendix W, Subsection 8.1.2:EPAComnlents on the 5/13/20I0 Supplemental N02 Air Quality Impact Analysis for the Avenal Energy Project Page 2

8.1 Source Data

8.1.2 Recommendations

a. For point source applications the load oroperating condition that causes maximunl ground-level concentrations should be established. As a minimum, the source should be modeled using the design capacity (100 percent load). Ifa source operates at greater than design capacity for periods that could result in violations ofthe standards or PSD increments, this load) [footnote omitted] should be modeled. Where the source operates at substantially less than design capacity, and the changes in the stack parameters associated with the operating conditions could lead to higher ground level concentrations, loads such as 50 percent and 75 percent ofcapacity should also be modeled. A range ofoperating conditions should be considered in screening analyses; the load causing the highest concentration, in addition to the design load, should be included in refined modeling. For a steam power plant, the following (b-h) is typical ofthe kind ofdata on source characteristics and operating conditions that may be needed. Generally, input data requirements for air quality models necessitate the use ofmetric units; where English units are common for engineering usage, a conversion to metric is required.

c. Stackparameters. For all stacks, the stack height and inside diameter (meters), and the temperature (K) and volume flow rate (actual cubic meters per second) or exit gas velocity (meters per second) for operation at 100 percent, 75 percent and 50 percent load. 

### j. Line source modeling ofstreets and highways requires data on the width ofthe roadway and the median strip, the types and amounts ofpollutant emissions, the number oflanes, the emissions from each lane and the height ofemissions. The location ofthe ends ofthe straight roadway segments should be specified by appropriate grid coordinates. Detailed information and data requirements for modeling mobile sources ofpollution are provided in the user's manuals for each ofthe models applicable to mobile sources.


### Comment

### 3: Avenal's May 

### 13, 2010 I-hourN02 

### submittal did not include a discussion ofwhether startup or shut-down emissions were included in the analysis. The submittal should include an analysis ofstartup and shutdown emissions and a description ofhow they were addressed

.. Comment 4: Avenal's May 

### 13, 2010 I-hourN02 

### submittal did not appropriately address the instackratios of N02

### INOx emissions and background ozone concentrations. Key model inputs for both the OLM and PVMRM options arethe in-stack ratios ofN02

### INOx emissions and background

ozone concentrations. While the representativeness ofthese key inputs is important in the context ofthe annual N02 

### standard, theywill generally take on even greaterimportance for an hourly standard. Recognizing the potential importance ofthe in-stackN02

### INOx ratio for hourly N02 

### compliance demonstrations,we recommend that in-stack ratios used with eitherthe OLM or PVMRM options bejustified based on the specific application, i.e., there is no "default" ratio for either OLM orPVMRM. It is our understanding that the upcoming EPA guidance on the applicability ofAppendix W Modeling Guidance for honrly N02 

### NAAQS will also provide further clarification on this issue.

Comment 5a: Avenal's May 

### 13,2010 I-hourN02 

### submittal did not include appropriate justification ofthe method thatwas used for combining arrlbient airquality datawith the modeled

source and nearby source impact data, based on combining monitored background concentrationsEPAComments on the 5/13/2010 Supplemental N02 Air Quality Impact Analysis for the Avenal Energy Project Page 3



### and modeled concentrations on an hour-by-hour basis. The submittal should provide a justification

as to why the method should be deemed acceptable.

Comment 5.b: Avenal's May 13,2010 I-hour N02 

### submittal labeled hours with missing ambient monitored background N02 

### as missing for combined modeled and monitored impact,which effectively discards valid modeled data. An alternative method,which would provide a conservative monitored background value for every valid modeled hour, should be selected.

Comment 6: Avenal's May 13,2010 I-hour N02 

### submittal did not include any discussion ofhow building downwash is addressed. The analysis should include an appropriatediscussion ofhow building downwash is addressed, following the recommendations of40 CFRPart51, AppendixW Subsection 6.2.2, Good EngineeringPractice StackHeight. Also note that building downwash influences on other nearby sources included in the modeling analysis should be addressed.

Comment 7: Avenal's May 13,2010 I-hour N02 

### submittal did not include anyjustification ofthe representativeness ofthe meteorological data. The representativeness ofmeteorological data ofthe conditions at the project site should be consistentwith the recommendations of40 CFRPart 51, AppendixW, Subsection 8.3,MeteorologicalInputData, 

### as quoted below. The analysis should include a discussion ofhow the proposed site addresses these recommendations. This analysis should include a discussion ofthe representativeness ofthe surface characteristics. The surface characteristics inputto AERMET should be based on theland covercharacteristics in the vicinity ofthe meteorological tower. Othercandidate meteorological stations should be discussed. The representativeness ofthe upper air station used for this analysis should be discussed. The AERMOD Implementation Guide, revised March 19, 2009, specifically addresses meteorological data representativeness and representativeness ofsurface characteristics for AERMOD.

8.3 Meteorological Input Data

a. The meteorological data used as inputto a dispersion model should be selected on the basis ofspatial and climatological (temporal) representativeness as well as the ability ofthe individual parameters selected to characterize the transport and dispersion conditions in the area ofconcern. The representativeness ofthe data is dependent on: (1) The proximity ofthe meteorological monitoring site to the area under consideration; (2) the complexity ofthe terrain; (3) the exposure ofthe meteorological monitoring site; and (4) the period oftime during which data are collected. The spatial representativeness ofthe data can be adversely affected by large distances between the source and receptors ofinterest and the complextopographic characteristics ofthe area. Temporal representativeness is a function ofthe year-to-year variations in weather conditions. Where appropriate, data representativeness should be viewed in terms of the appropriateness ofthe data for constructing realistic boundary layer profiles and three dimensional meteorological fields, as described in paragraphs (c) and (d) below.

c. Regulatory application ofAERMOD requires careful consideration ofminimum data for input to AERMET. Data representativeness, in the case ofAERMOD, means utilizing data of
an appropriate type for constructing realistic boundary layer profiles. Ofparamount importance is the requirement that all meteorological data used as input to AERMOD must be both laterally and vertically representative ofthe transport and dispersion within the analysis domain. Where surface conditions vary significantly overthe analysis domain, the emphasis in to adequate characterization oftransport and dispersion between the source(s) ofconcern and areas where maximum design concentrations are anticipated to occur. The representativeness ofdata that were collected off-site should bejudged, in part, by comparing the surface characteristics in theEPAComments on the 5/13/2010 Supplemental N02 Air Quality Impact Analysis for the Avenal Energy Project Page 4
vicinity ofthe meteorological monitoring site with the surface characteristics that generally describe the analysis domain. The surface characteristics input to AERMET should be based on the topographic conditions in the vicinity ofthe meteorological tower. Furthermore, since the spatial scope ofeach variable could be different, representativeness should bejudged for each variable separately. For example, for a variable such as wind direction, the data may need to be collected very near plume height to be adequately representative, whereas, for a variable such as tenlperature, data from a station several kilometers away from the source may in some cases be considered to be adequately representative.



### Comment 8: Avenal's May 13,2010 I-hour N02 

### submittal did not include any analysis showing the representativeness ofairquality data at the Hanford sitewith respect to the conditions at the project. The submittal should include the appropriate analysis, and othercandidate ambient air quality monitoring stations should be discussed.

Comment 9: The method used to substitutefor missing hourly ambient 

### 03 concentrations for use with the PVMRM option is generally ofgreaterimportance for the hourly standard than for the annual standard. The approach for replacing missing hourly ambient 

### 03 concentrations from the Hanford monitoring station with hour-appropriatevalues from the previous or next day (discussed in Avenal's submission at section 2.5.1 Data Substitution-Ozone) is not fully defined and may overstate the ozone limiting potential in some cases,which could underestimate ambient N02 

### concentrations. This method for substituting missing 

### 03 concentrations should be replaced with a clearly defined approach that includes a reasonable assurance that substituted values will not result in underestimates ofambient N02 

### concentrations.