1 August 10, 2012 Addendum to the 2008 Lead NAAQS Implementation Questions and Answers Signed on July 11, 2011, by Scott Mathias

(The following is a continuation of the Emissions Inventory Section, Question 10)

EMISSIONS INVENTORY

10a Q. What is the threshold for po int sources for the 2011 base year inventory that will be used in

the attainment demonstration SI P? Is it 0.5 tons per year (tpy) ? Is this the same as in the Air Emissions Reporting Rule , 40 CFR Part 51 (AERR)? If it is diff erent, is it mandatory for states to submit a more stringent threshold?

A: The threshold for point sources for the Pb SIP inventories is 0.5 t py. This is in the Pb implementation rule and is not the same as the thre shold in the AERR. That doe s not pose a particular problem because the AERR is a separate reporting re quirement from the SIP i nventory requirements in the CAA and implementation rules. Given that the 0.5 tpy threshold is in the Pb NAAQS implementation rule, it is mandatory for the SIP inventories.

10b Q. Are actual emissions required for the 2 011 base year inventory for use in the Lead

Attainment Demonstration SIPs?

A: Yes, for the base-year inventor y, actual emissions are what should be provided. The inventory year is not necessarily 2011 (see Question 6 in the Pb Q& A memo, dated July 8, 2011). The EPA recommends using either 2010 or 2011 as the base year for the contingency measure calcul ations, but does provide flexibility for using other inventory years if stat es can show another year is more appropriate.

10c Q. Should 2011 base year point, area, nonroad, and on road mobile source emissions be

submitted with this SIP?

A: Yes, the CAA requires for Pb SIPs that all sources of Pb emissions in the nonattainment area must be submitted with the base-year inventory. This is separate from the modeling requirements and the issue of which sources must be explicitly included in the modeling needed for Pb nonattainment SIPs.

10d Q. What is required for the attainment year inventory? Projected actual with controls or

maximum allowable emissions? Ar e projection year point, area, nonroad, and on road mobile emissions required for the a ttainment year inventory?

A: Maximum allowable emissions should be included for the attainment year inventory, which includes only those sources within the modeli ng domain. The modeling guidance in Guideline on Air Quality

Models (U.S. EPA, 2005) provides advice on wh ich sources need to be included explicitly (i.e., as point sources) in the modeling and provides for including the impacts of smaller and diffuse sources through the use of background concentratio ns and other less specific techni ques given the relatively lower significance of such sources to the SIP demonstration.2 10e Q. Please provide an example of calculat ing Reasonable Further Progress (RFP) emissions reductions using the formula in 6 Q.

A: Annual average RFP = [Attainment level em issions (2015 or 2016, depending on the designations effective date) - Base year emissions (most likely 2010 or 2011)] ÷ 5 (or the number of years between the attainment year and the base year).

Assume that Attainment level emissions = 0.4 tpy Base year emissions = 1.0 tpy Annual average RFP = [0.4 tpy - 1.0 tpy] ÷ 5 = - 0.60 tpy ÷ 5 = - 0.12 tpy. The annual average RFP is - 0.12 tons per year.

(The following is a continuation of th e modeling section, Questions 11 - 17)

MODELING

18 Q. How should model concentrations and back ground concentrations be properly accounted

for in attainment demonstrations?

A: In order to properly account fo r cumulative effects, background concentrations should be added to

modeled concentrations to calcu late a design value. Background concentrations should reflect contributions from natural sources, nearby sources other than the one(s) being explicitly modeled, and unidentified sources. Beginning with versi on 11103, AERMOD can now include background

concentrations in the model simulation. AERMOD can accept a variety of temporally varying background concentrations, from hourly background to an annual concentration. See Section 2.4 of the AERMOD User’s Guide addendum (U.S . EPA, 2011a) for more details.

General guidance on background concentratio ns can be found in Section 8.2 of the Guideline on Air Quality Models (U.S. EPA, 2005). For isolated single sources, the Guideline discusses two options of determining background concentrations . The first, discussed in Secti on 8.2.2.b is the use of air quality data collected in the vicinity of the source to determine the background concentrations. Background concentrations are determined by excluding observati ons when the source being modeled is impacting the monitor. The guideline offers guidance that mon itors inside a 90-degree sector downwind of the source may be used to determine the area of impact. Meteorological data used in the source contribution analysis should be representative of the monitore d area. Because observed va lues often represent a 24- hour sample, it may be difficult to separate hours with in a sample when modeled sources are impacting the monitor. In these cases, it may be necessary to exclude many 24-hour values entirely, such that the remaining observations are no longer robustly representative. This may necessitate the use of the second option, as discussed in Section 8.2.2.c. This option is to use a “regional site” when there are no monitors located in the vicinity of th e source. As defined in the Guideline , a regional site is one that is located away from the area of interest but is imp acted by similar natural and man-made sources.

For multi-source areas, section 8.2.3 of the Guideline offers guidance about two components of background, contributions of nearby sources and c ontributions of other sources. Nearby sources are those sources that are expected to cause a significant concentration gradient in the vicinity of the source(s) being modeled. These nearby sour ces should be explicitly modeled.3 19 Q. How should fugitives be mode led in attainment demonstrations?

A: Fugitives can be characterized as volume sources or area type sources (rectangular, circular, or polygon). If the exact locations of fugitive emissions are unknown or are widespread over a particular area, such that their emissions can be combined into one representative source, the fugitives may be modeled as some type of area source. However, if the locations are known, it may be better to model them as volume sources, unless the placement of recepto rs would mean that recep tors would be within the volume source exclusion zone (2.15 x Sigma Y + 1 meter). In those cases, smaller area sources may be used. Also, volume sources allow for meander under light wind conditions, whereas area sources do not. For details regarding source input parameters fo r volume or area type s ources in AERMOD, see 3.3 of the AERMOD User’s Guide (U.S. EPA, 2004a; U.S. EPA. 2011a).

If the reviewing authority has adequate technical da ta (i.e., soil samples) and additional information to support the inclusion of re-entrainment of lead from the soil, this can be simulated as an area of volume source type in the model.

20 Q. What is the level of captu re efficiency that should be used in modeling of total enclosure

emissions?

A: For modeling of secondary lead smelters, capture e fficiency is needed for modeling of total enclosure emissions. At this time, 100% capture efficiency is not considered technically achievable in common practice. At this time, states that impose total en closure controls in a manner consistent with the National

Emission Standard for Hazardous Air Pollu tants from Secondary Lead Smelting ,77 FR 555 (which includes requirements for enclosures and housekeepi ng), can assume a capture efficiency for total enclosures of no greater than 95%. A greater le vel of capture efficiency (up to 99%) may be demonstrated on a case-by-case basis taking into account site-specific factors and additional design or housekeeping provisions that go beyond what is assume d in the NESHAP. States should consult with their respective Regions for consid eration of case-specific demonstrat ions claiming greater than 95% capture efficiency.

21 Q. What is the best w ay to model ambient air?

A: Ambient air is considered to be the air in t hose areas where the public generally has access. Nonambient air generally includes proper ty owned or controlled by the sour ce to which access by the public is prohibited by a fence or othe r effective physical barrier.

Another issue with ambient air in modeling is the s ituation of multiple facilities in an area. As noted above, facility property is not ambient relative to its own emissions but is ambient relative to other sources’ emissions. For example, there may be a situ ation with two sources, S ource A and Source B. In this situation, the impacts of Source A on the air over Source A are not consid ered to be impacts on ambient air, but the impacts of Source A on the ai r over Source B are considered to be impacts on ambient air, and vice versa. This situation is discu ssed in the March 1985 me morandum “Applicability Determinations for Columbian Chemical Company 1 .”

1 http://www.epa.gov/region07/ air/nsr/nsrm emos/ccc.pdf4 In modeling these situations, there are two ways to handle ambient air over multiple facilities.

1. Divide the model runs into several modeling doma ins: A) a receptor networ k that is outside the property lines for all facilities for which all s ources are modeled, and B) separate receptor

networks and model runs over each facility for which that facility’s emissions are not included. For this case, design values can be calculated for each receptor network using LEADPOST. LEADPOST results from all receptor networ ks can be concatenated together.

2. Create a receptor network that co vers all ambient air and facilities. Include all emissions in the model runs and generate monthly POSTFILES by source group, with each source group representing a separate facility. After the model runs are finished, for receptors over a specific facility zero out the concentrations from that facility leaving the ot her facilities’ contributions as they are. The new concentration files can be i nput into LEADPOST to calculate design values

for cumulative concentrations.

22 Q. How should ASOS 1-minute data 2 be used in modeling?

A: In AERMOD, concentrations are not calculated for variable wind (i.e., mi ssing wind direction) and calm conditions, resulting in zero concentrations for those hours. These light wind conditions may be the controlling meteorological circumstances in some cases because of the limited dilution that occurs under low wind speeds which can lead to higher concentr ations. The exclusion of a greater number of

instances of near-calm conditions from the modeled concentration distribution may therefore lead to underestimation of monthly av erage concentrations.

To address the issues of calm and variable winds a ssociated with the use of NWS meteorological data, the EPA has developed a preprocessor to AERMET, called AERMINUTE (U.S. EPA, 2011b) that can read 2-minute ASOS winds and calculate an hourly average. Beginning with ye ar 2000 data, NCDC has made the 2-minute average wind data, reported every minute from the ASOS network freely available. The AERMINUTE program reads these 1-minute winds and calculates an hourly average wind. In AERMET, these hourly averaged winds replace the standard observation time winds read from the archive of meteorological data. Th is results in a lower number of calm hours and missing wind direction

hours and an increase in the number of hours used in averaging concentrations. For more details regarding the use of National Weat her Service (NWS) data in regulat ory applications see Section 8.3.2 of Appendix W (U.S. EPA, 2005) and for more info rmation about the processing of NWS data in AERMET and AERMINUTE, see the AERMET (U.S. EPA, 2004b; U. S. EPA, 2011c) and AERMINUTE User’s guides (U.S. EPA, 2011b).

Since the release of AERMINUTE in 2011, some perm itting agencies have expressed concern that the inclusion of AERMINUTE output in AERMOD will lead to an increase in the conservatism of AERMOD output. This perceived increase in conserva tism is due to an increase in hours with lower wind speeds input into AERMOD. The purpose of AERM INUTE is not to lead to more conservative concentration estimates, but to increase the data quality and representative ness of the meteorological inputs into AERMOD. Concentrations are not calculated for hours with reported calm winds or variable

winds. These calm or variable winds are due to the METAR reporting code used to report ASOS

2 The purpose of this section is to addres s the use of 1-minute data when using year 2000 and later ASOS airport data. This section does not address the use of pre-ASOS vs. post-ASOS data. The reviewing authority should use the meteorological data they consider most representative of the particular application.5 observations. In the METAR coding used to report surface observations beginning July 1996, a calm wind is defined as a wind speed less than 3 knots a nd is assigned a value of 0 knots. The METAR code

also introduced the variable wind observation that may include wind sp eeds up to 6 knots, but the wind direction is reported as missing, if the wind direction varies more than 60 degrees during the 2-minute averaging period for the observation. These are ofte n hours of interest because these are light wind conditions and could lead to higher concentrations. With the use of AERMINUTE, hourly averages can

be calculated for those hours with reported calm or missing winds, b ecause the 2-minute average winds in the one-minute data files have not been subjec ted to the METAR coding. In effect, AERMINUTE is obtaining data that was unavailable because of METAR coding, making the meteorological data more representative of the area.

23 Q. What is the proper recep tor spacing in modeling?

A: The model receptor grid is unique to the particul ar situation and depends on the size of the modeling domain, the number of modeled so urces, and the complexity of the terrain. Emphasis should be placed on resolution and location, not the total number of r eceptors (Section 7.2.2 (U.S. EPA, 2005)). Receptors should be placed in areas that are considered ambient air (see ambien t air discussion a bove) with respect to the source(s) being modeled and placed out to a distance such that all areas of violation can be detected from the model output. Re ceptor placement should be of sufficient density to provide resolution needed to detect significant gradients in the concentrations with receptors placed closer together near the source(s) to detect local gradients and placed farther apart away from the source(s). In addition, the user should place recepto rs at key locations such as around facility fence lines (which define the ambient air boundary for a particular source) or monitor locati ons (for comparison to

monitored concentrations for m odel evaluation purposes). The receptor network should cover the modeling domain. If modeling indicates elevated levels of Pb (near the standard) near the edge of the receptor grid, consideration should be given to expanding the grid or conducting an additional modeling

run centered on the area of concern. As noted above, terrain complexity should also be considered when setting up the receptor grid. If complex terrain is included in the model cal culations, AERMOD requires that receptor elevations be included in the model inputs. In those cases, the AERMAP terrain processor (U.S. EPA, 2004c; U.S. EPA, 2011d) should be used to ge nerate the receptor elevat ions and hill heights. The latest version of AERMAP (09040) can proce ss either Digitized Elev ation Model (DEM) or National Elevation Data (NED) data files. The AE RMOD Implementation Guide recommends the use of NED data since it is more up to date than DEM data, which is no longer updated (Section 4.3 of the AERMOD Implementation Guide (U.S. EPA, 2009).

24 Q. How should haul roads fo r lead facilities be modeled?

A: Useful information regarding the modeling of haul roads in and aroun d lead facilities can be found in the Final Report of the Haul Roads Wor kgroup, available on EPA’s SCRAM website at Haul Road Workgroup Final Report Submission to EPA-OAQPS, March 12, 2012.

The report details the efforts of the Haul Roads Workgroup, which was a collaborative effort between the EPA and state/local modelers. The workgrou p has recommended a methodology for modeling haul roads (pages 4-6 of the report). These recommendations are:

 Model all haul roads as adjacent volume sources, unless ambient air receptors are in the volume source exclusion zone (2 .15 x Sigma Y + 1 meter)

 Top of plume height set to 1.7 x the vehicle height

 Release height of volume source set to half the plume height6  Width of the plume should be ve hicle width + 6 m for si ngle-lane roads or road width + 6 m for

2-lane roads

 The initial Sigma Z should be set to plume height/2.15

 Initial Sigma Y should be set to plume width/2.15

 Emission rate in grams/second

For cases where volume sources cannot be used due to ambient air receptors be ing located in the volume source exclusion zone, haul roads can be modeled as area sources with:

 Length set to length of link

 Top of plume, release height, plume width, and Sigma Z set to values listed above for volume

sources.

 Emission rate in grams/second/m 2

For more details, users are str ongly encouraged to review the Haul Road Workgroup Final Report Submission to EPA-OAQPS, March 12, 2012.

References

U.S. EPA, 2004a: User's Guide for the AMS/ EPA Regulatory Model – AERMOD. EPA-454/B-03-001. U.S. Environmental Protection Agency, Research Triangle Park, NC 27711.

U.S. EPA, 2004b: User’s Guide for the AERM OD Meteorological Preprocessor (AERMET). EPA454/B-03-002. U.S. Environmental Protection Agency, Research Triangle Park, NC 27711.

U.S. EPA, 2004c: User's Guide for the AERM OD Terrain Preprocesso r (AERMAP). EPA-454/B-03- 003. U.S. Environmental Protection Agency, Re search Triangle Park, North Carolina 27711.

U.S. EPA, 2005. Guideline on Air Quality Models . 40 CFR Part 51 Appendix W.

U.S. EPA, 2009: AERMOD Implementation Guide. U. S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711.

U.S. EPA, 2011a: Addendum – User’s Guide fo r the AMS/EPA Regulatory Model – AERMOD. EPA454/B-03-001, Research Triangl e Park, North Carolina 27711.

U.S EPA, 2011b: AERMINUTE User’s Guide. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711.

U.S. EPA, 2011c: Addendum - User’s Guide for the AERMOD Meteorological Preprocessor (AERMET). EPA-454/B-03-002. U.S. Environmental Pr otection Agency, Research Triangle Park, NC

27711.

U.S. EPA, 2011d: Addendum - User's Guide for the AERMOD Terrain Pr eprocessor (AERMAP).

EPA-454/B-03-003. U.S. Environmental Protection Ag ency, Research Triangle Park, North Carolina

27711.