Overview of Dispersion Modeling in Air Permitting

Arizona Department of Environmental QualityAir Quality DivisionRobert Arpino P.E.

Main Topics

IntroductionADEQ Air JurisdictionTypes of ADEQ Air PermitsUses of Dispersion ModelingCommon Regulatory Air ModelsModeling Review ProcessTribal Air Program JurisdictionADEQ Tribal PolicyJoint Agency EngagementAir Modeling Resources/Contacts

State of Arizona Facts

•Total area of roughly 114,000 square miles

•15 counties

•2 Class I National Parks (Grand Canyon, Petrified Forest)

•10 Class I National Wilderness Areas

•21 Federally Recognized Native American Tribes - covering 28% of the land base

Map of Arizona Counties

Overview of ADEQ Jurisdiction

Source categories under exclusive ADEQ jurisdiction•Metal ore smelters•Petroleum Refineries•Coal-fired electrical generating stations•Portland cement plants•Other sources under State asserted jurisdiction -A.R.S. 49-402

Maricopa, Pima, Pinal County permit programs•Cover sources within those jurisdictions (except those listed above)•ADEQ covers remaining counties

Types of ADEQ Air Permits

Class I Permits•All Prevention of Significant Deterioration (PSD) determinations•All New Source Review determinations•All other types of new major source permits (Title V permits)

Class II Permits•All new minor source and synthetic minor source permits Synthetic minor sources are sources that have agreed to restrictions to limit their potential to emit below major source thresholds

General Permits•Covers specific classes of sources

ADEQ General Permits

•Emission calculations and dispersion modeling are already performed by ADEQ to verify protection of NAAQS

•Production and throughput limits set based on emissions analysis and dispersion modeling (where applicable) performed by ADEQ

•Public hearing process has already been done once so each source will not need to be public noticed again

•Usually more restrictive than individual source permit but less expensive and faster since the technical analysis has already been performed by ADEQ

List of ADEQ General Permit Source Classes

•Crematories (Expires November 30, 2014)•Soil Vapor Extraction Units (Expires June 30, 2016)•Crushing and Screening (Expires April 23, 2017)•Hospitals (Expires November 14, 2014)•Hot Asphalt Plants (Expires April 23, 2017)•Dry Cleaners (Expires July 19, 2016)•Generators (Expires July 19, 2016)•Concrete Batch Plants (Expires June 08, 2015)•Boilers (Expires May 12, 2014)

Purposes of Dispersion Modeling

•Protection of NAAQS •Protection of PSD increment•Protection of Air Quality Related Values (AQRV) such as Class I area visibility•Determine if air monitoring is required and the best location for the monitors•Protection of Arizona Standards for HAPs

AAAC – Acute Ambient Air Concentrations CAAC – Chronic Ambient Air Concentrations

USES OF DISPERSION MODELING AT ADEQ

Permit Modeling

SIP Modeling

State Implementation Plan (SIP) Modeling

•Can be used along with monitoring data to determine the attainment status of a region and if a (SIP) is required

•Regional scale modeling over a large area

•Large emission inventory

•Demonstrate effectiveness of control measures used to achieve attainment with NAAQS (e.g. PM-10)

Permit Modeling

•Modeling may be required when a source submits an air permit application (AAC R18-2-407)

•Modeling requirement may depend on:- Magnitude of the potential emissions- Location of the source near sensitive populations- Level of emission control - proposed minor NSR rule

AAC R18-2-334 provides an option for a source to forego modeling if Reasonably Available Control Technology (RACT) is applied

Common Regulatory Dispersion Models

•AERSCREEN – A conservative screening model that is relatively easy to run and can be used to determine if refined modeling is necessary

•AERMOD – The “workhorse” of permit modeling for near field. Replaces ISC model

•CALPUFF – A very comprehensive model which requires very detailed meteorological and geographical data sets. Very resource intensive!

AERSCREEN

•EPA-recommended screen model to determine if refined modeling is needed•Can model a single source to obtain 1-hr worst-case concentrations •Easy-to-use Gaussian dispersion model•Accounts for terrain and downwash effects using AERMAP and BPIPPRM •Generates worst-case meteorology using MAKEMET program which utilizes: - ambient air temperature - minimum wind speed, site-specific - surface characteristics

AERMOD Overview

•EPA-preferred model for near field (<50 km)

•Steady-state Gaussian plume model

•Can handle simple and complex terrain

•Incorporates advanced building downwash algorithms

•Uses turbulence theory to estimate degree of dispersion

AERMOD Overview (cont’d)

AERMOD can model a variety of source types:

•Point sources – stacks

•Area Sources – e.g. storage piles

•Volume Sources – e.g. haul trucks

•Line Sources

•Flares

AERMOD Subprograms

•AERMET – Processes surface met data, upper air data, and land use parameters to generate surface and profile met data files ready for use by AERMOD

•AERMAP – Processes terrain data to generate receptor grid with elevations for each receptor

•AERSURFACE – Analyzes USGS land coverage data to provide surface characteristics such as albedo, Bowen Ratio, and surface roughness for use in AERMET

AERMOD Subprograms (cont’d)

•BPIP PRIME – Building Profile Input Program with Plume Rise Model Enhancements

•Uses building height, width, stack height and location to calculate downwash parameters for use in AERMOD

•Improved building downwash calculations over the old BPIP which was used with ISC3 model

CALPUFF Overview

•EPA-preferred long range model (50 km – 300 km)

•Non-steady state Langrangian puff model

•Requires complex data input e.g. MM5 Met data, precipitation data, geographical data and is more resource intensive than AERMOD

•Can account for chemical transformations

•Can perform visibility impact analysis (CALPOST)

CALPUFF Overview (cont’d)

Main programs/subprograms:

CALMET – Meteorological pre-processor that processesmeteorological and geophysical data for CALPUFF

CALPUFF – Processes input source data and CALMETdata to calculate impacts

CALPOST – Post processing program that uses CALPUFFresults to average and report concentration, wet/dry deposition,and visibility impacts

CALPUFF Modeling System (simplified)

Model Review Process at ADEQ

Modeling Protocol

Modeling Report

Modeling Protocol

Document submitted to agency (in advance of performing the model) describing the modeling approach and supporting methodologies used. Strongly recommended to avoid having to rerun model!

•Provide details of the pollutants considered, emission sources, source types, facility layout, ambient air boundary

•Describe model selection and version used. Important since different versions can give different results (e.g CALPUFF 5.8 versus CALPUFF 6.4)

•Justify the use of any non-default settings (e.g. Low-wind beta settings)

Modeling Protocol (cont’d)

•Describe regional climate/meteorology, topography

•Discuss choice of met data set and ambient background concentrations used in the model. Must justify that choices are representative of site area per EPA Guidelines (40 CFR 51 App. W Sec. 8.0)

•Detailed discussion of building downwash, BPIPPRM inputs, Good Engineering Practice stack height, cavity zone impacts

Modeling Protocol (cont’d)

•Proposed receptor grid details (course/fine/discrete) and extent of modeling domain

•Provide details of terrain data sets and discuss any effects that terrain may have on modeled results

•Describe modeling approach proposed and any special considerations, such as unit load analysis

•PSD Sources – Significance, NAAQS, increment, visibility, Class I area modeling, soil/vegetation impact etc.

Modeling Protocol (cont’d)

•Provide details of any model option or methodology used (e.g. deposition option, OLM/PVMRM for NO2 etc. etc.)

•Discussion of approach to model intermittent sources, fugitive sources

•Discussion of approach to model variable load sources (engines)

•List of protocol elements and specific recommendations is found in Appendix A of ADEQ Modeling Guidelines

Modeling Report

Organizes and tabulates results, compares and discusses results relative to a standard (e.g. NAAQS) and also any specific issues or deviations from protocol.

•Compare modeled impacts to appropriate standard (NAAQS, increment, visibility, AAAC/CAAC)

•Use of any “non-default” settings or deviations from protocol

•Discussion of case-specific issues in results

Modeling Report (cont’d)

Maps showing facility boundary, sources, roads, buildings, sensitive areas, monitoring sites (if applicable)

Provide all input/out files, met data files, and any post-processing files

If applicable, Class I Area analysis results suchas increment analysis, visibility, other air quality relatedvalues (AQRVs)

Modeling Report (cont’d)

•Verify that emission rates used in model are consistent with the permit application emission rates

•Tabulate results in the correct form for specific pollutant

•Confirm that the appropriate land managers were sent copies of the modeling report

Tribal Air Program Jurisdiction

•Most Tribes in Arizona are under federal EPA jurisdiction

•Some tribes in Arizona have EPA approved programs - Gila River Indian Community - Fort McDowell Yavapai Nation - Navajo Nation - Salt River Pima-Maricopa Indian Community

•April 28, 2003 ADEQ established Tribal Policy basic principles governing ADEQ relations with Tribal governments in Arizona

ADEQ Tribal Policy

Establishes the following:

Recognizes that pollution is not restricted by political boundaries

Respects sovereignty of Tribal governments under federal law

Federal government has primary role for assisting Tribes

Supports strengthening Tribal capacity for management/regulation

ADEQ is committed to developing cooperative relationships and mutual respect for environmental concerns

ADEQ Tribal Policy (cont’d)

ADEQ assistance to develop environmental programs • Provide technical assistance• Share data (e.g. monitoring data, emissions etc. etc.)

-Reciprocity requested from Tribes• Conduct joint Tribal-State projects• Cooperatively resolve environmental issues• Will open training to Tribes whenever possible

ADEQ activities in Tribal land • Requires invitation from appropriate Tribal official

ADEQ Tribal Policy (cont’d)

Intergovernmental Agreements/Memoranda of Understanding• ADEQ will enter when considered mutually appropriate

ADEQ will work with Arizona Tribes to •Increase EPA funding available for Tribes•Develop Tribal capacity for federal environmental programs

Notification of permit decisions that may affect Tribes• ADEQ will provide early notification• ADEQ requests reciprocity

ADEQ Tribal Policy (cont’d)

ADEQ will not impose environmental fees/taxes on• Tribes or Tribal entities operating solely within reservation• Non-Tribal activities within reservation

Staff will relay Tribal issues/requests for technicalAssistance as quickly as possible

Staff must obtain approval from Division Director before initiating contact with Tribes

Joint Agency Engagement

NEPA – National Environmental Policy Act

Joint Engagement Case Study – Denison Mines

NEPA – National Environmental Policy Act

•Establishes a national environmental policy and requires the federal government to consider environmental factors and impacts in decision making

•Applies to resources under federal jurisdiction that involve federal funds and require federal permits

•Three levels of NEPA analysis:Categorical Exclusion

Environmental Assessment (EA) Environmental Impact Statement (EIS)

The NEPA Process

NEPA (cont’d)•The agency with the greatest expertise and regulatory authority becomes the Lead Agency for NEPA process

-Serves as single point of contact for public-Coordinates all activity with local/state/federal agencies

-Usually federal agency – e.g. EPA, BLM, NPS etc.

•Cooperating Agency – 40 CFR 1508.5State and/or Tribal agencies with jurisdiction/special

expertise may serve as a Cooperating Agency.

NEPA (cont’d)•Cooperating Agency – means any Federal agency other than the Lead Agency which has jurisdiction and/or special expertise regarding a proposal/federal action significantly affecting the quality of the human environment.

•Cooperating agencies can provide specific information used in assessing environmental impacts:

- Monitoring data for use as background concentration - Emissions data for specific sources in the area - Insight into specific local air quality issues and concerns - Dispersion modeling related information

NEPA (cont’d)

•Council of Environmental Quality (CEQ) coordinates federal environmental efforts and oversees the NEPA process

•July 28, 1999 CEQ memo urges federal agencies to solicit participation of State, Tribal, local gov’t as cooperating agencies

NEPA (cont’d)

•CEQ regulations/guidance do require agencies to provide Tribes opportunities to comment at various stages of the NEPA process

•Federal agencies are required to provide early consultation with Tribes in NEPA process - See 40 CFR 1501.2(d)(2)

Joint Engagement Case Study

Denison Mines – Four underground Uranium mines located in northern Arizona near Grand Canyon and Tribal Areas

•Sensitive issues due to nearby lands

•ADEQ legally obligated to issue permit if applicant has met applicable requirements

•ADEQ provided extensive notification to Tribes including Navajo, Hopi, Hualapai, Havasupai and Paiute Tribes

Joint Engagement Case Study

•Denison Mines are minor sources subject to:

-40 CFR 63 Subpart ZZZZ - backup generators -40 CFR 61 Subpart B – mine vent radon monitoring -A.A.C. Title 18, Chapter 2, Articles 6, 8 – fugitive dust, smoke, opacity

•Additional requirements above and beyond that legally required -Dispersion modeling (AERMOD/CALPUFF) to assess cumulative air impact on NAAQS, visibility, regional haze analysis (Grand Canyon) -Numerous public outreach meetings -Extended public comment period beyond required period

Joint Engagement Tribal Involvement

•Participation requested and encouraged! Your Tribal voice is important so please attend meetings to express concerns/issues

•ADEQ requests specific comments on the permit application and associated analyses

•To foster better communication, please identify the appropriate Tribal officials to serve as “point of contact” for air related issues

Effective Comments on Permits

Comments should:•Be specific and describe the exact nature of the problem •Avoid generic descriptions •Provide supporting documentation for the comment when possible•Identify the rule/requirement that applies to the problem•Suggest changes to draft permit or propose alternative approach

Comments have resulted in additional requirements such as:•Dust control plans•Radiation surveys •Ambient Monitoring

Effective Comment Example

Generic Comment Example (bad):“The dispersion modeling is not accurate or valid because it wasn’t performed correctly and the assumptions are not right.”

Specific Comment Example (good):“The dispersion modeling is not valid because it utilizes meteorologicaldata from site XYZ, located in town ABC, some 40 miles northwest of the proposed site. The area around the selected met data station has markedly different terrain characteristics from the proposed site location and is therefore not spatially and temporallyrepresentative of the local climate characteristics of the proposed site in accordance with EPA guidelines on air quality models.(See Sec. 8.3 of 40 CFR Appendix W Part 51).

Effective Comment Example 1 (cont’d)

“Additionally, the complex terrain of the proposed site is characterized by BigTall mountain range to the east, and Bumpy Mountain Rangeto the southeast which will cause wind channeling effects etc. etc. ……”

“Therefore, due to the significant terrain and elevation differences between the met data site and the proposed site for the source, the agency should require installation of an on-site met data towerto collect at least 1-year of on-site data to be used in the dispersion modeling or should require the source to install ambientmonitors after construction of the site to ensure compliance withthe NAAQS for NO2 and PM-10.”

Modeling Resources

ADEQ Dispersion Modeling Guidelines for Air Quality Permitshttp://www.azdeq.gov/environ/air/download/modeling.pdf

40 CFR Appendix W – Guideline on Air Quality Models

EPA Support Center for Regulatory Air Models (SCRAM)( http://www.epa.gov/scram001/ )

ADEQ Modeling Resources Webpage – Coming soon!

ADEQ Modeling Contacts

Feng Mao Ph.D., P.E. (Lead Modeler)Phone: 602-771-4529 Email: mf8@azdeq.gov

Robert Arpino P.E. Phone: 602-771-4896Email: rca@azdeq.gov