OFFICE OF ENVIRONMENTAL HEALTH HAZARD ASSESSMENT

Risk Assessment Guidelines

Guidance Manual for

Preparation of Health Risk Assessments

February 2015

Air, Community, and Environmental Research Branch Office of Environmental Health Hazard Assessment California Environmental Protection Agency

Air Toxics Hot Spots Program

Page Intentionally Left Blank

February 2015

Air Toxics Hot Spots Program

Risk Assessment Guidelines

The Air Toxics Hot Spots Program Guidance Manual

for Preparation of Health Risk Assessments

Office of Environmental Health Hazard Assessment

California Environmental Protection Agency

George V. Alexeeff, Ph.D., Director

i

Project Leads: Daryn E. Dodge, Ph.D.a and Gregory Harris b

Reviewed by:

Melanie A. Marty, Ph.D.a

Assistant Deputy Director, Division of Scientific Affairs

David Siegel, Ph.D.a

Chief, Air, Community, and Environmental Research Branch

OEHHA acknowledges the following contributors:

Abdullah Mahmud, Ph.D b

Anthony Servin, P.E.b

Steven Yee b

Yan-Ping Zuo b

James F. Collins, Ph.D., D.A.B.T.a

Andrew G. Salmon, M.A., D.Phil.a

Aijun Albert Wang, Ph.D.a

a Air, Community, and Environmental Research Branch Office of Environmental Health Hazard Assessment

b California Air Resources Board

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Air Toxics Hot Spots Program Guidance Manual February 2015

Table of Contents

Preface ........................................................................................................................... 1

1 - Introduction ........................................................................................................... 1-1

1.1 Development of Guidelines ............................................................................... 1-1 1.2 Use of the Guidance Manual ............................................................................. 1-2 1.3 Who is Required to Conduct a Risk Assessment ........................................... 1-3 1.4 The Hot Spots Analysis and Reporting Program (HARP) Software............... 1-4 1.5 Risk Assessment Review Process ................................................................... 1-4 1.6 Uncertainty in Risk Assessment....................................................................... 1-5 1.7 Tiered Approach to Risk Assessment.............................................................. 1-7 1.8 References.......................................................................................................... 1-7

2 - Overview of Health Risk Assessment ................................................................. 2-1

2.1 The Model for Risk Assessment ....................................................................... 2-1 2.2 Hazard Identification.......................................................................................... 2-1 2.3 Exposure Assessment....................................................................................... 2-1 2.4 Dose-Response Assessment ............................................................................ 2-2 2.5 Risk Characterization......................................................................................... 2-3

2.5.1 Point Estimate Approach ........................................................................ 2-4 2.5.2 Stochastic Exposure Assessment........................................................... 2-5 2.5.3 Tiered Approach to Risk Assessment ..................................................... 2-6

2.6 References.......................................................................................................... 2-6

3 - Hazard Identification - Air Toxics Hot Spots Emissions.................................... 3-1

3.1 The Air Toxics Hot Spots List of Substances and Emissions Inventory....... 3-1 3.2 References.......................................................................................................... 3-2

4 - Air Dispersion Modeling....................................................................................... 4-1

4.1 Air Dispersion Modeling in Exposure Assessment: Overview ..................... 4-1 4.2 Emission Inventories ......................................................................................... 4-5

4.2.1 Air Toxics Hot Spots Emissions .............................................................. 4-5 4.2.2 Landfill Emissions ................................................................................... 4-9

4.3 Source Characterization .................................................................................... 4-9 4.3.1 Source Type ........................................................................................... 4-9 4.3.2 Quantity of Sources .............................................................................. 4-11

4.4 Terrain Type...................................................................................................... 4-11 4.4.1 Terrain Type Land Use ...................................................................... 4-12 4.4.2 Terrain Type - Topography ................................................................... 4-14

4.5 Level of Detail: Screening vs. Refined Analysis........................................... 4-14 4.6 Population Exposure ....................................................................................... 4-15

4.6.1 Zone(s) of Impact.................................................................................. 4-15

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Air Toxics Hot Spots Program Guidance Manual February 2015

4.6.2 Screening Population Estimates for Risk Assessments........................ 4-17 4.6.3 Refined Population Estimates for Risk Assessments............................ 4-18 4.6.4 Sensitive Receptor Locations ............................................................... 4-20

4.7 Receptor Siting................................................................................................. 4-20 4.7.1 Receptor Points .................................................................................... 4-20 4.7.2 Centroid Locations................................................................................ 4-22 4.7.3 Spatial Averaging.................................................................................. 4-22

4.8 Meteorological Data ......................................................................................... 4-27 4.8.1 Meteorological Data Formats................................................................ 4-29 4.8.2 Treatment of Calms .............................................................................. 4-29 4.8.3 Treatment of Missing Data.................................................................... 4-30 4.8.4 Representativeness of Meteorological Data ......................................... 4-31 4.8.5 Alternative Meteorological Data Sources.............................................. 4-33 4.8.6 Quality Assurance and Control ............................................................. 4-33

4.9 Model Selection................................................................................................ 4-34 4.9.1 Recommended Models ......................................................................... 4-34 4.9.2 Alternative Models ................................................................................ 4-35

4.10 Screening Air Dispersion Models ................................................................... 4-35 4.10.1 AERSCREEN ....................................................................................... 4-36 4.10.2 Valley Screening................................................................................... 4-37 4.10.3 CTSCREEN .......................................................................................... 4-37

4.11 Refined Air Dispersion Models ....................................................................... 4-39 4.11.1 AERMOD .............................................................................................. 4-39 4.11.2 CTDMPLUS .......................................................................................... 4-42

4.12 Modeling to Obtain Concentrations used for Various Health Impacts ........ 4-43 4.12.1 Emission Rates for Cancer, Chronic, and Acute Health Impacts .......... 4-43 4.12.2 Modeling and Adjustments for Inhalation Cancer Risk at a Worksite.... 4-43 4.12.3 Modeling and Adjustments for Noncancer 8-Hour RELs ...................... 4-45 4.12.4 Modeling and Adjustment Factors for Noncancer Chronic RELs .......... 4-48 4.12.5 Modeling and Adjustments for Oral Cancer Potencies and Oral RELs . 4-48 4.12.6 Modeling One-Hour Concentrations using Simple and Refined Acute

Calculations .......................................................................................... 4-49 4.13 Modeling Special Cases; Specialized Models ............................................... 4-50

4.13.1 Building Downwash .............................................................................. 4-50 4.13.2 Deposition............................................................................................. 4-51 4.13.3 Short Duration Emissions ..................................................................... 4-51 4.13.4 Fumigation ............................................................................................ 4-52 4.13.5 Raincap on Stack.................................................................................. 4-52 4.13.6 Landfill Sites ......................................................................................... 4-53

4.14 Specializ