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New Source Review for Air ToxicsPowerPoint Presentation

New Source Review for Air Toxics

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Presentation Transcript

What is ToxicsNew Source Review (NSR)?

- Evaluation of the health risk impacts to nearby exposed individuals (receptors)
- Calculate health risk indices
- Health risk indices cannot exceed thresholds

When is Toxics NSR Applied?

- When a new or modified source causes an increase in Toxic Air Contaminants (TAC), Toxics NSR is required
- SCAQMD Rule 1401 – New Source Review of Toxic Air Contaminants
- Also Rule 219 permit-exempt equipment if health risk may exceed thresholds

Implications of Toxics NSR

- Permit denied if calculated health risk is too high
- Public notice required if cancer risk increase exceeds 1 in one million
- CEQA is triggered if combined project cancer risk increase exceeds 10 in one million
- May require Environmental Impact Report

Implications (continued)

- May set permit conditions
- Example: Natural Gas Engine
- Toxic Air Contaminants from internal combustion must be evaluated for Toxics NSR
- If health risk calculations show that a limit on operation is necessary to stay below health risk thresholds, a daily or monthly limit on natural gas use may become a permit condition

- Carefully consider all possible toxic emissions for any new source

What Toxics are Considered?

- Toxic Air Contaminants (TAC) are listed in Rules 1401 and 1402
- Carcinogenic: 153 compounds
- Acute: 58 chemicals
- Chronic: 125 chemicals

- Risk factors are assigned by the California EPA Office of Environmental Health Hazard Assessment (OEHHA)
- New TAC’s being added over time

Health Risk Index - MICR

- Maximum Individual Cancer Risk (MICR)
- Long term impact
- Probability that an individual will contract cancer over 70 years (resident receptor) or 40 years (commercial receptor)
- Must be < 1 x 10-5 (10 in one million) for new equipment
- <1 x 10-6 to avoid public notice

Health Risk Index - Chronic

- Chronic Hazard Index (HIC)
- Long term, non-cancer health effects
- Must be < 1.0 for all target organs

Health Risk Index - Acute

- Acute Hazard Index (HIA)
- Short term (1-hour average) health effects
- Must be < 1.0 for all target organs

What Are Target Organs?

- Specific systems in the human body that are affected by TACs

Risk Assessment Tiers

- Tier 1: Screening Emission Levels
- Use Table 1A to check if emission rates are below thresholds

- Tier 2: Screening Risk Assessment
- Use Tables 2-10 to determine dispersion factors, etc.

- Tier 3: Screening Dispersion Modeling
- Use SCREEN3 to determine dispersion factors

- Tier 4: Detailed Risk Assessment
- Use HARP for highest fidelity model, full meteorology

Less Conservative

Tier I Screening Evaluation

- Max Annual Controlled Emissions (tons/year)
- Max Hourly Controlled (lbs/hr)
- Look up tables in: “Risk Assessment Procedures for Rules 1401 and 212”
- Check for most recent version!

- If emissions are lower than screening levels, Rule 1401 is satisfied. If not, proceed to Tier II

Tier II Health Risk Assessment

- Max Annual Controlled Emissions (tons/year)
- Max Hourly Controlled (lbs/hr)
- Look up tables in: “Risk Assessment Procedures for Rules 1401 and 212”
- If health risk indices lower than thresholds, Rule 1401 is satisfied. If not, proceed to Tier III

Tier II Risk Assessment for MICR

- MICR = CP x DI x MP
- CP: cancer potency factor (mg/kg-day)-1
- DI = Dose inhalation (mg/kg-day)
- DI = Cair x DBR x EVF x 10-6
- Cair = concentration in air (µg/m3)
- DBR = daily breathing rate (L/kg-day)
- EVR = Exposure value factor (unitless)
- 1 x10-6 = convert µg to mg(10-3 mg/µg), liters to cubic meters (10-3 m3/l)

- Cair = Qtonsx X/Q x AFannx MET
- Qtons = Emission rate (tons/year)
- X/Q = Dispersion Factor ((µg/m3)/(ton/yr)
- AFann = Annual Averaging factor
- MET = meteorological correction factor (unitless)

- MP: multipathway factor (unitless)

- MICR = CP x ((Qtonsx X/Q x AFannx MET) x DBR x EVF x 10-6) x MP

Chronic Index Equation

HIC Chronic hazard index (calculated for each target organ)

TACSum of the contribution for each Toxic Air Contaminant (TAC)

QyrTACEmission rate of each TAC (tons/year)

X/Q Annual average dispersion factor (g/m3)/(ton/year)

RELTACChronic Reference Exposure Level (g/m3) for each TAC

MP Multi-pathway adjustment factor (n.d.)

MET Meteorological correction factor (n.d.)

Acute Index Equation

HIA Acute hazard index (calculated for each target organ)

TACSum of the contribution for each Toxic Air Contaminant (TAC)

QhrTACEmission rate of each TAC (lb/hour)

X/QhrHourly average dispersion factor (g/m3)/(lb/hour)

RELTACAcute Reference Exposure Level (g/m3) for each TAC

Cancer Burden Calculation

- Only Needed if MICR >10-6
- Estimate Area (km2) with Risk >10-6
- Multiply Area by 4,000 - 7,000 persons/ km2
- Multiply Total Persons by MICR
- If Burden >0.5
- More detailed calculations or modeling required

Tier III Health Risk Assessment

- Similar to Tier II
- Use SCREEN3 to determine dispersion factors (X/Q) instead of from tables
- Exhaust temperature and velocity are included
- Simple building downwash effects
- Single source
- Equation is the same
- If health risk indices lower than thresholds, Rule 1401 is satisfied. If not, proceed to Tier IV

Tier IV Health Risk Assessment

- Most detailed health risk assessment
- Requires details of building dimensions, local topography, and local meteorology
- Use Hot Spots Analysis and Reporting Program (HARP) to calculate dispersion factors and health risk indices
- Free download from CARB website www.arb.ca.gov/toxics/harp/harp.htm

- Multiple sources in different locations

TAC’s from Natural Gas

- Ventura County APCD did testing of internal & external combustion equipment in 1995 for TAC’s
- “Ventura Factors” can be used for emission factors for external combustion only
- Use EPA’s AP-42 emission factors for internal combustion

TAC’s from External Combustion

*As determined by Ventura APCD

TAC’s from Internal CombustionEPA: AP-42 Emission Factors, Table 3.2-3

Rule 1401 Limitations

- MICR of 1 X 10-6 Without T-BACT *
- MICR of 1 X 10-5 With T-BACT
- Cancer Burden, excess cancer cases in the population subject to a risk greater than (1 x 10-6), of 0.5
- Acute and Chronic Hazard Index of < 1
* T-BACT Criteria Similar to Existing BACT

Rule 1401 Exemptions

- Emergency Internal Combustion Engines
- Modifications with no increase in toxic emissions
- Functionally identical replacement
- Contemporaneous Risk Reductions
- No MICR increase at any location >1x10-6, and
- Reduction occurs within 100 m of new equipment

- Alternative Hazard Index <10

Example

- Facility adding three large, natural-gas fueled, cogeneration engines
- Four existing emergency diesels
- Nearby residents
- Each engine passed Rule 1401 with MICR of 9 in one million
- CEQA triggered due to combined MICR of 27 in one million

Example (continued)

- We calculated that cogeneration engines resulted in less usage of diesel backup engines
- Diesel health risk is high
- Contemporaneous health risk reduction allowed project to proceed without requiring an Environmental Impact Report

Risk is Dependent On:

- Source and Receptor Location
- Emission Rate
- Emission Species
- Meteorology
- Stack Parameters
- Operating Schedule

Strategies

- Locate equipment away from adjacent residents or workers
- Raise stack height
- Perform detailed modeling to determine risk impacts to specific receptors
- Source test for actual toxic emissions
- Tests showed high destruction of PAH across catalyst

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