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What Every EHS Staff Should Know about
Monitoring and Modeling
Robynn Andracsek, P.E.
816-822-3596
www.burnsmcd.com/columns
May 11, 2016
The Air Really is Getting Cleaner…
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reas
Year
The EPA Approved Models
Class II Area Modeling
– AERMOD – current EPA-accepted model
NAAQS and Class Prevention of Significant Deterioration (PSD) II increment
Class I Area Modeling
– CALPUFF model
– Visibility, Deposition and PSD Class I increment
Front-end software usually used
– Breeze, BEEST, Lakes
Modeling Stages (Construction Permitting)
1. Stage 1 – Model the Project
– Modeling significance
– Monitoring significance
– If below both, modeling for PSD is done
2. Stage 2 – Refined (Cumulative) Modeling
– National Ambient Air Quality Standards
– Prevention of Significant Deterioration Increment Standards
– Neighboring sources included
Significance Modeling
Model the new (Project) emissions
If modeling significant impact level is exceeded
– Model entire facility and inventory sources within radius of impact plus 50 km
If monitoring de minimis level is exceeded
– Install your own monitor and gather one year of data
– Use an existing monitor (if state will allow that)
Pollutant Average
Class II Modeling
Significant Impact Level
(SIL) µg/m3
Monitoring de Minimis
Level µg/m3
PM10 24-hour 5 10
PM2.5
24-hour 1.2 4
Annual 0.3 --
SO2
1-hour 7.8 --
3-hour 25 --
24-hour -- 13
NO2
1-hour 7.52 --
Annual 1 14
CO 1-hour 2,000 --
8-hour 500 575
Radius of Impact (ROI)
Model only the new sources
Find farthest distance to an impact greater than or equal to SIL (example shows 17 km as significance impact area)
Add 50 km to get ROI
ROI is 67 km
Include all neighboring sources inside ROI
NAAQS vs. PSD Increment
National Ambient Air Quality Standards
– Ceiling of air quality pollution allowed
– Most point sources at facility and neighbors within 50-100 km radius
– Plus add in background
Prevention of Significant Deterioration Increment
– Incremental degradation allowed above baseline in areas with good air quality
– Only sources modified after baseline date
– Specifies the maximum extent to which the ambient concentration may be allowed to increase above the legally defined baseline concentration in an area with clean air.
Baseline Date Rule of Thumb
Anything constructed before 1977 is NOT PSD increment consuming
NAAQS
Pollutant Average µg/m3 ppm
PM10 24-hour 150 --
PM2.5
24-hour 35 --
Annual 12 --
SO2
1-hour 195 0.075
3-hour 1,300 0.5
NO2
1-hour 188 0.1
Annual 100 0.053
Ozone 1-hour -- 0.12
8-hour -- 0.070
CO 1-hour 40,000 35
8-hour 10,000 9
Lead 3-hour rolling 0.15 --
Notes: • Models results are
in terms of
micrograms per
cubic meter (µg/m3)
• Standards for
gaseous pollutants
are in parts per
million (ppm)
• Ozone (volatile
organic compounds
[VOC]) is not
usually modeled
NAAQS Averaging Periods
By Average
Annual – PM2.5, NOX
24-hour – PM2.5, PM10
3-hour – SO2
1-hour, – CO, SO2, NOX
8-hour – CO , Ozone
By Pollutant
PM2.5 – 24-hour, annual
PM10 – 24-hour
NOX – 1-hour, annual
SO2 – 1-hour, 3-hour
CO – 1-hour, 8-hour
Ozone
More Than Just Emissions
Emergency Generator Coal-fired Boiler
Dispersion Modeling – Challenges
NOx
– Previously only annual average
– 1-hour NO2 NAAQS Standard
– 1-hour NO2 level that triggers inclusion of nearby sources
– May use “Tier 3” methods for reducing impacts
New methods are being reviewed (ARM2)
PM2.5 NAAQS standard
– Low standard
– High backgrounds
– Increment hard to meet
“How Tall Should the Stack Be?”
Good Engineering Practice (GEP) stack height
– Maximum stack height allowed in model
– Roughly 2.5 times building height
– Dominant building can be a building on which the stack is not located
Minimum stack height dictated by dispersion modeling to meet NAAQS, increment
– Not every project requires modeling
Modeling Issues to Expect
Site-layout/building/stack design to play a significant role
Downwash from buildings can impact results significantly
Issues with neighboring sources
Background values can be very high
Modeling operating loads and startup/shutdown emissions
Site size
If the project will be installed in phases, expect to perform modeling for the entire project to avoid any surprises
Can look at combining stacks
Sources
Point – Stacks
Volume – Drop points
– Roads
Area – Piles (wind erosion)
– Roads (depends on state)
Point Sources
Temperature
Velocity
Diameter
Height
Location
Base elevation
Emission rate
Initial Stack Dispersion
} }
Temperature
Velocity
Rain Caps
} Temperature
Velocity = 0
Use “tractor flap”
exhaust if possible
Rain Caps are BAD
Downwash “Shadow”
Receptors
Fence line
– Physical barrier
– Not the same as the property line
Spacing
– Along fence
– Larger spacing farther away from plant
– “Hot Spot” grids
Import terrain elevations
Receptor Grid Example
•Along the fence line boundary at a spacing of 25 meters
•25-meter out to 100 meters
•100-meter out to one kilometer
•500-meters out to five kilometers
•1,000-meter out to twelve kilometers.
Meteorological Data
5 years of hourly data
– Surface plus upper air
– Usually a nearby airport
Some states provide data sets that must be used
State may require on-site meteorological data (1 year delay)
Windrose
Graphical Output
How Accurate Do Modeling Inputs Need to Be
My Personal Rules of Thumb for Tolerance
Height 1 foot or < 10%
Diameter 6 inches or < 5%
Velocity < 5%
X,Y location ± 5 feet
Elevation ± 5 feet
Temperature ±20°F
Emissions ± 2%
What To Do If Model Doesn’t Pass
Apply advanced methods
Use hour-of-day limits
Raise stacks
Add controls
Water roads or piles
Make stacks vertical unobstructed
Move fence line out to property line
Move equipment
Limit operation of “intermittent” sources
Modeling Review
Modeling is an art and a science
Start conservative and work towards reality
Rain caps are evil
Ambient air is outside the physical fence
Good Engineering Practice (GEP) stack height is maximum stack height allowed (not recommended or minimum)
Limits in modeling become limits in permit
Questions?
Robynn Andracsek, P.E.
816-822-3596
www.burnsmcd.com/columns
