HF Modeling Task

Mike Williams

November 19, 2013

Objective• Objective: To estimate and compare short-term

concentrations of HF associated with emissions from the Intel’s Rio Rancho facility to the Texas Commission on Environmental Quality (TCEQ) short-term Environmental Screening Level (ESL) for Hydrogen Fluoride (HF) (15 micrograms per cubic meter at the altitude of Intel). The screening level was developed by the TCEQ based on studies by Lund in 1999 (see http://www.tceq.state.tx.us/assets/public/implementation/tox/dsd/final/october09/hydrogen_fluoride.pdf).

Background• “Spikes” in contaminant concentrations are a

concern to some people in the community• HF (Hydrogen Fluoride) is emitted by chip

production facilities and may be a health concern at low concentrations

• HF was mentioned in the draft ATSDR report on community health issues at Rio Rancho

• Short-term, elevated concentrations of HF are of more concern than are long-term average concentrations

Background (cont.)

• Texas Commission on Environmental Quality (TCEQ) short-term Environmental Screening Level (ESL) for Hydrogen Fluoride (HF), 15 micrograms per cubic meter (μg/m3), was selected as an appropriate yardstick for assessing HF concentrations

• The TCEQ ESL was one of the standards that was suggested by Kowalski of ATSDR when we asked what he thought would be appropriate for this work

Background (continued)• The TCEQ ESL was based on a study involving

exposures of 25 healthy, male volunteers to three levels of HF for an hour period. The lowest level was divided by a factor of 30 to adjust for the small sample size and the selected population, which was healthy males aged between 20 and 50. The screening level is used as a planning tool to decide if further studies or different options are required for a new facility. If modeled levels are below the screening level no further studies or options need to be used.

Approach

• Estimate short-term HF concentrations with an EPA approved air quality model

• Use on-site meteorological data and model parameters consistent with EPA approved procedures

• Use median measured emission rates for HF

• Use three years, 2010, 2011, and 2012, of measured meteorological data

Approach (cont.)

• Use source parameters consistent with the most recent permit applications

• Once the results are obtained, examine the variations from one receptor to the next to assure that the receptor spacing is appropriate

• Examine the variation in measured emission rates to see if the conclusions are sensitive to fluctuations in emissions

Task Apportionment

• Class 1 prepares meteorological inputs• Kurt Parker provides median emission

levels from HF stack measurements• Class 1 prepares basic source inputs• Mike Williams runs the model & analyzes

the results

Model-choice AERMOD

• AERMOD is an EPA approved model for estimating concentrations from industrial sources

• It includes parameterizations for treating the dispersion produced by building wakes

• It is particularly appropriate for near source estimations where travel times are short

Receptor locationsReceptor Locations

3897000

3897500

3898000

3898500

3899000

3899500

3900000

3900500

3901000

3901500

347500 348000 348500 349000 349500 350000 350500 351000

UTM -Easting

UTM

-Nor

thin

g

Series1

Boundary-Line Receptors

Line Receptors

38982003898400389860038988003899000389920038994003899600389980039000003900200

348600 348800 349000 349200 349400 349600 349800

Line Receptors

Source Characteristics

• 22 emission points• Stack heights and emission rates vary

greatly from one source to the next• Emissions also vary with time so that the

highest emissions from one of the major sources are 35% higher than the median emissions used in the modeling

Source Locations

Boundary Receptors & Sources

38982003898400389860038988003899000389920038994003899600389980039000003900200

348600 348800 349000 349200 349400 349600 349800

UTM Easting

UTM

Nor

thin

g

Series1

Model Options• Appropriate for desert, semi-rural conditions• Used one “beta” option designed to improve

estimates in low wind conditions• “Beta” options must be approved for

regulatory applications.  While these meteorological data sets have not been reviewed by the regulatory agency, it followed the same methodology previously approved by the department

Results

• Highest concentration is 7.5 μg/m3 on 11/25/2012 @4 am. The screening level is 15 μg/m3.

• Next Highest is 7.3 at a nearby receptor• Highest concentrations in 2011 and 2010

were 5.7 and 5.3 μg/m3• Nearby concentrations were very similar

Source Locations & Highest HitsBoundary Receptors & Sources

38982003898400389860038988003899000389920038994003899600389980039000003900200

348600 348800 349000 349200 349400 349600 349800

UTM Easting

UTM

Nor

thin

g

Series1

2012

2011

2010

Boundary receptors, sources, & highest concentrations during 19 events

Boundary Receptors, Sources, & Hit Receptors

3898000

3898500

3899000

3899500

3900000

3900500

348500 349000 349500 350000

UTMX (meters)

UTM

Y (m

eter

s)

Boundary Receptors

SourcesHit Receptors

ILLUSTRATION OF “SPIKES”with constant emissions

HF Concentrations on 11/25/2012

0

1

2

3

4

5

6

7

8

0 5 10 15 20 25 30

Hour

Conc

entra

tions

(ug/

m3)

HF levels

Modeled for a single receptor

Environmental Screening Level=15μg/m3 at the altitude of Intel

Odor threshold is 30 to 110 μg/m3

Conclusions• EPA approved model estimates HF

concentrations lower than the screening level• Receptor locations were sufficiently close to one

another that the results are not sensitive to the choice of receptor locations

• Measured emissions showed more variation with time than expected, but not enough to change the conclusions

• However, the modeled concentrations did not provide a large margin for error so that further examination of the role of model options might be advisable

Possible Next Steps

• Rerun model without “beta” option• Use old tracer measurements to check

validity of plume downwash model• Examine other pollutants released by the

scrubbers and scale to obtain model estimates for them

Why is downwash model important

• The manner in which buildings cause dilution is very important in near source concentrations

• Risk Assessment reports maximum HF hourly estimated concentrations of 12ug/m3 for Prime downwash (used in our modeling) versus 33ug/m3 for Schulman-Scire downwash (tables A-4 & A-5)

• Risk Assessment describes comparison between modeled and measured concentrations and prime model underestimated measurements by a factor of 2.2 while Shulman-Scire underestimated by 1.12 (for highest tracer measurements, table 4-3)

Differences between Risk Assessment and Current Work

• RA used occupational limits divided by a factor of 100 for acceptable level of 25ug/m3 versus 15ug/m3 (at altitude)

• RA had different source configueration• RA used higher emissions, RA had a rate equivalent to

12,603 pounds per year (table 3-4) while our rate is 5287 pounds per year

• RA used CalPuff model, I used AERMOD• I used 3 years of recent met. data and they used older

data• I got 7.5ug/m3 and they got 12ug/m3 for the prime

downwash

Possible Next Steps

• Examine other contaminants from scrubbers

• Rerun without beta model• Compare new AERMOD with old tracer

measurements• Conduct & compare HF measurements

with AERMOD estimates

Estimations for other contaminants

• Examine risk assessment & ATSDR reports to find candidates

• Choose appropriate screening levels• Ratio emissions to HF & estimate

concentrations• Downwash concerns remain

Rerun without Beta Options

• Requires rerunning met. model with new inputs

• Probably not much change• Downwash modules still a concern

Compare AERMOD results to old tracer measurements

• Make revised model inputs – emissions & meteorological inputs

• Represents only 2 months meteorology• Source configueration is much different

Measure HF concentrations in the future & compare to future

estimates• HF emissions must be estimated• Can the FT-IR sampling be done with

adequate minimum detection levels • Where could the resources to support

such a study be obtained?