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 entation/tox/dsd/final/october09/hydrogen_fluori de.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 locations

Boundary-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

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 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 Hits

Boundary receptors, sources, & highest concentrations during 19 events

ILLUSTRATION OF “SPIKES” with constant emissions 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?