Progress Update on Additional Scrubber Contaminants
The HF study was based on three elements: (1) a provisional screening level for short-term HF
concentrations, (2) measured emissions of HF from the scrubbers, and (3) AERMOD modeling for shortterm HF concentrations beyond the Intel fence line. The results from the HF modeling can be extended
to other contaminants once the emissions for the contaminants and the relevant provisional screening
levels are known. Construction of the emission levels requires the help of ERM, so we. Sara, Paul Wade,
and I decided to try and determine what the most important contaminants from the scrubbers would
be. Sara said that in addition to HF, the other contaminants that were measured from the scrubbers
were Chlorine and Hydrogen Chloride. We decided we would try to find provisional levels of these two
contaminants and see how they related to HF.
I have examined a number of sources and used the comments from Mr. Kowalski of ATSDR to address
this question. The best source of potential screening levels that I have found appears to be the Texas
Commission on Environmental Quality’s Environmental Screening Levels. These levels are expressed in
two ways: (1) the mass of the contaminant in a cubic meter in units of micrograms per cubic meter and
(2) the fraction of molecules in a volume that are contaminant molecules divided by the total of all the
molecules of all kinds in the same volume. The latter is expressed in units of parts per billion. For
example the HF ESLs are 18 micrograms per cubic meter and 22 parts per billion. We have similar forms
for the emissions, they can be expressed in grams per second or in parts per million in the gas stream.
When Sara talked about the measurements she was using parts per million rather than grams per
second so we should use ratios relating to parts per billion rather than micrograms per cubic meter to
gauge the relative importance of the contaminants. The ESLs are:
TCEQ ESLs
Contaminant
micrograms per cubic meter
parts per billion
HF
18
22
HCL
190
130
CL2
15
5
This information suggests that for emissions expressed as parts per million in the scrubber exhaust, CL2
is more important than HCL and would be the first candidate for a detailed examination of the emission
rate.
While we don’t have detailed measurements of emissions, we do have estimated emissions in the Risk
Assessment. They list the emissions as: CL2 5,071 lbs/year, HCL 1,323 lbs/year, and HF as 12,603
lbs/year. On this basis it looks like Chlorine is more likely to be a problem than HCL and we should
consider getting detailed emissions for it first.
There is a question that arise from this analysis. What about contaminants that were below detection
levels in the testing done for HF, are any of these significant? I looked at the Risk Assessment to see
what other contaminants were released from the scrubbers and the associated ESLs.
Contaminant
NH3
NH3CL
NH3F
Arsine gas
CCL4
Ethyl Nonofluorobutyl Ether
Ethyl Nonofluoroisobutyl Ether
Emissions lbs/year
10,214
5,436
7,327 as HF
41
3,000
4,860
7,200
ESL micrograms per cubic meter
170
100
18 as HF
2
130
200
200
Ethylene Glycol
389
260
NO
15,281
4500
Phosphiene
19
4.2
SF6
600
600
Octofluorocyclopentene
2,500
10000
This table suggests that only NH3F might be of comparable importance to HF. In the case of NH3F, we
need to ask the question do the emission tests report NH3F as HF or are the NH3F emissions something
we need to add to the HF emissions. There are also questions about whether the emissions in the table
are representative of today’s emissions.