MEMORANDUM

TO:  Portland Cement Docket

SUBJECT:  THC Modeling and Good Combustion Practices

FROM:  Keith Barnett, USEPA/OAQPS/SPPD/MMG

DATE:  December 8, 2006

	The Portland Cement Association had expressed concerns about a
potential new source THC standard based on the performance of a wet
scrubber.  The had also discussed with EPA how to define “good
combustion practices”.  

The PCA provided a description of what they consider “good combustion
practices” in the attached email attachments.

The PCA also proposed performing THC modeling to demonstrate that THC
emissions are below the level that would result in health or adverse
environmental impacts, similar to the analysis done for hydrogen
chloride.  Ths information is also attached to the email.

We adopted some of the language for good combustion practices into the
rule.

We also reviewed the PCS THC modeling.  Based on the information
provided it is not possible to determine that THC emission pose no risk
to human health or the environment.  The legal authority that we use for
HCl only applies to non-carcinogens, and the THC clearly includes
carcinogens.  The modeling would also not be suitable to develop
potential site-specific risk exemptions.  In order to perform that
analysis all HAP have to be modeled, not just the organic HAP present in
the THC emissions.

  

