Texas Air Control Board Austin Texas Interoffice From: Louis R. Roberts, Ph.D., P.E., Director of Permits and Source Evaluation Division To: Permits Engineering Staff Date: December 5, 1980 Subject: Best Available Control Technology (BACT) determinations for modified old facilities Construction permit 1651 was recently amended to delete the requirement that the asphalt batch plant meet twenty percent opacity and the operating permit was issued accordingly. I wish to emphasize that this was a case-by-case BACT determination, and is not intended to set precedent for if modified grandfathered facilities. The facility in question is an old small unit built prior to 1970. The cost to bring the unit into compliance with the twenty percent opacity requirement was judged to be unreasonable, and this particular unit was permitted to continue operating within the thirty percent opacity limit. The Legal Division confirms that "modified" facilities, even if they are only modified by changing location, are subject to BACT requirements. Each case is to be considered on its own merits. Economics continues to be a factor in BACT determinations.