UNITED STATES ENVIRONMENTAL PROTECTION AGENCY Office of Air Quality Planning and Standards Research Triangle Park, NC 27711

July 10, 2002
Mr. Edward R. Herbert III Director of Environm ental Affairs National Ready Mixed Concrete Association 900 Spring Street Silver Spring, MD 20910
Dear Mr. Herbert: Your April 30, 2002, letter requests a review from the Environm ental Protection Agency (EPA) regarding the inclusion of control devices on pneum atically loaded cem ent silos in the “potential to em it” calculations f o r ready m i xed concrete plants. W e agree with your assessm ent that, for potential to em it calculations, the control devices on the silos generally should be considered as an inherent part of the process for loading ready m i xed cem ent silos.
Criteria for Determ ining W h ether Equipm ent is Air Pollution Control Equipm ent or Process Equipm ent For purposes of calculating a source’s potential to em it, it is necessary to consider the effect of air pollution control equipm ent. Current EPA regulations and policy allow air pollution control equipm ent to be taken into account if enforceable requirem e nts are in place requiring the use of such air pollution control equipm ent. There are, however, situations for which case-by-case assessm ents are needed regarding whether a given device or strategy should be considered as air pollution control equipm ent, or as an inherent part of the process. The EPA believes that the following list of questions should be considered in assessing whether certain devices or practices should be treated as pollution controls or as inherent to the process:
1. Is the prim ary purpose of the equipm ent to control air pollution?
2. W h ere the equipm ent is recovering product, how do the cost savings from the product recovery com p are to the cost of the equipm ent?
3. W ould the equipm ent be installed if no air quality regulations are in place? If the answers to these questions suggest that equipm ent should be considered as an inherent part of the process, then the effect of the equipm ent or practices can be taken2

into account in calculating potential em issions regardless of whether enforceable im itations are in ef f ect. Analysis of the criteria for control devices on pneum atically loaded cem ent silos The equipm ent used for pneum atic loading is com m only referred to as bag houses or dust collectors. Based on the inform ation supplied to date by you, the EPA believes that, overall, the above criteria are satisfied as follows:
Criteria 1. The prim ary purpose of the control devices on pneum atically loaded cem e nt silos is not to control air pollution but to provide a restricted air flow from the silo so that the silo will fill properly without excessive loss of product.
Criteria 2. The cem ent collected by the f ilters f a lls into the silo and is recovered f o r use as product. The cost savings from this pr oduct recovery varies depending on such factors as silo capacity, am ount of product in the silo, and the efficiency and cost of the control device.
Criteria 3. The inform ation you have provided suggests strongly that air quality regulations are not the driving factor for installation of the control equipm ent. The control devices would be installed regardless of air quality requirem e nts. Cautions The views expressed above regarding the use of the control devices for loading cem ent silos are specific for ready m i xed concrete facilities using pneum atic loading. W h ile we believe the views in this letter are applicable f o r the m a jority of ready m i xed concrete facilities with pneum atic loading, there m a y be circum stances that would need to be considered on a case-by-case basis. For exam ple, there m a y be situations where air pollution control regulations or a com p any’s desire to lim it its potential to em it for regulatory purposes result in the com p any’s installation or use of bag houses with a greater collection efficiency than would be the case if product recovery or other process considerations were the only factors at work. Should such circum stances arise, source owners and operators are encouraged to work with their perm itting authorities if they have questions. This letter is not intended to set a precedent for control equipm ent for other source types, which m u st be reviewed separately. This letter also does not assess the control efficiency or em issions from the baghouses. Also, this determ ination does not exem pt these sources f r om otherwise applicable perm itting or other regulatory requirem e nts. These requirem e nts are determ ined by the appropriate perm itting authority.3

If you have any further questions regarding this m a tter, please call m e at (919) 541-4718, or Mike Sewell at (919) 541- 0873.

Sincerely, original signed by Robert Kellam for
W illiam T. Harnett Director, Inform ation Transfer and Program Integration Division

cc: Regional Air Division Directors Mario Jorquera, OECA Greg Foote, OGC Karen Blanchard, IIG Steve Hitte, OPG Kirt Cox, OPG Mike Sewell, IIG