Although the Agency has concluded that it is reasonable to set the same mercury standard for all cement kilns, we acknowledge the unique challenges that the highest emitting sources may face in meeting the reductions within the regulatory compliance timeline. In particular, as discussed at length above, the two highest emitting kilns – the kilns located in Durkee and Tehachapi -- have unusually high levels of mercury in their proprietary limestone quarries, which, as typifies this sector, are located proximate to kiln operations. The mercury content of source materi al is the key factor in the high levels of emissions experienced at these kilns and a complicating consideration in their ability to achieve compliance in a timely manner. We also recognize that this challenge presents a unique opportunity to achieve substantial reductions in this naturally occurring, persistent, and widespread contaminant in an amount and on a schedule that exceeds what will be required in the final rule. The Agency believes that the two sources in question may be able in the near term to install aggressive controls, including activated carbon injection, that would result in dramatic near term reductions in mercury emissions (a s much as 90 percent or two tons of mercury emissions in the first two years of operation). If they were to do so, these sources would emit substantially less mercury in the next few years than the alternative of allowing these facilities to continue to emit at current levels for three additional years, as would otherwise be the case. This would be a very substantial reduction in emissions of this pollutant. Annual emissions of mercury from all sources (not just cement kilns) are estimated to be 50 tpy 1 , and emission s form from the ent ire rie source categ or oe y are currently approximately 7.5 tons per year, so that a tw o ton reduction is a substantial reduction of mercury emissions.

1 2005 National Air Toxics Assessment April 14, 2010. Comment [ A 1]: I don’t have a URL for this Comment [ A 2]: Is this available publicly? I can’ Comment [ A 3]: Can you provide a citation?We understand that one of the two high emitting kilns has already installed activated carbon injection, but that its performance co uld be further optimized. See 74 FR 21148. The other kiln would have to install activated carbon injection and both kilns would need to install dust shuttling. The net benefit to the environment and public health would extend a number of years beyond the MACT compliance deadline. If the Durkee and Tehachapi kilns were willing to make a near term reduction (e.g., 90 percent) in their mercury emissions significantly before the compliance date in the rule, the Agency would consider providing these kilns a compliance schedule that extends beyond the three to four years specified in this rule. The purpose of such an approach would be to provide a substantia l net benefit to the environment; therefore ultimate compliance with the MACT standard would need to be by a date that ensures the long term emissions from these sources would be significantly lower than their emissions from meeting the standard on the schedule in the rule. Given the nature of mercury and the additional reductions that could be obtained, the Agency is interested in exploring this

concept. Finally, EPA notes that the same early reduction opportunities for mercury do not appear to exist for the rest of the Portland cement industry. It typically takes on the order of three years to install activated carbon inj ection technology. One of the high mercury plants has recently completed installation of ACI and has just commenced full scale operation of the kiln with ACI installed. The other kiln faces less installation barriers than other kilns. This is because the company has tested carbon injection and dust shuttling on one of its other kilns, and is al ready using dust shuttling to reduce emissions at another kiln, and is therefore better positioned to rapidly install controls after one year.To our knowledge, these circumstances are not applicable to the rest of the Portland cement source category, and could not even be duplicated at all the other facilities owned by these companies due to limitations in infrastructure available to design and build these

systems.