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 material 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 (as 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 tpy1, and emissions form from the entirerie source categoroey are 

currently approximately 7.5 tons per year, so that a two ton reduction is a substantial 

reduction of mercury emissions. 

 

1 2005 National Air Toxics Assessment April 14, 2010. 

Comment [A1]: I don’t have a URL for this 

Comment [A2]: Is this available publicly? I can’

Comment [A3]: 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 could 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 substantial 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 injection 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 already 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.