1

September 1, 2010

MEMORANDUM

TO: Phil Mulrine

FROM: Sandy Burns

RTI International

SUBJECT: Maximum Achievable Control Technology (MACT) Allowable Emission 

Estimates

Section 112(f)(2) of the Clean Air Act (CAA) directs EPA to assess the risk remaining 

(residual risk) after the application of maximum achievable control technology (MACT) 

standards under section 112(d). EPA is to promulgate more stringent standards for a category or 

subcategory of sources subject to MACT standards under section 112(d) if promulgation of such 

standards is necessary to protect public health with an ample margin of safety or to prevent 

(taking into consideration various factors) adverse environmental effects.

For the most part, the emissions values from the EPA National Emissions Inventory 

(NEI) represent actual emission levels for steel pickling and HCl acid regeneration operations. 

The use of actual emissions versus the use of “MACT allowable” emissions for residual risk 

assessments was discussed both in the final Coke Oven Batteries residual risk rule (70 FR 

19998-19999, April 15, 2005) and in the proposed and final Hazardous Organic National 

emission standard for hazardous air pollutants (HON) residual risk rules (71 FR 34428, June 14, 

2006, and 71 FR 76609, December 21, 2006, respectively). In those previous actions, EPA

noted that assessing the MACT allowable levels of emissions (i.e., the highest emission levels 

that could be emitted while maintaining the same activity level and still complying with the 

NESHAP requirements) is inherently reasonable since they reflect the maximum level sources 

could emit and still comply with national emission standards. It is reasonable to consider actual 

emissions, where such data are available, in both steps of the risk analysis, in accordance with 

the Benzene NESHAP. (54 FR 38044, September 14, 1989). Sources typically seek to perform 

better than required by emission standards to allow for variability in manufacturing processes 

and control device performance. Considering only “MACT allowable” emissions data in

developing risk estimates would unrealistically inflate estimated risk levels.

The most prudent approach to a risk assessment of the steel pickling industry is to 

consider both the actual emissions and the “MACT allowable” emissions. Hydrochloric acid 

(HCl) steel pickling lines are subject to a numeric emission limit of 18 parts per million by 
2

volume (ppmv) for HCl; HCl regeneration facilities are subject to numeric emission limits of 25 

ppmv for HCl and 6 ppmv for chlorine (Cl).

Because NEI emissions data are in tons per year (tpy), they cannot be directly compared 

to allowable emissions. The NEI data set does not contain enough detailed process information 

to calculate emissions in ppmv (e.g., flow rate, velocity, operating hours). Therefore we searched 

the permits of steel pickling facilities and HCl regeneration facilities from states that have their 

permits available online. We were unable to find an HCl regeneration facility with the 

appropriate data to calculate emissions in ppmv. Out of five steel pickling facilities whose 

permits we were able to obtain, only one, Charter Steel in Saukville, Wisconsin, had test data and 

enough additional process information to calculate emissions in ppmv. We calculated actual 

emissions for this facility at two pickling lines over three years (2007, 2008, and 2009). The 

emission concentration of HCl is presented in Table 1, and ranged from 4.63 ppmv to 17.36 

ppmv. This level of variability is typical of the industry, and coincides with the variability seen 

in the NEI data for this source category. 

Based on this limited data, and the fact that the allowable emissions for steel picking 

facilities is 18 ppmv, we conclude that actual and allowable emissions are equivalent for this 

source category.

Table 1. Calculated HCl concentration from Charter Steel Pickle Line Acid Scrubber Stacks

Device

1

Year HCl concentration 

(ppmv)

P2 2007 4.63

P3 2007 8.40

P2 2008 5.24

P3 2008 17.34

P2 2009 5.36

P3 2009 17.36

References

1. State of Wisconsin Department of Natural Resources, Bureau of Air Management. Charter Steel Emission 

Summaries, 2007-2009. Available at: http://dnr.wi.gov/cias/am/amexternal/AM_PermitTrackingSearch.aspx