From:    Keith Barnett/RTP/USEPA/US                                                       

To:      Cortney_Higgins@omb.eop.gov                                                      

Cc:         Charlotte Bertrand/DC/USEPA/US@EPA, Steven Silverman/DC/USEPA/US@EPA             

Date:    07/29/2010 10:38 AM                                                              

Subject: Information on Pollutant by Pollutant approach                                   

I have attached excerpts from federal register notices dealing with the legal

aspects of the pollutant by pollutant approach.

(See attached file: Polutant‐by‐pollutant.docx)

Note that the statement that the different controls requited for the various

pollutants can operate independently is also applicable here.

For example:

   Five kilns have PM controls followed by wet scrubbers

   One of those five has a PM control followed by the wet scrubber

   followed by a regenerative thermal oxidizer.

   One kiln  has a PM control followed by carbon injection followed by a

   second fabric filter.

There are no technical reasons that the controls required cannot work in

sequence.

However, as I  have previously noted, some of the controls can remove multiple

pollutants.  ACI can remove both mercury and THC. If you also add some types of

alkaline reagent (such as lime), a single control system (sorbet injection

followed by a second fabric filter) could conceivably remove mercury, THC, HCl,

and PM.  So you get all four pollutants with one control system.

For a high sulfur applications a wet scrubber could remove HCl, SO2, and mercury.  

You can also use additives to improve scrubber performance by oxidizing the

mercury.

Keith W. Barnett

USEPA/OAQPS/SPPD/MMG

Mail Code D243‐02

Research Triangle Park, NC  27711

919‐541‐5605

barnett.keith@epa.gov
Form 51382 Federal Register / Vol. 74, No. 192 / Tuesday, October 6, 2009 / Rules and 

RegulationsThis is a section 129 regulation, byt the legal isue re relevant to a section112 rule.2. 

2. Pollutant-by-Pollutant Approach 

Comment: Numerous commenters objected to our continued use of the EPA’s longstanding 

pollutant-bypollutant approach to choosing the best performing HMIWI. The commenters 

argued that this approach essentially created a hypothetical ‘‘super unit’’ and resulted in the 

selection of a set of new and existing MACT floors (and standards) that no one existing source 

has completely achieved and that cannot be simultaneously achieved by any of the best 

performing sources. The commenters stated that the ‘‘best performing’’ sources must be real 

sources, not theoretical or hypothetical, based on the statute and legislative history. S. Rep. No. 

228, 101st Cong., 1st Sess. 169 (1989). According to the commenters, the proposed standards 

do not reflect the performance of actual sources, and as such, these proposed standards are not 

legal under Section 129. 

One commenter argued that Section 129(a)(2) (and the similar Section 112(d)(3)) does 

not speak in terms of the best performing source for each listed pollutant but the best existing 

source for all pollutants and what these sources can achieve on an overall basis. The commenter 

claimed that Congress abandoned Section 112’s previous focus on individual pollutant standards 

in the 1990 CAA Amendments and also adopted the technology-based multipollutant approach 

to regulating toxics in use under the Clean Water Act (CWA). See S. Rep. No. 228, 101st 

Cong., 1st Sess. 133–34 (1989). The commenter concluded that if one source can achieve a 

tight degree of control for one pollutant but not for another, there may be no justification for 

including it in the set of sources from which the floor is calculated. See, e.g., Tanners’ Council 

of America v. Train, 540 F.2d 1188, 1193 (4th Cir. 1976) (CWA effluent limitations guidelines 

were deemed not achievable where plants in EPA’s data base were ‘‘capable of meeting the 

limitations for some, but not all, of the pollutant parameters’’). 

Two commenters stated that under CAA Sections 129(a)(2) and 112(d)(2) consideration 

of a higher level of control than the average aggregate levels achieved by the best sources (i.e., 

using the pollutant-by-pollutant approach instead of basing floors on levels of the full set of 

pollutants achieved by particular units) must be done only as a ‘‘beyond-the-floor’’ assessment, 

required to weigh economics and other factors, and not be ‘‘hidden’’ in the floor evaluation, in 

which costs may not be considered. 

Multiple commenters also questioned the technical feasibility of EPA’s pollutant-bypollutant approach. According to the commenters, establishing MACT standards based on the 

best achievable emissions limits for each type of pollution control equipment assumes that the 

equipment can be combined in the same system and that the emissions limits of each system are 

additive. The commenters stated that, in practice, this outcome is likely not achievable due to 

the challenge of finding pollution control equipment (e.g., fabric filters for PM removal and wet 

scrubbers for HCl removal) that can work in concert with each other. The commenters said that 

EPA should consider how the different emissions controls may interfere with each other if 

employed simultaneously. As an example, one commenter noted that employing a wet scrubber 

to control HCl would saturate the gas stream, which would bind the bags in the fabric filter used 

to control PM, thereby compromising the filter’s effectiveness. Some of the commenters also 
noted that the interrelationships between pollutants must be considered in order to ensure that the 

emissions control is operating effectively for control of all of the related pollutants, and not just a 

single pollutant. For example, commenters noted that improving combustion to control CO may 

affect NOX. 

Multiple commenters suggested EPA should revisit the MACT floors for HMIWI and 

choose the best performing sources on an overall basis, so that at least one source can meet all of 

the new source standards and a certain portion of the existing sources can meet the existing 

source standards. One commenter suggested that EPA combine the individual pollutants into a 

single analysis to determine which control provides the best overall control or otherwise 

determine that the MACT floor resulting from the analysis is actually achieved by those sources 

identified as the ‘‘best controlled.’’ According to various commenters, one possible way for 

doing this would be to establish rankings for how a HMIWI performs for each of the regulated 

pollutants and then sum the individual pollutant rankings to determine the overall ranking for the 

HMIWI. 

Response: We disagree with the commenters who object to setting MACT floors on a pollutantby-pollutant basis. We continue to interpret Section 129 as supporting the pollutant-bypollutant 

approach. Section 129(a)(4) says that the standards promulgated under Section 129 shall specify 

numerical emissions limitations for each pollutant enumerated in that provision. Section 

129(a)(2) requires EPA to establish standards requiring ‘‘maximum degree of reduction of 

emissions.’’ ‘‘Maximum degree of reduction of emissions,’’ in turn is defined in Section 

129(a)(2) as including a minimum level of control (the so-called MACT floor). EPA, therefore, 

believes—and has long believed—that the combination of Section 129(a)(4), requiring numerical 

standards for each enumerated pollutant, and Section 129(a)(2), requiring that each such standard 

be at least as stringent as the MACT floor, supports, if not requires, that floors be derived for 

each pollutant based on the emissions levels achieved for each pollutant. 

We also disagree with the commenters who complain that there may not be any operating 

unit that currently employs the complete suite of MACT technologies and meets the revised 

limits. The suite of MACT floor controls identified by the final rule approach (specifically, the 

combination of dry and wet control systems) is already used by four existing HMIWI that meet 

most of the MACT floor standards. For example, one HMIWI, equipped with a high efficiency 

particulate air (HEPA) filtering system, carbon bed adsorber, and rotary atomizing wet scrubber, 

is estimated to meet all nine revised emissions limits in the final rule; another HMIWI, equipped 

with a lime injection system, powdered activated carbon injection system, baghouse, and vertical 

upflow two-stage multimicroventuri scrubber system, is estimated to meet eight of the nine 

revised limits. Also, an estimated 42 of the 57 HMIWI are estimated to meet both the CO and 

NOX revised limits simultaneously with existing combustion controls. (See 2009 memorandum 

entitled ‘‘Revised Compliance Costs and Economic Inputs for Existing HMIWI,’’ which is 

included in the docket for today’s rulemaking.) The MACT control techniques for the various 

pollutants are fully integratable and compatible. There do not appear to be any conflicts where 

meeting the standard for one pollutant may jeopardize the achievability of meeting another 

pollutant’s limit. This conclusion is supported in part by a review of available data and 

information. As discussed above, there are currently four units that are achieving most, if not all, 

of the floor standards (based on actual data for each pollutant) using the complete suite of MACT 
floor controls. Thus, we conclude that our approach results in compatible MACT controls. 

Further, an evaluation of the emissions data from units that have measured data for all pollutants 

supports our conclusion. Our analysis shows that 12 percent (7 of 57 units) simultaneously meet 

all of the MACT floor emissions levels. (For further information, see 2009 memorandum 

entitled ‘‘Revised Compliance Costs and Economic Inputs for Existing HMIWI,’’ which is 

included in the docket for today’s rulemaking.) 

We also disagree with commenters claiming that it is inappropriate to consider a suite of 

floor control techniques that may not be currently in use by the source category. There is no 

reason not to consider emissions data and controls in use at sources that may be the best 

performers from some pollutants but not for other pollutants. The MACT floor controls 

applicable for one pollutant do not preclude the use of MACT floor controls for another 

pollutant. Therefore, it is appropriate to consider controls at sources employing MACT controls 

for some pollutants, but not all. For example, floor controls for existing large HMIWI include 

wet scrubbers for HCl control, dry scrubbers or combination dry/wet systems for PM and metals 

control, activated carbon injection for CDD/CDF control, and wet scrubbers or dry scrubbers for 

SO2 control. As noted previously, wet and dry systems are demonstrated to be compatible, and 

it would be inappropriate to exclude from the MACT floor pool those units equipped with wet or 

dry systems because some of the control systems do better with some pollutants (e.g., wet 

scrubbers with HCl) than others (see previous memorandum). 

EPA disagrees strongly with commenters arguing that Congress has directly addressed 

the issue of whether the MACT floor can be established on a pollutant-by-pollutant basis. With 

respect to the MACT floor mandate of Section 112, there appears, rather, to be a substantial 

ambiguity in the statutory language about whether the MACT floor is to be based on the 

performance of an entire source or on the performance achieved in controlling particular 

hazardous air pollutants. The language regarding best performing ‘‘sources’’ (or, for new 

sources, ‘‘source’’) could apply either to the sources’ (or source’s) performance as a whole, or 

performance as to a particular pollutant or pollutants. The same is true of the definition of 

‘‘emission limitation’’ in Section 302(k), which refers to ‘‘air pollutants,’’ but does not address 

whether the limitation must apply to every pollutant emitted by a source, or just some of them. 

(The same is true of the reference to ‘‘air pollutants’’ (in the plural) in Section 112(d)(2).) In this 

regard, we note that commenters in other MACT rulemakings have assumed that Section 129, 

which governs today’s rule and which uses language essentially identical to Section 112 in 

mandating MACT, requires a pollutant-by-pollutant approach to establishing floors, because 

EPA is commanded to establish standards for enumerated pollutants under Section 129(a)(4). 

We further note that the DC Circuit, when reviewing the floor determinations we made in 

1997 for HMIWI under Section 129 in Sierra Club v. EPA, noted that they were set pollutantby-pollutant and found no error in this approach (see 167 F.3d at 660) (although this aspect of 

the rule was not challenged specifically). Indeed, the commenters who object so vehemently to 

the pollutant-bypollutant approach in this rule raised no such objection when the opportunity to 

litigate the same approach in establishing the 1997 HMIWI standards was first presented. EPA 

also believes that the commenters’ reference to basing MACT floors on the performance of a 

hypothetical or theoretical unit, so that the limits are not based on those achieved in practice, is 

not only wrong factually (see above), but just re-begs the question of what the language in 
Sections 112(d)(3) and 129(a)(2) is referring to. We did not base the controls or emissions levels 

on theoretical sources, but on the performance of actual units in the HMIWI source category. All 

of the MACT floors are achieved in practice (since they are based on actual performance data). 

Moreover, the DC Circuit has emphasized that EPA may use any reasonable means to determine 

what levels of performance are achieved in practice. Sierra Club v. EPA, 167 F.3d at 663, 665. 

The commenters’ reliance on cases that they claim preclude EPA’s use of a pollutant-bypollutant approach does not compel a unit-based approach, and the issue is not critical to EPA’s 

position in any event, since the record shows that some units are meeting all of the floor limits 

and many are meeting several of them. At the very least, the CMA v. EPA decision under the 

CWA supports the proposition that a technology-based standard can be considered achievable 

even if all limits are not yet met by a single unit. Since the floor standards are demonstrably 

being achieved in practice by some sources, this issue is largely academic. In short, EPA is not 

persuaded that the floors must be established on the basis of a unit’s performance for all 

pollutants overall. 

We continue to believe, as we explained in the 1997 final rule, that such a reading would 

lead to results that are at odds with evident congressional intent (and with the Court’s rulings in 

NLA II, CKRC and Brick MACT). To argue that Congress compelled this type of result is at 

odds with both the language of Sections 112 and 129 and common sense. Indeed, it would 

necessarily suggest that EPA could continue to adopt floors that reflect ‘‘no emissions 

reduction,’’ even after the DC Circuit so emphatically forbade that approach in the Brick MACT 

ruling (Sierra Club v. EPA, 479 F.3d 875 (DC Cir. 2007). As we stated in the preamble to the 

1997 regulation (62 FR 48363), we recognize that the pollutant-by-pollutant approach for 

determining the MACT floor can, as it does in this case, cause the overall cost of the regulation 

to increase compared to what would result under a unit-based methodology. For example, the 

pollutant-by-pollutant approach for the HMIWI regulation results in a stringent MACT floor for 

HCl based on control using a wet scrubber, and stringent MACT floors for PM and metals based 

on control using a dry scrubber. We interpret Section 129 of the CAA to require that the MACT 

floor be determined in this manner, and we believe that Congress did in fact intend that sources 

subject to regulations developed under Section 129 meet emissions limits that are achieved by 

the best controlled unit for each pollutant, as long as the control systems are compatible with 

each other. To our knowledge, there is no technical reason why these two air pollution control 

systems cannot be combined. (62 FR 48363–4) Combined dry/wet scrubber systems are 

currently in operation on several HMIWI. In response to commenters’ concerns regarding the 

technical feasibility of combined dry/wet systems, available data on the performance of 

combined dry/wet scrubber systems indicate that the MACT floor emissions levels are 

achievable and technically feasible. The performance of dry scrubbers with activated carbon 

injection and the performance of wet scrubbers are well documented. The available data for 

combination dry/wet systems provide no indication of operational or emissions problems that 

occur as a result of combining dry and wet control systems. Regarding the inverse relationship 

between CO and NOX with regard to combustion control, it is incumbent upon the HMIWI 

facility to determine whether combustion conditions can be adjusted to meet both standards and, 

if not, install add-on NOX controls as necessary, e.g., SNCR systems. 

The MACT floor reflects the least stringent emissions standards that EPA may adopt in 

accordance with Section 129(a)(2) regardless of costs. Other statutory provisions are relevant, 
although they also do not decisively address this issue. Section 129(a)(4) requires MACT 

standards for, at a minimum, PM, opacity, SO2, HCl, NOX, CO, Pb, Cd, Hg, and CDD/CDF 

emitted by HMIWI. This provision certainly appears to direct maximum reduction of each 

specified pollutant. Moreover, although the provisions do not state whether there is to be a 

separate floor for each pollutant, the fact that Congress singled out these pollutants suggests that 

the floor level of control need not be limited by the performance of devices that only control 

some of these pollutants well. (62 FR 48364) 

Regarding the commenter’s suggestion that EPA choose the best performing sources on 

an overall basis, so that at least one source can meet all of the new source standards and a certain 

portion of the existing sources can meet the existing source standards, we reviewed this approach 

and found that the suggested approach does not consistently result in emissions limits that are at 

least as stringent as would have resulted in 1997 if we had actual emissions data and used the 

correct methodology. We estimate that four emissions limits for large and small non-rural 

HMIWI and five emissions limits for medium and small rural HMIWI calculated using the 

suggested overall unit-based approach would be higher than the 1997 emissions limits. Further, 

because not all pollutants are required to be tested (e.g., NOX and SO2), a substantial fraction of 

available emissions data would have to be discarded in order to rank only those HMIWI with a 

complete set of data for all nine pollutants (PM, SO2, HCl, NOX, CO, Pb, Cd, Hg, and 

CDD/CDF). Specifically, we would have to discard emissions data for 30 percent of large, 40 

percent of medium, 100 percent of small non-rural, and 50 percent of small rural HMIWI in 

order to calculate MACT floors using the suggested approach. (See 2009 memorandum entitled 

‘‘Revised MACT Floors, Data Variability Analysis, and Emission Limits for Existing and New 

HMIWI,’’ which is included in the docket for today’s rulemaking.) 

A unit-based approach would tend to result in least common denominator floors where, 

as here, multiple pollutants are emitted, whereby floors would no longer be reflecting 

performance by the best performing sources for those pollutants. For example, if the best 

performing 12 percent of units for HAP metals did not control acid gases as well as a different 12 

percent of units, the floors for acid gases and metals would not reflect best performance. Having 

separate floors for metals and acid gases in this example certainly promotes the stated purpose of 

the floor to provide a minimum level of control reflecting what best performing units have 

demonstrated the ability to do. 

Similarly, a unit-based approach that employs ranking of a weighted average of 

pollutants would require EPA to assume priority for certain pollutants (one unit may have lower 

NOX emissions but higher CDD/CDF, for example). This approach would similarly tend to 

require EPA to disregard the factual levels reflecting the best performers for individual 

performers, but based on value judgments regarding the risks presented by various pollutants. 

Such considerations are antithetical to strictly performance-based analyses such as MACT floor 

determinations. Indeed, reviewing EPA’s primary copper smelters MACT standard, the DC 

Circuit rejected the argument that risk-based considerations have any place in the MACT context 

(see Sierra Club v. EPA, 

 
From the HCW rule October 12, 2005 

c. Comment: The commenter disputes EPA’s conclusions that failure of sources to meet all of the 

standards based on a straight emissions methodology at once shows that the methodology is 

flawed. The standards are not mutually dependent, so the fact that they are not achieved 

simultaneously is irrelevant. There is no reason a best performer for one HAP should be a best 

performer for other HAP. 

Response: EPA agrees with this comment. On reflection, EPA believes that because all 

our standards are not technically interdependent (i.e., implementation of one emission control 

technology does not prevent the source from implementing another control technology), the fact 

that sources are not achieving all the standards simultaneously does not indicate a flaw in a 

straight emissions approach. See Chemical Manufacturers Ass’n, 870 F. 2d at 239 (best 

performing sources can be determined on a pollutant-by-pollutant basis so that different plants 

can be best performers for different pollutants). 

d. Comment: Several commenters took the opposite position that EPA must assure that all 

existing source standards must be achievable by at least 6 percent of the sources, and that all new 

source standards must be achievable by at least one existing source. 

Response: As discussed above, we are not obligated to establish a suite of floors that are 

simultaneously achievable by at least six percent of the sources because the standards are not 

technically interdependent. Nonetheless, the SRE/Feed methodology does result in existing floor 

levels (when combined with the other floor levels for sources in the source category) that are 

simultaneously achievable by at least six percent of the sources (or, for source categories that 

have fewer than 30 sources, by at least two or three sources).90 However, for the new source 

standards, three of the source categories do not include any sources that are simultaneously 

achieving all the standards (incinerators, cement kilns, and lightweight aggregate kilns). Again, 

similar to existing sources, EPA is not obligated to establish a suite of new source floors that are 

simultaneously achievable by at least one existing source because these standards are not 

technically interdependent. We conclude that a new source can be designed (from a back-end 

control perspective) to achieve all the new source standards.