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August 24, 2005

LAUREN E. FREEMAN 

DIRECT DIAL: 202-778-2248

EMAIL: lfreeman@hunton.com

FILE NO: 31531.200001

VIA E-DOCKET

John M. Mooney, Chief

Criteria Pollutant Section (AR-18J)

U.S. Environmental Protection Agency

Region 5

77 West Jackson Boulevard

Chicago, Illinois 60604

Comments of the Utility Air Regulatory Group on EPA’s Proposed Disapproval of 

Revisions to the Ohio Implementation Plan for Particulate Matter 

(Docket R05-OAR-2005-OH-0002)

Dear Mr. Mooney:

The following comments are submitted on behalf of the Utility Air Regulatory Group 

(“UARG”) in response to EPA’s proposed disapproval of particulate mater rule revisions 

submitted by Ohio for inclusion in its State Implementation Plan (“SIP”). 70 Fed. Reg. 36901 

(June 27, 2005). UARG is a voluntary, nonprofit association of electric generating companies 

and organizations, and four national trade associations. UARG’s purpose is to participate on 

behalf of its members collectively in EPA rulemakings and other Clean Air Act (“CAA”) 

proceedings that affect the interests of electric generators, and in litigation arising from those 

proceedings. Although comments on the proposal were initially due by July 27, 2005, EPA 

reopened the comment period until Aug. 24, 2005. 70 Fed. Reg. 49526 (Aug. 24, 2005). 

UARG’s comments focus on EPA’s conclusion that Ohio must perform modeling 

because its revised rule would provide a “less stringent set of opacity limits” than the existing 

SIP-approved rule. 70 Fed. Reg. at 36903. As UARG stated in its recent comments in 

response to EPA’s “Request for Comments on Potentially Inadequate Monitoring in Clean Air 

Act Applicable Requirements and on Methods to Approve Such Monitoring” (70 Fed. Reg. 

7905; Feb. 16, 2005), UARG believes that by establishing unreasonable hurdles for states’ 

demonstrations to show that their proposed revisions are consistent with the requirements of 

CAA § 110, EPA is missing a significant opportunity to improve compliance monitoring for 
John M. Mooney, Chief

August 24, 2005

Page 2

opacity. See UARG ANPR Comments, OAR-2003-0180-0051 (June 17, 2005) at 39-40 

(relevant excerpts from those comments are provided in Attachment A). EPA’s proposed 

disapproval of Ohio’s request for a SIP revision designed to allow use of continuous opacity 

monitoring systems (“COMS”) to determine compliance is another illustration of that lost 

opportunity, and the reasoning upon which EPA bases its proposed disapproval is seriously 

flawed.

Ohio’s current SIP-approved opacity rule establishes a limit of 20 percent opacity over 

a six-minute average, but exempts one six-minute average per hour between 20 percent and 60 

percent opacity. Rule 3745-17-07.1 Like many other states’ SIP-approved rules, Ohio’s SIPapproved rule designates Method 9 of Appendix A to 40 C.F.R. Part 60 as the sole method for 

determining compliance. Rule 3745-17-03-(B)(1).

Although many SIP sources monitor and report opacity using data from COMS under 

40 C.F.R. Part 51, Appendix P, those data are not used to determine compliance with the 

standard directly unless the applicable state rule provides for that use. Appendix P allows 

states to decide how best to use the data. Ohio has implemented Appendix P in Rule 3745-17-

03(C), which simply requires that the excess emissions data be reported along with information 

regarding the magnitude of excess emissions, cause and corrective action taken.

In states where Method 9 is specified as the compliance method, but COMS also are 

required, COMS data generally are used by the source to monitor performance of the control 

device and by regulators to trigger further investigation and testing. This is the model set out 

in EPA’s New Source Performance Standards (“NSPS”). See UARG ANPR Comments, 

Attachment A, at 15-18. Ohio presumably uses COMS data for these purposes. Limitations on 

the use of COMS data are necessary in states like Ohio, because the state did not evaluate the 

achievability of the opacity standard using the control equipment upon which the standard was 

based, if enforced with COMS data (as opposed to Method 9). See, id., at 7-14, 18-24 

(explaining the standard setting process and why compliance methods in rules can only be 

changed through rulemaking).

 

1

 Although the rule also provides exemptions for startup, shutdown, malfunction, 

uncombined water and certain other conditions, those exemptions are not at issue in the SIP 

revision request.
John M. Mooney, Chief

August 24, 2005

Page 3

Ohio’s revised opacity rule provides certain sources the option of an alternative 

compliance procedure that relies on COMS as the method for determining compliance.2 Ohio 

was able to specify COMS as the compliance method for the alternative procedure because, 

unlike the current SIP-approved rule, the state established the procedure by examining COMS 

data to determine the achievability of the limit with COMS (as opposed to Method 9). 

Specifically, Ohio analyzed ten years of COMS data from the source category to which the 

alternative procedure applies and set the level of allowed excess emissions based on the 95th

percentile of that database (i.e., the point at which 95 percent of the source data would be in 

compliance based on COMS data). See Ohio Responsiveness Summary at 17.3 This data set 

represents the level of performance actually achieved by sources subject to the current SIPapproved rule. Use of the 95th percentile of that database is consistent with the statistical 

procedures EPA used to establish the opacity standards in the NSPS at 40 C.F.R. Part 60. See 

Ajax, “The Effect of Compliance Test Frequency on the Stringency of Technology Based 

Standards (Mar. 13, 1995) at 5-7 (Attachment B); see also UARG ANPR Comments, 

Attachment A, at 14.

Under Ohio’s alternative limit, sources are allowed additional excess emissions 

between 20 and 60 percent opacity for up to 1.10 percent of the operating time in a calendar 

quarter (referred to as nonexempt values), as long as the total number of hours of exempt and 

nonexempt excess emissions periods (not including startup, shutdown, and malfunction) does 

not exceed 10 percent of the operating time in a quarter. OAC 3745-17-03(B)(1)(b). Ten 

percent of operating time is equivalent to the sum of all of the one per hour six-minute periods 

allowed under the SIP-approved rule. As a result, the sole difference between the alternative 

compliance procedure and the existing rule is that the alternative procedure does not restrict the 

excess emissions that occur to one per hour. 

EPA argues that the alternative procedure is a relaxation because it allows excess 

opacity on occasions that excess emissions are currently prohibited “without any compensating 

prohibitions.” 70 Fed. at Reg. 36903. As an example, EPA says that a source that “routinely 

has 1 full hour of excess opacity and then 9 subsequent hours of no excess opacity” would 

comply with the alternative procedure “but would clearly violate the existing SIP rule.” Id. 

 

2

 Ohio’s alternative limit applies to coal-fired boilers with heat input greater than 250 

mmBtu/hr that are controlled with either a baghouse or an electrostatic precipitator. OAC 

3745-17-03.

3

 Although Ohio was asked to extend the option to a wider range of source categories, 

Ohio specifically limited its rule to those sources for which the appropriate statistical analysis 

had been done. Ohio Responsiveness Summary at 16.
John M. Mooney, Chief

August 24, 2005

Page 4

EPA then concludes that because Ohio’s alternative compliance procedure is not an adequate 

substitute for the SIP-approved rule, Ohio must perform modeling to show that that the revised 

rule “would not interfere with attainment or other applicable requirements.” 70 Fed. Reg. at 

36903. EPA bases that conclusion on CAA § 110(l), which prohibits EPA from approving “a 

revision of a [state implementation] plan if the revision would interfere with any applicable 

requirement concerning attainment . . . or any other applicable requirement of this Act.” EPA 

is wrong on both points. 

First, as described above, under a Method 9-enforced limit, COMS data are only used 

to determine, based on the source’s overall level of excess emissions (e.g., the total percent of 

time of excess emissions), whether the source and its emission controls are being operated 

properly. If the overall level of excess emissions is reasonable, the source would to be deemed 

in compliance with the existing rule and no action would be taken. If the overall level is not 

reasonable, the state (or EPA) likely would conduct an inspection and/or order performance of 

Method 9 tests as required under the rule. As a result, the sort of routine emissions EPA 

described in its example would be unlikely to result in any violation of Ohio’s SIP-approved 

opacity rule, unless the total number of excess emissions over the quarterly reporting period 

were deemed unacceptable. Thus, although an opacity limit enforced with COMS data that 

excuses excess emissions based on percent of time sets fewer restrictions on when excess 

emissions can occur, it more than compensates for that difference by automatically designating 

all excess emissions over the allowed percentage as measured by the COMS (that are not 

otherwise exempt under the rule) as violations.4 

The only theory under which EPA could conclude that a COMS-enforced limit like 

Ohio’s alternative procedure is a relaxation would be to assume that the COMS already could 

be used to establish violations. Although EPA asserts in the preamble to its proposed 

disapproval of Ohio’s rule that “[c]urrently, COMS data may be used as credible evidence of 

violations” (70 Fed. Reg. 36903), EPA is wrong. For one, in Ohio’s case, Ohio has never 

adopted a “credible evidence” rule. And, EPA’s “credible evidence” rule is not selfimplementing. Clean Air Implementation Project v. EPA, 150 F.3d 1200, 1207 (D.C. Cir. 

1998) (CAIP). Moreover, even in a state that has adopted a “credible evidence” rule, the 

 

4

 EPA’s concern that sources would routinely operate with a full hour of excess 

emissions under the new rule is also overblown. Other applicable regulatory requirements, like 

the Compliance Assurance Monitoring (CAM) rule at 40 C.F.R. Part 64 and the NSPS “general 

duty” in 40 C.F.R. § 60.11(d), impose enforceable duties to respond to excess emissions (even 

when those excess emissions are otherwise allowed) that would make routine operation as 

described in EPA’s example unlikely. 
John M. Mooney, Chief

August 24, 2005

Page 5

existence of a “credible evidence” rule does not by itself convert COMS data into the 

compliance method. 

Even according to EPA, a “credible evidence” rule like the one EPA adopted does not 

change the compliance method, but merely allows its use as evidence in a judicial proceeding 

in which a judge or jury would be the “ultimate, independent arbitrator of the evidence’s 

admissibility and credibility.” 62 Fed. Reg. 8314, 8317. And, to the extent that EPA or a state 

attempted to enforce a Method 9-based opacity limit with COMS data, the affected source 

would be entitled to a determination by that judge or jury of the lawfulness of that application 

before a violation could be established. CAIP, 150 F.3d at 1205. It is for these reasons that 

EPA has agreed that sources cannot be compelled to use COMS data when certifying their 

compliance status with respect to Method 9-enforced standards. Natural Resources Defense 

Council, Inc. v. EPA, 194 F.3d 130, 138 (D.C. Cir. 1999). In other words, it is not reasonable 

for EPA to interpret an opacity limit, which on its face identifies Method 9 as the sole method 

for determining compliance, as automatically allowing for the use of COMS to establish 

violations even if a “credible evidence” rule has been adopted by the state, let alone do so in a 

state where no “credible evidence” rule exists. 

When evaluating a state’s conclusion that an alternative compliance procedure based on 

COMS is not less stringent than an existing Method 9-enforced opacity limit, EPA must 

evaluate the Method 9-enforced limit consistent with its inherent limitations and not as if it 

allowed use of COMS to establish violations. This is particularly true where the state itself 

interprets its SIP-approved rules as imposing restrictions on the use of COMS data. EPA has 

no authority to override a state’s interpretation of its own SIP. See., e.g., Fla. Power & Light 

Co. v. Costle, 650 F.2d 579 (5th Cir. 1981). When evaluated under the appropriate criteria, it is 

clear that Ohio’s alternative compliance procedure will provide equivalent or greater emission 

reductions than the existing SIP. Because Ohio has substituted a measure that is at least as 

stringent as the existing procedures, Ohio’s SIP revision request must be approved.

Second, even if a state’s alternative opacity limit were not as stringent as its existing 

SIP-approved rule, modeling would only be required to support a SIP revision if the state relied 

upon the existing opacity rule in its demonstration of compliance with the particulate matter 

National Ambient Air Quality Standard (NAAQS). CAA § 110(l) is not an anti-backsliding 

provision, but a requirement to assure that states continue to meet requirements for attainment 

and maintenance of the NAAQS, despite changes in its SIP. EPA has made clear in other 

contexts that modeling is not needed to satisfy § 110(l) when the state did not rely on the 

measures being changed to show attainment of the applicable air quality standard in its existing 

SIP. See 70 Fed. Reg. 39413, 39421 (July 8, 2005). In short, EPA has no basis to require 

modeling to support a SIP revision to remove restrictions on how many excess emissions of 

opacity occur in an hour, and to provide an alternative percent of time compliance procedure in 
John M. Mooney, Chief

August 24, 2005

Page 6

its place, unless the state relied upon that restriction to comply with the particulate matter 

NAAQS. EPA similarly has no authority to base its evaluation of a SIP revision on the 

existence of COMS as “credible evidence” of a violation of the opacity limit, unless the state 

relied upon the use of COMS data as “credible evidence” of a violation (as opposed to 

evidence to trigger further action) in the existing SIP.

In this case, there is no evidence that Ohio relied upon sources’ compliance with the 

one per hour restriction on excess emissions or the use of COMS as “credible evidence” under 

the existing SIP-approved opacity regulation to show attainment of the particular matter 

NAAQS.5 Although EPA might prefer that states, like Ohio, adopt a more stringent opacity 

standard by retaining the one-per hour restriction on excess emissions and imposing COMS as 

the compliance method, EPA has no authority to compel that result. Congress’ intended that 

states retain flexibility in carrying out their responsibilities for pollution control. 70 Fed. Reg. 

at 39422.

* * * * *

In sum, EPA has no basis under CAA § 110(l) to disapprove Ohio’s submittal for SIP 

approval of its alternative opacity compliance procedure. EPA should re-examine the criteria 

upon which it based its review of this request, and other similar SIP revision requests, and 

propose approval. Approval of this request, and other similar SIP revision requests would 

benefit regulators, sources, and the public by providing for more direct use of COMS data to 

assure compliance without unlawfully altering the underlying particulate matter control 

requirement. 

Please contact me if you have any questions about these comments. 

Sincerely,

 / s /

Lauren E. Freeman

Attachments

 

5

 And, as noted above, application of the CAM rule at 40 C.F.R. Part 64 to the sources 

eligible for the alternative opacity compliance procedure should be sufficient to ensure that the 

applicable particulate matter limits are enforced consistent with attainment of the NAAQS, 

without regard to the opacity standard itself.
ATTACHMENT A
BEFORE THE

UNITED STATES

ENVIRONMENTAL PROTECTION AGENCY

)

Request for Comments on Potentially )

Inadequate Monitoring in Clean Air Act ) Docket OAR-2003-0180

Applicable Requirements and on Methods )

To Approve Such Monitoring )

)

70 Fed. Reg. 7905 )

)

COMMENTS OF THE UTILITY AIR REGULATORY GROUP

 Counsel:

Lauren Freeman

HUNTON & WILLIAMS LLP

1900 K Street, N.W.

Washington, D.C. 20006-1109

(202) 955-1500

lfreeman@hunton.com

Dated: June 17, 2005
TABLE OF CONTENTS

I. EPA Was Correct To Exclude Post-1990 NSPS/NESHAPs From Its Notice .................... 2

II. EPA Has Already Addressed Monitoring For Pre-1990 Standards Through The 

Compliance Assurance Monitoring (CAM) Rule and “Periodic Monitoring” ................... 4

III. Any New Monitoring Requirements Can Only Be Imposed Though Rulemaking............ 7

A. The Importance Of Rulemaking On The Standard ......................................................9

1. The CAA And The Standard Setting Process......................................................... 9

2. Use Of “Excess Emissions” Monitoring............................................................... 15

3. Changing Compliance Monitoring Methods........................................................ 18

B. Consideration Of Costs And Burdens........................................................................23

IV. PM CEMS Currently Are Not A Reasonable Option For Compliance Monitoring......... 24

A. Available Data Do Not Support Use Of PM CEMS Technology..............................25

B. PS 11 Will Not Ensure That PM CEMS Data Are Sufficient For Compliance 

Purposes.....................................................................................................................29

C. Application Of PM CEMS Would Require Review Of PM CEMS Data In 

Relation To The Applicable Standard And Evaluation Of The Costs 

Associated With PM CEMS ......................................................................................34

V. Additional Steps EPA Can Take To Improve Monitoring................................................ 37

A. Improve Procedures for Streamlining........................................................................37

B. Approve Revisions To Provide “Percent Of Time” And Other Exclusions For 

Sources Using Continuous Monitoring......................................................................39

C. Exempt “Excess Emissions” And Control Device Monitoring Regimes From 

Application Of “Credible Evidence” Rules...............................................................41

VI. Comments On EPA’s “Categories Of Potential Monitoring Inadequacies”..................... 43
Comments of the Utility Air Regulatory Group (UARG) in Response to EPA’s 

Request for Comment on “Potentially Inadequate Monitoring in Clean Air Act 

Applicable Requirements and on Methods to Improve Such Monitoring”

These comments are filed on behalf of the Utility Air Regulatory Group (UARG) in 

response to EPA’s advance notice of proposed rulemaking (“ANPR”) with “Request for 

Comment on Potentially Inadequate Monitoring in Clean Air Act Applicable Requirements and 

on Methods to Improve Such Monitoring,” 70 Fed. Reg. 7905 (Feb. 16, 2005).1 UARG is a 

voluntary, nonprofit association of electric generating companies and organizations and four 

national trade associations (the Edison Electric Institute, the American Public Power 

Association, the National Rural Electric Cooperative Association and the National Mining 

Association). UARG’s purpose is to participate on behalf of its members collectively in EPA 

rulemakings and other Clean Air Act (“CAA” or “the Act”) proceedings that affect the interests 

of electric generators and in litigation arising from those proceedings. 

As EPA know, UARG supports EPA’s January 2004 final action (69 Fed. Reg. 3202) 

committing to address any improvements in monitoring that go beyond imposition of “periodic 

monitoring” or Compliance Assurance Monitoring (“CAM”) under Part 64 through notice and 

comment rulemaking, rather than allowing permitting authorities to revise monitoring 

requirements case-by-case in permitting proceedings. UARG believes that position is the only 

one that is consistent with the CAA, and EPA’s previous commitment to use rulemaking to make 

any needed improvements to Federal standards. See 57 Fed. Reg. 32250, 32278 (1992). 2 As 

 

1

 On April 15, 2005, EPA published notice that the comment period was extended to June 

17, 2005. 70 Fed. Reg. 19914.

2

 UARG’s interpretation of the statute and Part 70 regulations addressing Title V 

monitoring requirements is set out in the Joint Brief of Intervenors in Support of Respondent, in 

Environmental Integrity Project, et al., v. EPA, Case No. 04-1083 (and consolidated case No. 04-

1243) (D.C. Cir. filed May 16, 2005). 
- 2 -

described below, rulemaking proceedings are necessary when making any significant change to 

emissions monitoring requirements in order to evaluate the costs imposed and the effect on the 

achievability of the standard, and to ensure consistency between sources.

UARG also applauds EPA’s decision to issue this ANPR and appreciates the opportunity 

to provide comments. Although EPA could have simply proceeded on its own, UARG believes 

that EPA’s actions will be better informed following its review of comments on the status of 

monitoring in various regulations, and the types of issues that will need to be examined in the 

course of any future rulemakings. UARG believes that EPA already has met its statutory duty 

under Title V and the “enhanced monitoring” provision of § 114 through promulgation of the 

“periodic monitoring” rule and the CAM rule. However, UARG also believes that there are 

steps that EPA and states could take that would improve monitoring without imposing new costs 

or making existing standards unachievable. As described below, those steps include the 

streamlining of inconsistent and redundant monitoring requirements to make monitoring results 

more consistent and understandable, creating percent of time and other exclusions for sources 

choosing to use continuous monitors to demonstrate compliance with “periodic” standards, and 

creating exclusions from the “credible evidence” rules to encourage use of new technologies and 

better parameter monitoring methods as “indicator” or “excess emissions” monitoring. 

I. EPA Was Correct To Exclude Post-1990 NSPS/NESHAPs From Its Notice

EPA states that it is not seeking comments on or otherwise reopening New Source 

Performance Standards (“NSPS”) and National Emission Standards for Hazardous Air Pollutants 

(“NESHAP”) promulgated after 1990 because they were already required to meet the improved 

monitoring requirements of the 1990 Clean Air Act Amendments and are unlikely to contain 

inadequate monitoring. 70 Fed. Reg. at 7908. This has been EPA’s position since at least 1992. 

In the Preamble to Part 70, for example, although EPA agreed to conduct rulemakings for any 
- 7 -

III. Any New Monitoring Requirements Can Only Be Imposed Though Rulemaking 

EPA requests comment on what kinds of “programmatic or other changes” should be 

used to make improvements in inadequate monitoring. According to EPA, options include 

“conducting rulemaking to revise emission standards, issuing guidance or policy, or other 

approaches.” To the extent EPA identifies any inadequate monitoring, UARG believes that EPA 

has already articulated numerous policy reasons for proceeding by rulemaking. 69 Fed. Reg. 

3202. Those reasons include reduction in burdens on sources and permitting authorities, 

consistency in monitoring requirements, broader public input, better consideration of economic 

impact and other burdens, and greater clarity for sources. Id. UARG agrees with those policy 

reasons.

UARG also strongly believes, however, that new monitoring methods can only legally be 

imposed through rulemaking (e.g., under CAA § 504(b)) and that new direct compliance 

monitoring methods can only legally be imposed using the same procedure that was used to 

establish the original compliance method. For example, EPA’s CAM Rule did not require 

rulemaking on each standard because it did not impose a direct compliance monitoring method 

that could impact the achievability of the standard. It did, however, require rulemaking, which 

was important to assess the costs and burdens of the additional requirements and ensure 

consistency. Similarly, streamlining of emission monitoring methods does not require 

rulemaking because it is adopted at the source’s option. On the other hand, specification of new 

direct compliance methods in Federal rules can only be accomplished in rulemaking conducted 

by EPA on the applicable standard, and new direct compliance methods in SIP rules can only be 
- 8 -

accomplished in rulemakings conducted by the state on the applicable standard.3 While policy 

and guidance documents may have some use in providing technical information, like EPA has 

provided in parts of its CAM Technical Guidance Document, they cannot be used to establish 

substantive requirements. 

UARG believes that rulemaking on the standard is necessary in order to evaluate the 

impact of the new compliance method on the stringency or achievability of the existing standard, 

and to comply with CAA requirements. Such rulemakings may result in adjustments to the 

standard’s averaging time or level to account for previously unevaluated emissions variability. 

They also may require addition of exceptions to the standard for startup, shutdown or 

malfunction, or for other periods, since those periods may not have been evaluated when the 

standard was set. Rulemaking also is necessary in order to consistently address other issues, 

such as feasibility of the method, and any concerns about its accuracy and precision. Finally, 

rulemakings are necessary in order to comply with other regulatory review requirements 

intended to ensure that rules do not impose unreasonable costs or burdens on those affected by 

them.

As for EPA’s request for comment on the type of revisions to monitoring EPA should 

consider (e.g., more frequent monitoring using existing monitoring methods or the collection of 

data that is more representative of control device operation or of the industrial process), UARG 

believes that if monitoring is going to be changed, the best approach can only be determined in a 

rulemaking that considers the issues listed above and described below. 70 Fed. Reg. at 7909.

 

3

 Although EPA’s “periodic monitoring” rule allows permitting authorities to specify 

periodic monitoring in Title V permit proceedings, under UARG’s interpretation of that rule the 

permit authority is limited to specifying a reasonable frequency for performing the promulgated 

compliance method and tha t new methods (e.g., use of a CAM-like monitoring method) to 

satisfy the “periodic monitoring” requirement could only be required at the source’s option.
- 9 -

A. The Importance Of Rulemaking On The Standard

UARG anticipates that the primary focus of comments submitted in response to this 

ANPR will be on standards that rely on “periodic” methods for demonstrating compliance (e.g., 

periodic stack tests) and discussion of whether those standards should be revised to require use 

of “continuous” direct compliance methods. Some sources using “periodic” compliance methods 

already are (or will be) required to collect other data, either under the CAM rule or under “excess 

emissions” monitoring requirements, that provide continuous data but that are not used as a 

direct measure of compliance. Other sources are not required to collect other data (e.g., source 

not subject to CAM or an NSPS). As a result, UARG anticipates that EPA will receive 

comments suggesting that all sources should collect continuous data and that those data should 

be used as a direct measure of compliance. 

Imposing a new “continuous” compliance method or converting CAM or “excess 

emissions” monitoring into a direct measure of compliance would be a significant revision to an 

emission standard that could only be accomplished through a rulemaking on the standard. 

UARG (and others) discussed at length the importance of such rulemakings in their comments on 

the original “enhanced monitoring” proposal, 58 Fed. Reg. 54648 (1993), which EPA later 

abandoned in favor of CAM. Because the concepts addressed in those comments are relevant to 

the questions EPA has asked, UARG is including a discussion of them here. 

1. The CAA And The Standard Setting Process

Each CAA emission standard adopted by EPA (or a state) must satisfy express statutory 

criteria that are separate and independent from the authority to require monitoring or testing. For 

example, each NSPS adopted by EPA under § 111 must be established at a level consistent with 

“best demonstrated technology” (“BDT”) – a criterion that, by requiring consideration of a 

number of factors, ensures that the NSPS do not impose unreasonable costs. CAA § 111(a)(1). 
- 10 -

To ensure that revised NSPS are only applied to new sources, § 111 also provides that each 

NSPS can only be applied to sources that commence construction after the publication date of 

the proposed standard. Id. §§ 111(a)(2) and (b)(1)(B). NESHAPs, on the other hand, are 

governed by substantive criteria in § 112. Although NESHAPs are not limited to new sources, 

revisions to § 112 in 1990 established new criteria that must be satisfied whenever a pre-1990 

NESHAP is revised. Id. § 112(q). Promulgation and revision of the NSPS and NESHAPs are 

also governed by the procedural requirements in § 307(d), including a requirement that EPA 

provide data to support the proposed standard. Id. § 307(d). Moreover, because they are part of 

federally uniform programs, only EPA (and not the states) has the authority to promulgate or 

revise the NSPS and pre-1990 NESHAPs. Id. §§ 111(b)(1)(B) and (c) (delegation to states 

limited to implementation and enforcement of existing requirements) and 112(b) and (d).

State emission standards designed to ensure attainment and maintenance of national ambient air 

quality standards are similarly promulgated pursuant to state administrative procedures and 

incorporated into SIPs following approval by EPA. Id. §§ 110(a)(1) and (k). Many SIP 

standards are based, like the NSPS and NESHAPs, upon control technology identified by EPA, 

or a state, as satisfying certain statutory criteria.4 

By definition, "technology-based" standards, like the NSPS, NESHAPs, and most SIP 

standards, must be established at levels that reflect the performance of, and are achievable with, 

the underlying emission control technology. For example, if EPA identified a particular 

technology as BDT, the numerical NSPS based on that BDT will be valid only if it is reliably

and consistently achievable with that BDT. In making a judgment of achievability, EPA must 

 

4

 Most pre-1990 NESHAPs are based on “best available control technology,” see Natural 

Resources Defense Council v. EPA, 824 F.2d 1146, 1148, 1157 (D.C. Cir. 1987), and many SIP 

limits are based on technologies identified by EPA under the NSPS.
- 11 -

either evaluate, or make assumptions about, the variability in (1) the source’s emissions, (2) the 

performance of the installed control technology, and (3) the test method used to measure 

emissions. The importance of variability to standard-setting, and the Agency’s long-time 

practice for addressing variability in NSPS, are described in detail in a paper by Robert Ajax, a 

former Chief of the Emission Standards Development Branch in EPA’s Office of Air Quality 

Planning and Standards, who oversaw development of the NSPS.5

As Ajax explains, over the years, EPA has developed two types of NSPS: (1) periodic 

test-based standards -- where performance of the source and the proposed technology is 

determined based on projections from limited “snapshots” of emissions collected using shortterm tests (hereinafter referred to as “periodic” standards); and (2) continuous monitoring-based 

standards -- where the performance of the source and the proposed technology is determined 

from continuous monitoring data collected during all operating conditions (hereinafter referred to 

as “continuous” standards). 

The primary characteristic of “periodic” standards is the limited amount of data used in 

their development. Those data generally consist of between one and ten short-term emission 

tests that were typically done at steady-state, full load conditions with control equipment that 

was nearly new or in optimum condition. 6 The result of this limited data collection is that the 

data supporting “periodic” standards (1) are not themselves sufficient to identify the actual shortand long-term variability that would be seen if all emissions were measured over an extended 

 

5

See Ajax, “The Effect of Compliance Test Frequency on the Stringency of Technology 

Based Standards” (Mar. 9, 1995) (“Ajax Paper”). A former Director of the OAQPS Division that 

oversees the work of the ESD Branch agreed with the concepts outlined in the Ajax paper. See

Farmer Letter (Mar. 13, 1995) (attached to the Ajax paper).

6 Ajax Paper 3. The actual length of the test was usually determined by the time it took 

to conduct the EPA test method, which could be anywhere from 6 minutes (for an opacity test) to 

3 hours (for an SO2 stack test). Id.
- 12 -

period of time, (2) are too limited to allow for meaningful statistical analyses to assess this 

variability, and (3) do not evaluate all operating conditions associated with the unit or its control 

technology. Ajax Paper 2-8, 10-11. 

In 1979, contemporaneous with the promulgation of the first “continuous” NSPS, the 

Subpart Da NSPS for utility boilers, EPA observed:

Almost all emission limitations to date have not been based upon 

continuous monitoring data. The majority of existing stationary 

source emission limitations are based upon manual stack tests

which in most cases represent the ability to control emissions 

under the best possible circumstances. This is true for both State 

regulations and emission limits established by EPA for new

sources. A reevaluation of many emission limitations may result 

as a by-product of implementation of the proposed program which 

would provide a means of measuring continual compliance.7

In other words, most standards were “periodic” standards. 

In contrast to “periodic” standards, “continuous” standards are established based on longterm, continuous emissions data or continuous operating parameter data. Such data allow actual 

short- and long-term emissions variability to be evaluated and considered in setting the standard, 

and allow meaningful statistical analyses to assess the numerical level that can be achieved over 

a specific averaging time. Ajax Paper 11-13. By this route, the Agency has been able, for 

“continuous” standards, to identify and specify averaging times of sufficient length (usually 30-

day rolling averages) to smooth out short-term emissions variability (or create percent of time 

exceptions if a shorter averaging time is imposed), and to choose a numerical standard level that 

 

7

Pearson, “Development Plan for Implementation of Continuous Monitoring of Air 

Pollution Sources” 9 (Jan. 17, 1979).
- 13 -

can be achieved continuously over the relevant period (e.g., no more than one predicted 

exceedance in ten years) with the chosen technology. See Id. 11-14; 8

The compliance methods specified for numerical standards generally are the same as the 

methods used in establishing the standards. Thus, because short-term stack tests were used to 

collect the data for “periodic” standards, the specified compliance method for such standards was 

the same periodic test performed under “representative” (but not all) operating conditions. See, 

e.g., 40 C.F.R. § 60.46, Subpart D. Similarly, because continuous data were used to develop 

“continuous” standards, that method was specified for determining compliance with those 

standards. See, e.g., 40 C.F.R. § 60.48a, Subpart Da. The standard and compliance method were 

proposed as part of the same rulemaking to allow for public notice and comment on the effect 

that any difference between the methodology used to set the standard and the methodology used 

to enforce the standard might have on the validity of the standard.

Use of the same method (i.e., the same test, performed at the same frequency, and under 

the same conditions) is often necessary to ensure achievability of standards. For example, in 

some cases, use of a different test method or procedure can lead to fundamental differences in 

results, due to differences in analytical method, data reduction, or measurement location. 9 Even

if the same (or a comparable) method is used, testing under conditions different from, or 

conducted more frequently than, the testing considered in setting the standard can reveal 

operating variability that was unknown or ignored when the standard was set.

 

8

See also 54 Fed. Reg. 34008, 34014, (1989); 50 Fed. Reg. 46464, 46465 (1985) 

(explaining that a 7-day average, and not a 3-hour average, was chosen for the FCCU NSPS to 

ensure that exceedances would not occur due to normal FCCU or control system variability).

9

See, e.g., 52 Fed. Reg. 9778, 9779, 9781 (1987) (acknowledging cases where in-stack 

opacity readings with a COM and stack outlet readings with Method 9 may differ, and that most 

problems with COMs operations result in positive biases that are detrimental to the source).
- 14 -

The frequency of testing can significantly impact a standard, due to variability in 

emissions and testing.10 For a “periodic” standard set at the 90 percent probability level, 

properly operated and maintained control technology would be expected to “fail” a performance 

test only once every 10 years when tests are performed annually. See Ajax Paper 7-8.11 That 

frequency would increase to an expected failure of 36 tests per year, if testing were performed 

on a daily basis. Id. 7-8. An exponentially greater number of failures would be expected if 

compliance were evaluated every three hours.

The U.S. Court of Appeals for the D.C. Circuit recognized the integral relationship 

between numerical standards and compliance methods in Portland Cement Association v.

Ruckleshaus, which involved a challenge to the NSPS for portland cement plants. After finding 

that the methods for sampling in the final rule were different from those used in the tests to 

establish the standards, this Court explained that “a significant difference between techniques 

used by the agency in arriving at standards, and requirements presently prescribed for 

determining compliance with standards, raises serious questions about the validity of the 

standard,” and remanded the rule to EPA for further action. 12 Courts have relied on this 

 

10 See, e.g., 45 Fed. Reg. 44202 (1980) (amending the primary aluminum reduction plant 

NSPS to allow excursions above the standard level to account for emissions variability, in 

conjunction with a new requirement to conduct monthly performance tests); see also Ajax Paper 

7-8, 13-14 (explaining the relationship between the probability of exceedance and testing 

frequency in determining the achievability of a standard). 

11 An expected failure rate of one in 10 years (99.99 percent confidence level) is typically 

used by EPA in setting “continuous” standards. See, e.g., 43 Fed. Reg. 42154, 42159 (1978). 

12 486 F.2d 375, 396 (D.C. Cir. 1973); see also Amoco Oil v. EPA, 501 F.2d 722, 743 

(D.C. Cir. 1974); Essex Chemical Corp. v. Ruckelshaus, 486 F.2d 427, 436 (D.C. Cir. 1973. 
- 15 -

fundamental principle to reject attempts by EPA to use methods other than the specified test 

method to determine compliance, without undertaking rulemaking on the standard.

13

2. Use Of “Excess Emissions” Monitoring

The fundamental design principle underlying “technology-based standards” is that any 

source that properly installs and operates the required technology will be in compliance with the 

standard.14 To determine whether the reference technology is in place, sources conduct 

technology “performance tests” under “representative” (but not all) operating conditions, 

consistent with the “snapshot” data on which these standards were based. See, e.g., 40 C.F.R. 

§ 60.8(c). Performance tests must be conducted after start-up and then periodically, but 

infrequently, thereafter.15 

To ensure that the technology continues to be properly operated and maintained, the 

NSPS and NESHAPs include a “general duty” to “maintain and operate any affected facility 

including associated air pollution control equipment in a manner consistent with good air 

pollution control practice for minimizing emissions.” See 40 C.F.R. §§ 60.11(d), § 61.12(c). 

Thus, even though compliance with the numerical element of “periodic” standards is evaluated 

through short-term tests conducted under limited operating conditions, the “general duty” 

requirement provides an independent and fully enforceable assurance that emissions will be 

 

13 See Donner Hanna Coke Corp. v. Costle, 464 F. Supp. 1295, 1304 (W.D.N.Y. 1979); 

see also Appalachian Power Co. v. EPA, 208 F.3d 1015 (D.C. Cir. 2000).

14 See 38 Fed. Reg. 28564, 28565 (1973) (explaining how the combination of 

performance testing and the “general duty” requirement ensure compliance with the NSPS); see 

also Goodwin, “NSPS Policy Regarding Excess Emissions During Start-Up, Shutdown, 

Malfunction and Maintenance” (Aug. 30, 1976) [hereinafter “Goodwin Letter”].

15 40 C.F.R. §§ 60.8(a); see also Ajax 11 (discussing the role of frequency of testing in 

the NSPS standard-setting process). The NESHAPs have similar testing requirements. 40 

C.F.R. § 61.13(a) and (b). 
- 16 -

controlled between performance tests in a manner consistent with the performance obligation of 

the standard.16 

Some NSPS, NESHAPs, and SIP standards specify additional “indicator monitoring” 

requirements that are independent of the specified compliance testing method. Ajax Paper 10. 

In some cases, the additional monitoring requirement was promulgated along with the original 

standard and compliance method. In other cases, it was added later. Where additional 

monitoring is required, the rule usually identifies a purpose for that data. 

For example, many NSPS and NESHAPs, and some SIP standards, require use of 

continuous monitors or continuous operating parameter monitoring (e.g., temperature 

measurements) and reporting of “excess emissions” based on such monitoring. 17 However, the 

rules make clear that these “excess emissions” data are not to be used to assess compliance with 

the numerical emission limitations, unless the individual standard specifically authorizes that 

use.18 EPA has consistently reiterated this position both in Federal Register publications,19 and 

in EPA enforcement guidance.20 

 

16 The NSPS and NESHAPs provide that compliance with the “general duty” can be 

based on “information available to the Administrator which may include, but is not limited to, 

monitoring results, opacity observations, review of operating and maintenance procedures, and 

inspection of the source.” 40 C.F.R. §§ 60.11(d), 61.12(c) (emphasis added). Failure to identify 

a specific compliance method or procedure for the “general duty” requirement is reasonable, 

because that requirement does not depend upon a particular data set for its justification. 

17 See, e.g., 40 C.F.R. §§ 60.45(g), 60.49a(h), 60,73(e), 60.105(e), 60.284(d).

18 See, e.g., 38 Fed. Reg. 10820 (1973) (explaining the intent of 40 C.F.R. §§ 60.11(a) 

and (d) and promising that if EPA in the future required that compliance be determined using 

CEMS, the Agency would revise the applicable standard to reflect the change).

19 See, e.g., 52 Fed. Reg. 36440 n.1 (1987) (“Emission data measured by [CEMS] can be 

either excess emission data or direct compliance information depending on how the use of the 

[CEMS] is defined in the applicable subpart. The applicable subpart must specify the [CEMS] 

as the compliance method for the emission data measured by the [CEMS] to be direct 

(continued...)
- 17 -

In recognition of the fact that these “excess emissions” data were not the direct 

compliance method, EPA guidance described the appropriate uses for the data. For the NSPS 

and NESHAPs, the primary purpose of “indicator monitoring” is to assess compliance with the 

“general duty” requirement.21 Other uses of excess emissions data include: 

(1) to screen a source’s compliance status (with both emission 

limitations and O&M requirement); (2) to select which sources 

should be inspected or compliance (stack) tested; (3) to document 

the severity (e.g., duration, magnitude, and frequency) of a

source’s excess emissions; and (4) to document that a compliance 

test was performed during “non-representative” operating

conditions.22

EPA even issued guidance establishing recommended follow-up actions based on these “excess 

emissions” data,23 and in some cases added “percent of time” exceptions directly to the “excess 

emissions” provision in the standard.24 

 

(continued from prior page)

compliance information.”). EPA reiterated this position in 1996. See 61 Fed. Reg. 47840, 47844 

(1996). 

20 See, e.g., Bennett, “Guidance Concerning EPA’s Use of Continuous Emission 

Monitoring Data” (Aug. 12, 1982) (making clear that CEMS would be used for compliance 

determinations only when they have been promulgated or approved by the Agency as the official 

compliance method).

21 See, e.g., Enclosure to Goodwin Letter (explaining that data from CEMS required to be 

installed under the NSPS will be used by EPA to determine compliance with the general duty 

requirement under § 60.11.(d)); Memorandum from DSSE, “NSPS Policy Regarding Excess 

Emissions During Malfunction” (July 25, 1977) .

22 Id.; see also Emison, “Transmittal of Reissued OAQPS CEMs Policy” (Mar. 31, 1988).

23 See, e.g., Seitz, “Transmittal of SO2 Continuous Compliance Strategy” (July 5, 1988); 

Pfaff Letter to State and Local Air Program Directors attaching Region IV CEM Enforcement 

Plan (May 5, 1989).

24 See, e.g., 40 C.F.R. § 60.285 (establishing allowable excess emissions periods for 

purposes of determining compliance with the “general duty” under the NSPS for kraft pulp mills, 

Subpart BB).
- 18 -

EPA’s CAM Rule is based on the same concept as “excess emissions” monitoring but 

adds an enforceable requirement for follow-up investigation and corrective action by the source 

(without waiting for a request from EPA or the state agency) whenever a trigger level is 

exceeded. In this manner, the CAM rule ensures that the “general duty” is enforced and that 

required emission controls are continuously operated at the level necessary to comply with the 

standard. As discussed above, UARG believes that this monitoring under CAM is more than 

“adequate.”

3. Changing Compliance Monitoring Methods

If EPA were to decide that a change in a compliance method was appropriate, the CAA 

and states’ laws would require that specific procedures be used. For example, under §§ 111 and 

307(d), before EPA can revise a compliance method in an NSPS, EPA must develop a 

rulemaking record that compares the level of control required by the NSPS as revised with the 

level of control required by the BDT on which the standard was based. A revision to an existing 

NSPS that makes that NSPS more stringent is not authorized by § 111. Otherwise, sources that 

have already installed technology consistent with the original BDT determination might be 

required to abandon that technology or incur costs never contemplated when the NSPS was 

promulgated.

This principle is best illustrated by a rule change that would convert a “periodic” testbased NSPS to a “continuous” monitoring-based NSPS. Revising a standard based on snapshot 

data from a periodic stack test method, to a “continuous” standard that assesses compliance 

during all operating conditions (e.g., with CEMS or COMS data), requires that the Agency 

evaluate the variability of emissions that will be measured by the new continuous compliance 

method. As this Court observed in National Lime Ass'n v. EPA, in setting NSPS, “due 

consideration must be given to the possible impact on emissions of recognized variations in 
- 19 -

operations and some rationale offered for the achievability of the promulgated standard given the 

tests conducted and the relevant variables identified.” 627 F.2d 416, 434 (D.C. Cir. 1980) 

(emphasis added). 

As a result, to evaluate the impact on BDT of converting an existing “periodic” NSPS to 

a “continuous” NSPS enforced over the same short-term period required to conduct a stack test 

(e.g., a 3-hour averaging time), EPA would have to (1) identify the BDT evaluated in the original 

rulemaking (e.g., low sulfur coal, low NOx burners, precipitators, or scrubbers); (2) evaluate 

short-term (e.g., 3-hour) data collected using the new compliance method (e.g., CEMS) at units 

using these BDTs; and (3) perform a statistical analysis of emissions variability to demonstrate 

that affected units could still achieve the standard using the original BDT with a new compliance 

method that continuously measures compliance on a short-term basis (e.g., over every 3 hour 

period). If this statistical analysis indicates that the original BDT could not achieve the standard 

on a short-term continuous basis, § 111 would require EPA to modify the averaging time or 

increase the numerical limit to assure that the standard can be continuously achieved using the 

BDT, when enforced using the new continuous method. 

Prior rulemakings undertaken by EPA for utility and industrial boilers illustrate these 

points. EPA proposed NSPS for SO2 and NOx emissions from such boilers in 1971 (i.e., the 

Subpart D NSPS). 36 Fed. Reg. 24876 (1971). EPA based the 1971 Subpart D NSPS for SO2

and NOx on a limited amount of data collected using EPA Test Method 6 and 7 (stack testing 

procedures with a minimum sampling time of approximately 3 hours) and on 1971 technology. 

The variability of SO2 and NOx emissions was unknown when these standards were adopted, 

because there were no continuous emission data collected over extended periods. Because 

Subpart D was established based on limited, periodic reference method test data, EPA made clear 
- 20 -

that compliance would be determined using the Method 6 and 7 reference method tests run 

periodically under “representative” conditions. 40 C.F.R. § 60.46; 48 Fed. Reg. 48960 (1983).

In 1978, EPA proposed to revise this NSPS (for utility boilers only) based on continuous 

data and better control technology that had become available after 1971. 43 Fed. Reg. 42154 

(1978). Because of the variability that those continuous data disclosed, EPA recognized that 

even with improvements in technology since 1971, EPA could not require CEMS compliance 

with NOx or SO2 limits in the same numerical range as the Subpart D limits using 3-hour CEMS 

data.25 As a result, EPA initially proposed a 24-hour average continuous compliance standard 

for SO2 and NOx (43 Fed. Reg. 42154) and then in 1979 adopted a 30-day average in the final 

Subpart Da NSPS for SO2 and NOx (which only applies to units constructed or modified after the 

Subpart Da proposal). 44 Fed. Reg. 33580 (1979). This 30-day average was largely based on 

CEMS data collected at units subject to the 1971 Subpart D standards,26 thus underscoring the 

unachievability of a 3-hour CEMS standard using the 1971 Subpart D BDT. 27

In 1986-87 and 1990, EPA again revised the boiler NSPS, establishing Subpart Db and 

Dc NSPS for industrial and smaller utility boilers, which were similar to the Subpart Da SO2 and 

NOx NSPS.28 EPA again analyzed continuous data and reached the same conclusions it had in 

 

25 EPA’s 1978 proposal included limitations for SO2 and NOx that were equivalent to the 

numerical limits in Subpart D as applied to units burning high sulfur coal (SO2) and lignite coal 

(NOx). 

26 Although Methods 6 and 7 were the Subpart D compliance methods, Subpart D also 

required installation of CEMS and reporting of “excess emissions” on a 3-hour average basis, in 

order to evaluate compliance with the independent “general duty” requirement under 40 C.F.R. § 

60.11(d).

27 See Sierra Club v. EPA, 657 F.2d 298, 364 (D.C. Cir. 1981) (affirming EPA’s 1979 

revisions to Subpart D establishing the new standard -- Subpart Da -- based on a prediction of 

the capabilities of 1978 scrubber technology). 

28 51 Fed. Reg. 42768 (1986); 52 Fed. Reg. 47826 (1987); 55 Fed. Reg. 37674 (1990).
- 21 -

1978 regarding the numerical level of the standard and the need for a 30-day average for these 

“continuous” NSPS to be achievable with then-available BDT. 29 

Any “improvements” in monitoring that would allow determinations of compliance using 

3-hour SO2 and NOx CEMS data collected at Subpart D units, would convert the Subpart D SO2

and NOx standards into 3-hour “continuous” standards, thus requiring sources subject to the 1971 

Subpart D NSPS to install technology was not even available when the later Subpart Da, Db, and 

Dc standards were developed, let alone when the 1971 standards became applicable.30 This point 

was recognized by EPA in 1979, shortly before it promulgated the Subpart Da “continuous” 

NSPS, and is dramatically illustrated by a rulemaking EPA began in 1983 to change the 

compliance method for the 1971 Subpart D SO2 standard from a “periodic” standard to a 

“continuous” standard. 48 Fed. Reg. 48960 (1983). 

Before issuing its proposal to revise the Subpart D NSPS compliance method in 1983, 

EPA did an extensive analysis to determine whether use of SO2 CEMS data, in lieu of periodic 

stack test data, to determine compliance was consistent with the Agency’s 1971 BDT 

determination. Based on that analysis, EPA’s proposal, consistent with its conclusions in the 

1978 Subpart Da rulemaking, expressly rejected use of 3-hour average SO2 CEMS data (even 

though those data were most similar in length to the stack test data) in favor of a 30-day rolling 

average of the SO2 CEMS data.31 

 

29 49 Fed. Reg. 25102, 25137; 51 Fed. Reg. 22384, 22413 (1986); 54 Fed. Reg. 24792, 

24804 (1989).

30 As a result of emission reductions made under other programs, such as the Acid Rain 

Program, many Subpart D sources probably can comply with that more stringent standard as a 

practical matter even if they could not be required to under the NSPS. However, that is not true 

for all sources or for other standards.

31 See 48 Fed. Reg. 48961 (1983) (“The proposed revision would make Subpart D 

consistent with the intent and anticipated effect at the time it was adopted and does not make it a 

(continued...)
- 22 -

EPA’s proposal was based on its finding that use of the 3-hour averaging period on a 

continuous basis would preclude use of the low-sulfur coal upon which EPA had based the 

standard, and would be unachievable with SO2 scrubbers installed to comply with the standards 

at units using high-sulfur coals. See 48 Fed. Reg. 48960-61 (1983). In short, EPA concluded a 

3-hour averaging time was not consistent with the Agency’s 1971 BDT determination that 

defined the compliance obligation of Subpart D sources, and thus would make the numerical 

limit more stringent. 

EPA never completed the 1983 Subpart D rulemaking. Thus, the Subpart D NSPS is a 

“periodic” standard and the method specified in the subpart for determining compliance with that 

standard remains a stack test (and not a CEM). 40 C.F.R. §§ 60.46(b)(4) and (5).

This detailed discussion of the boiler NSPS is but one illustration of the dramatic impact 

“improvements” in monitoring could have on all technology-based standards, including the 

NSPS, NESHAPs, and SIP standards. UARG is confident that many other standards would 

show problems, particularly if the improvements transformed “periodic” based standards into 

“continuous” based standards. For example, EPA’s own statistical analysis of excess emissions 

data from EPA Region V suggests that few sources could achieve the “periodic” NSPS for 

opacity if it were transformed into a “continuous” standard enforced using COMs rather than 

data from Method 9 tests (the compliance test method for most “periodic” test based opacity 

 

(continued from prior page)

more stringent regulation with which to comply.... [T]he proposal provides an averaging time 

[30-day rolling] that is consistent with the capability of the control technology.”). 
- 23 -

standards). 62 Fed. Reg. 8319. This is because even well operated sources experience “excess 

emissions” some small percentage of the time (e.g., 1-2 percent per year).32 

In sum, without a proper evaluation by EPA or state, the impact of a change in the 

monitoring method on any particular standard cannot be known. Accordingly, in order to impose 

new monitoring methods (particularly those that convert “periodic standards” into “continuous 

standards”), EPA and states will have to conduct standard specific rulemakings to examine the 

impact or limit the use of the new method to the sole election of the source owner.33

B. Consideration Of Costs And Burdens

Rulemaking also is necessary to fulfill the requirements of Executive Order 12866 (for 

“significant” regulatory actions), the Paperwork Reduction Act, the Regulatory Flexibility Act, 

and other regulatory review requirements. Policy or guidance specifying requirements for state 

review and specification of new monitoring could result in imposition of significant costs on 

sources and/or permitting authorities without complying with these important requirements. For 

example, because installation and certification of some direct monitoring technologies (like PM 

CEMS) could cost a single source hundreds of thousands of dollars in a single year, an action 

that resulted in use of that technology could easily be deemed a “significant” action. Parameter 

 

32 See Region 5 Opacity Excess Emissions Reports; 62 Fed. Reg. 8325. Notably, this 

percentage of time is also much greater than that used by the Agency to define the achievability 

of NSPS (e.g., no more than one predicted exceedance in ten years).

33 EPA took this approach when it EPA amended the Part 60 general provisions in 1985 

to allow the use of COMs to evaluate compliance during “performance testing,” in lieu of the 

existing compliance method, EPA did not conduct standard specific rulemakings. Instead, EPA 

only authorized the use of COMs for compliance purposes at the option of the source owner. 52 

Fed. Reg. 9778 (1987), amending 40 C.F.R. § 60.11(e). Responding to commenters’ concerns 

about future use of the COMS data for determining compliance, EPA even clarified the rule to 

say that the owner could revoke the option at any time simply by notifying the Administrator. 

Id. 9780. Unfortunately, EPA’s “credible evidence” rule has effectively eliminated the 

safeguards this provision was designed to provide.
- 24 -

monitoring can also be expensive (in 1997, EPA estimated the total cost of implementing CAM 

would be $50 million a year). Even increasing the frequency of periodic stack testing can result 

in significant costs that may not be warranted for some units. Rulemaking, including compliance 

with any regulatory review requirements, is the only means by which the costs and benefits of 

additional monitoring can be fully and consistently addressed.

IV. PM CEMS Currently Are Not A Reasonable Option For Compliance Monitoring 

EPA asks whether opacity is an effective means of determining compliance with PM 

limits in pre-1990 applicable requirements or whether other approaches or technologies, such as 

PM CEMS, would be more cost-effective and reliable. 70 Fed. Reg. at 7909. As UARG has 

previously commented, UARG does not believe that PM CEMS technology is sufficiently 

developed for use as a compliance method. The primary problem with the use of PM CEMS to 

determine compliance with PM emission limits is the limitations of the technology. Current PM 

CEMS technologies cannot measure PM concentration or mass directly, but instead provide only 

an indirect measure by calibrating the monitor’s response to a short term EPA test method (such 

as EPA Method 5). Although there are other technologies, EPA has determined that only two of 

the “commercially available” technologies, the light scattering devices and beta ray attenuation 

devices (called beta gauges), could meet the correlation criteria in EPA’s performance 

specification (discussed below), and are suitable for long term application. See Status of 

Particulate Matter Continuous Emission Monitoring Systems for Application to Electric Utility 

Steam Generating Units (Sept. 7, 2004), OAR-2005-0031-0057 (“Status Report on PM CEMS”) 

at 1-6. 

In its recently Proposed Standards of Performance for Electric Steam Generating Units, 

which proposes revisions to 40 C.F.R. Part 60, Subparts Da, EPA asserted based on analysis of 

“available data, [that] there is no technical reason that PM CEMS cannot be installed and 
- 37 -

V. Additional Steps EPA Can Take To Improve Monitoring

EPA asks whether there are other categories of “potential monitoring inadequacies” in 

SIPs or Federal rules that EPA should address. 70 Fed. Reg. 7908-9. Although new compliance 

methods can only be imposed through rulemaking, UARG believes that there are other steps 

EPA and states can take (and have taken) to improve monitoring and EPA that should support 

those efforts. Among those efforts are streamlining of emission monitoring requirements, quick 

approval of SIP revisions intended to facilitate use of continuous monitoring, and exemptions 

from the “credible evidence” rules. 

A. Improve Procedures for Streamlining

UARG has identified at least two circumstances under which emissions monitoring 

requirements being incorporated into Title V permits could be improved by streamlining. First, 

many sources seeking Title V permits are subject to multiple emission standards for a single 

pollutant, each of which specifies its own monitoring method. For example, many sources 

subject to SO2 or NOx standards under an NSPS also are subject to SO2 or NOx standards under 

SIP rules or preconstruction permits. In some cases, imposition of a more recent standard will 

result in source emissions that are significantly below an older standard, such that demonstrating 

compliance with one effectively ensures compliance with the other. For example, a PSD BACT 

limit for NOx for a combustion turbine may be significantly more stringent than the applicable 

NSPS limit under Subpart GG. Second, even if the emission standards themselves are such that 

individual compliance determinations are necessary, those standards may have monitoring 

methods that are redundant and/or conflicting. For example, many states automatically specify 

use of Part 60 CEMS certification and QA/QC requirements for demonstrating compliance with

pre-construction emission limits (in addition to the NSPS standards to which they automatically 

apply), which are both redundant of and inconsistent with Part 75 CEMS requirements with 
- 38 -

which electric utilities must comply under the Acid Rain (and in some cases the NOx Budget 

Program). 

 In 1996, EPA issued guidance on streamlining multiple applicable requirements in White 

Paper Number 2 for Improved Implementation of the Part 70 Operating Permits Program (March 

5, 1996). Although that guidance was intended to address the two circumstances above by 

allowing the source at its option to subsume less stringent requirements into more stringent 

requirements (whether they be emission limits or monitoring requirements), the guidance was so 

complex and the analysis so time-consuming that few sources were able to take advantage of it. 

In some cases, permitting authorities faced with complying with the guidance simply refused to 

consider streamlining because the source failed to request it in the initial permit application 

submittal. In other cases, the analysis was not done simply because it was too complex to 

complete. Thus many permits were issued without any streamlining.

In the past, EPA regions have issued source specific applicability determinations when 

requested, but that process is time consuming and can lead to inconsistent results. EPA recently 

has taken, or proposed to take, regulatory action to address some of the conflicts between Part 60 

and Part 75 CEMS requirement by authorizing use of Part 75 in lieu of Part 60. EPA has done 

this both in individual NSPS and in a recent proposal to revise Part 60. See, e.g., 70 Fed. Reg. 

9706 (February 28, 2005). However, much more could be done. 

Although UARG agrees that such streamlining can only be implemented at the source’s 

option, UARG encourages EPA to facilitate streamlining by allowing states more latitude in 

making practical determinations regarding the relative stringency of emission limits and 

emission monitoring requirements (subject to the Part 70 public and EPA review process) and by 

taking a more proactive role in identifying regulatory solutions. Streamlining of duplicative and 
- 39 -

inconsistent requirements benefits all stakeholders by reducing burdens and clarifying 

compliance procedures. 

B. Approve Revisions To Provide “Percent Of Time” And Other Exclusions For 

Sources Using Continuous Monitoring

As discussed above, most NSPS and many SIP limits established prior to 1980 (and 

almost all opacity standards) specify an EPA test method as the compliance method (e.g., 

Method 9 for opacity) but also require the reporting of “excess emissions” monitoring with a 

CEMS or continuous opacity monitoring system (“COMS”) to evaluate compliance with the 

“general duty” under § 60.11(d) and similar SIP rules. Over the years, EPA and states developed 

guidance for evaluating “excess emissions” reports and policies establishing “percent of unit 

operating time” triggers to determine whether follow-up action should be taken. See, supra n.23;

EPA “Handbook for the Review of Excess Emission Reports,” EPA-340/1-86-011 (May 1986). 

Most policies considered excess emissions less than 2 percent of operating time to be good 

performance and only required stack testing if excess emission exceeded 5 percent of operating 

time. 

When EPA promulgated the “credible evidence” rules, EPA also cited opacity excess 

emissions of 2 percent at NSPS sources as evidence that the standards are achievable. EPA then 

suggested that any source that believes that a standard cannot be met “across some meaningful 

range of normal operating conditions,” or that exemptions beyond those already provided are 

proper (e.g., beyond startup, shutdown, and malfunction for the NSPS), petition for amendment 

of the standard at issue or “propose more specific permit conditions so that the matter can be 

fully assessed and addressed through the regulatory process.” 62 Fed. Reg. 8314, 8326. 

Although UARG is not aware of any source petitions, a number of states have attempted 

to improve monitoring by formally codifying their 2 percent of time exemption for any source 
- 40 -

that chose to use its COMS as a compliance method rather than merely for “excess emissions” 

monitoring. Other states that did not have “startup, shutdown, and malfunction” exceptions to 

their opacity standards, also have attempted to revise their SIPs to incorporate such exceptions. 

Although EPA has approved one state’s limited startup/shutdown exemption (Ohio), EPA has 

either not responded to or responded unfavorably to other state’s attempts to use this mechanism 

to improve compliance monitoring consistent with the original standard. And, although EPA 

recently proposed to approve a “percent of time” SIP revision for North Carolina, EPA 

significantly limited the exception the state had originally adopted even though it was well below 

the historical 2 percent of operating time exception for “excess emissions.” 

UARG believes that EPA is missing a significant opportunity to improve compliance 

monitoring for opacity by establishing unreasonable hurdles for states’ demonstrations to show 

that their proposed revisions are consistent with the requirements of CAA § 110. EPA should 

approve these SIP revisions without requiring overly burdensome demonstrations and should 

consider conducting rulemaking to provide similar exclusions in Federal rules. At least two 

Courts have already found a two percent of operating time exception to be reasonable. See 

National Parks Conservation Ass’n v. TVA, 175 F.Supp.2d 1071 (E.D. Tenn. 2001) (upholding 

as reasonable the state’s conversion of the standard from Method 9 to COMS with a 2 percent 

exception); Sierra Club v. TVA, Memorandum Opinion, Case No. 02-CV-2279 (N.D. AL Sept. 

24, 2004) (upholding the state’s interpretation of its regulation as including a 2 percent 

exception). 
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C. Exempt “Excess Emissions” And Control Device Monitoring Regimes From 

Application Of “Credible Evidence” Rules

As discussed above, EPA has long distinguished between “excess emissions” monitoring 

and direct compliance monitoring. When EPA promulgated its 1997 “credible evidence” rules in 

40 C.F.R. §§ 60.11(g ) (NSPS), 61.12 (NESHAPS) and issued a SIP-call to require similar state 

rules under 40 C.F.R. §§ 51.212 and 52.12, EPA eliminated that important distinction by 

allowing use of “excess emissions” data to establish violations of emission limitations in 

enforcement proceedings under certain circumstances.38 UARG believes that EPA’s “credible 

evidence” rules created significant impediments to improvements in monitoring by creating huge 

disincentives for sources to gather and report information from methods other than the specified 

compliance method, to agree to “excess emissions” monitoring using new technologies (like PM 

CEMS), or to develop correlations of control device parameters to emission limits where direct 

monitoring is not used. So-called “credible evidence” rules also interfere with Title V 

compliance certifications by injecting a level of complexity to such determinations that results in 

inconsistency between sources and can make certifications difficult to interpret. 

Historically, EPA used “excess emissions” monitoring regimes under the NSPS as a 

means of taking advantage of continuous monitoring technology in those cases where it was not 

appropriate to employ them as a direct compliance method. Examples include (1) use of SO2

and NOx CEMS as “excess emissions” monitors under Subpart D, when those monitors were 

relatively new technology that had not been sufficiently demonstrated and no CEMS data was 

 

38 Although UARG (and others) challenged the legality of the “credible evidence” rule, 

the U.S. Court of Appeals for the D.C. Circuit refused to rule on its legality, finding instead that 

the effect of the rule in any particular case was not yet clear and therefore the rule itself was not 

“ripe” for review. See Clean Air Implementation Project v. EPA, 150 F.3d 1200 (D.C. Cir. 

1998). 
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available to set the standard, (2) use of COMS as “excess emissions” monitors for opacity when 

the standard was established with only a few Method 9 tests during controlled particulate matter 

testing, and (3) use of water/steam-to-fuel ratios to report “excess emissions” for combustion 

turbines when the standard was set with stack test data and use of NOx CEMS was not 

considered cost-effective or feasible. By eliminating the clear distinction between direct 

compliance methods and “excess emissions” monitoring in the “credible evidence” rule, EPA 

has effectively eliminated these uses of “excess emissions” monitoring in future rules (and 

created potential liability for sources subject to existing rules that still employ excess emissions 

monitoring regimes). See Comments of the Utility Air Regulatory Group on Proposed Standards 

of Performance for Stationary Combustion Turbines, Docket OAR-2004-0490-0195 at 28-32. 

In UARG’s view, since EPA promulgated the “credible evidence” rule, EPA’s options for 

using continuous data as a compliance tool are limited. EPA must either establish a “continuous 

standard” based on a thorough evaluation of continuous data with the proposed compliance 

method (e.g., CEMS or COMS), or make clear in the applicable rule that continuous data cannot 

be used to establish violations of the applicable emission limit (i.e., that they cannot be used as 

“credible evidence”). Use of continuous parameter data (like those collected under the CAM 

rule) to directly enforce standards also should be prohibited not only because the standard likely 

was set using “periodic” data, but also because there are insufficient data to show that a change 

in the parameter sufficient to be recorded as an “excess emission” is necessarily enough to 

demonstrate that the emission limit was not met. 

As a result, UARG believes that elimination of the “credible evidence” rules in these 

types of applications would further the advancement of new monitoring technologies (which are 

not ready to be used as compliance monitors), allow EPA and states additional flexibility in the 
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standard setting process by allowing standards to be set without exhaustive collection of 

continuous emissions monitoring data, and create incentives for sources to develop better 

correlations between control device and other operating parameters and applicable emission 

limits. 

VI. Comments On EPA’s “Categories Of Potential Monitoring Inadequacies”

To “focus analysis and comment,” EPA provided in its notice a list of what it called 

“categories of potential monitoring inadequacies.” 70 Fed. Reg. at 7908. UARG has the 

following comments on those categories.

• “No monitoring of any kind is required” or “Monitoring is specified for certain 

units, but no monitoring is required for other units.”

As an initial matter, EPA’s description is misleading. UARG does not believe there are 

any Federal standards that do not specify a monitoring or measurement method or require testing 

when specified by the Administrator. And, although there may be SIP standards that do not, 

EPA’s own rules identify EPA’s reference methods as the default for such SIP standards and 

allow EPA to require testing. As a result, this category is likely limited to those rules that would 

fall under EPA’s “periodic monitoring” rule because there is no frequency specified directly in 

the rule. UARG understands that EPA plans to solicit comment on the handling of “periodic 

monitoring” requirement later this summer. 

UARG also believes that there are cases where “no ongoing monitoring” is appropriate. 

For example, in some cases permitting authorities will establish limits for pollutants solely for 

the purposes of performance testing upon startup to confirm the applicability or accuracy of 

some assumption regarding the level of emissions. In such cases, once testing confirms the 

assumption it may be appropriate not to require any further testing. In other cases, EPA has 

acknowledged (in its own standards and in Part 51, Appendix P) that ongoing monitoring is not 
ATTACHMENT B