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1. The Time Frame for Conducting Stack Tests
2. Stack Test Waivers
3. Stack Test Notifications
4. Observation of Stack Tests
5. Representative Testing Conditions
6. Stoppages
7. Postponements
8. Test Reports
2. Stack Test Waivers
3. Stack Test Notifications
4. Observation of Stack Tests
5. Representative Testing Conditions
6. Stoppages
7. Postponements
8. Test Reports
4. OBSERVATION OF STACK TESTS
• The primary issue with respect to observing stack tests to determine and demonstrate
compliance is whether a delegated agency should have an observer present for all stack tests, and
if not, how often should the delegated agency be present to observe the tests.
• There is no requirement that delegated agencies be present to observe all stack tests. However,
whenever possible, trained staff from delegated agencies should observe the tests to ensure that
the regulatory testing requirements are being met; the site-specific test plan is being followed;
and the results are being accurately and completely recorded and documented in the test report.
The observer should have the access necessary to ensure that the test is being conducted properly
and results reported accurately. Furthermore, the observer should be present for the duration of
the test, including all test runs. The presence of an observer helps to reduce the likelihood of
sample recovery and handling errors, as well as equipment errors, and to ensure that testing is
conducted under the proper process conditions. Ultimately, the presence of a state/local observer
reduces the number of retests. Therefore, the test date(s) and approximate start/end time of the
test should be acceptable to both the delegated agency and the facility to allow the delegated
agency an opportunity to observe the test, if desired.
Page 14
• If the delegated agency chooses not to observe the test, prior review of the site-specific test
plan is even more critical to ensure that the test is conducted in such a manner so as to satisfy the
regulatory requirements.
• If the delegated agency was not provided timely notification and an opportunity to observe the
stack test consistent with applicable regulatory requirements, the resulting test data may be
rejected and a new stack test may be required. If this situation prevents the facility from
completing a valid stack test within the requisite time frame, the facility is in violation of the
requirement to conduct a stack test and demonstrate compliance. However, if the facility
provided timely notice and the delegated agency did not respond or declined to observe the test,
the test results should not be rejected solely because the test was not observed by
agency personnel.
5. REPRESENTATIVE TESTING CONDITIONS
• The CAA requires that facilities comply with emissions limitations and emissions standards on
a continuous basis. The Act defines the terms "emissions limitation " and "emission standard "
in Section 302(k), 42 U.S.C. § 7602(k), as meaning "a requirement established by the state or the
Administrator which limits the quantity, rate, or concentration of emissions of air pollutants on a
continuous basis . . . ." (emphasis added). The statute also authorizes penalties for multiple days
of violations and establishes a presumption of continuing violations if certain conditions are met.
CAA Section 113(e)(1) and (2), 42 U.S.C. §§ 7413(e)(1) and (2). EPA has consistently, in
rulemaking and policy statements over many years, taken the position that the CAA requires
continuous compliance with emissions limits except where compliance is explicitly excused.
See, e.g., Guidance entitled "Definition of ‘Continuous Compliance’ and Enforcement of
O&M Violations," (June 24, 1982) ("In the strict legal sense, sources are required to meet,
without interruption, all applicable emissions limitations and other control requirements, unless
such limitations specifically provide otherwise."); Credible Evidence Rulemaking, 62 FR 8314,
8323, 8324, 8326 8314 (Feb. 24, 1997) (emissions limits require continuous compliance
(consistent with any averaging times) except during periods when compliance is
specifically excused).
• Since the CAA requires continuous compliance with emissions limits except where explicitly
excused, EPA interprets applicable regulations to require that any stack test that is conducted
within the scope of this guidance must demonstrate that a facility is capable of complying with
the applicable emissions standards at all times.4 The NSPS and MACT programs require that
performance tests be conducted under such conditions as the Administrator specifies based upon
the representative performance of the affected facility. See 40 CFR §§ 60.8© and 63.7(e). The
MACT program further defines representative performance as normal operating conditions.
43 CFR § 63.7(e). Operations during periods of startup, shutdown and malfunction do not
constitute representative conditions for the purposes of a performance test. 40 CFR §§ 60.8(c)
4 Complying with the applicable standards "at all times " does not include allowable
periods of start-up, shutdown, and malfunction as provided in 40 CFR §§ 60.8 (c) and 63.7(e)(1).
Page 15
and 63.7(e). The Part 61 NESHAP program requires that emission tests be conducted “under
such conditions as the Administrator shall specify "based on design and operational
characteristics of the source." 40 CFR § 61.13(e). Individual standards may more specifically
define operating conditions under which performance tests should be conducted. In the absence
of such specifications, the question often arises as to what operating conditions should be used
when conducting a stack test. If operating conditions are not indicated by the applicable
requirements in individual standards, they should be developed as part of the site-specific
test plan.
• In light of the fact that: (a) the Act requires that facilities continuously comply with emission
limits; (b) the NSPS, MACT, and NESHAP programs all require that performance tests be
conducted under such conditions as the Administrator specifies; and © the NSPS and MACT
programs further require that such tests be conducted under representative operating conditions;
EPA recommends that performance tests be performed under those representative (normal)
conditions that:
-represent the range of combined process and control measure conditions under which
the facility expects to operate (regardless of the frequency of the conditions); and
-are likely to most challenge the emissions control measures of the facility with regard
to meeting the applicable emission standards, but without creating an unsafe condition.
• The following are factors that should be considered in developing the plan for a performance
test that challenges to the fullest extent possible a facility’s ability to meet emissions limits.
-For a facility operating under an emission rate standard (e.g., lb/hr) or concentration
standard (e.g., µg/m3), normal process operating conditions producing the highest
emissions or loading to a control device would generally constitute the most challenging
conditions with regard to the emissions standard. If operating at maximum capacity
would result in the highest levels of emissions, operating at this level would not create an
unsafe condition, and the facility expects to operate at that level at least some of the time,
EPA recommends that the facility should conduct a stack test at maximum capacity or the
allowable/permitted capacity.
-For a facility operating under a control or removal efficiency standard (e.g., 98 percent
control or removal of a specified pollutant), lower emissions loading at the inlet of a
control device within the range of expected process operating conditions may often be
the most challenging emissions control scenario for purposes of achieving the applicable
standard. For facilities required to achieve such control or removal efficiency standards,
EPA recommends that the performance test include operating the facility under such
expected lower emissions loading conditions.
-The test plan should generally include use of fuel, raw materials, and other
Page 16
process/control equipment that the facility expects to use during future operations that
would present the greatest challenge in meeting applicable emissions standards. To
demonstrate the facility’s ability to meet concentration standards and emissions rate
standards, for example, the facility generally should use the fuel or raw materials that it
expects to use and that have the highest emissions potential for the regulated pollutant(s)
being tested. In instances where alternative processing materials are expected to be used
by the facility and those materials are known to adversely impact emissions quality or the
functioning of control measures, the facility generally should use the material that is
likely to cause the greatest challenge in meeting applicable emissions standards. For
concentration and emissions rates standards, the facility generally should process the
material that it expects to use during future operations that is likely to cause the highest
emissions. For control or removal efficiency standards, other factors may apply such as
using fuels or raw materials that contain or produce pollutants that are more difficult to
combust or otherwise remove.
• A facility is not required automatically to retest if the initial test does not represent the range of
combined process and control measure conditions under which the facility expects to operate, or
if the test does not challenge to the fullest extent possible the facility’s ability to meet applicable
emission standards without creating an unsafe condition. Furthermore, the facility is not
required automatically to retest if the facility’s operating conditions subsequently vary from
those in place during the performance test. The delegated agency must determine whether
retesting is warranted; however, in both instances, the facility is responsible for demonstrating to
the satisfaction of the delegated agency that the facility is able to continuously comply with the
emissions limits when operating under expected operating conditions, taking into consideration
the factors discussed above in this section.
• This guidance does not affect the ability of delegated agencies to prohibit a facility from
operating at levels of capacity different from the level used during the stack test, or to restrict
production to reflect conditions equivalent to those present during the stack test.
Soot-Blowing:
• Soot-blowing is the cleaning of heat exchanger surfaces by the use of steam or air to dislodge
accumulated material such as ash. The Agency guidance on this issue states that soot-blowing is
a routine operation constituting representative process conditions. Emissions from soot-blowing
cannot be discarded as being the result of an upset condition, and it would be erroneous to stop
soot-blowing for the purpose of conducting a stack test. Agency guidance outlines the
procedures for including soot-blowing while stack testing. The frequency with which facilities
perform soot-blowing can vary significantly and the agency guidance addresses this issue by
allowing facilities to weight the soot-blowing data in the performance tests based on the
frequency of the soot-blowing.5 See Memoranda from John S. Seitz to David Kee "Inclusion of
5 Under EPA-approved SIPs, some states may allow soot-blowing emissions to be
excluded as an element of a comprehensive stack test. This approach, however, is not applicable
Page 17
Soot-Blowing Emissions in Subpart D Compliance Testing" (August 31, 1987); from
Kathleen M. Bennett to Directors, Air & Waste Management Divisions "Restatement of
Guidance on Emissions Associated with Soot-Blowing" (May 7, 1982); from Edward E. Reich
to Sandra S. Gardebring "Representative Testing Requirements" (November 21, 1980);
Memoranda from Edward E. Reich to Leslie Carothers "Integration of Soot-Blowing Emissions
with Routine Operating Data for Existing Facilities" (March 12, 1979); from Edward E. Reich
to Enforcement Division Directors, Air and Hazardous Material Division Directors, and
Surveillance and Analysis Division Directors "NSPS Determination - Subpart D"
(March 6, 1979); and Memoranda from Edward E. Reich to Robert L. Markey "Determination
of Applicability to Subpart D" (June 29, 1977).
• The primary issue with respect to observing stack tests to determine and demonstrate
compliance is whether a delegated agency should have an observer present for all stack tests, and
if not, how often should the delegated agency be present to observe the tests.
• There is no requirement that delegated agencies be present to observe all stack tests. However,
whenever possible, trained staff from delegated agencies should observe the tests to ensure that
the regulatory testing requirements are being met; the site-specific test plan is being followed;
and the results are being accurately and completely recorded and documented in the test report.
The observer should have the access necessary to ensure that the test is being conducted properly
and results reported accurately. Furthermore, the observer should be present for the duration of
the test, including all test runs. The presence of an observer helps to reduce the likelihood of
sample recovery and handling errors, as well as equipment errors, and to ensure that testing is
conducted under the proper process conditions. Ultimately, the presence of a state/local observer
reduces the number of retests. Therefore, the test date(s) and approximate start/end time of the
test should be acceptable to both the delegated agency and the facility to allow the delegated
agency an opportunity to observe the test, if desired.
Page 14
• If the delegated agency chooses not to observe the test, prior review of the site-specific test
plan is even more critical to ensure that the test is conducted in such a manner so as to satisfy the
regulatory requirements.
• If the delegated agency was not provided timely notification and an opportunity to observe the
stack test consistent with applicable regulatory requirements, the resulting test data may be
rejected and a new stack test may be required. If this situation prevents the facility from
completing a valid stack test within the requisite time frame, the facility is in violation of the
requirement to conduct a stack test and demonstrate compliance. However, if the facility
provided timely notice and the delegated agency did not respond or declined to observe the test,
the test results should not be rejected solely because the test was not observed by
agency personnel.
5. REPRESENTATIVE TESTING CONDITIONS
• The CAA requires that facilities comply with emissions limitations and emissions standards on
a continuous basis. The Act defines the terms "emissions limitation " and "emission standard "
in Section 302(k), 42 U.S.C. § 7602(k), as meaning "a requirement established by the state or the
Administrator which limits the quantity, rate, or concentration of emissions of air pollutants on a
continuous basis . . . ." (emphasis added). The statute also authorizes penalties for multiple days
of violations and establishes a presumption of continuing violations if certain conditions are met.
CAA Section 113(e)(1) and (2), 42 U.S.C. §§ 7413(e)(1) and (2). EPA has consistently, in
rulemaking and policy statements over many years, taken the position that the CAA requires
continuous compliance with emissions limits except where compliance is explicitly excused.
See, e.g., Guidance entitled "Definition of ‘Continuous Compliance’ and Enforcement of
O&M Violations," (June 24, 1982) ("In the strict legal sense, sources are required to meet,
without interruption, all applicable emissions limitations and other control requirements, unless
such limitations specifically provide otherwise."); Credible Evidence Rulemaking, 62 FR 8314,
8323, 8324, 8326 8314 (Feb. 24, 1997) (emissions limits require continuous compliance
(consistent with any averaging times) except during periods when compliance is
specifically excused).
• Since the CAA requires continuous compliance with emissions limits except where explicitly
excused, EPA interprets applicable regulations to require that any stack test that is conducted
within the scope of this guidance must demonstrate that a facility is capable of complying with
the applicable emissions standards at all times.4 The NSPS and MACT programs require that
performance tests be conducted under such conditions as the Administrator specifies based upon
the representative performance of the affected facility. See 40 CFR §§ 60.8© and 63.7(e). The
MACT program further defines representative performance as normal operating conditions.
43 CFR § 63.7(e). Operations during periods of startup, shutdown and malfunction do not
constitute representative conditions for the purposes of a performance test. 40 CFR §§ 60.8(c)
4 Complying with the applicable standards "at all times " does not include allowable
periods of start-up, shutdown, and malfunction as provided in 40 CFR §§ 60.8 (c) and 63.7(e)(1).
Page 15
and 63.7(e). The Part 61 NESHAP program requires that emission tests be conducted “under
such conditions as the Administrator shall specify "based on design and operational
characteristics of the source." 40 CFR § 61.13(e). Individual standards may more specifically
define operating conditions under which performance tests should be conducted. In the absence
of such specifications, the question often arises as to what operating conditions should be used
when conducting a stack test. If operating conditions are not indicated by the applicable
requirements in individual standards, they should be developed as part of the site-specific
test plan.
• In light of the fact that: (a) the Act requires that facilities continuously comply with emission
limits; (b) the NSPS, MACT, and NESHAP programs all require that performance tests be
conducted under such conditions as the Administrator specifies; and © the NSPS and MACT
programs further require that such tests be conducted under representative operating conditions;
EPA recommends that performance tests be performed under those representative (normal)
conditions that:
-represent the range of combined process and control measure conditions under which
the facility expects to operate (regardless of the frequency of the conditions); and
-are likely to most challenge the emissions control measures of the facility with regard
to meeting the applicable emission standards, but without creating an unsafe condition.
• The following are factors that should be considered in developing the plan for a performance
test that challenges to the fullest extent possible a facility’s ability to meet emissions limits.
-For a facility operating under an emission rate standard (e.g., lb/hr) or concentration
standard (e.g., µg/m3), normal process operating conditions producing the highest
emissions or loading to a control device would generally constitute the most challenging
conditions with regard to the emissions standard. If operating at maximum capacity
would result in the highest levels of emissions, operating at this level would not create an
unsafe condition, and the facility expects to operate at that level at least some of the time,
EPA recommends that the facility should conduct a stack test at maximum capacity or the
allowable/permitted capacity.
-For a facility operating under a control or removal efficiency standard (e.g., 98 percent
control or removal of a specified pollutant), lower emissions loading at the inlet of a
control device within the range of expected process operating conditions may often be
the most challenging emissions control scenario for purposes of achieving the applicable
standard. For facilities required to achieve such control or removal efficiency standards,
EPA recommends that the performance test include operating the facility under such
expected lower emissions loading conditions.
-The test plan should generally include use of fuel, raw materials, and other
Page 16
process/control equipment that the facility expects to use during future operations that
would present the greatest challenge in meeting applicable emissions standards. To
demonstrate the facility’s ability to meet concentration standards and emissions rate
standards, for example, the facility generally should use the fuel or raw materials that it
expects to use and that have the highest emissions potential for the regulated pollutant(s)
being tested. In instances where alternative processing materials are expected to be used
by the facility and those materials are known to adversely impact emissions quality or the
functioning of control measures, the facility generally should use the material that is
likely to cause the greatest challenge in meeting applicable emissions standards. For
concentration and emissions rates standards, the facility generally should process the
material that it expects to use during future operations that is likely to cause the highest
emissions. For control or removal efficiency standards, other factors may apply such as
using fuels or raw materials that contain or produce pollutants that are more difficult to
combust or otherwise remove.
• A facility is not required automatically to retest if the initial test does not represent the range of
combined process and control measure conditions under which the facility expects to operate, or
if the test does not challenge to the fullest extent possible the facility’s ability to meet applicable
emission standards without creating an unsafe condition. Furthermore, the facility is not
required automatically to retest if the facility’s operating conditions subsequently vary from
those in place during the performance test. The delegated agency must determine whether
retesting is warranted; however, in both instances, the facility is responsible for demonstrating to
the satisfaction of the delegated agency that the facility is able to continuously comply with the
emissions limits when operating under expected operating conditions, taking into consideration
the factors discussed above in this section.
• This guidance does not affect the ability of delegated agencies to prohibit a facility from
operating at levels of capacity different from the level used during the stack test, or to restrict
production to reflect conditions equivalent to those present during the stack test.
Soot-Blowing:
• Soot-blowing is the cleaning of heat exchanger surfaces by the use of steam or air to dislodge
accumulated material such as ash. The Agency guidance on this issue states that soot-blowing is
a routine operation constituting representative process conditions. Emissions from soot-blowing
cannot be discarded as being the result of an upset condition, and it would be erroneous to stop
soot-blowing for the purpose of conducting a stack test. Agency guidance outlines the
procedures for including soot-blowing while stack testing. The frequency with which facilities
perform soot-blowing can vary significantly and the agency guidance addresses this issue by
allowing facilities to weight the soot-blowing data in the performance tests based on the
frequency of the soot-blowing.5 See Memoranda from John S. Seitz to David Kee "Inclusion of
5 Under EPA-approved SIPs, some states may allow soot-blowing emissions to be
excluded as an element of a comprehensive stack test. This approach, however, is not applicable
Page 17
Soot-Blowing Emissions in Subpart D Compliance Testing" (August 31, 1987); from
Kathleen M. Bennett to Directors, Air & Waste Management Divisions "Restatement of
Guidance on Emissions Associated with Soot-Blowing" (May 7, 1982); from Edward E. Reich
to Sandra S. Gardebring "Representative Testing Requirements" (November 21, 1980);
Memoranda from Edward E. Reich to Leslie Carothers "Integration of Soot-Blowing Emissions
with Routine Operating Data for Existing Facilities" (March 12, 1979); from Edward E. Reich
to Enforcement Division Directors, Air and Hazardous Material Division Directors, and
Surveillance and Analysis Division Directors "NSPS Determination - Subpart D"
(March 6, 1979); and Memoranda from Edward E. Reich to Robert L. Markey "Determination
of Applicability to Subpart D" (June 29, 1977).
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