Continuous Emission Monitoring. James A. Jahnke
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A specified for the source category (e.g. acid plant, electric utility) (U.S. EPA 2020c).
Section 60.11 incorporates a requirement that has been central to U.S. EPA stationary source regulatory policy. This requirement [§60.11(d)] states:
At all times, including periods of startup, shutdown, and malfunction, owners and operators shall, to the extent practicable, 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. Determination of whether acceptable operating and maintenance procedures are being used will 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.
This policy, formulated in the early 1970s, is reprised in the compliance assurance monitoring and credible evidence rules that resulted from congressional concerns addressed in the 1990 Clean Air Act Amendments (which is discussed below).
Section 60.13 incorporates important requirements for Part 60 CEM systems. This section is sometimes forgotten after a CEM program has been implemented, but nevertheless, contains essential program requirements. Among these requirements are given as follows:
Performance Specification Tests. Part 60 installed systems must show that they meet performance specifications of 40 CFR 60 Appendix B (U.S. EPA 2020d) by conducting a performance specification test (Note: “performance specification tests” are used to certify CEM systems and are not the same as the “performance tests” of §60.8 conducted to determine source compliance with emission limits).
Quality Assurance Requirements. In the absence of other quality assurance requirements, as a minimum; the system must conduct a zero and span drift check once every 24 hours, zero and span adjustments must be made if the drift exceeds twice the value of the drift performance specification of Appendix B, and the zero and span check procedures must be written.
Representativeness. All CEM systems are to be installed such that measurements representative of actual emissions are obtained.
Alternative Performance Test Requirements. An alternative to conducting reference method tests for determining relative accuracy may be requested if the pollutant emissions are less than 50% of the emissions limit (60.13(j)(1)). When applicable, this allows conducting a cylinder gas test (audit) (CGA) instead of a relative accuracy test audit (RATA).
NESHAP, 40 CFR 61
The National Emission Standards for Hazardous Air Pollutants (NESHAP), formerly legislated under Section 112 of the Clean Air Act, require continuous monitoring for a limited number of sources covered under Part 61 of Title 40. As in Part 60, general monitoring instructions regarding notification, recordkeeping, etc. are given in the “general provisions” prior to the source requirements. Few pollutants were regulated under the NESHAP program due to uncertainties associated with risk assessments and scheduling mandates (Mohin 1992). Source categories affected by this subpart and monitoring requirements are discussed further in Chapter 13 on monitoring hazardous air pollutants.
The Air Toxics Program, 40 CFR 63
Title III of the 1990 Clean Air Amendments replaced the previous NESHAP program. Title III identified 189 hazardous air pollutants (HAPs) (later reduced to 187), to be regulated for sources emitting more than 10 tons/year of any one listed pollutant or 25 tons/year of a combination of listed pollutants. EPA has promulgated emission limits and engineering standards for the principal sources emitting HAPS (or “air toxics”). The sources must apply “maximum achievable control technology,” where MACT technology is the best control achieved in practice by 12% of the best controlled similar sources. However, MACT encourages process changes or other pollution prevention activities rather than the application of control equipment.
The air toxics, or “MACT standards,” also incorporate monitoring requirements to determine, on a continuous basis, whether emission limits are being met. Most MACT standards require parameter monitoring, in other words a “continuous parameter monitoring system (CPMS)” that is described in a “monitoring plan,” rather than the installation of CEM systems. However, where control devices are used that can be effectively monitored, such as carbon adsorbers and incinerators, CEM systems are either required or suggested as an alternative to parameter monitoring. The Part 63 Subparts give the emissions standards and monitoring requirements for HAPs emitted from 174 listed industries. Rather than requiring the monitoring of specific pollutants from the list of 187 HAPs, the use of surrogate analyzers is often allowed (such as a particulate monitor to monitor metal emissions or a total hydrocarbon monitor rather than a speciating instrument). Sources required to monitor HAPs and methods used to measure them are discussed further in Chapter 13.
Compliance Assurance Monitoring (CAM) 40 CFR 64
The compliance assurance monitoring program (CAM) was initiated from a congressional requirement included in the 1990 Clean Air Act Amendments (§702 (b) of the amendments). This amendment to Section 114 of the Clean Air Act states:
The Administrator shall in the case of any person which is the owner or operator of a major stationary source, and may in the case of any other person, require enhanced monitoring and submission of compliance certifications. Compliance certifications shall include (A) identification of the applicable requirement that is the basis of the certification, (B) the method used for determining the compliance status of the source, (C) the compliance status of the source, (D) whether compliance is continuous or intermittent, (E) other such facts as the administrator may require.
The amendment addressed the concern of Congress that the compliance status of most emission sources was determined only periodically by conducting manual stack tests. It was viewed that since source operations may be highly tuned during such testing, operations may not necessarily be representative of day‐to‐day performance. Congress gave EPA the task to devise a strategy that can assure Congress (and the public) that emissions standards and limitations are being met continually, not just intermittently.
The Compliance Assurance Monitoring (CAM) rule was developed as a response to the requirement that essentially places the burden back upon the source. The CAM rule applies to sources required to obtain a Part 70 or 71 air permit and having emission units with active control devices, whose potential pre‐control device emissions are at or above the emission thresholds that define a “major” source (such as 100 tons per year). Affected sources are to develop a “CAM Plan” that will provide assurance to the agency that they are meeting their emissions limitations (Neulicht et al. 1996). The CAM plan provides for the recording of work practice procedures, equipment monitoring, and inspection procedures related to pollution control compliance. CEM systems that measure pollutant emissions directly or by parameter monitoring techniques that provide indirect determinations may also be used. A guidance document on how to write a plan has been prepared by the U.S. EPA (OAQPS 1998).
Methods incorporated into the plan are to specify indicator ranges, within which the emission source is assumed to be in compliance. The range may be simply a range of pollutant concentration, or a range of pressure drops, temperatures, voltage settings, fuel flow, gas flows, and so on. Exceeding the range then triggers a requirement for initiating corrective action.
The CAM program emphasizes the use of plant sensors and parameter monitoring techniques to avoid the installation of CEM systems. This was due to public comment on an earlier “enhanced monitoring” rule intended to meet the requirements of §702 (b) of the 1990 CAA amendments. This earlier rule, viewed as a “CEM rule,” was withdrawn, due in part to outcry over assumed CEM system costs. However, the costs associated with developing CAM plans, modifying plans when plant operations change, and