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Learning that your site will undergo a 40 CFR75 (aka Part 75) field audit can be a very challenging experience for any system owner. If you or your plant management receive a field audit notification (via phone call, e-mail, vicious rumor, etc.), then it is time to locate your records and get prepared for --- (drum roll) --- the field auditor.

Although the likelihood of a Part 75 field audit is unpredictable, the protocol should not be. The EPA published the Part 75 CEMS Field Audit Manual and its companion Part 75 CEMS Field Audit Manual: Appendix A - Example Audit Forms and Guide Sheets in July 2003. The original manual and companion guide offer a record-keeping road map designed to assist you in Part 75 audit preparation, audit readiness, and (most importantly) audit survival. While the original publication still refers to some antiquated electronic programs, such as CAMD's Monitoring Data Checking (MDC), it is still a decent reference guide that provides you with an overview and approximation of the auditor's expectations upon arrival.

Audit Preparation

It is important to remember that Part 75 audits are about not only your quarterly and annual emissions reporting, but also the maintenance of your CEMS equipment. At a minimum, you should be able to provide the documentation listed below, covering the scope of the previous five years.

  1. Copies of Air Permits - Title V, Title IV, and State-issued
  2. Current Part 75 Certificate of Representation
  3. Most recent analyzer span evaluations
  4. Four quarters of quarterly emissions summary data
  5. Hard or soft copies of the CEMS QA/QC manuals
  6. Opacity Standards for your site, if applicable (NOTE: CEMS can also include COMS documentation, where an opacity monitor is identified within your monitoring plan.)
  7. Hard copies of the current ECMPS monitoring plans for each affected uni
  8. Hard copies of ECMPS quarterly (re)certification event records for the previous four quarter
  9. Hard copies of ECMPS quarterly (re)certification test records for the previous four quarter
  10. Hard copies of the most recent relative accuracy tests (RATA) for all stack pollutants, stack flow, and mercury, where applicable. (Optionally, it never hurts to include copies of the reference gas certificates of analysis from the gas supplier for all linearity and RATA testing.)
  11. Hard copies of any Part 75 fuel system (flowmeter, primary element inspection, and transmitter/transducer), recertification testing under Appendix D submitted within the previous four quarters, if applicabl
  12. Any previous Part 75 audit findings and dates of resolutions, if applicable
    Any pre-audit phone interviews with an auditor may include the above list, plus other suitably related materials.

Day of the Audit (Bring coffee, doughnuts, and a warm handshake)

More than likely, your auditor will be prepared to receive and begin a comprehensive review of this information upon arrival. You (and any associated CEMS personnel) should be prepared to participate in audit interviews, conduct a site tour of your facility, and identify CEMS equipment in relation to the monitoring plan and recertification test/event records. Everyone should be prepared to provide answers to diverse technical and regulatory questions regarding standard work on all operations, maintenance, calibration, and recertification of the CEMS equipment from “the stack to the shack,” meaning that the auditor may ask you questions about the stack probe, sample line, equipment rack, or the CEMS reports.

Your auditor will most likely want to review the CEMS shelter maintenance log to ensure that any periodic maintenance and recertification activities (those that occur daily, weekly, monthly, quarterly, and annually) are identified and performed in accordance with the Part 75-mandated QA/QC plan, which outlines any preventive and corrective maintenance action plans for the system's equipment.

Additional questions regarding the content of your quarterly emissions, quality assurance reports, and unit monitoring plans are to be expected as a measure of your site's CEMS program knowledge and record-keeping ability. Don't panic-just answer these questions to the best of your ability.

Post Audit

Much of the time, a full CEMS audit takes about a day per unit onsite. Audits may last longer than one day due to a lack of information, lack of available personnel, or audit findings that merit additional investigation. Audits can be quick or slow, depending upon the auditor and any discoveries that occur during this time.

The post-audit review will occur either at the end of the site visit or at a later date. The end of the audit is meant to be informal, allowing you and the auditor to discuss any new findings or any progress on previous audits. Regardless, all past or present findings require evidence to support them. Be prepared to discuss these findings and the evidence, if possible. You can dispute a finding by your auditor, but you will need an opportunity to provide alternate information as part of your response. It is common for an audit to require further investigation if major issues are encountered. If this happens post-audit, you and your auditor have the option to table the discussion until a future date.


The audit process is meant to be comprehensive, but it's not a witch hunt. The protocols described here are examples of what can occur, not necessarily what will occur. Any Part 75 CEMS audit is meant to examine your site's ability to perform within the regulatory requirements of federal law. Having a well-trained staff, good record-keeping skills, and an effective QA/QC plan for your equipment and testing can greatly reduce your chances of adverse audit findings.

Trinity Consultants helps many organizations with EHS auditing, and many other environmental efforts. For assistance, please contact Trinity at (800) 229-6655 or complete the Contact Us form on our website.