Environmental Stack Testing Providers

The buyer problem

A facility operating under a Title V, NSPS, or NESHAP air permit is typically required to periodically prove, through direct measurement, that a specific stack or vent stays under its permitted emission limit. That proof has to come from an outside firm running one or more EPA reference test methods, using calibrated equipment and a field crew with documented competence, on a schedule the facility usually cannot move once it is set with the permitting agency. Most EHS managers and plant engineers do not have the background to tell a properly accredited, adequately staffed stack testing firm from one that is under-resourced or working outside its real capability. Hiring the wrong vendor can produce a voided test run, a report the agency sends back for revision, or a missed compliance deadline, and a retest adds cost and schedule risk on top of what was already budgeted.

What a environmental stack testing providers vendor does

An environmental stack testing provider, also called a source testing or emissions testing firm, sends a field crew to measure pollutant concentration and stack gas flow at a specific stack, duct, or vent using standardized EPA reference methods. A typical engagement includes drafting a pre-test protocol and submitting it to the permitting agency for review, running multiple timed test runs on-site with calibrated sampling trains and analyzers, recovering samples and shipping some of them, such as metals or halogen samples, to an outside laboratory for analysis, and delivering a final report stating whether the source met its permitted emission limit. Some firms also perform periodic relative accuracy testing on continuous emissions monitoring systems (CEMS), a related but separate service from one-time source testing.

Methods and techniques

• EPA Method 1: Sample and velocity traverse point selection for stationary sources
• EPA Method 2: Stack gas velocity and volumetric flow rate via Type S pitot tube
• EPA Method 3: Gas analysis for CO2, O2, excess air, and dry molecular weight
• EPA Method 4: Determination of moisture content in stack gas
• EPA Method 5: Determination of particulate matter (PM) emissions from stationary sources
• EPA Method 6/6C: Determination of sulfur dioxide (SO2) emissions
• EPA Method 7/7E: Determination of nitrogen oxides (NOx) emissions
• EPA Method 9: Visual determination of the opacity of stack emissions
• EPA Method 10: Determination of carbon monoxide (CO) emissions
• EPA Method 18: Measurement of gaseous organic compound emissions by gas chromatography
• EPA Method 22: Visual determination of fugitive emissions and smoke from flares
• EPA Method 25A: Total gaseous organic concentration using a flame ionization analyzer
• EPA Method 26/26A: Determination of hydrogen halide and halogen emissions
• EPA Method 29: Determination of metals emissions from stationary sources (multi-metals train)
• EPA Method 301: Field validation protocol for proposing an alternative pollutant measurement method

What to verify before you retain

• Current basis of AETB accreditation. ASTM D7036 (Standard Practice for Competence of Air Emission Testing Bodies) was withdrawn by ASTM in 2025. As of this writing, A2LA's Air Emission Testing Body (AETB) accreditation program still lists D7036 as one of three possible bases for accreditation, alongside ISO/IEC 17025 and TNI's Field Sampling and Measurement Organization (FSMO) Volume 1 standard. Ask the vendor directly which document their current accreditation is issued against, and confirm it with the accrediting body rather than taking a website badge at face value.
• Accreditation certificate and scope. Request the firm's actual AETB accreditation certificate and scope of accreditation from A2LA or the Stack Testing Accreditation Council (STAC), and confirm the scope covers the specific pollutants and methods your permit requires, not a general claim of being accredited.
• Individual crew certification. Ask which field team members assigned to your test hold Source Evaluation Society (SES) QSTI (Qualified Source Testing Individual) certification, and in which exam group: isokinetic/particulate, manual gaseous, instrumental gaseous, or metals. A firm can be accredited at the organizational level while still assigning an uncertified technician to a given job.
• Analytical laboratory accreditation. For methods that require off-site analysis, such as Method 29 for metals or Method 26/26A for halogens, ask which laboratory processes the samples and what accreditation that lab holds for the specific analytes being tested.
• Calibration records for sampling equipment. Request current calibration documentation for the pitot tubes, thermocouples, dry gas meters, and analyzers that will be used on your test, traceable to the calibration procedure specified in the relevant method.
• Pre-test protocol and agency coordination history. Ask for a redacted example of a pre-test protocol the firm has submitted to a state or local air permitting agency, and how they typically handle agency comments or requested changes before the scheduled test date.

Questions to put in your RFP

1. What accreditation does your firm currently hold as an Air Emission Testing Body, which accrediting body issued it (A2LA, STAC, or other), and against which standard or program document?
2. Which staff members will be assigned to our project, and which of them hold current SES QSTI or QSTO certification, and in which method group?
3. Can you provide a redacted copy of a pre-test protocol you submitted to a state or local air agency for a comparable source and pollutant set?
4. Which laboratory will analyze samples requiring off-site analysis, such as metals or halogens, and what accreditation does that lab hold?
5. What is your standard turnaround time from the last day of testing to delivery of the draft report, and to the final agency-ready report?
6. How do you handle a voided or invalid test run during our test event, including any change in cost or schedule?
7. What calibration standards and frequency do you use for pitot tubes, thermocouples, dry gas meters, and gas analyzers on this project?
8. Can you share results from your firm's most recent performance or systems audit under your quality program?
9. What does your final data package include, such as raw field data sheets, chain-of-custody records, and calibration records, and is it formatted for direct submission to our permitting agency?
10. What professional liability or errors-and-omissions insurance coverage does your firm carry?

Red flags

• Cannot produce an actual AETB accreditation certificate and scope of accreditation, only a general claim of being accredited or a website badge.
• No SES QSTI-certified staff proposed for the method group your test requires.
• Reluctant or unable to describe a process for submitting a pre-test protocol to your permitting agency in advance.
• Vague or shifting answers about which laboratory performs off-site analysis for metals or halogen samples.
• A bid significantly below competing quotes with no explanation, which can indicate an undersized crew, skipped calibration or audit steps, or reliance on uncertified staff.
• No documented, traceable calibration records available for sampling equipment upon request.
• No clear answer on how a voided test run is handled, financially or logistically, before you sign a contract.

Standards and governing bodies

Bodies referenced in this category. Listed for context; they do not endorse this index or any provider. Verify any credential directly with the issuing body.

EPA

U.S. Environmental Protection Agency. Develops and maintains the numbered reference test methods (Methods 1 through 29, published in 40 CFR Part 60 Appendix A) that state and local agencies cite in air permits; method upkeep is handled by EPA's Emission Measurement Center (EMC).

ASTM

ASTM International. Published D7036, the standard practice defining quality-management and competency requirements for Air Emission Testing Bodies (AETBs). ASTM withdrew D7036 in 2025; confirm with any vendor and accreditor how AETB competence is currently being assessed.

STAC

Stack Testing Accreditation Council. The industry council that oversees AETB accreditation criteria and has partnered with A2LA (since a 2014 MOU) to conduct assessments; ask for a current accreditation certificate rather than a general reference to STAC.

A2LA

American Association for Laboratory Accreditation. Accredits testing organizations to ISO/IEC 17025 and administers the AETB accreditation program under its 2014 MOU with STAC; assessors conducting AETB assessments must themselves hold SES QSTI or QSTO credentials. Its current program lists ISO/IEC 17025, TNI's FSMO Volume 1 standard, and ASTM D7036 as alternative or combinable bases for accreditation.

TNI

The NELAC Institute. Publishes the Field Sampling and Measurement Organization (FSMO) Volume 1 standard, one of the documents A2LA accepts as a basis for AETB accreditation.

SES

Source Evaluation Society. Administers the QSTI/QSTO (Qualified Source Testing Individual / Qualified Source Testing Observer) certification exams that credential individual field test team leaders and observers by method group, separate from firm-level accreditation.