Compliance Stack Testing and Audit Sample Requirements

Audit Samples for Compliance TestingOn June 16th of 2013, the EPA moved forward with one phase of their Stationary Source Audit Sample Program. The program will require audit samples to be required for specific source tests, if those tests are to be used for the demonstration of compliance with emission limits or federal standards.

An audit sample, the composition of which is unknown to the Stationary Source Tester and Laboratory, is used during a particular test event to evaluate whether the Stationary Source Tester and/or Analytical Laboratory can produce measurement results within specified acceptance criteria. Audit samples are not analyzed on a regular schedule; rather, they are analyzed only during the particular event (e.g., a compliance test) that is being audited. Audit samples are analyzed, or collected and analyzed, as part of the batch of field test samples using the same personnel, procedures, and materials.

At this time, audits are only available for particular pollutants by EPA Methods. The list of current available/required audits is provided in the table below. Other methods that will have audits, but are still unavailable and thus not required, are:

  • Dioxins/Furans by Method 23
  • Non Methane Organic Compounds by Method 25
  • Methylene Chloride by Method 315

The EPA restructured program requires that two accredited providers be available, and audit samples must be available and listed on the provider website for 60 days before audits are required to be utilized with compliance tests.

Table – Currently Required Audit Samples for Compliance Testing


EPA Method

NELAC Analyte Code

Inorganics in Impinger Solution

Sulfur Dioxide (SO2)

Methods 6 and 8


Sulfuric Acid Mist (H2SO4)

Method 8


Oxides of Nitrogen (NOx)

Method 7


Fluoride (F)

Methods 13a, 13b


Hydrogen Chloride (HCl)

Methods 26, 26a


Hydrogen Fluoride (HF)

Methods 26, 26a


Metals on Glass/Quartz Fiber Filters and in Impinger Solution

Antimony (Sb)

EPA Method 29


Arsenic (As)

EPA Method 29


Barium (Ba)

EPA Method 29


Beryllium (Be)

EPA Method 29


Cadmium (Cd)

EPA Method 29


Chromium (Cr)

EPA Method 29


Cobalt (Co)

EPA Method 29


Copper (Cu)

EPA Method 29


Lead (Pb)

EPA Method 29


Manganese (Mn)

EPA Method 29


Nickel (Ni)

EPA Method 29


Selenium (Se)

EPA Method 29


Silver (Ag)

EPA Method 29


Thallium (Tl)

EPA Method 29


Zinc (Zn)

EPA Method 29


Mercury (Hg)

EPA Method 29


Lead (Alt. Method)

EPA Method 12



Note that in the case of the criteria gases NOx and SO2, compliance audits are only necessary for the wet chemistry methods 6, 7, and 8. Testing utilizing continuous emissions monitors (CEMS) by Methods 7e and 6c do not require audit samples.

Audit samples add a variable cost to the sampling activities, depending on how many samples under what methods are required, and take 4 – 6 weeks to prepare. It is advised to begin preparations as much as two months before doing any required testing, in the same period of time that test plans or test protocols are drafted and submitted to state or federal regulators.

An audit sample has to be prepared specific to the source being tested. In order to prepare the audit, the preparatory lab would need the following information for the source.

  • Analyte/pollutant being measured.
  • Emission limit (lb/hr)
  • Estimated in-stack gas concentration (mg/dscm)
  • Stack flow rate (dscfm)
  • The sampling rate (m3/hr)
  • Length of the sampling run (hr)

The audit sample must be present on-site during the conduct of the compliance test, and the sample must be included and analyzed by the analytical laboratory in the same batch and the same manner as the samples collected from the actual compliance testing. Failure to provide for those factors may delay regulatory acceptance of the compliance test, or cause the test report to be rejected.

In all compliance testing, an experienced partner is crucial to ensuring results acceptable to the regulators. A qualified stack testing firm such as ESS can include the organization, procurement, and analysis of audit samples in the scope of the testing project, leading to less headaches, and a compliance test for your facility that is accurate and follows all necessary protocols and procedures.

Environmental Source Samplers, Inc. (ESS) was founded in 1979 and has been conducting point source, ambient and industrial hygiene air quality testing and consulting. ESS utilizes modern and consistently maintained equipment to conduct its testing services world-wide. They are qualified to conduct a wide range of air testing methodologies in almost any environment – and for almost any industry. ESS clients have easy access to the reliable and accurate reporting of test results through a secure online client portal. accessible at their main website,

If you have a compliance demonstration required for your facility, give ESS a call today: 910-799-1055.

For more information about the EPA required audit samples for source tests, visit the NELAC Stationary Source Audit Sample Program site at the following link:


Brian Mellor About Brian Mellor

Brian Mellor works with Environmental Source Samplers, Inc. (ESS), an environmental consulting firm specializing in stack testing, CEMS Testing, and EPA air emissions compliance.

ESS has conducted international stack testing projects at Johnson Atoll, in the Philippines, the Dominican Republic, Hong Kong, and various parts of Europe. If you need a team that will do your international job with efficiency and effectiveness, call ESS at (910) 799-1055 or visit