What is EPA Method 9?

If Method 9 is required in a Title V permit, the person who conducts the visible emission observations (VEO) is typically referred to as the observer. The observer must be trained and currently certified in accordance with the Method — i.e., having attended a hands-on smoke school and passed qualification testing periodically.

Because the Method is a subjective tool, two observers may report different opacity values on the same plume at the same time. If both observers have valid certification, either observation is valid, even in a deposition or in court.

The frequency of Method 9 readings is governed by the air permit or compliance plan for the facility.

A single Method 9 reading requires a total of 24 visible emissions observations taken at 15-second intervals, for a total of six (6) minutes. Those observations are averaged to calculate the opacity value.

Permits may require more than 24 observations — they may specify 12, 18, or 30 minutes, yielding a greater number of observations and requiring custom VEO forms. VEO forms must contain required Method 9 fields but can be customized to fit a facility's requirements.

New Source Performance Testing (NSPT) typically requires three (3) one-hour observations for each source.

Opacity values are expressed as a percent and are calculated using a running average.

All subjective methods have an associated error and Method 9 is no exception. The efficacy of the Method has been proven in field tests. The results of an EPA study involving 769 sets of 25 observations for each type of smoke (black and white) yielded:

• Black plumes: 100% of the sets were estimated with a positive error of less than 7.5% opacity. 99% were estimated with a positive error of less than 5% opacity.
• White plumes: 99% of the sets were estimated with a positive error of less than 7.5% opacity. 95% were estimated with a positive error of less than 5% opacity.

Source: EPA Method 9 Document

Continuous opacity monitors (COMs) are available to track opacity measurements on stacks. This is a complex subject — the following is a broad overview of the issues related to COMs:

COMs are widely used but are prone to drift offsets and downtime. Their reliability results in many facilities owning a backup COM to cover mechanical failures. COMs can be more accurate, but a visible emissions reader is considered more reliable in case law. Additionally, COMs operate on stacks only — operations such as rock crushing, storage piles of material, handling areas, and transfer points require manual methods.

Method 9 allows for a percentage of error. Acceptable error levels were determined by field trials at the time the Method was promulgated. The determination of a pass/fail on a field test run is determined using percentages of error and standard deviations.

To pass a field test run, an observer must achieve a score of 37 deviations or less. One field run consists of 25 black smoke point observations and 25 white smoke point observations. The score is calculated as follows:

• Each point observation can be 15% on either side of the correct opacity level. For example, if a plume with 25% opacity is shown, an observer can answer as low as 10% or as high as 40% and be within the 15% allowance.
• Each point observation is assigned a deviation value:
  • Zero (0) for exact observations.
  • One (1) for observations within 5% accuracy.
  • Two (2) for observations within 10% accuracy.
  • Three (3) for observations within 15% accuracy.
  • If an observation is outside of the 15% accuracy, it is considered a failed observation. One failed observation constitutes a failed run.

At the end of the 50 test point observations (25 white, 25 black), scores are added together. A score of 37 deviations or below is a pass; 38 or above, or one failed observation, is not a pass.

Note: An observer can certify with two contiguous passed runs. For example, if white smoke is failed on Run #1 but black smoke is passed on Run #1, and then white smoke is passed on Run #2 — that equals 50 contiguous observations, and if deviations are within the passing parameters, the observer certifies for Method 9.