Monitoring Requirements

Under the Act and in concert with the operating permit program, the EPA has the authority to require expensive enhanced monitoring for determining compliance with the permit conditions. Enhanced monitoring may include continuous emissions monitoring systems (CEMS) or continuous emissions rate monitoring systems (CERMS) instead of periodic stack tests or simple emissions calculations, which has often been sufficient for compliance monitoring to date. CEM systems use techniques such as infrared or chemiluminescent analysis to measure emissions of NOX, SO2, CO, CO2, particu-lates, and other regulated air pollutants.

Figure 16-7 is a representative example of the basic CEM process using dry extraction. As outlined in the exhibit, a sample probe is used to draw out stack gases on a continuous basis (except for short purge cycles) and filter out particulate material. The sample is pumped from the probe to the rest of the CEM via the sample transport line. The sample gas is hot and wet, and thus contains a certain amount of water vapor.

So that condensation does not occur in the sample transport line, the line is heated along its whole length so that the sample gas may be delivered unchanged to sample conditioning. In sample conditioning, the sample is chilled, condensing out the moisture. The now dry gas sample is filtered again and passed through a manifold to the appropriate device for sample analysis.

The concentration of the substance of interest (e.g., NOX, CO, etc.) in the gas sample is measured and sent in the form of an analog electric signal for data conditioning. The analog signals from the analyzers are translated into a form acceptable for computer communication (e.g., the RS-232 serial communications protocol) and sent to the central computer for data management. The information received from the data conditioner is converted to the appropriate units, validated, and reported in the required format.

CEMS may not be required if alternative methods are available that provide sufficiently reliable and timely information for determining compliance. This has been

Basic CEM Process (Dry Extractive)

Basic CEM Process (Dry Extractive)

Fig. 16-7 Basic CEM Process (Dry Extractive).

an area of debate in evolving regulations. The high cost of CEMS can have significant detrimental effects on project economics for small and intermediate sized systems. A lower cost alternative to CEMS is the use of predictive (or parametric) emissions monitoring (PEM) systems. These use predictive rather than actual-measured emissions monitoring based on combustion, scientific computer modeling, and confirmation by actual tests.

Compliance Schedule

As part of the permit application, applicants need to include a schedule of compliance. As part of that schedule, the facility will need to report, to the permitting agency every 6 months, its progress in meeting the conditions contained in the permit.

Under the CAAA, although this part of the operating program has created some controversy, an approved operating permit program must provide for certain changes within a permitted facility without requiring a permit revision. The changes may not be modifications under the ozone nonattainment requirements of the Act and they may not exceed the total emissions or emissions rates allowable under the permit. The facility must provide EPA and the permitting agency with written notification at least 7 days before the change, or a shorter time for emergencies.

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