Alternative test method approval or variation to a Federal Reference Method (FRM) has always been on a “case-by-case” bases. At the discretion of the Administrator, the following allowable alternatives can be made:
- Approve minor changes to the reference test methods;
- Approve an equivalent method;
- Approve an alternative method which has been demonstrated adequate for determining compliance at a specific source; and
- Waive the requirements for performance testing.
The Administrator is a Regional EPA official or officials of other agencies, such as regional, state, and local personnel.
In general, for an alternative method to be accepted, it must:
- Be applicable and properly executed;
- Include a detailed, written description of option in test report; and
- Provide supporting data and rationale to show validity of option in the specified application.
In considering an alternative to a Federal Reference Method, Agency criteria for evaluating minor modifications should determine that:
- Effect (or changes to the methodology) will be insignificant on final emission data results;
- Changes will accommodate a situation that is considered unique and would apply only to sample site for which it is allowed;
- All allowable alternative procedures in reference method will provide emission results of equal or greater value than standard procedures (Bias Concept); and
- Agency can use same bias concept technique when evaluating alternative methods.
With reference to the question, the source would have to provide the needed information to show that the two sampling ports are equivalent and that a negative bias does not exist at the lower port. In essence, the source should complete the Alternative Method Approval Request, found at the back of your Student Workbook. This form contains four major sections: 1. Requesting Organization; 2. Specific Application of the Alternative Method; 3. Description of the Alternative Method; and 4.Support Data.
As part of this request, the source would provide data (to support the selection of the lower port) showing that cyclonic flow does not exist at the lower port, both velocity profiles are representative of the source emissions and do not vary within 10 % of each other, and if a gas test method is being performed, the concentration profiles for O2 (or CO2) are within 10 % of each other as determined by a portable O2/CO2 continuous emission monitoring (CEM) system.
The source would provide this support data as Part 4 of the Alternative Method Approval Request.