In general, unless otherwise specified in a rule/regulation or otherwise approved by BTS, the following practice should be employed when reporting stack test results that include non-detect (ND) fractions and/or ND blanks.

-  ND blanks should be counted as zero.  One should never subtract a ND blank.

-  If all sample fractions are ND, the detection limit should be used for each fraction and the result reported as a “less than” value.

-  If one or more sample fractions are ND but not all fractions are ND, the ND fractions should be counted as zero UNLESS by including the ND fraction(s) a compliant result would become a non-compliant result.  In the latter case, the results should be reported as a range, with the first result counting the ND fractions as zero and the second result using the detection limit for each ND fraction.

Should you feel that a deviation from this reporting practice is warranted for your particular test, you should contact BTS to discuss the case-by-case circumstances.