A sample with the highest calculated BOD, within the same sample group, should be no more than 30% of the sample with the lowest calculated BOD. Group Toxicity, gT, flag will appear if the rule failed.
The 30% variation is referenced from Standard Methods 5210B (23/24th editions), where if the sample group fails this rule, there is potentially a toxic substance/contamination or an analytical issue.
Here is an example:
| Sample Name | BOD |
| BMF | 2.02 |
| BMF | 1.99 |
| BMF | 1.54 |
where the highest value is 2.02, and the lowest value is 1.54.
Taking 30% of 1.54 is 0.462 = 2.00.
Therefore, since the highest BOD value is more than 30% varying than the lowest BOD value, the sample group will be flagged for Group Toxicity, gT.