Tracer dye is added to Illuminating Paraffin to enable its detection once it is mixed into diesel. The presence of the tracer dye can only be detected through laboratory testing or specialized mobile equipment. The Department collects fuel samples randomly at service stations to test for the presence of the tracer dye, amongst others.
It is precisely this random testing that led to the detection of adulteration when the presence of the tracer dye was detected at the laboratory.