40 CFR § 761.274 - Reporting PCB concentrations in samples.
(a) Report all sample concentrations for non-liquid PCBs on a dry weight basis as micrograms of PCBs per gram of sample (ppm by weight). Report surface sampling results as µg/100 cm 2. Divide 100 cm 2 by the surface area and multiply this quotient by the total number of micrograms of PCBs on the surface to obtain the equivalent measurement of micrograms per 100 cm 2.
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