In addition to the usual quality control measures, soil and dust audit samples were introduced into each laboratory's sample input system such that the persons doing sample preparation or analytical determinations were unaware that the samples were for quality assessment. The samples were introduced as unknowns along with other USLADP project soil and dust samples with their identification known only to the laboratory quality assurance officer.

Acceptance of lead analysis data for individual groups of samples, without qualification, was based partially on whether the values for lead in the double-blind audit samples were within value limits calculated from the statistical treatment of multi-laboratory test data.