Thanks all. Redpicker: I was thinking the same thing about re-checking the results. We weren't thrilled with the method but weren't sure what else to do on a time crunch bearing in mind we couldn't do any destructive sample-taking.
Thanks for the quick responses. We'll do the same non-contact test (I'm not sure what process it is, we brought in a third-party steel mill's equipment to check this). While I'm not certain what the lead contamination threshold needed to satisfy the customer is, I can say it is lower than it is...
I have a large steel structure (the surface of concern is ASTM A572) that has been tempered in an oven at ~1200 deg F. Accidentally, a considerable amount of lead was left on the surface before the heat treatment. The lead subsequently melted and contaminated the surface of the steel...