The lead is within bounds of the WP:LEAD in terms of number of paragraphs, but I'd prefer if there were a bit more information in there. For instance, it might be useful to readers to state when the preparations started, name a couple of prominent related officers, and somehow indicate scale of the operation. The latter might be achieved by indicating how many film packets and Geiger counters were deployed/ready for deployment or in some similar way. I find these to be particularly useful since there is no infobox designed for this type of article which could cover any omissions made in the lead in respect of providing quick information for readers. Still, nothing elaborate is needed regarding this.
Is there any information offered by the sources on how the Manhattan Project used the materials provided from the Operation Peppermint? If so, a sentence or two would be good to have (possible procedures developed or discarded, simply stored, disposed of or whatever else).