Under what circumstances may "personal (written or oral) communications" be cited in scholarly publications? [007]

The use of "personal (written or oral) communications" is permitted when referring to auxiliary information that is not essential to ensuring others can replicate the results or evaluate the validity of the data used to support the conclusions of the scholarly publication. It may not refer to USGS-funded data used to support the results and conclusions presented in scholarly publications. These in-text citations must identify the name and affiliation of the personal contact, the type of communication (oral or written), and include a date of communication. If the individual was retired at the time of the personal communication, the author may use affiliation “retired U.S. Geological Survey employee” if desired. If the individual has no professional affiliation, provide location information (city and state or equivalent) of the individual. Refer to FAQ 015 for additional information.