The note is located on a table in a lab in the Enclave research facility, in the room just past cell block B. Although the note is about mole miners, it is in a room containing tubes that hold mirelurks.
I almost pity this one. The scouts recovered 2 of them from Welch. We suspect they were once the residents.
They do appear to have a moderate amount of intelligence. However, upon the removal of the respiration device on one subject it suffocated almost instantly.
Further study may be worth while.