It can be found on a table near the locked blue double doors at Kerwood mine.
Squire Schultz: Scouting report. Brotherhood Squire Schultz. Kerwood Mine is almost completed flooded. Going down into that brine without Power Armor or a stronger set of lungs seems suicidal. It's too bad. My recon instincts are telling me there could be something good down there. Maybe a way into that locked room.