Senior Airman Leah Erlandson demonstrates a positive and negative bacteria water samples at Joint Base Charleston - Air Base April 16. Bioenvironmental engineers perform health risk assessments for everyone on base to keep them safe from whatever exposures their job may present. Airman Erlandson is a 628th Aerospace Medicine Squadron bioenvironmental engineering technician. (U.S. Air Force photo by Airman 1st Class George Goslin/Released)