Abstract: At 4:00 p.m. on May 24, 2019, Employee #1, a farmer, entered a 1,500 gallon bulk milk tank to clean it. He was using a paste of cleaning granules and well water. The employee died within 20 minutes of entry into the tank due to the inhalation of excess concentrations of hydrogen sulfide (H2S) that evolved from well water that was contaminated with naturally-occurring hydrogen sulfide. The lack of ventilation in the tank trapped the gas. Lab tests of the vapor space above a sample of the well water showed more than 1,000 ppm H2S versus the allowable 8-hour exposure limit of 10 ppm. The cleaning granules did not play a role in the event.