Boiler Blowdown — You might catch this surprising plume of steam if you are passing through Hill City in the morning around 8:15. So what is a Blowdown? A certain amount of dissolved impurities are always found in the water utilized in boilers. Under the heat and pressure of boiling these impurities precipitate out as solids which sink to the bottom of the boiler, concentrating in a region referred to as the “mud ring.” If left alone, this sludge-like material would cause increased corrosion and