Located in north-central Montana, the City of Havre is located in a geography that sees summer temperatures over 100oF (38oC) and winter temperatures that can plunge as low as -40oF (-40oC) accompanied by sustained arctic winds of over 20 mph. These dramatic swings in temperature can wreak havoc on disinfectant levels in the summer by creating a “stratified” tank environment conducive to pathogen growth and allow for ice formation in the tank during the winter. Ice formation can lead to tank coating and appurtenance damage as large chunks of ice can suddenly drop from a higher tank elevation and create catastrophic tank damage.
Normally, above ground water storage tanks tend to have their water collect in layers of similar temperature. This phenomenon can be experienced in swimming pools during the summer which often exhibit this “stratification”. Cooler water is experienced at the bottom of a summer pool and warmer water collects near the surface due to inherent density differences between warm and cool water. In the summer, warm water layers near the top of a water tank have the least amount of chlorine disinfectant which can promote the growth of “bio-film” often observed in rings near the top of a tank. Conversely, cool water layers at the bottom of the tank have adequate chlorine concentrations. Trouble in the form of taste and odor complaints or even Bac-T or coliform “hits” can occur when a tank is pumped down and layers of water with low chlorine concentration hit the downstream distribution network.