Since SLWSD was formed in 1996, managing icy conditions and maintaining water quality in their only tank, a 300,000 gallon pedosphere, has been a concern (Figure 1). “This tank is at the end of our system,” explained Foster White, Operation/Manager of SLWSD. “While we have only 220 active meter services, we have nearly 230,000 gallons in volume in our pipes to provide for fire flow as well as regular consumption. It can take up to a week for water to make it through our system and into the tank, and this makes managing water quality inside the tank a challenge.”
In winter, icing issues inside the tank were severe. “We often see daytime temperatures no higher than 10 to 20 degrees Fahrenheit and nights well below zero for an entire month,” noted White. “We would commonly find a girdle of ice 4 - 6 inches thick and 2 - 3 feet wide where the water level around the outer tank wall fluctuated.” The ladder access tube passes through the center of the tank and a “pineapple ring” of ice 4 - 6 inches thick would form around the access tube and float up and down with the tank level. The scraping action of this ice ring scoured the paint, requiring repairs every time a tank inspection was done by divers. The damage was increasing to the point, that in a few years, the tank would have to be taken off line, drained, sand blasted and repainted. A repair of that magnitude would require the tank to be out of service for 3 - 4 weeks and would create a severe problem for a system with only one tank.