We are a young student science group looking for solutions to real world problems. We are currently working on ways to keep our city water mains from freezing in the winter. Our team is researching adding propylene glycol to the city water supply in the winter when the weather forecast is really cold and could freeze older water mains (approximately -20 degrees F). Our older water mains are not deep enough to provide adequate protection against freezing and it is too costly to replace them all.
How much and what kind of food grade propylene glycol we need to add per gallon to keep the mains from freezing (or how to calculate it)? The city uses about 10,000 gallons of water per day.
When would we need to add it to keep the mains from freezing? We don't want to add it to the water if it's not needed.
How easy it is to dissolve and will it stay dissolved for at least 24 hours?
Will it interact with what the city already adds to the water supply, chlorine, polyphosphate and fluoride?