Under what condition is it acceptable to use low point drains on a main line?

• A. When Freeze Depth Is No More Than 3 Ft
• B. In Arid Regions Only
• C. When Depth of Freeze Is 3-6 Ft
• D. When Freeze Depth Is Less Than One Foot

Answer: (D)

Low point drains on a mainline are meant to purge water from the line so it won’t freeze when temperatures drop. This works reliably only when the soil frost depth is very shallow. If the freeze depth is less than one foot, draining at the low point will remove the water from the line before it can freeze, keeping the mainline protected. When frost penetrates deeper—such as depths around 3 feet or more—the water remaining in the buried portions of the mainline can freeze despite a drain, so a single shallow drain isn’t sufficient and additional frost protection is needed. Arid regions or other depths don’t change this fundamental requirement about frost depth and drainage effectiveness.