04-07-26 City Council Meeting Packet

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Name:City Watermain Standards – DIP versus CIP Date:March 31, 2026 Page:3 Document5 6. Corrosion Resistance PVC has an advantage in this category as it is a non-corrosive material. However, while DIP is coated to prevent the effects of corrosion, in Lake Elmo it is installed with polyethylene wrapping for added protection against effects from corrosive soils. In the majority of past projects in Lake Elmo where watermain was installed, corrosive soils have not been present. 7. Cold Weather Performance During stretches of extreme cold weather in Minnesota watermain can freeze, this has happened in Lake Elmo and residents have experienced interruptions in water service. Thawing a frozen DIP watermain is more forgiving than PVC because the pipe material is metallic, thermally conductive and more heat tolerant. For thawing DIP, electric current is introduced to the pipe by clamping an electrode to a hydrant. Electric current flows through the pipe generating heat and the ice melts from the inside out. For thawing PVC, warm water is injected into the main through a hydrant and circulated through the system to melt the ice. The method of warm water injection is riskier as it is difficult to control temperatures during injection, if the water is introduced at too high of a temperature the PVC can experience thermal shock which causes pipe rupture. Injecting water also poses potential for contamination and proper flushing and disinfection must be completed if this method is used. Recommendation While PVC pipe may be less expensive now, when considering changing from a DIP system to PVC it is not just a material switch, it is an operational and risk-management shift. The factors for operating and managing the city’s water distribution safely and effectively need to be considered above others. Based on this information it is staff’s recommendation that DIP remain the City Standard for watermain pipe.