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. . . Memorandum March 14,2005 Page 5 Philosophv of Svstem Maintenance and Capital Improvements Our general philosophy has been to ensure that the high priority infrastructure is inspected and improved as necessary. The north water tower and booster station have been rehabilitated recently and we are planning to inspect the sonlh water tower in 2005. We have begun a systematic replacement of valves and hydrants in neighborhoods in conjunction with PMP projects as well as replacement of distribution pipe when physical condition from observations warrant (e.g. Edgewater neighborhood). The useful lifespan of distribution and trunk watennain pipe varies based upon its material, the surrounding soils and the construction methods used to install it. Ductile iron pipe and plastic pipe last longer than cast iron pipe however there are miles of cast iron pipe throughout the metro area which are over 70 years old and stjll serviceable. Most of the pipe in Arden Hills is Ductile Iron or plastic and ranges from I year to approximately 45 years old. A small amount of cast iron pipe exists which is typically over 40 years old. The recent history of water main breaks does not indicate a clustering of breaks in a single area or single pipe material. A series of watennain breaks along Old Highway lOa few years ago lead to a Capital Improvements project to replace several hundred feet oftrunk watermain with new plastic pipe. Cast iron pipe represents the greatest risk to the City in terms of potential to break due to its age and material composition. Areas with cast iron pipe which are being evaluated for street reconstruction should receive serious consideration for replacement of watermain. (Ridgewood Neighborhood has CIP) PROJECTS\ARDENHIL\3795! \GENERAL\Documents\Agenda Memo3-14-0S Infrastructur doc