Main Replacement Project 2012

The District currently maintains an 8" ductile iron water main that is located on the south side of the bridge. MDOT facilitated a utility coordination meeting that was attended by York Water District and Wright-Pierce.  During that meeting the MDOT’s bridge consulting engineer (VHB) explained the constraints imposed on the new bridge design that had important implications for maintaining the water main on the new bridge.  The design constraints are predominately focused on maintaining the historic character of the existing bridge and concealing the water main from exposed view. 

As a consequence, the available space for installing a new water main on the replacement bridge is very limited, and similar to the existing situation.   The available space would likely allow the installation of a new 8" main with insulation, but it would be a less than ideal situation from a maintenance perspective.  The available space would make future maintenance of the water main (insulation, protective jacket, heat trace replacement etc.) very difficult based on the space that can be provided.  Based on discussions with VHB, it is apparent that they cannot provide any additional area to install the water main because they are limited by historic design constraints and need to provide a pre-determined vehicle load capacity for the structure.  Our engineer @ Wright-Pierce would not recommend installing an 8" main on the bridge under these space limiting constraints unless there were no other alternatives. 

Wright-Pierce completed a master plan for the District a few years ago.  The hydraulic modeling completed for the master plan and follow up analysis recently completed has determined that the 8" main is not large enough to meet the hydraulic needs for that area of the system in terms of fire protection. Wright-Pierce recommended that the 8" pipe be replaced with a 12" main to improve hydrant flow capacity.

The space limitations will not allow for the installation of a 12" main on the bridge, and the installation of two 8" mains on the bridge would not provide equivalent flow capacity, create additional maintenance concerns, and reduce space available for electric and communication utilities.  The existing and new bridge is not very high over the water and the existing main has been hit by boats during certain periods of the tide range, which has required several repairs of the insulation and jacket system by operations staff over the years.  

The bridge design constraints combined with the need to upgrade the existing main to 12" initiated an evaluation of alternatives to installing a new 8" main on the replacement bridge. Three options were considered and were evaluated for technical feasibility, environmental impact, and capital cost.  


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