MOOSE RIVER WATER MAIN CROSSING IN ST. JOHNSBURY
10.09.17
The finished water transmission main conveys potable water from the water treatment plant located near Stiles Pond in Waterford, Vermont to Saint Johnsbury. The cast iron water main travels about 2 miles cross country before passing under the Moose River and under an inactive adjacent railroad line. The unlined cast iron water main was installed in 1933 and was mechanically cleaned and cement lined under a 2008 improvement project. During the cleaning and lining project, a leak under the Moose River was identified and repaired but inspections revealed the Moose River had scoured under the water main over the past 80 years resulting in sections of the main being unsupported and subject to flood damage. Due to the precarious nature of this section of water main, Town officials identified the Moose River crossing as the most critical component of their transmission infrastructure. After passing a local bond article, in 2016 Town officials obtained gran/loan funding from USDA Rural Development for this project.
The water main's location was a particular design challenge. The river crossing is in an area where US Route 2 and the railroad are close to the river on the west side and there is a steep embankment down to the river on the east side. There is also a sizeable wetland area on the east side of river in the location of the water main. In addition to these challenges, borings indicated that directional drilling was not a viable option for this project. Therefore, several permits were required to allow construction to occur by open cut methods. The design was completed and all permits were received by early 2017. Construction bids were obtained in March of 2017 and ranged from $369,900 to $527,711. The project was awarded to the low bidder, Alliance Consulting and Excavation. Due to the site conditions, 16-inch diameter class 56 ball and socket pipe was selected to replace the 14-inch diameter cast iron main. The new pipe was installed sufficiently deep to provide 4 feet of cover above the top of the pipe beneath the river bottom.
Due to a 16 week lead time for ball and socket pipe, construction began in late September and the 400 linear feet of pipe was completed on October 4, 2017. The pipe passed pressure and leakage testing. After disinfection, the new pipe was placed on line in late October of 2017. The old 14-inch cast iron pipe was removed after providing about 85 years of service.
