The Town of Duxbury, MA faced many issues with its water system including multiple dead ends and an aging Culvert at the Lower Chandler Pond Dam. In 2012, Environmental Partners was selected by the Town to provide modeling, permitting, design, bidding assistance, and construction administration for the extension of the public water system from Lake Shore Drive.
Work included installation of approximately 5,400 linear feet of 8” ductile-iron water main, hydrants, valves, and new service connections, and replacement of the Lower Chandler Pond Dam outlet structure and 60” corrugated metal culvert, which discharged into a perennial stream. The Dam was a significant hazard dam under the jurisdiction of the Office of Dam Safety. The project goals were to bring the dam into compliance with safety regulations, pass the spillway design flood and replace the deteriorating culvert.
To document prior and proposed conditions, EP developed hydrologic stormwater models using HydroCAD which were used to analyze the flow through the old and newly proposed outlet control structure and culvert. In order to perform these calculations, drainage areas for each design point were identified, and a runoff hydrograph was developed for various storms. EP supervised the collection of soil borings at locations along the route of the new water main to characterize the soils, estimate extent of bedrock, and determine groundwater levels and samples were taken to a laboratory for multiple tests including grain size distribution and moisture/density relation curves. These tests directly contributed to a Geotechnical Recommendations Report completed by EP. The report included a summary of subsurface explorations and conditions encountered during field investigations including test borings with blow counts and foundation and construction considerations for the culvert.
Based on recommendations after the analyses, the existing culvert and outlet control structure at the dam were replaced with a precast concrete box culvert, outlet control structure and associated wing walls. This strategy allowed for quick installation and minimized the road closures and impacts to the residential neighborhood.
To ensure stormwater runoff quality, EP developed and monitored both the installation and maintenance of the erosion and sediment control techniques for the project. Additional drainage improvements were implemented including placing riprap on slopes adjacent to the culvert and outlet control structure, and installing permanent turf reinforcement to prevent erosion. Work also included design, bidding, and construction services for the installation of 5,500 feet of 8-inch ductile iron water main for an extension of the water system along Lake Shore Drive and Pine Street.
This project was completed in 2014, and benefited the Town in many important ways including providing many homes access to the Public Water System. The three dead ends at Lake Shore Drive, Mill Pond Lane, and Chandler Mill Drive were looped to improve water quality and available fire flow. As a result of the improvements to and extension of the Public Water System, firefighting capacity and overall water quality have been improved throughout the community.