North Metropolitan Sewer Study

The MWRA owns and operates a 9-foot diameter 120+ year old brick interceptor, also referred to as the North Metropolitan Sewer (NMS), that conveys wastewater from the cities of Chelsea, Revere, East Boston and Winthrop to the Deer Island Wastewater Treatment Plant. Hazen developed a detailed rehabilitation plan for this critical asset; to inform this effort, a series of comprehensive investigations were conducted, including CCTV inspection, a LIDAR scan of the pipe, H2S and chloride sampling, manhole inspections, shotcrete core samples, and a hydraulic and traffic evaluation along the pipe alignment.

Wilson mwra interceptor aerial — The MWRA owns and operates a 9-foot diameter 120+ year old brick interceptor, also referred to as the North Metropolitan Sewer (NMS), that conveys wastewater to the Deer Island Wastewater Treatment Plant. Since the NMS runs through a peninsula, dense urban neighborhoods, and business districts in Winthrop, disruptive construction techniques are not tolerable.

The NMS runs for a length of 17,000 feet and was rehabilitated in two phases during the 1990s using a combination of shotcrete and epoxy materials. The first phase of rehabilitation utilized epoxy for protection against corrosion. The epoxy liner failed shortly after installation, leaving the rehabilitated pipe vulnerable to corrosive attack. As such, the second phase of rehabilitation utilized a shotcrete mixture with microsilica for protection against corrosive attack.

For more information, please contact Chuck Wilson.

Related Topics:

Wilson mwra interceptor core sampler — LiDAR scans can produce misleading data if in-pipe conditions are variable; it is important that “raw” data be adjusted using record drawings, and field investigations (including core samples) to ensure an accurate condition assessment.

Due to the differing rehabilitation methods, conditions in the pipeline were highly variable. These variable conditions led Hazen to develop a unique procedure to correct the LIDAR pipe scan data, which did not accurately represent the degree of pipe degradation in raw form due to interference caused by the failed epoxy liner.

Wilson mwra interceptor drawing — Detailed investigation of the sewer’s history and materials used in prior repairs was critical to understanding the remaining wall thickness and developing a viable long-term solution.

The location, size, shape, condition, and history of the NMS present several challenges that make rehabilitation difficult. Since the NMS runs through a peninsula, dense urban neighborhoods, and business districts in Winthrop, disruptive construction techniques are not tolerable. Furthermore, the amount of flow the NMS conveys (21 mgd during dry weather and 135 mgd during wet weather) preclude the construction of a temporary bypass pumping apparatus to achieve a dry pipe, which is required for many trenchless pipe rehabilitation techniques. A detailed analysis of rehabilitation techniques and their applicability to the NMS was performed to determine the optimal rehabilitation approach. Ultimately, a combination of slip lining and segmental lining was recommended in two construction phases.

Hazen developed a detailed rehabilitation plan for this critical asset; to inform this effort, a series of comprehensive investigations were conducted, including CCTV inspection and , a LIDAR scan of the pipe.

Project Outcomes and Benefits

Detailed investigation of the sewer’s history and materials used in prior repairs was critical to understanding the remaining wall thickness and developing a viable long-term solution.
Development of a replicable procedure to verify and adjust LiDAR data to ensure accurate representation of in-pipe conditions. LiDAR scans can produce misleading data if in-pipe conditions are variable; it is important that “raw” data be adjusted using record drawings, and field investigations (including core samples) to ensure an accurate condition assessment.
Performed a full market analysis of rehabilitation technologies and evaluated bypass pumping considerations and challenges specific to the sites, before settling on the most viable solutions.