Annual Inflow/Infiltration Program

Town-wide Flow Metering Project in Shrewsbury, MA

In 2011, the Town of Shrewsbury selected Weston & Sampson to conduct a town-wide flow metering project of the sanitary sewer system.

Weston & Sampson installed and calibrated 33 continuous flow meters to measure wastewater flows throughout the town. The meters recorded flows for a period of 10 consecutive weeks. We also used pump station flow data to analyze sanitary sewer flows.

Our team used the results of the town-wide metering effort to determine the quantity of inflow and infiltration (I/I). Based on the flow metering information, Weston & Sampson developed an Annual Inflow and Infiltration Identification and Removal Program. The program is a phased approach to investigate and rehabilitate the Shrewsbury sewer system on a continuous, set schedule. We prioritized sewer subareas for investigation and rehabilitation based on the results of the metering program.

As part of this project, Weston & Sampson developed a policy and ordinance language for the implementation of a private inflow removal program. The policy included a written protocol for the identification of inflow sources, notification of property owners, and timelines for removal. Weston & Sampson provided suggested frameworks for potential reimbursement or amnesty programs to augment the private inflow removal program, and to encourage participation in the program and ultimately removal of inflow sources.

The annual program consists of infiltration investigations such as flow isolation, television and manhole inspections, and inflow investigations such as building inspections and smoke testing.

To date, the town has completed 10 years of the investigation portion of the program, and design and construction of sewer system rehabilitations of Years 1 through 9 of the program. Year 11 Investigations are currently underway.

Key Project Features:

  • annual infiltration/ inflow program
  • wastewater feasibility and capacity analysis
  • infiltration investigations: flow isolation, television inspection, manhole inspection
  • constraints of intermunicipal agreements for cost of transportation & treatment
  • farming sewer system capacity through I/I removal
  • sustainable water management/water balance project


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