A Historic Bay State Town's Approach to the Reduction of I/I from its Aging Infrastructure

摘要

The Town of Dedham, Massachusetts is a residential community located southwest of Boston. Wastewater collected in the town drains east to the Boston line where it enters the Massachusetts Water Resources Authority (MWRA) interceptor. The flow is ultimately treated at the Deer Island Wastewater Treatment Plant. The town's wastewater collection system consists of approximately 94 miles of gravity sewer. The Town-Wide Sewer Management Program (Annual Program) incorporated by the Town of Dedham, Massachusetts is an effective method to operate, maintain, and manage their aging collection system while removing extraneous infiltration and inflow (I/I) and helping to keep sewer related costs low. In 2006, a new regime was faced with a neglected sanitary sewer collection system, first constructed in 1901, and increased costs associated with operation and maintenance. The Town of Dedham then immediately began a comprehensive investigation and rehabilitation program. The approach incorporated in the Annual Program benefits the town by identifying and removing extraneous I/I while repairing structural deficiencies within the collection system before emergency repairs are required. The program began by analyzing the entire 94-mile sewer collection system and separating it into 26 sewer basins. The sewer basins were then prioritized for investigation and rehabilitation based on age, known problem areas, amount of work previously completed and increased flow rates during wet weather. The town investigates and makes necessary repairs to the entire system over the course of a five-year period. Each phase of the Annual Program includes television inspection, manhole inspection, data evaluation, cost-effective analysis, GIS mapping, reporting, survey, design of recommended repairs, public bidding, and construction. In addition, inflow related investigations including smoke and dye testing have been conducted town-wide and private building inspections have been conducted in approximately 40% of the town. Every five years, a town-wide flow metering project is conducted to analyze the program's success and reprioritize it. This ensures that the sewer system is operating efficiently and new sources of I/I are identified regularly, accounting for degradation of structures over time. The Annual Program is meant to treat the collection system like a valuable asset that requires routine maintenance. As a result the town's commitment to the annual program, they have seen their flow share at the regional treatment facility (Massachusetts Water Resources Authority) drop consistently over the past ten years as a result of the removal of extraneous flows. The I/I removed from the sewer system is no longer needlessly treated and allows for sewer costs to increase at a rate of 75% less than neighboring communities. It is estimated that the annual program has saved rate payers approximately $10 million over the short life of the program. The goal of this presentation is to provide an understanding of how the Town of Dedham's Annual Program is a model tool to operate and maintain a communities collection system and save money.