DUFRESNE GROUP | Consulting Engineers

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Wastewater Collection

In New England, most of the wastewater collection systems were installed in the early part of the 20th century. Most of the larger systems used vitrified clay tile pipe that if properly installed proved to be virtually indestructible and many of these collection mains are still in service. However, many of the collection systems were combined systems that received both sanitary sewer and stormwater and the costs of separating these two different types of water have proved to be an economic hardship on many communities. In some cases the older collection pipes can be used for collection of stormwater with new sanitary sewers installed to convey wastewater without inflow or infiltration. However, in some cases the older pipes require replacement or relining using various “insitu” methods. The ten cent federal dollars are no longer available and utility replacement costs have never been higher.

Most communities have only partial mapping of either or both the wastewater and stormwater collection system. Many of these systems were installed before record drawing requirements and many of these systems were installed without design plans. The vertical and horizontal location of these facilities is the initial step in allowing communities to develop wastewater and stormwater master plans. Knowledge of the collection system including the condition of structures, pump stations, outfalls, and pipe is best organized into geographical information systems (GIS). Dufresne Group typically performs a search of local files and records and scans this information into a file that will serve as one of the sources of data for the ultimate GIS. Once scanned, the digital files are now protected in storage and backup systems. Many communities have only the ragged paper copies now nearly a century old (and fading fast). Once the available information is scanned and made available to Dufresne Group, field engineers begin the task of locating the three dimensional position of the sanitary and stormwater collection system components. During the survey, photos are taken of the structures, sketches are made of the inlets and outlets of each utility, invert elevations are taken, diameters are recorded, materials of construction are logged, and condition of inverts and structures are prepared in report format. Each of these data files are embedded into the GIS and become available at the touch of a button.

Once this data is input into the system, a list of deficiencies is developed and alternative solutions can be evaluated. Sometimes additional evaluation activities such as dye testing, smoke testing, and television inspection activities are required to better define conditions. Once the existing database is complete and a master plan is developed, the list and priority of improvements can be developed and cost estimates can be factored into local improvement budgets and combined with other infrastructure improvement projects.

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