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EFFECTIVE I/I REMOVAL WITH FOOTING DRAIN DISCONNECTION AS A SOLUTION FOR SSO AND BASEMENT FLOODING

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Many communities are actively seeking ways to control the excessive inflow and infiltration (I/I) that plague their sewer systems. This wet weather flow can cause sanitary sewer overflows (SSOs) and basement flooding, when affecting sewer systems with insufficient flow capacities.

Residents of the city of Ann Arbor, Michigan (population 114,775) have experienced basement backup problems dating back to 1968. Additional widespread backup events occurred in 1975, 1976, 1998, and 2000. Ann Arbor created a task force in 1999 to evaluate options and determine a plan for preventing basement backups and SSOs. The group consisted of city staff, residents from the affected areas, local environmental organizations, and professionals. The task force found that capacity problems observed in many of the sanitary sewers were primarily the result of stormwater from foundation footing drains located around residential structures. While solutions such as storage basins and increased collection system capacity were reviewed, source control via footing drain disconnection was selected for citywide application.

The footing drain disconnection (FDD) program began in 2001 as the preferred solution to reducing the primary source of I/I to the city's sewer system. The FDD program is coordinated by a construction management team, consisting of city staff and a consultant. Contractors are involved in two phases of the work. First, a directional drilling company installs a shallow high density polyethylene (HDPE) drainage pipe network (curb drains) to accept sump pump flows from individual residences and transport the water to the storm drain system. Then, a pre-qualified plumbing contractor team works in individual residences to disconnect the footing drains, install new sump pump systems, and connect the sump pumps to the new curb drains.

A key element of this program is the public engagement activities, without which the program would not have gained public acceptance of the work. For participating property owners, the FDD program includes such informational materials as information packets, newsletters, a project Web site, and video. Neighborhood meetings are held, with 15 to 30 properties per grouping, followed by one-on-one meetings at each property between the construction manager and property owner to review their basement configuration and explain all of the remaining program steps.

Another aspect of the project is ongoing validation of the flows generated by the new sump pump discharges. Initial work has shown average dry weather I/I flows around 0.01 gallons per minute (gpm). Peak wet weather footing drain flows at single residences have been measured over 30 gpm, with average peak flows exceeding 2.0 gpm during the largest rain events. The city of Ann Arbor is continuing to use the footing drain flow data, along with a citywide sanitary sewer model, to prioritize future FDD work areas and project long-term deficiencies. A total of 500 properties have been completed since 2001 and the FDD program may continue for the next 20 to 30 years to perform the projected total of 20,000 residential disconnections required throughout the city.
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Document Type: Research Article

Publication date: 2005-01-01

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