BLENDING FIELD EXPERIENCE AND THEORY TO IMPROVE INFILTRATION AND INFLOW CONTROL
Abstract:Contractors and construction inspection personnel often complain that the specifying engineers don't know what it takes to build the designs. Nonetheless, efficiency encourages specialization that results in separate groups writing standard specifications, drafting design documents, and inspecting the field construction. Technical staff at the Milwaukee Metropolitan Sewerage District (MMSD) sees re-establishment of the standards-designconstruct linkages as a key to reversing the historic growth of infiltration and inflow rates.
In the late 1970s MMSD was served with court orders requiring elimination of all wet weather overflows from the separated sanitary sewer systems. By 1982, sewer system evaluation surveys throughout the 28 communities tributary to the MMSD network identified the cost effective level of sewer rehabilitation. The communities committed to repair the defects, and MMSD amended rules and regulations requiring that all new sewer plans conform to Standard Specifications specifically upgraded to limit opportunities for infiltration and inflow. The planners thought the infiltration and inflow would decrease, and new facilities were sized accordingly.
By the late 1990s, a number of basement backups and sanitary sewer overflows (SSOs) in the communities and in the metropolitan interceptor system made it apparent that the infiltration and inflow were not under control. This paper summarizes the many provisions and programs that MMSD is developing to more effectively control the infiltration and inflow into the metropolitan interceptors and the connected community sewers. It emphasizes those provisions where Rules, Standards Specifications and design documents are improving by virtue of incorporating feedback from field observation of construction practices.
MMSD technical staff work with the Public Works Industry Improvement Program committee to upgrade the Standard Specifications for Sewer & Water Construction in Wisconsin to better exclude rainwater from sanitary sewers. The MMSD Rules now require, and subsidize, limited sewer system investigations leading to infiltration and inflow reduction plans for basins where the peak to average day flow ratio is high. MMSD is increasingly attentive to new sewer plan reviews, consistently requiring that sewer plans meet a standard that will not increase future peak flows above planned levels.
MMSD also provides quality assurance of ongoing sewer construction throughout the 420 square mile service area. The quality assurance inspector, like the sewer plan reviewer, often observes provisions of the Standard Specifications and the Rules that are being circumvented, ignored or simply not effectively implemented. They work together with the specification engineer, municipal design engineers, contractors and the facility planners to identify more effective provisions or technologies to exclude infiltration and inflow from the constructed sewers.
The paper will summarize lessons learned about the effectiveness (or ineffectiveness) of the range of system wide infiltration and inflow reduction alternatives tested in the MMSD service area during the past 25 years. Infiltration and inflow reduction measures tested include:
Complete Sanitary Sewer Evaluation Surveys
Rules and standard specifications requiring sealed manhole lids
Rules and standard specifications requiring downspout connection
Rules and standard specifications requiring verifiable sump pump discharges away from the foundation
Rules and standard specifications prohibiting cross connection with storm sewers
Rules subsidizing manhole inspection, smoke testing and flow monitoring to identify inflow sources
Grants offered for projects expected to demonstrate and measure effective infiltration and inflow control technologies
Document Type: Research Article
Publication date: 2002-01-01
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