It Just Goes Away
Duluth is located on the north shore of Lake Superior. It is a community of 86,000 people, it is 26 miles long and 8 miles wide, with changes in elevation in the city from 602 feet to approximately 1300 feet above sea level. Some of this elevation occurs in less than 2 miles. The City of Duluth's Collection System was constructed beginning in 1881 and continued through 1923. In following years the system was added to as the city expanded and is still growing today. The system was built of clay tile pipe, brick arch sewers, wood sewer pipe, and blasted tunnels through bedrock, parts of which were originally a silver mine. Although there are no records on file, some of the employees recall wooden sewers in the early years. The system consists of approximately 420 miles of sanitary sewer main of which only 96 miles is PVC, with over 8,000 manholes. We also operate 260 miles of storm sewers with about 4,950 manholes, 9,400 catch basins and 42 named streams, 10 of which are cold water trout streams. Our weather conditions vary from −35 below zero in the winter to 90ish in the summer. Precipitation averages are about 32 inches of rain and 84 inches of snowfall. This poses some unique challenges in cleaning and maintaining our municipal sanitary sewer collection system. For example:
In the winter we have filled our vactors with hot water from our steam plant to prevent the vehicles from freezing and have found that it also works very well to remove grease from the walls of pipes from our identified “grease lines”
Velocity also has a huge impact on our system. During adverse weather conditions, it carries a tremendous amount of solids that have settled in flat lines which can cause catastrophic pipe failure and related property damage. However on the positive side, velocity aids in scouring of the pipe and the prevention of septic conditions.
Document Type: Research Article
Publication date: January 1, 2004
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