You reap what you sow

av Adrian Højfeldt
Sverre Sondresen
Marco Casagrande
Kolbotn, Norway

– -The remediation of Kolbotn lake
Kolbotn is a suburban site located 12 km south of Oslo. This place started as farmland until the sewer pipe system was completed in 1957. This changed Kolbotn from being a countryside location to a
satellite city. Between 1957 and 1978 there was a great increasing number of residents that settled down around the lake in Kolbotn.

The lake is an important part of the identity of Kolbotn and has been extensively used for swimming, rowing boats, fishing, and more. Unfortunately during the years, the lake has gradually been more and more contaminated as a result of rivers with polluted water that ends in the lake.
After the beginning of the year 2000, the city center of Kolbotn was torn down and replaced with Kolben culture house and a new square that had many new shops and apartments for the residents of Kolbotn. The lake however has gradually been more contaminated and has not been recommended for anyone to use for swimming since then. The sewer pipe system that was completed in 1957 had to accommodate increasing numbers of inhabitants, and maintenance/expansion became necessary. So far 40 % of the existing sewer pipe system has been replaced and enhanced.
The sewer pipe system combined with old surface water pipes is another reason for the increased polluted streams that find their way to the lake. As a result of this. The lake is suffering from the increasing growth of blue-green algae and coliform bacterias.