City of Kolkata is a conglomeration of 3 villages:

• Sutanuti
• Govindapur
• Calcutta

Sewer Cleaning

 
The drainage system dates back to the 1870’s (town system) and was constructed under British Engineers supervision. Sewer Cleaning / Sewer Rehabilitation was very much in need. The following are the catchments that now exist:
 

Sewer Repair

55% of the city is serviced by sewers, the remainder by septic tank / other. The Storm Sewer is used to carry foul as well. The system has adequate capacity during dry weather flow but inadequate capacity during storm / monsoon season so there was a definite need for Sewer Repair.

The following problems had been identified in Cleaning the Sewers:

• Alignment of the manholes above the sewer causes problems for winching / jetting (offset manholes)
• Some manhole are side entry to facilitate the tram tracks that run throughout the cities streets
• Poor access to manholes due to lack of step irons
• Only a few pump stations are able to maintain a low flow level in the sewers
• Security of machinery can be a problem
• Problems with disposal of silt due to high levels of ~ lead, cadmium, chromium III, chromium VI and  mercury   (although a landfill facility has now been set aside to receive the silt by KMC)
• Financial problems to date

The original scope of work was for the Open Cut Replacement of 36.271 kms of brick sewer ranging in sizes from 600mm to 1500mm x 1100mm. However, it has now been decided that open cut is not an alternative.

Historically, there has been low to zero maintenance of the system and Sewer Upgrading was very much needed. In general the majority of the sewers are over 50% silted. The brick and mortar have degenerated leading to poor structure and serviceablility. In 2005, there were 72 reported Sewer Collapses. Maintenance to date has been reactive rather than proactive. The presence of heavy metals in the sewers combined with ash and grit have made the de-silting of sewers by manual labour hazardous.

Sewer Upgrading – Project Background

After deciding that open cut was not an alternative, KMC decided to clean the old sewers using trenchless, non-man entry technology and sought information from experienced contractors. USSR LTD is the first contractor to start the Sewer Upgrading cleaning operation in Kolkata by non man entry Waste Water Recycling Equipment. The aim of this Project is to:

Phase-1

• Upgrade the capacity of the existing sewer by removing the slit completely.
• Assess the existing structural condition of the sewer.

Phase-2

• Sewer Reline and Sewer Repair where required.

USSR Pvt. Ltd, the Indian Counterpart of USSR LTD along with one local contractor Progressive Construction Co. was awarded the contract to carry out Phase-1 of the project. Phase 1 of the project involves Desilting and CCTV Surveys of the following diameters:

• 600ø
• 900ø
• 1500ø

An example of the volumes of silt that have been removed to date on sections of brick sewer can be seen in table 1.0 below:

Scope of Work:

• Topographical Survey
• Over pumping, diversion of sewer flow using sandbags/stoppers to minimise the water level to satisfactory level.
• Traffic Management
• De-silting by recycler Super-2000
• CCTV survey
• Health and Safety