Dewatering - why does it smell and is it safe? Your questions answered.

Dewatering – What is it?

  • In order to facilitate installation of pipes deep underground (storm or sanitary sewer pipes, for example) excavations must be “dewatered”.
  • This involves pumping out the ground water during a trench excavation, to draw down the water table.
  • Once the water table is lowered, installation of the pipes and trench backfill material can be completed in dry conditions, which allows for proper installation and compaction.
  • This process is often required in Squamish due to our high water table and tide fluctuations, being at sea level.
  • This process requires pumps that operate around the clock for the duration of the dewatering.

 

What are the impacts to neighbourhoods?

  • We do our best to reduce the impact to the neighbours, however it is impossible to eliminate all impacts due to the nature of the work.
  • There is background noise from the pumps.
  • The water is often dark in colour and odourous. This is because of the decaying organic material in the deep layers of ground water that are being disturbed and pumped out.
  • Some residents are led to believe that this is a release of sewage due to its smell and colour. This is not true. There is no release of sewage, and there are no contaminants being pumped into our storm sewers, ponds or estuary.

Is there an environmental or health hazard?

  • Testing is undertaken to ensure there is no environmental or health hazard from the water that is being pumped.
  • The District ensures that testing on the groundwater discharge is done throughout the process to ensure that it meets provincial discharge regulations.
  • Air quality is also tested to ensure that levels of hydrogen sulphide are far below acceptable safety thresholds.
  • Our governing bodies include the federal Department of Fisheries and Oceans, and the provincial Ministry of Environment.

We understand and appreciate that this is not a pleasant process and the odours in particular can be unwelcome. The District works with local contractors to do our best to minimize impacts where at all possible, and we thank the neighbours for their patience while we complete the work.

 

November 2, 2018

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