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City of Williams Lake Effluent Release Response

Client Name
Ministry of Environment & Climate Change Strategy, City of Williams Lake, and Williams Lake First Nation
British Columbia

Project Description

On April 23, 2020, the Williams Lake River experienced high flows which significantly eroded the Williams Lake River banks, eventually exposing and destabilizing the City of Williams Lake wastewater treatment plant (WWTP) pipe system, causing it to fail at several locations. As a result of the flood damage, untreated, partially treated, and treated sewage was released into the Williams Lake River (BC Ministry of Environment Dangerous Goods Incident Release DGIR: 200295). DWB was initially retained to undertake water quality and sediment quality monitoring for the duration of the effluent releases and provide advice and recommendations to the emergency coordination environmental tripartite group (Williams Lake First Nation, City of Williams Lake, and Ministry of Environment & Climate Change Strategy). DWB was specifically named and retained by the tripartite group to address follow-up reporting required to address a pollution abatement order issued to the City of Williams Lake by the Williams Lake First Nation, including data summary reports, impact delineation report, and an overall impact assessment report.

DWB quickly established a sediment and water quality sampling program and provided qualified field staff to conduct a variety of sampling programs. Monitoring staff conducted daily, weekly, and biweekly water quality and sediment sampling, with river locations initially accessed by helicopter (flooding washed-out road access) throughout the duration of sewage releases. Sampling required establishment and adherence to rigid safety protocols, given the on-going Covid-19 pandemic, as well as handling of samples with potential for microbial contamination. Early data management and tracking was established to facilitate review of laboratory analysis and enable project team members to provide timely and insightful recommendations to the emergency operations. Data management required quality control and assurance, including independent expert review.
DWB responded to a variety of concerns relating to potential contamination of resources potentially utilized by the Williams Lake First Nation and tripartite group by scoping and executing additional targeted studies:

  • Initial fish and fish habitat assessment, to identify fish distribution and evaluate fish condition to assess potential effects of effluent release on the fish community.
  • Microbial contamination investigation of harvested vegetation and berries.
  • Hydrotechnical modelling evaluation of sewage dilution, to evaluate sewage dilution within the Williams Lake River (as opposed to the permitted release point in the larger Fraser River) and inform decision threshold for contingency planning and activation.
  • Sewage contamination differentiation sampling (sterol and stanol analysis), to differentiate non-point pollution sources within the drainage potentially mobilized by flooding from upstream sources and inform delineation of sewage material deposition in the environment.
  • Fish collection and tissue sampling to assess potential bioaccumulation of contaminants in edible tissue.

Environmental Services

  • Emergency and Spill Response Management Support
  • Environmental Monitoring
  • Soil & Water Analytical Results Interpretation and Summary
  • Fish, Fish Habitat and Fish Tissue Sampling, Assessment and Results Interpretation
  • Microbial Contamination Sampling and Analytical Results Interpretation


  • Effluent Release Dilution and Low-flow Concentration Modelling

GIS and Mapping

  • Spatial data management
  • Development of a web-based spatial monitoring data viewing platform
  • Figure production

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