Remediation of French Cable Wharf Site

Project Location: Dartmouth, Nova Scotia – (CFB Halifax)

Owner’s Name: Department of National Defence


Project Description:

The Canadian Federal Government committed to the remediation of contaminated sites with funding identified in the 2003 and 2004 Federal budgets. The objective of the increased funding was to reduce environmental liability through accelerated clean-up of contaminated sites. French Cable Wharf is a Department of National Defence (DND) property that was identified as having the potential to reduce environmental liability to the Federal government through remediation.

French Cable Wharf is located on the Dartmouth waterfront in the area of Halifax Harbour referred to as the Narrows. This area has been inhabited and industrialized for over 100 years resulting in historical contamination of the site. During operational years, French Cable Wharf was the site of a coal fired heating plant and underground fuel line for refueling ships. Assessment of contamination at the site identified polycyclic aromatic hydrocarbon and metals likely originating from coal ash. Limited petroleum hydrocarbon contamination was also identified, likely related to the former underground fueling lines.

Remediation at the French Cable Wharf site location posed several challenges to the project:

  • limited space for equipment operation and staging
  • adjacent to a salt water marine environment
  • tidal zone excavation
  • CN rail track crossing
  • tight completion schedule (3 weeks from award)
  • weather (late March – Snow/Rain)
  • existing wharf infrastructure
  • breakwater reconstruction

Dexter Construction was required to excavate and dispose of approximately 1800 cubic metres of soil, rock and debris. The excavated material consisted of over 2100 tonne of polycyclic aromatic hydrocarbon (PAH) and heavy metals contaminated soil, approximately 400 cubic metres of oversize rock and over 150 tonne of debris (steel cables and creosote timbers) from the vicinity of the French Cable Wharf (FCW) site in Dartmouth.

The excavated material was screened on site to remove oversize rock and debris. The oversized material was screened until the material was free of contaminated soil, and then reinstated in the excavation as backfill. The undersize (100 mm minus) contaminated material was then transported to an off-site, temporary stockpiling area for sampling and testing. The temporary stockpiles required polyethylene liners, covers and netting to prevent erosion and lose of soil from the stockpiles prior to disposal. Based on the results of the Consultant (CBCL Ltd) testing the final disposal / treatment options were confirmed. The site, once excavated was to be reinstated with clean surge rock and a gravel surface to form a suitable storage or parking area for future use.

The site excavation was completed to a depth of approximately 3 metres (low water – tidal limit) with environmental considerations for potential siltation into the marine environment. An environmental contingency plan was established for the site, including provision of a silt curtain if necessary.

Dexter Construction, working in conjunction with Envirosoil Limited was able to provide an economical treatment and disposal solution for all the soil and debris at the site. All the soil was impacted with PAH therefore all the screened soil was transported to the Envirosoil facility in Bedford for treatment via Low Temperature Thermal Desorption. As the representative sampling and testing of the screened stockpiled soil revealed, the metals concentrations and leachability within the soil were suitable for disposal at a local landfill facility once the soil has been treated for organic contaminates (PAHs), thus a complete solution was available.

In summation of the project, Dexter Construction and Envirosoil were able to complete the project on schedule and within budget and provide a complete solution to the entire project resulting in a successful remediation to the satisfaction of DND.