Since 2010, Public Services and Procurement Canada (PSPC) has managed the former Sambault landfill located 30 km south of Montreal in Canada. The site, with approximately 150,000 square meters of surface area, has experienced illegal dumping activities of various wastes from 1965 to 1986. The estimated 365,000 m3 of various wastes, including hazardous residual materials, have contaminated the soil, groundwater, and surface water. The pollution is beyond the regulatory criteria of the various classes of contaminants including heavy metals, petroleum hydrocarbons, and chlorinated solvents.
This situation prompted an urgent need for action to protect the drinking water supply to nearby private wells and, in the long term, for Saint-Isidore-de-Laprairie located less than 2 km from the site. This water supply is utilized by an agricultural neighborhood that includes organic corn and small scale direct-to-consumer market gardeners for whom irrigation is essential.
An environmental management approach was developed to address the contamination of the site and improve the surrounding areas affected by the pollution. Golder proceeded with profiling and capping the waste cells; installing a pumping hydraulic containment system to prevent the migration of the contaminated groundwater plume outside the site boundaries and into the bedrock aquifer; and constructing a treatment plant for the pumped water prior to its discharge back into the environment.
The project used a design-build delivery approach to achieve its objectives for the hydraulic containment and the groundwater treatment plant aspects. The team had to meet very high-performance standards to maintain the piezometric surface under a designated elevation and maintain catchment areas containing the contamination plume and meet the compliance of the discharge water quality to the acceptable criteria of 93 parameters. Following the initial design, the pilot tests were used to assess the performance of the pumping and treatment system.
Other tasks performed included:
- Hydrogeological modelling to determine the configuration of the pumping system as well as the flowrate to be treated.
- The design, supply, and installation of a primarily pneumatic pumping system including 47 pumping wells distributed over five networks and a system of 64 monitoring wells.
- The design, supply, and installation of a wireless data transmission system.
- The design, supply, and installation of a water treatment system with a design flow rate of 200 L/min, built using electrocoagulation and filtration technologies and ensuring the water quality discharge met the applicable criteria of 93 parameters.
- The design and construction of a 21×16 m steel building to house the water treatment system.
- Seeding and revegetating the capped waste cells at the site.
- Commissioning of the building and pumping and water treatment systems.
- Operation and maintenance of the pumping system and water treatment plant for two years, including environmental and hydrogeological site monitoring as well as the water quality discharge.
The design-build project delivery approach enabled the development and use of innovative tools and techniques such as 3D visualization, interpretation of very low flowrate pumping tests, acquisition of operation data by wireless transmission, and water treatment using innovative approaches such as electrocoagulation.
The compact and automated electrocoagulation system consisted of six lines of three reactors, which allowed the system to treat a wide range of contaminants and was adaptable to accommodate the seasonal variability in contaminant concentrations. This technology also reduced the quantity of filtration media and chemicals generally required for this type of application, thus limiting by-products and waste generated as well as operating costs.
The hydraulic containment system and the water treatment plant are in operation 24/7 and have been meeting performance criteria since Fall 2019. The remediation program applied a sustainable approach through the protection of the environment by meeting the continuity of local agricultural activity and improving the living environment by eliminating visual and odor nuisances as well as fire risks. The landfill, once a brownfield site, has become a controlled green space integrated into the landscape.