Site work for a mixed-use development in Thunder Bay, Ontario. Completed plans call for site work for a transportation facility.

The Department of Public Works and Government Services Canada (PWGSC), on behalf of Transport Canada, requires a contractor to perform remediation work at Thunder Bay International Airport in Thunder Bay, Ontario. The Work will include the installation of a Permeable Reactive Barrier (PRB) to treat groundwater. The PRB will be installed with a funnel and gate design. Work will include, but is not limited to, trenching/digging, staging area, and backfilling. The Contractor must perform and complete the Work within 21 weeks from the date of notification of acceptance of the offer. Documents are available at https://discovery.ariba.com/rfx/23370796 The Work generally consists of the installation of a permeable reactive barrier (PRB). The PRB will be installed with a funnel and gate design. The PRB will be 162 m in total length, with two 10 m long PRB gates constructed with granular activated carbon (GAC) (north gate and south gate) and the remaining length constructed of impermeable sheet pile walls directing groundwater flow towards the gates. The sheet piles will be driven into the ground to a depth of 1.0 m into the silt aquitard. Within the PRB footprint, the base of the upper aquifer ranges from approximately 3.7 to 6.2 mbgs, and the aquitard thickness ranges from approximately 0.4 to 3.2 m. The two sections of permeable gate will be 10 m long, 6.5 to 7.0 m wide, and extend to approximate depths of 5.7 and 6.2 mbgs. The soil will be excavated to the interface (but not puncturing) the silt aquitard. The actual excavation depth will be determined in the field by the Departmental Representative based on visual observations of stratigraphy changes. If the aquitard is punctured (potentially as thin as 0.3 metres at the location of the gates), the excavated soil will be backfilled with bentonite to the top of the aquitard. The base of the excavation will be fitted with 100 mm thick articulated concrete blocks (ACBs). The treatment zone in the gates will be made up of a mixture of sand and GAC and will be 0.5 to 1.0 meters thick. The upper portion of the gates is not expected to come into contact with impacted groundwater and will be backfilled with clean sand fill to reduce the costs associated with GAC. Gabion basket retaining walls are proposed on the inlet and outlet sides of the gates. These will be filled with rip-rap and the pore space infilled with sand. One row of monitoring wells will be installed in the gates (within the media). One monitoring well will be installed upgradient and one monitoring well will be installed downgradient of each gate. Additional monitoring wells will be installed at mid-points along the funnels and at the end of the funnels.