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CASE STUDY

Deep Aquifer Depressurization Project with High Heavy Metal Concentration Groundwater


SITUATION

A gas line replacement project required installation of a 300 mm (12 inch) HP gas main along a main road required trenching for installation of header pipe. 

The geologic formation beneath the site comprised of overburden fill materials and till deposits underlain by highly pressurized and saturated Oak Ridges Moraine Aquifer (ORMAC), with artesian pressure of up to 4 meters above ground surface. The confined aquifer’s concentrations of TSS and Zinc exceeded the regulatory sewer limits, and required treatment to meet water quality criteria prior to discharging into the sewer system.

To prevent the high potential for basal heave during reduction of the overburden layer and to maintain base stability of the open excavations during construction, depressurization of the confined aquifer was required to reduce the pressure head from 4 masl to 2 mbgs with a target drawdown of 6 m.

APPROACH AND OUTCOMEs

Aquatech designed, commissioned, maintained and decommissioned a 2500 l/m dewatering and discharge filtration & treatment system. Aquatech installed 12 6” diameter deep pumping wells (30m deep) with our dual rotary drill rig, fused and installed 650-meter HDPE header pipe, and 12 monitoring wells as per O.Reg. 903 to monitor the fluctuation of water levels and pressure levels. Each pumping well was commissioned with a submersible turbine pump and electrical control starter panel.

To meet regulatory discharge water quality requirements, Aquatech designed and successfully treated  Zinc and TSS with consistent results and in compliance with the regional discharge bylaw. Remote real-time monitoring systems with live alarms were installed to monitor operation and environmental performance including flow, water level and water quality including TSS/turbidity and it’s correlation with heavy metal.

Aquatech provided turn-key operation and maintenance of the treatment system and after-hour monitoring of water levels and water quality. Redundancy/backup equipment were provided to ensure uninterrupted operation of treatment system.