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CAMC/YPDT - High Park

ISSUE:

As part of a stormwater management project in High Park, the City of Toronto was decommissioning two flowing wells that were first drilled in 1959. The flowing wells were found during construction work on the existing ponds. Well records for the well indicated that bedrock had not been encountered when the well was terminated at a depth of 38.4 m (126 ft). Based on this, as well as on previous gravity work completed by the University of Waterloo (Gill and Karrow, 1996) it was suspected that one of the main outlets of the Laurentian River, a significant pre-glacial bedrock valley, was located in the vicinity of High Park. Because there are few high quality, detailed boreholes within the city the YPDT-CAMC study took advantage of this opportunity to drill a high-quality continuously cored borehole in this valley feature.

The Laurentian Channel is thought to connect Georgian Bay to Lake Ontario and may be a significant conductor of groundwater on a regional scale. The main channel has been traced to north to Nobleton, west of Barrie, and up into Georgian Bay with tributaries extending as far west as the Niagara Escarpment near Caledon East. Details regarding the sediment stratigraphy within the Laurentian valley and groundwater movement within the feature remain sketchy despite the valley having been known for some 100 years

RESULTS:

  • initial well drilled to the top of gravel aquifer at 38 m in July 2003 by All-Terrain Drilling
  • the well started flowing from 38 m depth during drilling, expelling water and sediment into the air (initial head was on the order of 18 to 23 m above ground surface)
  • packing off the borehole within the casing resulted in the two recently capped artesian wells beginning to flow again and springs emerged from the area surrounding the well
  • installation and pumping of a relief production well (drilled by G. Hart and Sons) depressurized the aquifer enough to allow for the initial well and springs to be grouted
  • initial flow was estimated at 300 to 500 GPM but declined to between 90 and 120 GPM after stabilizing
  • bedrock encountered at a depth of 44 m (45 mASL or 30 m lower than Lake Ontario)
  • water levels in three shallow monitoring wells show connection to deeper aquifer
  • controlled flow from the relief well to local creek continues to depressurize the aquifer

FURTHER CONSIDERATIONS:

Given the two flowing wells in the immediate area coupled with the fact that drilling took place along “Spring” Road in High Park, flowing conditions were expected; the magnitude of the flow was surprising. Given the proximity of Lake Ontario to the drilling location it was suspected that a hydraulic connection to the lake would keep groundwater levels in check. The highly confined conditions suggest that hydraulic communication between the Laurentian Valley aquifer at the High Park location and Lake Ontario to the south is poor. Further testing is required to fully quantify the hydraulic properties of the aquifer system.

    
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