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Soil & Groundwater

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Key Findings

  • The majority of the Study Area is within the Iroquois Plain physiographic region 1 except for a small portion north of Eglinton Avenue and Don Mills Road which is in the South Slope physiographic region. The Iroquois Plain is a lowland mainly composed of sand extending north up to 10 km from the shoreline of Lake Ontario. The South Slope extends from the base of the Niagara Escarpment to the Iroquois Plain. It is characterized by low-lying moraine (mass of rocks and sediment deposited by glacier) and knolls (hills and mounds).
  • Near-surface soils in the Study Area include sediment left by glaciers, lakes and rivers
  • The majority of the Study Area overlaps with a Highly Vulnerable Aquifer, an aquifer that is susceptible to contamination due to its location near the ground surface or the surrounding soils

1Physiographic regions are areas that share similar landforms shaped by common geomorphic processes and geological history

Spotlight Case

This photo, taken from Millwood Road and looking south towards Lake Ontario, shows the Don Valley in the Iroquois Plain physiographic region. Iroquois Plain sandy soils once supported forests, savannahs and prairies. While the formerly forested Iroquois Plain within the Study Area is heavily urbanized today, pockets of natural areas such as the Don Valley remain.

Image of Don Valley in the Iroquois Plan Physiographic Region

Don Valley in the Iroquois Plan Physiographic Region

Methods

Metrolinx conducted a review of available information to establish soil and groundwater existing conditions in the study area, including:

  • Ministry of the Environment, Conservation and Parks Open Data catalogue including Water Well Records; Source Water Protection Information Atlas
  • Toronto and Region Conservation Authority reports and resources including Source Water Protection Conceptual Understanding of the Water Budget Report (2007), Don River Watershed Plan: Geology and Groundwater Resources (2009), Toronto and Region Source Protection Area, Approved Updated Assessment Report (2015)
  • Ontario Geological Survey including The Physiography of Southern Ontario, Third Edition (1984); Paleozoic Geology of Southern Ontario (2007); Metropolitan Toronto Bedrock Contours (1961)

Preliminary Potential Impacts & Mitigation Measures for Further Study

Construction

Potential Impacts

  • There is a potential for structures to have foundations built below the local water table which may be affected by dewatering
  • Construction activities (e.g., excavation) could expose contaminated materials

Potential Mitigation Measures

  • Site-specific mitigation measures for impacts to groundwater quantity (e.g., avoiding or minimizing dewatering requirements)
  • Remedial action plans, risk assessment and risk mitigation plans for encountering contamination, as necessary
  • Regular site inspection and associated monitoring activities

Operations

  • No impacts to soil and groundwater are anticipated as a result of operations

Future Studies

  • Using the baseline information and identified preliminary impacts, soil and groundwater impact assessment will be undertaken
  • Construction Dewatering Management Plan, Groundwater Management Plan and Spill Prevention and Response Plan will be developed and implemented

 

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