Ontario Line

Potential effects and mitigation measures

Potential effects:

• Removal of/damage to trees, terrestrial vegetation and wildlife habitat.
• Impacts to aquatic/riparian vegetation.
• Erosion and sedimentation to waterbodies from construction.
• Disturbance or displacement of wildlife species and reduced habitat connectivity.
• Potential for impacts to fish and fish habitat.
• Risk of contamination to waterbodies as a result of spills.
• Introduction or spread of invasive species.

Mitigation measures:

• Sensitive wildlife timing restrictions for early works activities (e.g., removal of vegetation outside of the breeding bird period).
• Tree/vegetation removals will be kept to a minimum and limited to within construction areas.
• Tree removal compensation will be provided in accordance with the Metrolinx Vegetation Guideline (2020).
• Temporarily disturbed areas will be restored/re-vegetated.
• Erosion and sediment control measures will be implemented.
• Ensure that all in-water activities do not interfere with fish passage, constrict the channel width or reduce flows.
• Prior to early works activities, species-specific surveys will be completed to avoid or reduce potential impacts and meet all Species at Risk regulatory requirements.

Read more - Appendix B1 - Natural Environment Report

Potential effects and mitigation measures

Potential effects:

• Temporary increase in air pollution and odour (e.g., diesel combustion products such as NO2) as a result of construction vehicle emissions and increased traffic due to congestion associated with early works activities.
• Temporary increase in dust, silica and airborne particulate matter resulting from earthworks, material handling and transfer, and other construction activities.

Mitigation measures:

• Construction equipment will comply with all applicable regulatory emission standards.
• Contain (e.g., tarp) sources of dust such as soil stockpiles as required.
• Removal of accumulated mud, dirt and debris deposits, and regular truck washing.
• Reduction of activities during high wind conditions.
• Use dust suppressants such as water as required.
• Application of threshold triggers for implementation of specific and increasing intensity mitigation linked to specific construction activities.
• Application of threshold “Action Level” triggers for implementation of specific and increasing intensity mitigation activities linked to specific construction activities.

Read more - Appendix B2 - Air Quality Early Report

Potential effects and mitigation measures

Construction noise

Potential effects:

• Without mitigation, potential for noise level criteria exceedances at 180-190 Mill Street and the future residential developments at 125/131 Mill Street and 495 Front Street.

Mitigation measures:

• Establish and apply project-specific construction noise criteria/exposure limit.
• Use construction equipment compliant with noise level specifications in the Ministry of the Environment, Conservation and Parks’ NPC-115 and NPC-118 guidelines.
• Keep equipment in good working order and operate with effective muffling devices.
• Evaluate acoustic equipment enclosures for equipment such as compressors and generators.
• Use of upgraded construction hoarding (considering requirements from CSA Z107.9 for noise barriers) between construction equipment and noise sensitive receivers.
• Use of localized noise barriers for specific equipment and operations, including on corridor construction works.
• Reduce simultaneous operation of equipment where possible.
• Implement a no idling policy on site (unless necessary for equipment operation).
• Restrict construction hours where possible:
  • Perform construction during daytime hours where possible. If nighttime construction is necessary, activities with the highest noise levels should be conducted during day time periods.
  • If construction will occur outside of normal daytime hours, inform local residents of type of construction and expected duration prior to commencing work.
• Undertake noise monitoring and regular reporting throughout the construction phase as required.
• Develop a communications protocol for providing advance construction and vibration impact notices and addressing public complaints in a timely manner.

Construction vibration

Potential effects:

• Exposure to vibration may result in public annoyance and complaints. Vibration may also cause damage to buildings and other structures.

Mitigation measures:

• Utilize equipment with low vibration emissions where possible.
• Conduct off-site construction of components away from sensitive areas where possible.
• Operate construction equipment on lower vibration settings where available.
• Provide smooth surfaces for trucks to travel.
• Maximize distance between equipment and sensitive receivers.
• Restrict construction hours where possible:
  • Perform construction during daytime hours. If nighttime construction is necessary, the activities with the highest vibration levels should be conducted during day time periods.
  • If construction will occur outside of normal daytime hours, inform local residents in advance, describing type of construction and expected duration.
• Use alternative construction methods and/or equipment with lower vibration emissions or power settings, where City of Toronto prohibited limits are predicted to be exceeded.
• Conduct monitoring and pre-construction inspections in accordance with City of Toronto Bylaw 514 as required.
• Develop a communications protocol for providing advance construction noise and vibration impact notices and addressing public complaints in a timely manner.

Read more - Appendix B3 - Noise and Vibration Report

Potential effects and mitigation measures

Potential effects:

• Potential impacts to the 1856 abutment stones in the public space on the west side of the Lower Don River. They may require removal/relocation to accommodate construction activities related to early works
• No impacts as a result of construction vibration are anticipated. The Cherry Street Interlocking Tower was built to withstand vibration; however, the design vibration limits should be reviewed by a qualified specialist during the next phases of design.

Mitigation measures:

• For the public space related to the former location of the first railway crossing over the Don River, on the west side of the Lower Don River, consult with City of Toronto Heritage Planning to determine and obtain any approvals or permits required for physical impacts to the space as planning progresses.
  • If the 1856 abutment stones can remain in place during early works activities, install protective measures such as box or fence hoarding.
  • If the removal/relocation of the 1856 abutment stones is required prior to construction, mark the location of each 1856 abutment stone on the Detailed Design Plan and determine an appropriate removal plan and storage location. Remove 1856 abutment stone(s) prior to early works activities and reinstate afterward in the same location, if feasible.

Read more - Appendix B4 - Heritage Report

Potential effects and mitigation measures

Potential effects:

• Temporary lane closures along the Don Valley Parkway during non-peak hours and increase in construction vehicle traffic causing impacts to traffic flow on the local road network.
• Travel time delays for existing transit routes (i.e., TTC bus routes #72 Pape, #121 Fort York-Esplanade and #504A King Streetcar route) due to increase in construction vehicle traffic.
• Temporary closure of the Lower Don Trail underneath and in close proximity to the rail corridor may impact mobility and convenience to pedestrians and cyclists. Temporary full or partial closure of existing rail tracks, which may cause temporary reductions or detours of rail services.

Mitigation measures:

• Develop and implement a transit and traffic management plan as planning progresses.
• Consider scheduling early works activities during off-peak periods and weekends to reduce disruptions to traffic during the critical peak hours.
• Issue notifications and advisory signage to alert traffic and transit users of any upcoming road closures and disruptions as required.
• Ensure that appropriate signage and notifications are provided to direct pedestrians and cyclists around the closed section of the Lower Don River Trail. Consult and coordinate with the City of Toronto during early works planning, including consideration of route detours.
• Consult with rail companies (i.e., Canadian National Railway, Canadian Pacific Railway, and VIA Rail) that operate along the rail corridor to assess how track closures would impact their service and coordinate temporary schedules to accommodate all rail services on the open tracks.

Read more - Appendix B5 - Traffic and Transportation Report

Potential effects and mitigation measures

Potential effects:

• Potential for disturbance of surficial and/or deeply buried archaeological resources due to Lower Don Bridge and Don Yard early works activities.

Mitigation measures:

• Complete additional archaeological assessments where required as early as possible and in advance of any ground disturbance.
• If archaeological materials are encountered (or suspected) during early works activities, all work will stop. The site will be protected from impact and additional assessment will be undertaken.

Potential effects and mitigation measures

Potential effects:

• Potential impact on flooding conditions in the Don River floodplain.
• Potential flooding impacts on site during construction.
• Potential change in stormwater quantity and quality due to potential erosion of exposed soil and increased sediment loading which may impact receiving water bodies and/or municipal stormwater drainage system.

Mitigation measures:

• Floodplain impact assessment will be conducted as planning progresses following Toronto and Region Conservation Authority (TRCA) guidelines once details on the bridge abutment configuration and other design information are available.
• Develop a flood contingency plan with specific measures for any proposed work or temporary laydown and staging areas in the Don River floodplain, as project planning progresses.
• Develop the overall stormwater quality and quantity control strategy in accordance with all relevant municipal, provincial, and federal requirements.
• Develop a stormwater management plan and an erosion sediment control plan, as project planning progresses.
• The following stormwater management best practices will be considered and implemented as required:
  • Reduce amount of exposed soil;
  • Install sediment control measures before grading/land alterations begin;
  • Sequence early works activities so that soil is not exposed for long periods of time;
  • Protect storm drain inlets to filter out debris; and
  • Stabilize all exposed soil areas as soon as land alterations are complete.
• Discharge excess water into nearby municipal sanitary and storm systems where possible.
• TRCA, Waterfront Toronto, and City of Toronto will be consulted to avoid potential infrastructure conflicts and impacts to flood protection measures/initiatives.

Potential effects and mitigation measures

Potential effects:

• Potential for disruption to adjacent lands to accommodate early works activities.
• Nuisance effects (i.e., dust, noise and vibration) from early works activities.
• Visual effects from permanent public-facing structures and early works activities.
• Potential for light trespass, glare and light pollution effects.
• Permanent and temporary property acquisition (property requirements will be confirmed as project planning progresses).
• Potential temporary relocation or removal of streetscaping materials, furniture, and landscaping in the public realm.
• Potential temporary relocation of the “No Shoes” sculpture.

Mitigation measures:

• Maintain access to businesses.
• Develop an air quality management plan to mitigate potential impacts of dust during early works activities (see Air Quality Report for further detail and more mitigation measures).
• Specific permanent property requirements associated with the early works infrastructure components will be minimized to the extent feasible as planning progresses. Temporary property requirements associated with construction laydown and access will be minimized as planning progresses.
• Where possible, use equipment with low vibration emissions, provide smooth surfaces for trucks, and restrict construction hours (see Noise & Vibration for further detail and more mitigation measures).
• Reduce the visual effects of the bridge structure by selecting appropriate building materials and architectural design.
• Provide screened enclosures along early works site boundaries where necessary. 
• Provide temporary lighting and wayfinding signage around early works sites.
• Provide clearly marked pedestrian and cyclist detours where required.
• Following completion of early works, impacted lands will be restored to current City of Toronto standards wherever feasible. Temporary relocation or removal of streetscaping materials, furniture, and landscaping in the public realm will be minimized to the extent feasible.

Potential effects and mitigation measures

Soil

Potential effects:

• Displacement of soils as a result of early works activities may result in ground movement and settlement.
• Early works activities (e.g., excavation) could expose and/or result in the spreading of contaminated materials.

Mitigation measures:

• Complete detailed soil investigations, as project planning progresses.
• Employ excavation support systems as required and/or implement appropriate ground treatment such as jet grouting to reduce the risk of ground loss during early works activities.
• Develop management plan(s) for handling, management and disposal of excavated material.
• Develop and implement remedial action plans, risk assessment and risk mitigation plans for encountering contamination, as necessary.

Groundwater

Potential effects

• Subsidence/settlement of structures in the Zone of Influence* (ZOI) due to construction dewatering.
• Encounter previously contaminated groundwater during early works activities (e.g., dewatering).
• Construction dewatering may impact groundwater-dependent natural features (i.e., Don River as a result of decreases in groundwater discharge).

*The Zone of Influence refers to the area where groundwater levels will be lowered due to dewatering.

Mitigation measures:

• As project planning progresses, determine water taking quantities, quality, and resultant dewatering ZOI through a site-specific hydrogeological investigation, construction dewatering assessment and groundwater management plan.

• Subsidence/settlement impacts to existing structures can be mitigated with measures such as the completion of pre-construction inspections of structures in the dewatering ZOI and implementation of a detailed settlement monitoring program, complete with settlement triggers that result in changes to the dewatering program if surpassed.
• Adhere to source water protection best management practices where necessary, including the development of a salt management plan and a plan for handling and storage of chemicals.
• Develop remedial action plans, risk assessment and risk mitigation plans for encountering contaminated groundwater, as necessary.