Limited Foundation Groundwater Discharge Rules

Summary#

This item changes how Toronto handles water draining from building foundations and updates a water-quality limit for storm sewers. It adds limited flexibility so some groundwater can go into certain storm sewers, while keeping the main rule of protecting sewer and treatment plant capacity. It also raises the allowed level of manganese (a natural mineral) in water sent to storm sewers.

Key changes:

• Allows a small amount of foundation groundwater to discharge to storm sewers that flow directly to a river, creek, or Lake Ontario (no interaction with the combined sewer system), starting October 1, 2026.
• Sets maximum dry‑weather discharge rates for foundation drainage: 3 litres/second per hectare for sites larger than 0.7 ha, and 2 litres/second for sites 0.7 ha or smaller.
• Requires sites to still meet all stormwater targets in the City’s Wet Weather Flow Management Guidelines during wet weather.
• Keeps the ban on sending foundation groundwater to sanitary or combined sewers.
• Increases the manganese limit for storm sewer discharges in the Sewers By‑law from 0.05 mg/L to 2.0 mg/L (takes effect after Council approval).
• Keeps existing exemption pathways and grandfathering for applications submitted before January 1, 2022.

What is unclear:

• Which specific storm sewers “do not interact” with the combined system; detailed maps or lists were not provided in the report.

What it means for you#

• Developers and builders

  • You may discharge a limited amount of foundation groundwater to a qualifying storm sewer if:
    • Water meets all storm sewer quality limits in the Sewers By‑law (including the new manganese limit of 2.0 mg/L once approved).
    • The storm sewer outfalls directly to a watercourse or Lake Ontario and does not interact with the combined system.
    • Your dry‑weather foundation drainage does not exceed:
      • 3 L/s/ha for sites larger than 0.7 ha.
      • 2 L/s total for sites 0.7 ha or smaller.
    • Your total site discharge during wet weather (foundation drainage plus stormwater) meets the City’s Wet Weather Flow targets.
  • You still cannot send foundation groundwater to sanitary or combined sewers.
  • In areas of the city with combined sewers, projects that front a separate storm sewer that outfalls directly to a watercourse or the lake may benefit from this change; other sites may still need on‑site solutions (e.g., building above the water table, infiltration galleries, greywater reuse, or watertight foundations).
  • If your groundwater has manganese above 2.0 mg/L (often linked to non‑natural sources such as some brownfields), on‑site treatment or another solution would still be needed for storm sewer discharge.
  • Timing:
    • The amended Foundation Drainage Policy starts October 1, 2026. Existing applications subject to the FDP can be amended on or after that date to use the new rules.
    • The higher manganese limit in the by‑law takes effect after Council approval (earlier than the FDP change).

• Property owners near watercourses or the lake

  • The City considers the health and environmental risk of allowing limited groundwater discharges to be low. The report notes that volumes are limited and groundwater manganese is usually low. It also notes a possible cooling effect on streams during hot weather.

• Applicants with older approvals

  • Applications filed before January 1, 2022, and those with existing exemptions, remain outside the FDP or keep their exemption.

Expenses#

No direct public cost is identified in the available material. The City’s report states there are no financial implications, and the Chief Financial Officer reviewed and agreed.

Possible private impacts:

• Developers may face design, monitoring, and compliance costs to meet discharge rate caps and water-quality limits.
• The higher manganese limit could reduce the need for on‑site treatment at many sites with naturally occurring manganese.
• Sites without access to a qualifying storm sewer may still face costs for alternatives (e.g., watertight foundations, infiltration, or reuse systems).

Proponents' View#

• The changes appear intended to preserve sewer and wastewater treatment capacity needed for growth while offering targeted flexibility to support new housing starts.
• Allowing small, controlled foundation groundwater flows to storm sewers (not combined or sanitary) is based on hydraulic capacity analysis and is expected to maintain overall system performance.
• Keeping groundwater out of combined sewers avoids adding continuous flows to treatment plants and helps the City meet provincial requirements and long-term goals to reduce combined sewer overflows.
• Raising the manganese limit to 2.0 mg/L aligns with data showing most Toronto groundwater is at or below this level, is consistent with some nearby municipalities, and is expected to pose low risk because discharge volumes are limited.
• Limited groundwater discharges to storm outfalls could slightly cool urban streams during heat, which may help aquatic life.

Opponents' View#

• Development industry groups (BILD and RESCON) support the intent but say the proposed dry‑weather cap (3 L/s/ha; 2 L/s for small sites) may be too restrictive for many projects. They recommend treating foundation drainage as part of a site’s overall peak storm discharge target rather than a fixed dry‑weather cap.
• BILD and RESCON also ask for clearer identification of storm sewers that qualify in areas with combined sewers, more site‑specific flexibility (including potential, case‑by‑case discharge to combined sewers in exceptional situations), and transitional clarity so applications referencing the new policy are not required to comply before October 1, 2026.
• A developer (Hullmark) states that, in dense areas on combined sewers, the policy still forces watertight foundations, which can raise costs and embodied carbon compared to drained designs. They call for a performance‑based approach that could allow controlled, site‑specific discharge to combined sewers where impacts on treatment capacity are negligible and quality meets standards.
• Hullmark also notes that Council asked for clear exemption criteria in 2025 and says the proposed changes do not add objective criteria or a consistent, outcomes‑based path to exemptions.
• One concern is that the report does not provide detailed maps of which storm sewers meet the “no interaction with combined system” condition, which may make early feasibility assessments harder.