Infiltration

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Infiltration of stormwater into underlying soils is one the priority level 1. mechanisms to achieve MOECC runoff volume control targets. In many areas of Ontario, where municipal supplies of potable water are drawn from aquifers, it's also an important mechanism for groundwater recharge.

Infiltration is promoted through a number of LID BMPs:

Constraints[edit]

Infiltration practices are not recommended:

  1. over swelling clays or unstable sub-soils,
  2. over contaminated soils or sites with high risk of contamination from onsite activities,
  3. in flood prone areas where the wastewater system is sensitive to groundwater conditions causing sewer backups, and where LID BMPs have been found to be ineffective,
  4. in areas where the ecology and natural hydrology are dependent upon surface water,
  5. in areas where increased infiltration will result in elevated groundwater levels, which can be demonstrated to damage critical utilities or private property, or
  6. where prohibitions and/or restrictions exist per approved Source Protection Plans (see MOECC guidance).


Infiltration facilities should be designed with drainage modifications where:

  1. the underlying bedrock is within 1 m below the bottom of the proposed BMP, or
  2. the seasonal high groundwater level comes within 1 m below the bottom of the proposed BMP.

Designing with constraints[edit]

Infiltration can still be optimized over 'tight' soils with infiltration rates ≤ 15 mm/hr:

Where infiltration is impossible, LID design alternatives exist which can still capture and retain stormwater:

Planning[edit]

Hydrogeology[edit]

The Conservation Authorities Geoscience Group has prepared a guidance document which attempts to standardize the hydrogeological study requirements for development applications made to Conservation Authorities. It is a helpful guide for all low impact development applications which include infiltration. It is provided with the caveat that not all sections or content are necessary or appropriate for every case. Pre-consultation with your Conservation Authority and municipality is strongly recommended in all cases.

Hydrogeological Assessment Submissions Conservation Authority Guidelines for Development Applications

Beginning a BMP design?[edit]

See Design infiltration rates