Infiltration

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Infiltration of stormwater into underlying soils is one mechanism to achieving MECP 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 subsoils,
  2. contaminated soils or sites with high risk of contamination from on-site activities (i.e. pollution hot spots),
  3. in areas of known or implied karst topography,
  4. on unstable or steep slopes (>15%),
  5. to treat construction site runoff,
  6. to treat combined sewer overflows,
  7. in flood prone areas where the wastewater system is sensitive to groundwater conditions causing sewer backups,
  8. in areas where the ecology and natural hydrology are dependent upon surface water,
  9. in areas where increased infiltration will result in elevated groundwater levels that will damage critical utilities or private property, or
  10. where prohibitions and/or restrictions exist per approved Drinking Water Source Protection Plans (e.g. should not be used to treat pavement runoff within 2 year time of travel wellhead protection areas; see MOECC guidance).


Infiltration facilities should be designed with modifications where:

  1. the underlying bedrock is within 1 m below the bottom of the proposed BMP, or
  2. the seasonal high groundwater level (i.e. water table) 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 local conservation authority and municipality is strongly recommended in all cases.

Hydrogeological Assessment Submissions Conservation Authority Guidelines for Development Applications

Beginning an infiltration BMP design?[edit]

See Design infiltration rates


See also[edit]