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<p>Infiltration of stormwater into underlying soils is one the priority level 1. mechanisms to achieve MOECC Runoff Volume Control targets. </p>
===Potential Constraints===
<ol>
<li>Shallow bedrock </li>
<li>High groundwater or areas where increased infiltration will result in elevated groundwater levels, which can be demonstrated to damage critical utilities or private property. </li>
<li>Swelling clays or unstable sub-soils</li>
<li>Contaminated soils or sites with high risk of contamination from onsite activities </li>
<li> 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. </li>
<li> Areas where the ecology and natural hydrology are dependent upon surface water. </li>
<li> Prohibitions and/or restriction per approved Source Protection Plans (see MOECC guidance).
</ol>
<h4>Soil Infiltration Testing </h4><p>Infiltration tests must be undertaken at the location, depth and with a head of water that replicates the proposed design. </p><h4>Groundwater</h4><p> The bottom of the infiltration BMP must ≥ 1 m vertically separated from the seasonally high water table, and underlying bedrock. This reduces the risk of contaminating groundwater and helps to ensure reliable infiltration rates throughout the year. </p>
<div class="column clearfix"><table class="table table-bordered table-hover" >
<tr class="success">
<th rowspan="2">Catchment area</th><th colspan="3">Consequence of failure</th>
<tr class="success">
<th>No damage or inconvenience</th><th>Minor damage or inconvenience to external structures (e.g. ponding in parking lot)</th><th>Significant damage to buildings or infrastructure (e.g. flooding damage)</th>
<tr><td> <100 m<sup>2</sup></td><td>1.5</td><td>2</td><td>10</td></tr>
<tr><td > 100 - 1000 m<sup>2</sup><td>1.5</td><td>3</td><td>10</td></tr>
</table>
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Infiltration of stormwater into underlying native subgrade soils is one mechanism to achieving MECP [[runoff volume control targets]]. In many areas of Ontario, where municipal and private drinking water supplies are drawn from aquifers, it's also an important mechanism for groundwater recharge.
{{TextBox|1= Infiltration is promoted through a number of LID BMPs:
{{textbox|Drainage via infiltration be achieved through a number of LID BMP types:
*[[Infiltration chambers and trenches]] (underground)
*[[Infiltration chambers]] (underground)
*[[Infiltration basins]] (surface)
*[[Infiltration trenches]] (underground)
*[[Bioretention cells]] (surface)
*[[Exfiltration trenches| Exfiltration systems]] (underground)
*[[Bioswales]] (surface)
*[[Bioretention]] (surface, full- or partial-infiltration design variations)
*[[Bioswales]] (surface, full- or partial-infiltration design variations)
*[[Permeable pavements| Permeable pavements]] (surface, full- or partial-infiltration design variations)
*[[Stormwater Tree Trenches|Stormwater tree trenches]] (surface)
*[[Enhanced swales]] featuring check dams (surface)
*[[Dry ponds]] or infiltration basins (surface)
}}
}}
===Planning===
==Constraints==
Infiltration practices are not recommended:
#over-swelling clays or unstable subsoils,
#contaminated soils or sites with high risk of contamination from on-site activities (i.e. pollution hot spots),
#in areas of known or implied karst topography,
#on unstable or steep slopes (>15%),
# to treat construction site runoff,
#to treat combined sewer overflows,
#in flood prone areas where the wastewater system is sensitive to groundwater conditions causing sewer backups,
#in areas where the ecology and natural hydrology are dependent upon surface water,
#in areas where increased infiltration will result in elevated groundwater levels that will damage critical utilities or private property, or
#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).
<br>
See [[Site considerations]] for further guidance on potential site constraints and LID facility type selection and design considerations.
===Designing with constraints===
{{textbox|Infiltration facilities can be effective on low permeability soils with infiltration rates ≤ 15 mm/hr:
*See [[Underdrains| underdrains]] and
*Results from STEP studies of infiltration facilities located on [[low permeability soils]] in Ontario.
Infiltration facilities should be designed with modifications where:
#the underlying bedrock is within 1 m below the bottom of the proposed BMP, or
#the seasonal high groundwater level (i.e. water table) comes within 1 m below the bottom of the proposed BMP.
}}
{{:Groundwater}}
==Planning==
===Hydrogeology===
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.
'''[http://www.lsrca.on.ca/Shared%20Documents/permits/hydrogeological%20_guidelines.pdf?pdf=Hydrogeological-Guidelines Hydrogeological Assessment Submissions Conservation Authority Guidelines for Development Applications]'''
==Beginning an infiltration BMP design?==
See [[Design infiltration rates]]
----
==See also==
*[[Site considerations]]
[[category:Infiltration]]