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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.
| + | 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, partial-infiltration design variation) |
| + | *[[Enhanced swales]] or [[Swales |swales]] featuring check dams (surface) |
| + | *[[Dry ponds]] or infiltration basins (surface) |
| }} | | }} |
− | </p>
| + | |
− | ===Constraints===
| + | ==Constraints== |
| Infiltration practices are not recommended: | | Infiltration practices are not recommended: |
− | <ol>
| + | #over-swelling clays or unstable subsoils, |
− | <li>Where the bedrock is within 1 m below the bottom of the proposed BMP.</li>
| + | #contaminated soils or sites with high risk of contamination from on-site activities (i.e. pollution hot spots), |
− | <li>Where the seasonal high groundwater level comes within 1 m below the bottom of the proposed BMP. Or in areas where increased infiltration will result in elevated groundwater levels, which can be demonstrated to damage critical utilities or private property. </li>
| + | #in areas of known or implied [[Karst |karst topography]], |
− | <li>Over swelling clays or unstable sub-soils</li>
| + | #on unstable or steep slopes (>15%), |
− | <li>Over contaminated soils or sites with high risk of contamination from onsite activities </li>
| + | # to treat construction site runoff, |
− | <li>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. </li>
| + | #to treat combined sewer overflows, |
− | <li>In areas where the ecology and natural hydrology are dependent upon surface water. </li>
| + | #in flood prone areas where the wastewater system is sensitive to groundwater conditions causing sewer backups, |
− | <li>Where prohibitions and/or restrictions exist per approved Source Protection Plans (see MOECC guidance).
| + | #in areas where the ecology and natural hydrology are dependent upon surface water, |
− | </ol>
| + | #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 source water protection plans (e.g. should not be used to treat pavement runoff within wellhead protection area B, 2 year time of travel zones, nor within groundwater quality issue contributing areas where Sodium or Chloride is a threat). |
| <br> | | <br> |
− | <p>Without infiltration, many LID design alternatives exist which can still capture and retain stormwater:
| + | See [[Site considerations]] for further guidance on potential site constraints and LID facility type selection and design considerations. |
− | <ul>
| |
− | <li>[[Partially infiltrating bioretention]]</li>
| |
− | <li>[[Bioretention planters]]</li>
| |
− | <li>[[Rainwater harvesting]]</li>
| |
− | <li>[[Green roofs]]</li>
| |
− | </ul></p>
| |
| | | |
− | ===Planning=== | + | ===Designing with constraints=== |
− | <h4>Soil Infiltration Testing </h4>
| + | {{textbox|Infiltration facilities can be effective on low permeability soils with infiltration rates ≤ 15 mm/hr: |
− | <p>Infiltration tests must be undertaken at the location, depth and with a head of water that replicates the proposed design. </p>
| + | *See [[Underdrains| underdrains]] and |
− | <h4>Groundwater</h4>
| + | *Results from STEP studies of infiltration facilities located on [[low permeability soils]] in Ontario. |
− | <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>
| + | Infiltration facilities should be designed with modifications where: |
− | | + | #the underlying bedrock is within 1 m below the bottom of the proposed BMP, or |
− | <clearFix></clearFix>
| + | #the seasonal high groundwater level (i.e. water table) comes within 1 m below the bottom of the proposed BMP. |
− | <div class="column clearfix">
| + | }} |
− | <table class="table table-bordered table-hover" >
| + | {{:Groundwater}} |
− | <caption><strong>Suggested safety factors to be applied when designing infiltration facilities</strong></caption>
| + | ---- |
− | <tr class="success">
| + | [[category:Infiltration]] |
− | <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 style="white-space: nowrap"> 100 - 1000 m<sup>2</sup><td>1.5</td><td>3</td><td>10</td></tr>
| |
− | </table>
| |