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Minimum bioretention soil media depths recommended to target specific stormwater pollutants

<font size=3>'''Minimum bioretention soil media depths recommended to target specific stormwater pollutants. From [[References for bioretention|Hunt et al.]] (2012) and [[References for bioretention|Hathaway et al.]], (2011). NOTE: The [https://stormwater.pca.state.mn.us/index.php?title=MN_CSW_Permit_Section_16_Infiltration_Systems#16.12 Construction Stormwater permit] requires a 3 foot separation from the bottom of an infiltration practice and bedrock or seasonally saturated soils.'''</font size><br>
Link to this [[Minimum bioretention soil media depths recommended to target specific stormwater pollutants |table]]

<table class="sortable">
<tr>
<th>Pollutant</th>
<th>Depth of Treatment with upturned elbow or elevated underdrain</th>
<th>Depth of Treatment without underdrain or with underdrain at bottom</th>
<th>Minimum depth</th>
</tr>
<tr>
<td>Total suspended solids (TSS)</td>
<td>Top 2 to 3 inches of bioretention soil media</td>
<td>Top 2 to 3 inches of bioretention soil media</td>
<td>Not applicable for TSS because minimum depth needed for plant survival and growth is greater than minimum depth needed for TSS reduction</td>
</tr>
<tr>
<td>Metals</td>
<td>Top 8 inches of bioretention soil media</td>
<td>Top 8 inches of bioretention soil media</td>
<td>Not applicable for metals because minimum depth needed for  plant survival and growth is greater than minimum depth needed for metals reduction</td>
</tr>
<tr>
<td>Hydrocarbons</td>
<td>3 to 4 inch Mulch layer, top 1 inch of bioretention soil media</td>
<td>3 to 4 inches Mulch layer, top 1 inch of bioretention soil media</td>
<td>Not applicable for hydrocarbons because minimum depth needed for  plant survival and growth is greater than minimum depth needed for hydrocarbons reduction</td>
</tr>
<tr>
<td>Nitrogen</td>
<td>From top to bottom of bioretention soil media; Internal Water Storage Zone (IWS) improves exfiltration, thereby reducing pollutant load to the receiving stream, and also improves nitrogen removal because the longer retention time allows denitrification to occur underanoxic conditions.</td>
<td>From top to bottom of bioretention soil media</td>
<td>Retention time is important, so deeper media is preferred (3 foot minimum)</td>
</tr>
<tr>
<td>Particulate phosphorus</td>
<td>Top 2 to 3 inches of bioretention soil media.  </td>
<td>Top 2 to 3 inches of bioretention soil media.</td>
<td>Not applicable for particulate phosphorus because minimum depth needed for  plant survival and growth is greater than minimum depth needed for particulate phosphorus reduction</td>
</tr>
<tr>
<td>Dissolved phosphorus</td>
<td>From top of media to top of submerged zone.  Saturated conditions cause P to not be effectively stored in submerged zone.</td>
<td>From top to bottom of bioretention soil media</td>
<td>Minimum 2 feet, but 3 feet recommended as a conservative value; if IWS is included, keep top of submerged zone at least 1.5 to 2 feet from surface of media</td>
</tr>
<tr>
<td>Pathogens</td>
<td>From top of soil to top of submerged zone.</td>
<td>From top to bottom of bioretention soil media</td>
<td>Minimum 2 feet; if IWS is included, keep top of submerged zone at least 2 feet from surface of media</td>
</tr>
<tr>
<td>Temperature</td>
<td>From top to bottom of bioretention soil media; Internal Water Storage Zone (IWS) improves exfiltration, thereby reducing volume of warm runoff discharged to the receiving stream, and also improves thermal pollution abatement because the longer retention time allows runoff to cool more before discharge.</td>
<td>From top to bottom of bioretention soil media</td>
<td>Minimum 3 feet, with 4 feet preferred</td>
</tr>
</table>

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[[Category:Level 3 - General information, reference, tables, images, and archives/Tables/Bioretention]]
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