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<tr> | <tr> | ||
<th>Mix</th> | <th>Mix</th> | ||
− | <th> | + | <th>Composition in original Manual</th> |
− | <th>Proposed updated composition | + | <th>Proposed updated composition</th> |
<th>Pros</th> | <th>Pros</th> | ||
<th>Cons</th> | <th>Cons</th> | ||
Line 15: | Line 15: | ||
*55-65% construction sand | *55-65% construction sand | ||
*10-20% top soil | *10-20% top soil | ||
− | *25-35% organic | + | *25-35% organic matter<sup>2</sup> |
</td> | </td> | ||
<td> | <td> | ||
*60-70% construction sand | *60-70% construction sand | ||
*15-25% top soil | *15-25% top soil | ||
− | *15-25% organic | + | *15-25% organic matter<sup>2</sup> |
− | *to receive P credit for water captured by underdrain the P content must be less than 30 mg/kg per Mehlich III test; NOTE a minimum P concentration of 12 mg/kg is recommended for plant growth.</td> | + | *to receive P credit for water captured by underdrain the P content must be less than 30 mg/kg (ppm) per Mehlich III (or [[Design criteria for bioretention#Notes about soil phosphorus testing: applicability and interpretation|equivalent]]) test; NOTE a minimum P concentration of 12 mg/kg is recommended for plant growth.</td> |
<td>Likely to sorb more dissolved P and metals than mix B because it contains some fines; best for growth of most plants </td> | <td>Likely to sorb more dissolved P and metals than mix B because it contains some fines; best for growth of most plants </td> | ||
− | <td>Likely to leach P; if topsoil exceeds maximum allowed clay content, higher fines content could result in poor hydraulic | + | <td>Likely to leach P; if topsoil exceeds maximum allowed clay content, higher fines content could result in poor hydraulic performance and long drawdown times</td> |
</tr> | </tr> | ||
<tr> | <tr> | ||
Line 29: | Line 29: | ||
<td> | <td> | ||
*50-70% construction sand | *50-70% construction sand | ||
− | *30-50% organic | + | *30-50% organic matter</td> |
<td> | <td> | ||
*70-85% construction sand | *70-85% construction sand | ||
− | *15-30% organic | + | *15-30% organic matter |
− | *to receive P credit for water captured by underdrain the P content must be less than 30 mg/kg per Mehlich III test; NOTE a minimum P concentration of 12 mg/kg is recommended for plant growth.</td> | + | *to receive P credit for water captured by underdrain the P content must be less than 30 mg/kg per Mehlich III (or [[Design criteria for bioretention#Notes about soil phosphorus testing: applicability and interpretation|equivalent]]) test; NOTE a minimum P concentration of 12 mg/kg is recommended for plant growth.</td> |
<td>Easy to mix; least likely to clog</td> | <td>Easy to mix; least likely to clog</td> | ||
<td>Likely to leach P, lack of fines in mix results in less dissolved pollutant removal; harder on most plants than mix A because it dries out very quickly</td> | <td>Likely to leach P, lack of fines in mix results in less dissolved pollutant removal; harder on most plants than mix A because it dries out very quickly</td> | ||
</tr><tr> | </tr><tr> | ||
<td>C</td> | <td>C</td> | ||
− | <td>Not | + | <td>Not in original MN Stormwater Manual</td> |
<td> | <td> | ||
*85-88 percent by volume sand and | *85-88 percent by volume sand and | ||
*8 to 12 percent fines by volume, | *8 to 12 percent fines by volume, | ||
− | *3 to 5 percent organic matter by | + | *3 to 5 percent organic matter by volume |
− | *recommended P content between 12 and 30 mg/kg per Mehlich III test</td> | + | *recommended P content between 12 and 30 mg/kg per Mehlich III (or [[Design criteria for bioretention#Notes about soil phosphorus testing: applicability and interpretation|equivalent]]) test</td> |
<td>Likely to sorb more dissolved P and metals than mix B because it contains some fines; less likely to leach P than mix B because of low P content</td> | <td>Likely to sorb more dissolved P and metals than mix B because it contains some fines; less likely to leach P than mix B because of low P content</td> | ||
− | <td>Harder on most plants than mix A because it dries out very quickly. Research in Wisconsin indicates that in cold climates, excess of | + | <td>Harder on most plants than mix A because it dries out very quickly. Research in Wisconsin indicates that in cold climates, excess of Na ions can promote displacement of Mg and Ca in the soil, which breaks down soil structure and decreases infiltration rate, and can also cause nutrient imbalances<sup>1</sup></td> |
</tr> | </tr> | ||
<tr> | <tr> | ||
<td>D</td> | <td>D</td> | ||
− | <td>Not | + | <td>Not in original MN Stormwater Manual</td> |
<td> | <td> | ||
*All components below by dry weight: | *All components below by dry weight: | ||
*60-75% sand | *60-75% sand | ||
*Min. 55% total coarse and medium sand as a % of total sand | *Min. 55% total coarse and medium sand as a % of total sand | ||
− | *Less than 12% fine gravel less than 5 mm ( | + | *Less than 12% fine gravel less than 5 mm (Calculated separately from sand/silt/ clay total) |
*2 to 5 % organic matter | *2 to 5 % organic matter | ||
− | *recommended P content between 12 and 30 mg/kg per [ | + | *recommended P content between 12 and 30 mg/kg per [https://crops.extension.iastate.edu/encyclopedia/interpreting-results-mehlich-3-icp-soil-phosphorus-test Mehlich III] (or [[Design criteria for bioretention#Notes about soil phosphorus testing: applicability and interpretation|equivalent]]) test</td> |
<td>Best for pollutant removal, moisture retention, and growth of most plants; less likely to leach P than mix B because of low P content</td> | <td>Best for pollutant removal, moisture retention, and growth of most plants; less likely to leach P than mix B because of low P content</td> | ||
− | <td>Harder to find. Research in Wisconsin indicates that in cold climates, excess of | + | <td>Harder to find. Research in Wisconsin indicates that in cold climates, excess of Na ions can promote displacement of Mg and Ca in the soil, which breaks down soil structure and decreases infiltration rate, and can also cause nutrient imbalances</td> |
+ | </tr> | ||
+ | <tr> | ||
+ | <td>E</td> | ||
+ | <td>Not in original manual</td> | ||
+ | <td> | ||
+ | *60-80% sand meeting gradation requirements of MnDOT 3126, ―Fine Aggregate for Portland Cement Concrete | ||
+ | *20-40% MnDOT 3890 Grade 2 Compost | ||
+ | *30% organic leaf compost</td> | ||
+ | <td>High infiltration rates, relatively inexpensive</td> | ||
+ | <td>As compost breaks down, nutrients available for plants decreases</td> | ||
+ | </tr> | ||
+ | <tr> | ||
+ | <td>F</td> | ||
+ | <td>Not in original manual</td> | ||
+ | <td> | ||
+ | *75% loamy sand by volume: | ||
+ | **Upper Limit: 85-90% sand with %Silt + 1.5 times %Clay > 15%. | ||
+ | **Lower Limit: 70-85% sand with %Silt + 2 times %Clay < 30%. | ||
+ | **Maximum particle size < 1-inch | ||
+ | *25% MnDOT 3890 Grade 2 Compost</td> | ||
+ | <td>Finer particles in loamy sand holds moisture for better plant growth</td> | ||
+ | <td>Lower infiltration rates, requires careful soil placement to avoid compaction, requires custom mixing</td> | ||
</tr> | </tr> | ||
</table> | </table> | ||
<font size=0.5> | <font size=0.5> | ||
− | <sup>1 | + | <sup>1</sup>This problem can be avoided by minimizing salt use. Sodium absorption ratio (SAR) can be tested; if the SAR becomes too high, additions of gypsum (calcium sulfate) can be added to the soil to free the Na and allow it to be leached from the soil (Pitt et al in press).<br> |
+ | <sup>2</sup>[https://dot.state.mn.us/products/erosioncontrolandlandscaping/compost.html MnDOT Grade 2 compost] is recommended.</font size> | ||
− | <noinclude>[[ | + | <noinclude> |
+ | [[Category:Level 3 - General information, reference, tables, images, and archives/Tables/Trees, tree trench, tree box]] | ||
+ | [[Category:Level 3 - General information, reference, tables, images, and archives/Tables/Bioretention]] | ||
+ | [[Category:Level 3 - General information, reference, tables, images, and archives/Tables/Soil and soil properties]] | ||
+ | [[Category:Level 3 - General information, reference, tables, images, and archives/Tables/Media, compost, and media amendments]] | ||
+ | </noinclude> |
Comparison of pros and cons of bioretention soil mixes
Link to this table.
Mix | Composition in original Manual | Proposed updated composition | Pros | Cons |
---|---|---|---|---|
A |
|
|
Likely to sorb more dissolved P and metals than mix B because it contains some fines; best for growth of most plants | Likely to leach P; if topsoil exceeds maximum allowed clay content, higher fines content could result in poor hydraulic performance and long drawdown times |
B |
|
|
Easy to mix; least likely to clog | Likely to leach P, lack of fines in mix results in less dissolved pollutant removal; harder on most plants than mix A because it dries out very quickly |
C | Not in original MN Stormwater Manual |
|
Likely to sorb more dissolved P and metals than mix B because it contains some fines; less likely to leach P than mix B because of low P content | Harder on most plants than mix A because it dries out very quickly. Research in Wisconsin indicates that in cold climates, excess of Na ions can promote displacement of Mg and Ca in the soil, which breaks down soil structure and decreases infiltration rate, and can also cause nutrient imbalances1 |
D | Not in original MN Stormwater Manual |
|
Best for pollutant removal, moisture retention, and growth of most plants; less likely to leach P than mix B because of low P content | Harder to find. Research in Wisconsin indicates that in cold climates, excess of Na ions can promote displacement of Mg and Ca in the soil, which breaks down soil structure and decreases infiltration rate, and can also cause nutrient imbalances |
E | Not in original manual |
|
High infiltration rates, relatively inexpensive | As compost breaks down, nutrients available for plants decreases |
F | Not in original manual |
|
Finer particles in loamy sand holds moisture for better plant growth | Lower infiltration rates, requires careful soil placement to avoid compaction, requires custom mixing |
1This problem can be avoided by minimizing salt use. Sodium absorption ratio (SAR) can be tested; if the SAR becomes too high, additions of gypsum (calcium sulfate) can be added to the soil to free the Na and allow it to be leached from the soil (Pitt et al in press).
2MnDOT Grade 2 compost is recommended.
This page was last edited on 22 December 2022, at 21:13.