Difference between revisions of "Comparison of pros and cons of bioretention soil mixes"
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<th>Mix</th> | <th>Mix</th> | ||
<th>Current composition</th> | <th>Current composition</th> | ||
| − | <th>Proposed updated composition | + | <th>Proposed updated composition</th> |
<th>Pros</th> | <th>Pros</th> | ||
<th>Cons</th> | <th>Cons</th> | ||
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*55-65% construction sand | *55-65% construction sand | ||
*10-20% top soil | *10-20% top soil | ||
| − | *25-35% organic matter<sup> | + | *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 matter<sup> | + | *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 (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> | *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>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> | ||
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*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> | *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 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> | + | <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> | ||
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*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 [http://www.clemson.edu/sera6/M3%20Method%20SERA-6%2001_11-2010.doc Mehlich III] (or [[Design criteria for bioretention#Notes about soil phosphorus testing: applicability and interpretation|equivalent]]) test</td> | *recommended P content between 12 and 30 mg/kg per [http://www.clemson.edu/sera6/M3%20Method%20SERA-6%2001_11-2010.doc Mehlich III] (or [[Design criteria for bioretention#Notes about soil phosphorus testing: applicability and interpretation|equivalent]]) test</td> | ||
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</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> | + | <sup>2</sup>[http://www.dot.state.mn.us/pre-letting/spec/2005/3835-3973.pdf MnDOT Grade 2 compost] is recommended.</font size> |
<noinclude>[[category:table]]</noinclude> | <noinclude>[[category:table]]</noinclude> | ||
Revision as of 16:25, 8 April 2014
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The anticipated review period for this page is through March 2014
Comparison of pros and cons of bioretention soil mixes
Link to this table.
| Mix | Current composition | 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 currently in 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 currently in 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 |
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.