(Created page with "<Font size=3>'''Comparison of pros and cons of bioretention soil mixes'''</font size><br> Link to this table. <tabl...")
 
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<tr>
 
<tr>
 
<th>Mix</th>
 
<th>Mix</th>
<th>Current composition</th>
+
<th>Composition in original Manual</th>
<th>Proposed updated composition<sup>1</sup></th>
+
<th>Proposed updated composition</th>
 
<th>Pros</th>
 
<th>Pros</th>
 
<th>Cons</th>
 
<th>Cons</th>
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<td>
 
<td>
 
*55-65% construction sand  
 
*55-65% construction sand  
*10-20% top soil*25-35% organic leaf compost</td>
+
*10-20% top soil
 +
*25-35% organic matter<sup>2</sup>
 +
</td>
 
<td>
 
<td>
 
*60-70% construction sand  
 
*60-70% construction sand  
*15-25% top soil*15-25% organic leaf compost</td>
+
*15-25% top soil
 +
*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 (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 performanceand long drawdown times</td>
+
<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>
 
<td>B</td>
 
<td>B</td>
 
<td>
 
<td>
*50-70% construction sand *30-50% organic leaf compost</td>
+
*50-70% construction sand
 +
*30-50% organic matter</td>
 
<td>
 
<td>
*70-85% construction sand *15-30% organic leaf compost</td>
+
*70-85% construction sand
 +
*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 (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 currently in MN Stormwater Manual</td>
+
<td>Not in original MN Stormwater Manual</td>
 
<td>
 
<td>
*85-88 percent by volume sand and*8 to 12 percent fines by volume,*3 to 5 percent organic matter by dry weight
+
*85-88 percent by volume sand and
*P content between 12 and 36 mg/kg per Mehlich III test</td>
+
*8 to 12 percent fines by volume,
<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 oflow P content</td>
+
*3 to 5 percent organic matter by volume
<td>Harder on most plants than mix A because it dries out very quickly. Research in Wisconsin indicates that in cold climates, excess ofsodium 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>2</sup></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>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 currently in MN Stormwater Manual</td>
+
<td>Not in original MN Stormwater Manual</td>
 
<td>
 
<td>
*All components below by dry weight:*60-75% sand*Min. 55% total coarse and medium sand as a % of total sand*Less than 12% fine gravel less than 5 mm (Calculatedseparately from sand/silt/ clay total)*2 to 5 % organic matter*P content between 12 and 36 mg/kg per Mehlich III test</td>
+
*All components below by dry weight:
 +
*60-75% sand
 +
*Min. 55% total coarse and medium sand as a % of total sand
 +
*Less than 12% fine gravel less than 5 mm (Calculated separately from sand/silt/ clay total)
 +
*2 to 5 % organic matter
 +
*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 sodium 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>
+
<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>See soil guidelines for important specifics about soil components and other important parameters<br><sup>2</sup>This problem can be avoided by minimizing salt use. Sodium absorption ratio can be tested, if sodium adsorption ratio becomes too high, additions of gypsum (calcium sulfate) can be added to the soil to free the sodium and allow it to be leached from the soil (Pitt et al in press).</font size>
+
<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>[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>
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<noinclude>
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[[Category:Level 3 - General information, reference, tables, images, and archives/Tables/Trees, tree trench, tree box]]
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[[Category:Level 3 - General information, reference, tables, images, and archives/Tables/Bioretention]]
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[[Category:Level 3 - General information, reference, tables, images, and archives/Tables/Soil and soil properties]]
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[[Category:Level 3 - General information, reference, tables, images, and archives/Tables/Media, compost, and media amendments]]
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</noinclude>

Latest revision as of 12:42, 3 August 2022

Comparison of pros and cons of bioretention soil mixes
Link to this table.

Mix Composition in original Manual Proposed updated composition Pros Cons
A
  • 55-65% construction sand
  • 10-20% top soil
  • 25-35% organic matter2
  • 60-70% construction sand
  • 15-25% top soil
  • 15-25% organic matter2
  • to receive P credit for water captured by underdrain the P content must be less than 30 mg/kg (ppm) per Mehlich III (or equivalent) test; NOTE a minimum P concentration of 12 mg/kg is recommended for plant growth.
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
  • 50-70% construction sand
  • 30-50% organic matter
  • 70-85% construction sand
  • 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 (or equivalent) test; NOTE a minimum P concentration of 12 mg/kg is recommended for plant growth.
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
  • 85-88 percent by volume sand and
  • 8 to 12 percent fines by volume,
  • 3 to 5 percent organic matter by volume
  • recommended P content between 12 and 30 mg/kg per Mehlich III (or equivalent) test
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
  • All components below by dry weight:
  • 60-75% sand
  • Min. 55% total coarse and medium sand as a % of total sand
  • Less than 12% fine gravel less than 5 mm (Calculated separately from sand/silt/ clay total)
  • 2 to 5 % organic matter
  • recommended P content between 12 and 30 mg/kg per Mehlich III (or equivalent) test
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
  • 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
High infiltration rates, relatively inexpensive As compost breaks down, nutrients available for plants decreases
F Not in original manual
  • 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
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 3 August 2022, at 12:42.