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Line 1: + + − [[File:Sandy Bioretention Soil Mix.jpg|thumb|Sandy filter media mix]] − *70 - 80 % coarse sand+ − *10 - 15 % topsoil+ − + + + + + + + + + + + + + + + + + + + + + + + + + − + − The final blended product should have the following properties:+ + + + + + + + + + + + + + + + + + + + + + + + + − <table class = "table table-striped table-responsive"> − <caption><strong></strong></caption> − <tr class ='success'><th>Characteristic</th><th>Criterion</th><th>Recommended method</th></tr> − <tr><td>[[Texture]]</td><td><20 % fines</td><td>Hygrometer</td></tr> − <tr><td>[[Organic matter (OM)]]</td><td>5 - 10%</td><td>ASTM D2974-14, Standard test methods for moisture, ash and organic matter of peat and other organic soils. </td></tr> − <tr><td>[[Phosphorus]]</td><td>10 - 30 ppm</td><td>'Bray' is most common in Ontario. <br>Alternatives include 'Mehlich I or III', or 'Olsen'. <ref>Sawyer JE, Mallarino AP. Differentiating and Understanding the Mehlich 3, Bray, and Olsen Soil Phosphorus Tests 1. http://www.agronext.iastate.edu/soilfertility/info/mnconf11_22_99.pdf. Accessed August 1, 2017.</ref></td></tr> − <tr><td>[[Cationic exchange capacity(CEC)]]</td><td>> 10 meq/100g</td><td>ASTM D7503-10, Standard test method for measuring the exchange complex and cation exchange capacity of inorganic fine grained soils. </td></tr> − <tr><td>[[Hydraulic conductivity]]</td><td>> 25 mm/hr <br> <250 mm/hr</td><td>Falling head or constant head KSAT</td></tr> − </table> − + − <h3>Compost</h3>+ − + − '''[[Compost|Compost Specifications]]'''+ + + + + + − + + + + + + + + + + + + + + + + + + + + + + − <table class = "table table-striped table-responsive">+ − + − <tr class ='success'><th>Material</th><th>Benefits</th><th>Potential concerns</th></tr> − <tr><td>Coconut coir</td><td>Doesn't leach P</td><td>Requires importation</td></tr> − <tr><td>Wood chip</td><td>Doesn't leach P <br>Promotes nitrogen removal from water</td><td>TBD</td></tr> − − + − http://www.modularwetlands.com/new/wp-content/uploads/2015/11/2-Bioretention-Synthesis-2015-DAhearn.pdf+ − <h3>Wood derivatives</h3>+ − https://www.unh.edu/unhsc/sites/default/files/media/unhsc_bsm_spec_2-28-17_0.pdf+ − https://www.unh.edu/unhsc/sites/unh.edu.unhsc/files/STONE%20THESIS%20FINAL.pdf − https://jbioleng.biomedcentral.com/articles/10.1186/s13036-017-0057-4 (focus on denitrification) − ==Additives== − Typically these components would comprise 5- 10 % by volume of the filter media mixture. − It is recommended that this fraction be taken from the topsoil or the organic portion otherwise; keeping the sand as minimum 65 % by volume. </p> − </div>+ − <div class="col-md-4"> − <panelWarning> − <gallery mode="packed" widths=300px heights=300px> − Sandy Bioretention Soil Mix.jpg| Sandy filter media mix − </gallery> − </panelWarning> − </div> − <div class="col-md-12"> − ---- − <references />
no edit summary
[[File:Sandy Bioretention Soil Mix.jpg|thumb|Sandy filter media mix.]]
[[File:Media hand.jpg|thumb|Filter media being used for an online [[bioswale|bioretention swale]] (also of previous, more sandy specification)]]
{{TOClimit|2}}
{{TOClimit|2}}
It is recommended that the mixture comprises:
It is recommended that the mixture comprises:
{|Class="wikitable"
|+One of these two blend options
*10 - 15 % organic soil component
|-
!
!Blend A: Drainage rate priority
!Blend B: Water quality treatment priority
|-
!Application
|Impervious area to pervious area (I:P) ratio of 15:1 or greater
|
{{Plainlist|1=
*More diverse [[Plant lists|planting]] options,
*Improved [[heavy metals|metals]] and [[phosphorus]] retention.}}
|-
!Proportions
|
3 parts [[sand]]<br>
1 part [[Bioretention: Filter media#Organic components|organic soil components]] and [[Bioretention: Filter media#Additives|additives]]
|
3 parts [[sand]]<br>
2 parts [[topsoil]]<br>
1 part [[Bioretention: Filter media#Organic components|organic soil components]] and [[Bioretention: Filter media#Additives|additives]]
|-
!Porosity
|This mixture may be assumed to have a porosity of [[Bioretention media storage|'''0.4''']] unless demonstrated otherwise
|This mixture may be assumed to have a porosity of [[Bioretention media storage|'''0.35''']] unless demonstrated otherwise
|}
Filter media should be obtained premixed from a vendor and meet all municipal, provincial and federal environmental standards. Mixing of sand, topsoil and compost should be done in a manner that preserves topsoil peds. The mixture should be free of stones, stumps, roots, or other debris larger than 50 mm diameter. Samples of the filter media should be dried, ground and tested to ensure they meet the following specifications:
Filter media should be obtained premixed from the vendor and meet all municipal, provincial and federal environmental standards. To minimize transportation-related environmental impacts, filter media should be obtained from local vendors and blended from locally sourced materials. Topsoil used to produce the mix should be passed through a 5 centimetre (2 inch) screen to remove large rocks, roots and other debris, while retaining soil peds. Samples of the filter media should be dried, ground and tested by a certified soil testing laboratory to ensure they meet the following specifications:
{|class="wikitable"
|+ Bioretention filter media
|-
!Characteristic
!Criterion
!Recommended test method
|-
![[Grain size analysis| Particle-size distribution (PSD)]]
|< 25% silt- and clay-sized particles (smaller than 0.05 mm) combined; <br> 3 to 12% clay-sized particles (0.002 mm or smaller)||ASTM D6913/D6913M, Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis (pebble to sand fraction); and <br>
ASTM D7928, Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis (silt and clay fraction).
|-
![[Organic matter| Organic matter (OM)]]
|3 to 10% by dry weight||ASTM F1647, Standard Test Methods for Organic Matter Content of Athletic Field Rootzone Mixes.
|-
![[Phosphorus| Phosphorus, plant-available or extractable]]
|12 to 40 ppm||As measured by the 'Olsen' method for alkaline and calcareous soils (common in Ontario). Alternatives include 'Mehlich I or III', or 'Bray', which is better suited to acidic to slightly alkaline and non-calcareous soils. NB: Results from different test methods are not directly comparable.<ref>Sawyer JE, Mallarino AP. Differentiating and Understanding the Mehlich 3, Bray, and Olsen Soil Phosphorus Tests 1. http://www.agronext.iastate.edu/soilfertility/info/mnconf11_22_99.pdf. Accessed August 1, 2017.</ref>
|-
![[Cationic exchange capacity(CEC)| Cationic exchange capacity (CEC)]]
|> 10 meq/100 g||ASTM D7503, Standard Test Methods for Measuring the Exchange Complex and Cation Exchange Capacity of Inorganic Fine-Grained Soils.
|-
!Hydraulic conductivity, saturated (K<sub>f</sub>)
|> 75 mm/h; Blend A <br> > 25 mm/h; Blend B <br> < 300 mm/h; Blend A and B||ASTM D2434, Standard Test Method for Permeability of Granular Soils (Constant Head), when the sample is compacted to 85% of its maximum dry density in accordance with ASTM D698, Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort.
|}
Note that you may choose not to use particle-size distribution as a criterion for acceptance of a filter media blend, but saturated hydraulic conductivity should be one. While information on particle-size distribution and soil texture are useful in selecting plants, the disconnect between hydraulic conductivity and uniformity of gradation makes it far less important than measuring the saturated hydraulic conductivity directly<ref>CRC for Water Sensitive Cities. (2015). Adoption Guidelines for Stormwater Biofiltration Systems: Appendix C - Guidelines for filter media in stormwater biofiltration systems.</ref>
==Sand==
==Sand==
{{:Sand}}
{{:Sand}}
==Topsoil==
==Topsoil==
{{:Topsoil}}
{{:Topsoil}}
==Organic components==
==Organic component==
This is the first big opportunity to manage phosphorus export from a [[bioretention]] or [[stormwater planter]] system. While compost is the most common choice, designers working in nutrient-sensitive receiving waters are encouraged to explore the alternatives listed below. Some of these materials may be combined 50:50 with compost to balance providing the nutrients required by the [[plants]] with limiting the potential for leaching of excess nutrients.
Compost is the most widely used organic component. It's use in bioretention facilities is well established and documented. Low-phosphorus composts should always be sought for use in low impact development facilities, including bioretention. These are typically created from feedstocks including yard, leaf, and wood waste, and must exclude manures, biosolids, and food scraps.<ref>Hurley S, Shrestha P, Cording A. Nutrient Leaching from Compost: Implications for Bioretention and Other Green Stormwater Infrastructure. J Sustain Water Built Environ. 2017;3(3):4017006. doi:10.1061/JSWBAY.0000821.</ref><br>
===Compost===
[[Compost]] is the most widely used organic component. It's use in bioretention facilities is well established and documented. In Ontario, compost should comply with mandatory Ontario Compost Quality Standards for Category 'AA'.<ref>Ontario Ministry of the Environment and Climate Change (OMOECC). 2012. Ontario Compost Quality
Standards, July 25, 2012. PIBS 8412. Queen’s Printer of Ontario, Toronto, ON.
https://www.ontario.ca/page/ontario-compost-quality-standards.</ref> See [[Compost]] page for a summary of Category 'AA" compost standards. Compost should also be certified to meet quality parameters recommended under the Compost Council of Canada Compost Quality Alliance (CQA) program.<ref>A & L Canada Laboratories. 2004. Compost Management Program. London, ON.
http://www.alcanada.com/index_htm_files/compost_handbook.pdf.</ref> Low available phosphorus composts should always be sought for use in low impact development facilities, including bioretention. Low available phosphorus composts are typically created from feedstocks including yard, leaf, and wood waste, and excluding manures, biosolids, and food scraps.<ref>Hurley S, Shrestha P, Cording A. Nutrient Leaching from Compost: Implications for Bioretention and Other Green Stormwater Infrastructure. J Sustain Water Built Environ. 2017;3(3):4017006. doi:10.1061/JSWBAY.0000821.</ref><br>
<br>
Even low-phosphorus composts are known to export phosphorus over many years. The use of compost is not recommended in watersheds for which phosphorus pollution is a concern. There are alternatives which have undergone field study, each of which has a number of benefits and potential concerns:
===Organic component alternatives===
Even low-phosphorus composts are known to export phosphorus over many years. The use of compost is not recommended in nutrient-sensitive watersheds where phosphorus pollution is a concern, or an [[Additives| additive]] to enhance nutrient retention of the media should also be included in the blend, or a layer be included above the stone reservoir, or a reactive media vault be included in the treatment train downstream of the bioretention (see Additive below for available options). There are a number of alternative sources of soil organic matter which have undergone field studies which have benefits and potential concerns:
{|class="wikitable"
|+ Organic soil components
|-
!Material
!Benefits
!Concerns
|-
!Coconut coir<ref>Rheaume, A., Hinman, C., and Ahearn, D. (2015). “A Synthesis of Bioretention Research in Pacific Northwest.” Herrera, <http://www.modularwetlands.com/new/wp-content/uploads/2015/11/2-Bioretention-Synthesis-2015-DAhearn.pdf></ref>
|Doesn't leach phosphorus||Must be imported
|-
!Wood chips
|Doesn't leach phosphorus<br>Promotes nitrogen removal from water||
|-
!Peat moss
|Doesn't leach phosphorus||Must be unsustainably extracted from natural wetlands
|-
!Shredded paper (e.g., Pittmoss)
|Doesn't leach phosphorus<br>Promotes denitrification
|
|}
===Wood derivatives===
<caption><strong>Organic soil components</strong></caption>
The 2017 guidance from New Hampshire specifically rules against the inclusion of compost in their bioretention media.<ref>UNHSC Bioretention Soil Specification. (2017). Retrieved from https://www.unh.edu/unhsc/sites/default/files/media/unhsc_bsm_spec_2-28-17_0.pdf</ref> Instead they recommend ''"Shredded wood, wood chips, ground bark, or wood waste; of uniform texture and free of stones, sticks"''. The use of wood chip has been common in New Hampshire for some time, in this 2006 thesis 20% wood chips (not characterized) were incorporated into all of the test cases to match current practices at the time. <ref>Stone, R. M. (2013). Evaluation and Optimization of Bioretention Design for Nitrogen and Phosphorus Removal. University of New Hampshire. Retrieved from https://www.unh.edu/unhsc/sites/unh.edu.unhsc/files/STONE THESIS FINAL.pdf</ref>
</table>
<h3>Coconut coir</h3>
Shredded paper has been tested as an additional source of carbon and as an electron-donor to promote denitrification in a number of successful laboratory and field studies.
<ref>
==Additives==
Typically these components would make up 5 to 10% by volume of the filter media mixture.
{{:Additives}}
{{:Additives}}
==References==