Difference between revisions of "Bioretention: Filter media"

From LID SWM Planning and Design Guide
Jump to: navigation, search
(Compost)
 
(44 intermediate revisions by 2 users not shown)
Line 8: Line 8:
 
|-
 
|-
 
!
 
!
!Blend A: Drainage priority
+
!Blend A: Drainage rate priority
!Blend B: Water quality priority
+
!Blend B: Water quality treatment priority
 
|-
 
|-
 
!Application
 
!Application
|Higher I/P ratio
+
|Impervious area to pervious area (I:P) ratio of 15:1 or greater
 
|
 
|
 
{{Plainlist|1=
 
{{Plainlist|1=
*More diverse [[Plant lists|planting]],
+
*More diverse [[Plant lists|planting]] options,
 
*Improved [[heavy metals|metals]] and [[phosphorus]] retention.}}  
 
*Improved [[heavy metals|metals]] and [[phosphorus]] retention.}}  
 
|-
 
|-
Line 25: Line 25:
 
3 parts [[sand]]<br>  
 
3 parts [[sand]]<br>  
 
2 parts [[topsoil]]<br>  
 
2 parts [[topsoil]]<br>  
1 part sand [[Bioretention: Filter media#Organic components|organic soil components]] and [[Bioretention: Filter media#Additives|additives]]
+
1 part [[Bioretention: Filter media#Organic components|organic soil components]] and [[Bioretention: Filter media#Additives|additives]]
 
|-
 
|-
!
+
!Porosity
|This mixture may be assumed to have available water storage of [[Bioretention media storage|'''0.4''' unless demonstrated otherwise]]
+
|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 available water storage of '''0.35''' 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.
+
Filter media should be obtained premixed from a vendor and meet all municipal, provincial and federal environmental standards. 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:
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:
 
  
 
{|class="wikitable"
 
{|class="wikitable"
Line 40: Line 39:
 
!Characteristic
 
!Characteristic
 
!Criterion
 
!Criterion
!Recommended method
+
!Recommended test method
 
|-
 
|-
![[Texture]]
+
![[Grain size analysis| Particle-size distribution (PSD)]]
|<15 % fines||Hygrometer
+
|< 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 D7928, Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis.
 
|-
 
|-
![[Organic matter]] (OM)
+
![[Organic matter| Organic matter (OM)]]
|5 - 10 %||ASTM F1647-11, Standard test methods for organic matter content of athletic field rootzone mixes.
+
|3 to 10% by dry weight||ASTM F1647, Standard Test Methods for Organic Matter Content of Athletic Field Rootzone Mixes.
 
|-
 
|-
![[Phosphorus]]
+
![[Phosphorus| Phosphorus, plant-available or extractable]]
|12 - 40 ppm||As measured by the 'Olsen' method for alkaline and calcareous soils (common in Ontario). Alternatives include 'Mehlich I or III', or 'Bray', better suited to acidic to slightly alkaline and non-calcareous soils. Results from these are not directly translatable.<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>
+
|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)| Cationic exchange capacity (CEC)]]
|10 meq/100 g||ASTM D7503-10, Standard test methods for measuring the exchange complex and cation exchange capacity of inorganic fine grained soils.  
+
|> 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]]
+
!Hydraulic conductivity, saturated (K<sub>f</sub>)
|> 25 mm/hr <br> < 250 mm/hr||Falling head or constant head KSAT
+
|> 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 grain size distribution does not form part of the recommended acceptance criteria. Whilst this information may be useful in designing blends, the disconnect between hydraulic conductivity and the uniformity of gradation makes it far less important then measuring the 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>  
+
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==
Line 64: Line 63:
 
==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. Whilst compost is the most common ingredient, designers working in sensitive watersheds are encouraged to explore the alternatives listed below. Some of these materials may be combined 50:50 with compost to balance the nutrients required by the [[plants]] and the potential for leaching of excess nutrient.   
+
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===
 
===Compost===
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 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 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>
 
'''[[Compost|Compost Specifications]]'''
 
'''[[Compost|Compost Specifications]]'''
  
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:
+
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. There are a number of alternative sources of soil organic matter which have undergone field studies which have benefits and potential concerns:
  
 
{|class="wikitable"
 
{|class="wikitable"
Line 81: Line 80:
 
|-
 
|-
 
!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>
 
!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||Requires importation
+
|Doesn't leach phosphorus||Must be imported
 
|-
 
|-
!Wood chip
+
!Wood chips
|Doesn't leach phosphorus<br>Promotes nitrogen removal from water||-
+
|Doesn't leach phosphorus<br>Promotes nitrogen removal from water||
 
|-
 
|-
!Peat Moss
+
!Peat moss
|Doesn't leach phosphorus||Sustainability controversial
+
|Doesn't leach phosphorus||Must be extracted from natural wetlands
 
|-
 
|-
!Shredded paper <ref>Urban Drainage and Flood Control District. (2010). “Bioretention.” <http://udfcd.org/criteria-manual/volume-3/t-03-bioretention/> (Mar. 15, 2018).</ref> (see: Pittmoss)
+
!Shredded paper (e.g., Pittmoss)
|||
+
|Doesn't leach phosphorus<br>Promotes denitrification
 +
|
 
|}
 
|}
 
  
 
===Wood derivatives===
 
===Wood derivatives===
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 sphagnum peat or ''"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>
+
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>
  
 
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.  
 
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.  
Line 101: Line 100:
  
 
==Additives==
 
==Additives==
Typically these components would make up 5- 10 % by volume of the filter media mixture.  
+
Typically these components would make up 5 to 10% by volume of the filter media mixture.  
  
 
{{:Additives}}
 
{{:Additives}}
 
----
 
----

Latest revision as of 03:45, 14 July 2020

Sandy filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. mix.
Filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. being used for an online bioretention swale (also of previous, more sandy specification)

It is recommended that the mixture comprises:

One of these two blend options
Blend A: Drainage rate priority Blend B: Water quality treatment priority
Application ImperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. area to pervious area (I:P) ratio of 15:1 or greater
Proportions

3 parts sand
1 part organic soil components and additives

3 parts sand
2 parts topsoil
1 part organic soil components and additives

Porosity This mixture may be assumed to have a porosity of 0.4 unless demonstrated otherwise This mixture may be assumed to have a porosity of 0.35 unless demonstrated otherwise

Filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. should be obtained premixed from a vendor and meet all municipal, provincial and federal environmental standards. 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 mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. should be dried, ground and tested by a certified soil testing laboratory to ensure they meet the following specifications:

BioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.
Characteristic Criterion Recommended test method
Particle-size distribution (PSD) < 25% siltSoil or media particles smaller than sand and larger than clay (3 to 60 m)- and clay1. A mineral soil separate consisting of particles less than 0.002 millimeter in equivalent diameter. 2. A soil texture class. 3. (Engineering) A fine-grained soil (more than 50 percent passing the No. 200 Sieve) that has a high plasticity index in relation to the liquid limit. (Unified Soil Classification System).-sized particles (smaller than 0.05 mm) combined;
3 to 12% clay1. A mineral soil separate consisting of particles less than 0.002 millimeter in equivalent diameter. 2. A soil texture class. 3. (Engineering) A fine-grained soil (more than 50 percent passing the No. 200 Sieve) that has a high plasticity index in relation to the liquid limit. (Unified Soil Classification System).-sized particles (0.002 mm or smaller)
ASTM D7928, Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the SedimentationDeposition of material of varying size, both mineral and organic away from its site of origin by the action of water, wind, gravity or ice.Settling-out or deposition of particulate matter suspended in runoff. (Hydrometer) Analysis.
Organic matter (OM) 3 to 10% by dry weight ASTM F1647, Standard Test Methods for Organic Matter Content of Athletic Field Rootzone Mixes.
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.[1]
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 conductivityA parameter that describes the capability of a medium to transmit water., saturated (Kf) > 75 mm/h; Blend A
> 25 mm/h; Blend B
< 300 mm/h; Blend A and B
ASTM D2434, Standard Test Method for Permeability of GranularGravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices. 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 mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. blend, but saturated hydraulic conductivityA parameter that describes the capability of a medium to transmit water. should be one. While information on particle-size distribution and soil texture are useful in selecting plants, the disconnect between hydraulic conductivityA parameter that describes the capability of a medium to transmit water. and uniformity of gradation makes it far less important than measuring the saturated hydraulic conductivityA parameter that describes the capability of a medium to transmit water. directly[2]

SandMineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

Particle size distribution graph for C33 sandMineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm., as described in table
  • Coarse sandMineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm. for LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. construction shall be washed clean and free free of toxic materials.
  • The pH of the sandMineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm. shall be ≤ 7.0.
  • Manufactured sandMineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm. from limestone or dolostone parent material is not acceptable.
  • The coarse sandMineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm. shall have a fineness modulus index between 2.8 and 3.1 according to ASTM C33/C33M, or otherwise meet the gradation below.
Particle size distribution
Sieve Percent passing
9.5 mm 100
4.75 mm (No.4) 95 - 100
2.36 mm (No.8) 80 - 100
1.18 mm (No.16) 50 - 85
0.60 mm (No.30) 25 - 50
0.30 mm (No.50) 5 - 30
0.15 mm (No.100) 0 - 10
0.075 mm (No.200) ≤ 3

Topsoil

  • Topsoil may be material that was stripped from the project site and stored in stockpiles for re-use, or material imported to the site from a supplier provided the physical and chemical characteristics are within acceptable ranges.
  • Topsoil shall be in compliance with Ontario Regulation 153/04 Record of Site Condition standards for soil quality or as amended through Ontario Management of Excess Soil - A Guide for Best Management Practices.
  • Soil laboratory reports shall certify the material to be suitable for re-use on residential, parkland, institutional, industrial, commercial, or community landscapes for the germination of seeds and the support of vegetative growth.

The factors to consider in determining if a topsoil is suitable for use as planting soil for a vegetated stormwater practice, or use in producing a bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. mixture include the following:

  • Must be friable and capable of sustaining vigorous plant growth;
  • Must be free from toxic material and roots, stones or debris over 50 mm (2") in diameter;
  • Should not have been passed through sieves or screens smaller than 50 mm (2”) to avoid eliminating peds;
  • Should have a Loamy SandMineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm., Sandy Loam, Sandy Clay1. A mineral soil separate consisting of particles less than 0.002 millimeter in equivalent diameter. 2. A soil texture class. 3. (Engineering) A fine-grained soil (more than 50 percent passing the No. 200 Sieve) that has a high plasticity index in relation to the liquid limit. (Unified Soil Classification System). Loam, Loam or Silty Loam soil texture;
  • For use in producing bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. Blend B (water quality treatment priority), the topsoil must contain at least 9%, and not greater than 36% clay1. A mineral soil separate consisting of particles less than 0.002 millimeter in equivalent diameter. 2. A soil texture class. 3. (Engineering) A fine-grained soil (more than 50 percent passing the No. 200 Sieve) that has a high plasticity index in relation to the liquid limit. (Unified Soil Classification System).-sized particles.
  • Must contain a minimum of 5% organic matter by dry weight or be amended so, through addition of an organic soil conditioner;
  • Must have a pH of between 6.0 and 7.8;
  • Must have a sodium absorption ratio less than 15;
  • Must have a cationic exchange capacity greater than 10 milliequivalents per 100 grams (meq/100 g).

Specify that 4 litre samples of topsoil, from each source to be drawn upon, be provided to the consultant for visual inspection, along with topsoil quality test results from an accredited soil testing laboratory, or a quality assurance certificate from the supplier.

We recommend a planting soil or filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. depth of 300 mm to support grasses, 600 mm for shrubs and perennials, and 1000 mm for trees.

Organic component

This is the first big opportunity to manage phosphorus export from a bioretention or stormwater planter system. While compostDecayed organic material used as a plant fertilizer. Compost helps to support healthy plant growth through the slow release of nutrients and the retention of moisture in the soil. is the most common choice, designers working in nutrient-sensitive receiving watersWatercourses and Lake Ontario, to which Stormwater and Combined Sewer Overflows discharge. are encouraged to explore the alternatives listed below. Some of these materials may be combined 50:50 with compostDecayed organic material used as a plant fertilizer. Compost helps to support healthy plant growth through the slow release of nutrients and the retention of moisture in the soil. to balance providing the nutrients required by the plants with limiting the potential for leaching of excess nutrients.

CompostDecayed organic material used as a plant fertilizer. Compost helps to support healthy plant growth through the slow release of nutrients and the retention of moisture in the soil.

CompostDecayed organic material used as a plant fertilizer. Compost helps to support healthy plant growth through the slow release of nutrients and the retention of moisture in the soil. is the most widely used organic component. It's use in bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. facilities is well established and documented. Low-phosphorus composts should always be sought for use in low impact developmentA stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. facilities, including bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.. These are typically created from feedstocks including yard, leaf, and wood waste, and excluding manures, biosolids, and food scraps.[3]
Compost Specifications

Even low-phosphorus composts are known to export phosphorus over many years. The use of compostDecayed organic material used as a plant fertilizer. Compost helps to support healthy plant growth through the slow release of nutrients and the retention of moisture in the soil. is not recommended in nutrient-sensitive watersheds where phosphorus pollution is a concern. There are a number of alternative sources of soil organic matter which have undergone field studies which have benefits and potential concerns:

Organic soil components
Material Benefits Concerns
Coconut coir[4] Doesn't leach phosphorus Must be imported
Wood chips Doesn't leach phosphorus
Promotes nitrogen removal from water
Peat moss Doesn't leach phosphorus Must be extracted from natural wetlands
Shredded paper (e.g., Pittmoss) Doesn't leach phosphorus
Promotes denitrification

Wood derivatives

The 2017 guidance from New Hampshire specifically rules against the inclusion of compostDecayed organic material used as a plant fertilizer. Compost helps to support healthy plant growth through the slow release of nutrients and the retention of moisture in the soil. in their bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. media.[5] 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. [6]

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 mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. mixture.

A number of granularGravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices. amendments have been demonstrated to improve nutrient removal from discharge water in BMPs such as bioretention systems, stormwater planters, absorbent landscapes, sand filters or green roofs.

There are two primary processes involved, chemical precipitationAny form of rain or snow. and adsorptionThe attachment of gas, vapour or dissolved matter onto the surface of solid materials.. Both mechanisms are ultimately finite, but have been shown in come cases to make significant improvements on the discharged water quality over several years.

In our effort to make this guide as functional as possible, we have decided to include proprietary systems and links to manufacturers websites.
Inclusion of such links does not constitute endorsement by the Sustainable Technologies Evaluation Program.
Lists are ordered alphabetically; link updates are welcomed using the form below.

Filter Media Additives
Material Benefits Potential concerns
Biochar Renewable
Enhances soil aggregation, water holding capacity and organic carbon content
Currently expensive
Energy intensive to produce
Some sources say ineffective for phosphorus removal
Bold & GoldTM Documented total phosphorus removal of up to 71%[7] Proprietary
Iron filings or Zero valent iron (ZVI) Proven phosphorus retention
Retained phosphorus is stable
May harm plants[8]
Removal efficiency declines with increased concentration of incoming phosphorus
Red sand or Iron-enriched sand Proven phosphorus removal
Also removes TSSTotal suspended solids
Poor orthophosphate removal in hypoxic or anoxic conditions
Smart SpongeTM Removes phosphorus, as well as TSSTotal suspended solids, fecal coliform bacteria and heavy metals
Non-leaching
1-3 year lifespan, after which the product is removed as solid waste
Proprietary
Sorbtive MediaTM High phosphorus removal efficiency Proprietary
Water treatment residuals Waste product reuse Quality control (capabilities depend on source, treatment methods, storage time, etc of WTR)

  1. 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.
  2. CRC for Water Sensitive Cities. (2015). Adoption Guidelines for Stormwater Biofiltration Systems: Appendix C - Guidelines for filter media in stormwater biofiltration systems.
  3. 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.
  4. 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>
  5. UNHSC Bioretention Soil Specification. (2017). Retrieved from https://www.unh.edu/unhsc/sites/default/files/media/unhsc_bsm_spec_2-28-17_0.pdf
  6. 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
  7. Hood A, Chopra M, Wanielista M. Assessment of Biosorption Activated Media Under Roadside Swales for the Removal of Phosphorus from Stormwater. Water. 2013;5(1):53-66. doi:10.3390/w5010053.
  8. Logsdon SD, Sauer PA. Iron Filings Cement Engineered Soil Mix. Agron J. 2016;108(4):1753. doi:10.2134/agronj2015.0427.