Changes

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File:Bioretention No infiltration placementswap.png|thumb|center|400px|[[Stormwater planters|'''Stormwater planter / No infiltration bioretention''' ]] cell draining a parking lot. This design variation includes an impermeable liner, an underdrain and surface overflow pipes to allow excess water to leave the practice. This variation also includes a monitoring well to monitor drainage performance.  <small><span style="color:red">'''''Note''': The following is an "image map", feel free to explore the image with your cursor and click on highlighted labels that appear to take you to corresponding pages on the Wiki.''</span></small>

File:Bioretention No infiltration placementswap.png|thumb|center|400px|[[Stormwater planters|'''Stormwater planter / No infiltration bioretention''' ]] cell draining a parking lot. This design variation includes an impermeable liner, an underdrain and surface overflow pipes to allow excess water to leave the practice.  <small><span style="color:red">'''''Note''': The following is an "image map", feel free to explore the image with your cursor and click on highlighted labels that appear to take you to corresponding pages on the Wiki.''</span></small>

rect 1288 1419 1353 1483 [[Underdrains|Underdrain Access Structure]]

rect 1288 1419 1353 1483 [[Underdrains|Underdrain Access Structure]]

*easier access for construction, repairs or maintenance of the area.

*easier access for construction, repairs or maintenance of the area.

Where diverting flows around the facility is not possible, and its location requires that it be used as a temporary runoff detention basin, protection measures can prevent fine sediment from migrating into the subgrade. During construction, the area should only be excavated to 75 cm above the final post-construction base of the facility. This layer of native soil will retain fine particles so that they will not migrate down into the subsoils. To prevent compaction during bioretention construction, heavy equipment should not enter the footprint of the bioretention area. For more detailed guidance, see the LID Construction Guide <ref> Credit Valley Conservation. 2012. LID Construction Guide. https://cvc.ca/wp-content/uploads/2012/01/CVC-LID-Construction-Guide-Book.pdf </ref> and the Erosion and Sediment Control Guide for Urban Construction <ref> Toronto and Region Conservation Authority. 2019. Erosion and Sediment Control Guide for Urban Construction. https://sustainabletechnologies.ca/app/uploads/2020/01/ESC-Guide-for-Urban-Construction_FINAL.pdf </ref>.

Where diverting flows around the facility is not possible, and its location requires that it be used as a temporary runoff detention basin, protection measures can prevent fine sediment from migrating into the subgrade. During construction, the area should only be excavated to 75 cm above the final post-construction base of the facility. This layer of native soil will retain fine particles so that they will not migrate down into the subsoils. To prevent compaction during bioretention construction, heavy equipment should not enter the footprint of the bioretention area. For more detailed guidance, see the LID Construction Guide <ref> Credit Valley Conservation. 2012. LID Construction Guide. https://cvc.ca/wp-content/uploads/2012/01/CVC-LID-Construction-Guide-Book.pdf </ref> and the Erosion and Sediment Control Guide for Urban Construction <ref> Toronto and Region Conservation Authority. 2019. Erosion and Sediment Control Guide for Urban Construction. https://sustainabletechnologies.ca/app/uploads/2020/01/ESC-Guide-for-Urban-Construction_FINAL.pdf </ref>.

{{Clickable button|[[File:Bioretention.png|125 px|link=https://wiki.sustainabletechnologies.ca/wiki/Finishing_grades_and_surface_layer_installation:_vegetated_LIDs]]}}

{{Clickable button|[[File:Bioretention.png|125 px|link=https://wiki.sustainabletechnologies.ca/wiki/Finishing_grades_and_surface_layer_installation:_vegetated_LIDs]]}}

==Inspection and Maintenance==

==Inspection and Maintenance==

Bioretention requires regular, routine inspection and maintenance of the landscaping as well as periodic inspection of other parts of the facility. Routine maintenance should include weeding, pruning, and mulching, similar to other landscaped areas, as well as the removal of trash, debris and sediment accumulated in pretreatment areas, inlets and outlets. Watering may be needed until plant establishment (first 2 years). <br>

Bioretention requires regular, routine inspection and maintenance of the landscaping as well as periodic inspection of other parts of the facility. Routine maintenance should include weeding, pruning, and mulching, similar to other landscaped areas, as well as the removal of trash, debris and sediment accumulated in pretreatment areas, inlets and outlets. Watering may be needed until plant establishment (first 2 years). Periodic replacement of the top 5 cm of filter media around inlets (e.g., every 5 to 10 years) will help maintain treatment performance.<br>

<br>

Inspections should occur twice annually (spring and late fall) and after major storm events. Inspect for vegetation density (≥ 80% coverage), damage by foot or vehicle traffic, erosion, debris and sediment accumulation, and damage to pretreatment devices.<br>

Inspections should occur twice annually (spring and late fall) and after major storm events. Inspect for vegetation density (≥ 80% coverage), damage by foot or vehicle traffic, erosion, debris and sediment accumulation, and damage to pretreatment devices.<br>

Cleanouts and access points should be provided to allow clean-out of the underdrain and overflow pipe. Camera inspection of these pipes should be conducted every 5 years to ensure pipes are free of roots, sediment and debris. Hydraulic flushing or root removal may be needed to clear debris or obstructions.

Cleanouts and access points should be provided to allow clean-out of the underdrain and overflow pipe. Camera inspection of these pipes should be conducted every 5 years to ensure pipes are free of roots, sediment and debris. Hydraulic flushing or root removal may be needed to clear debris or obstructions.

{{Clickable button|[[File:Cover Photo.PNG|150 px|link=https://wiki.sustainabletechnologies.ca/wiki/Inspection_and_Maintenance:_Bioretention_%26_Bioswales]]}}

{{Clickable button|[[File:Cover Photo.PNG|150 px|link=https://wiki.sustainabletechnologies.ca/wiki/Inspection_and_Maintenance:_Bioretention_%26_Bioswales]]}}

==Performance==

==Performance==

|-

|-

|'''Bioretention with underdrain and liner'''

|'''Bioretention with underdrain and liner'''

|Partial-some volume reduction occurs through evapotranspiration

|No-some volume reduction occurs through evapotranspiration

|Yes-size for water quality storage requirement

|Yes-size for water quality storage requirement

|Partial-some volume reduction occurs through evapotranspiration

|Partial-some volume reduction occurs through evapotranspiration

|rowspan="4" style="text-align: center;" | Bioretention without underdrain

|rowspan="4" style="text-align: center;" | Bioretention without underdrain

|style="text-align: center;" |China

|style="text-align: center;" |China

|style="text-align: center;" |'''<u><span title="Note: Runoff reduction estimates are based on SWMM and RECARGA models applied to generate the runoff reduction percentages of a bioretention installation near one of China's and  expressway service area.">85 to 100%*</span></u>'''

|style="text-align: center;" |'''<span title="Note: Runoff reduction estimates are based on SWMM and RECARGA models applied to generate the runoff reduction percentages of a bioretention installation near one of China's and  expressway service area.">85 to 100%*</span>'''

|style="text-align: center;" |Gao, ''et al.'' (2018)<ref>Gao, J., Pan, J., Hu, N. and Xie, C., 2018. Hydrologic performance of bioretention in an expressway service area. Water Science and Technology, 77(7), pp.1829-1837.</ref>

|style="text-align: center;" |Gao, ''et al.'' (2018)<ref>Gao, J., Pan, J., Hu, N. and Xie, C., 2018. Hydrologic performance of bioretention in an expressway service area. Water Science and Technology, 77(7), pp.1829-1837.</ref>

|-

|-

|-

|-

|style="text-align: center;" |Texas

|style="text-align: center;" |Texas

|style="text-align: center;" |'''<u><span title="Note: Runoff reduction estimates are based on differences in runoff volume between the practice and a conventional impervious surface over the period of monitoring.">82%*</span></u>'''

|style="text-align: center;" |'''<span title="Note: Runoff reduction estimates are based on differences in runoff volume between the practice and a conventional impervious surface over the period of monitoring.">82%*</span>'''

|style="text-align: center;" |Mahmoud, ''et al.'' (2019)<ref>Mahmoud, A., Alam, T., Rahman, M.Y.A., Sanchez, A., Guerrero, J. and Jones, K.D. 2019. Evaluation of field-scale stormwater bioretention structure flow and pollutant load reductions in a semi-arid coastal climate. Ecological Engineering, 142, p.100007. https://www.sciencedirect.com/science/article/pii/S2590290319300070</ref>

|style="text-align: center;" |Mahmoud, ''et al.'' (2019)<ref>Mahmoud, A., Alam, T., Rahman, M.Y.A., Sanchez, A., Guerrero, J. and Jones, K.D. 2019. Evaluation of field-scale stormwater bioretention structure flow and pollutant load reductions in a semi-arid coastal climate. Ecological Engineering, 142, p.100007. https://www.sciencedirect.com/science/article/pii/S2590290319300070</ref>

|-

|-

|style="text-align: center;" |China

|style="text-align: center;" |China

|style="text-align: center;" |'''<u><span title="Note: Runoff reduction estimates are based on SWMM and RECARGA models applied to generate the runoff reduction percentages of a bioretention installation near one of China's and  expressway service area.">35 to 75%*</span></u>'''

|style="text-align: center;" |'''<span title="Note: Runoff reduction estimates are based on SWMM and RECARGA models applied to generate the runoff reduction percentages of a bioretention installation near one of China's and  expressway service area.">35 to 75%*</span>'''

|style="text-align: center;" |Gao, ''et al.'' (2018)<ref>Gao, J., Pan, J., Hu, N. and Xie, C., 2018. Hydrologic performance of bioretention in an expressway service area. Water Science and Technology, 77(7), pp.1829-1837.</ref>

|style="text-align: center;" |Gao, ''et al.'' (2018)<ref>Gao, J., Pan, J., Hu, N. and Xie, C., 2018. Hydrologic performance of bioretention in an expressway service area. Water Science and Technology, 77(7), pp.1829-1837.</ref>

|-

|-

A comparative performance assessment of bioretention in Ontario was conducted comparing 9 different bioretention facilities in the GTA. The results showed total suspended solids (TSS) load reductions between 88 to 99%, and total phosphorus load reductions between 68 and 92% for unlined facilities. Results for a lined bioretention swale for TSS and Total Phosphorus load reduction were 73 to 79% and -18 to -21% respectively.[https://sustainabletechnologies.ca/app/uploads/2019/10/STEP_Bioretention-Synthesis_Tech-Brief-New-Template-2019-Oct-10.-2019.pdf (STEP, 2019)]<ref>STEP. 2019. Comparative Performance Assessment of Bioretention in Ontario - Technical Brief.</ref>.  Negative TP load reduction values were observed because effluent concentrations were higher than influent concentrations, and volume reduction through evapotranspiration was not sufficient to offset the increase in phosphorus concentration in biofilter effluent. [https://sustainabletechnologies.ca/app/uploads/2020/11/CC-Bioswale-Tech-brief-2018-FINAL.pdf (STEP, 2018)]<ref> Sustainable Technologies Evaluation Program. 2018. Effectiveness of Retrofitted Roadside Biofilter Swales - County Court Boulevard, Brampton Technical Brief. https://sustainabletechnologies.ca/app/uploads/2020/11/CC-Bioswale-Tech-brief-2018-FINAL.pdf </ref>. Other STEP studies in the Greater Toronto Area have displayed similar results, with 90% reduction in TSS load when compared to nearby asphalt runoff samples having median TSS concentrations near the provincial 30 mg/L standard (median = ~19 mg/L) [https://sustainabletechnologies.ca/app/uploads/2015/01/ER-Bio-Tech-Brief-Final.pdf STEP, 2014] <ref>Sustainable Technologies Evaluation Program. 2014. Performance Evaluation of a Bioretention System - Earth Rangers. Prepared by Toronto and Region Conservation. September 2014. https://sustainabletechnologies.ca/app/uploads/2014/09/STEP-Bioretention-Report_2014.pdf</ref>.

A comparative performance assessment of bioretention in Ontario was conducted comparing 9 different bioretention facilities in the GTA. The results showed total suspended solids (TSS) load reductions between 88 to 99%, and total phosphorus load reductions between 68 and 92% for unlined facilities. Results for a lined bioretention swale for TSS and Total Phosphorus load reduction were 73 to 79% and -18 to -21% respectively.[https://sustainabletechnologies.ca/app/uploads/2019/10/STEP_Bioretention-Synthesis_Tech-Brief-New-Template-2019-Oct-10.-2019.pdf (STEP, 2019)]<ref>STEP. 2019. Comparative Performance Assessment of Bioretention in Ontario - Technical Brief.</ref>.  Negative TP load reduction values were observed because effluent concentrations were higher than influent concentrations, and volume reduction through evapotranspiration was not sufficient to offset the increase in phosphorus concentration in biofilter effluent. [https://sustainabletechnologies.ca/app/uploads/2020/11/CC-Bioswale-Tech-brief-2018-FINAL.pdf (STEP, 2018)]<ref> Sustainable Technologies Evaluation Program. 2018. Effectiveness of Retrofitted Roadside Biofilter Swales - County Court Boulevard, Brampton Technical Brief. https://sustainabletechnologies.ca/app/uploads/2020/11/CC-Bioswale-Tech-brief-2018-FINAL.pdf </ref>. Other STEP studies in the Greater Toronto Area have displayed similar results, with 90% reduction in TSS load when compared to nearby asphalt runoff samples having median TSS concentrations near the provincial 30 mg/L standard (median = ~19 mg/L) [https://sustainabletechnologies.ca/app/uploads/2015/01/ER-Bio-Tech-Brief-Final.pdf STEP, 2014] <ref>Sustainable Technologies Evaluation Program. 2014. Performance Evaluation of a Bioretention System - Earth Rangers. Prepared by Toronto and Region Conservation. September 2014. https://sustainabletechnologies.ca/app/uploads/2014/09/STEP-Bioretention-Report_2014.pdf</ref>.

Another group of studies of bioretention facilities examines nutrient removal of these LID installation, with mixed results. Some facilities have been observed to increase total phosphorus in infiltrated water (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>; Hunt and Lord, 2006<ref>Hunt, W.F. and W.G. Lord. 2006. Bioretention Performance, Design, Construction, and Maintenance. North Carolina Cooperative Extension Service Bulletin. Urban Waterways Series. AG-588-5. North Carolina State University. Raleigh, NC</ref> ; TRCA, 2008<ref>. Toronto and Region Conservation Authority. 2008. Performance Evaluation of Permeable Pavement and a Bioretention Swale, Seneca College, King City, Ontario. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario. https://sustainabletechnologies.ca/app/uploads/2013/03/PP_FactsheetSept2011-compressed.pdf</ref>). These findings have been attributed to leaching from filter media soil mixtures which contained high phosphorus content. To avoid phosphorus export, the plant-available (extractable) phosphorus content of the filter media soil mixture should be examined prior to installation and kept between 12 to 40 ppm (see [[Bioretention: Filter media | Filter media]]; Hunt and Lord, 2006). A design option to increase phosphorus removal performance of bioretention is to incorporate [[Additives | additives]] into the filter media bed, either blended into the media or as a layer in the aerobic portion of the filter bed, such as iron filings (i.e., zero valent iron)<ref>Erickson, A.J., Gulliver, J.S., Weiss, P.T. 2012. Capturing phosphates with iron enhanced sand filtration. Water Research. 46(9). 3032-3042. https://www.sciencedirect.com/science/article/abs/pii/S0043135412001728 </ref>, fly ash<ref>Zhang, W., Brown, G.O., Storm, D.E., Zhang, H. 2008. Fly-ash amended sand as filter media in bioretention cells to improve phosphorus removal. Water Environment Research. 80(6). 507-516. https://onlinelibrary.wiley.com/doi/abs/10.2175/106143008X266823 </ref> <ref>Kandel, S., Vogel, J., Penn, C., Brown, G. 2017. Phosphorus Retention by Fly Ash Amended Filter Media in Aged Bioretention Cells. Water. 9, 746. https://www.mdpi.com/2073-4441/9/10/746</ref>, iron (ferric) or aluminum hydroxide-based water treatment residuals (by-product from drinking water treatment)<ref>O'Neill, S.W., Davis, A.P. 2012a. Water treatment residual as a bioretention amendment for phosphorus. I. Evaluation studies. Journal of Environmental Engineering. 138(3). pp 318-327. https://ascelibrary.org/doi/10.1061/%28ASCE%29EE.1943-7870.0000409</ref> <ref>O'Neill, S.W., Davis, A.P. 2012b. Water treatment residual as a bioretention amendment for phosphorus. II. long-term column studies. Journal of Environmental Engineering. 138(3). pp 328-336. https://ascelibrary.org/doi/10.1061/%28ASCE%29EE.1943-7870.0000436</ref>, biochar <ref>Nabiul Afrooz, A.R.M., Boehm, A.B. 2017.  Effects of submerged zone, media aging, and antecedent dry period on the performance of biochar-amended biofilters in removing fecal indicators and nutrients from natural stormwater. Ecological Engineering. 102. 320-330. https://www.sciencedirect.com/science/article/abs/pii/S0925857417301209 </ref> <ref>Mohanty, S.K., Valenca, R., Berger, A.W., Yu, I.K.M., Xiong, X., Saunders, T.M., Tsang, D.C.W. 2018. Plenty of room for carbon on the ground: Potential applications of biochar for stormwater treatment. Science of the Total Environment. 625. 1644-1658. https://www.sciencedirect.com/science/article/abs/pii/S0048969718300378 </ref>, proprietary filter media additives or blends, or by using iron-rich sand in the filter media blend.  Read about a field evaluation comparing the phosphorus retention performance of parking lot bioretention cells featuring iron-rich sand and proprietary reactive media additive (Sorptive P^TM) in the STEP [https://sustainabletechnologies.ca/app/uploads/2019/06/improving-nutrient-retention-in-bioretention-tech-brief.pdf technical brief]<ref>Sustainable Technologies Evaluation Program. 2018. Improving nutrient retention in bioretention. Technical Brief. https://sustainabletechnologies.ca/app/uploads/2019/06/improving-nutrient-retention-in-bioretention-tech-brief.pdf</ref>.  While moderate reductions in total nitrogen and ammonia nitrogen have been observed in laboratory studies (Davis ''et al''., 2001<ref>Davis, A., M. Shokouhian, H. Sharma and C. Minami. 2001. Laboratory . Study of Biological Retention for Urban Stormwater Management. Water Environment Research. 73(5): 5-14.</ref>) and field studies (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>), nitrate nitrogen removal has consistently been observed to be low. Design innovations to enhance nitrate-nitrogen removal performance of bioretention is an area of active research.  Promising results have been observed from laboratory column and field-scale evaluations of underdrained practices featuring [[Bioretention: Internal water storage |internal water storage reservoirs]] containing mixtures of clear stone aggregate and shredded newspaper or wood chips, which creates low oxygen or anoxic conditions and promotes conversion of nitrate-nitrogen to nitrogen gas via denitrification <ref>Kim, H., Seagren, E.A., Davis, A.P. 2003. Engineered bioretention for removal of nitrate from stormwater runoff. Water Environment Research. 75(4). 335-367. https://onlinelibrary.wiley.com/doi/abs/10.2175/106143003X141169 </ref> <ref> Brown, R.A., Hunt, W.F. 2011. Underdrain configuration to enhance bioretention exfiltration to reduce pollutant loads. Journal of Environmental Engineering. 137(11). 1082-1091. https://ascelibrary.org/doi/abs/10.1061/(ASCE)EE.1943-7870.0000437 </ref> <ref> Wang, C., Wang, F., Qin, H., Zeng, X., Li, X. Yu, S. 2018. Effect of Saturated Zone on Nitrogen Removal Processes in Stormwater Bioretention Systems. Water. 10, 162. https://www.mdpi.com/2073-4441/10/2/162 </ref>. LeFevre et al. (2015) present a state-of-the-art review of dissolved stormwater pollutant sources (focusing on nutrients, toxic metals and organic compounds), typical concentrations, and removal mechanisms and fate in bioretention, along with design options to enhance their retention <ref> LeFevre, G.H., Paus, K.H., Natarajan, P., Gulliver, J.S., Novak, P.J., Hozalski, R.M. 2015. Review of Dissolved Pollutants in Urban Storm Water and Their Removal and Fate in Bioretention Cells. Journal of Environmental Engineering. 141(1). https://ascelibrary.org/doi/abs/10.1061/(ASCE)EE.1943-7870.0000876 </ref>.  

Another group of studies of bioretention facilities examines nutrient removal of these LID installation, with mixed results. Some facilities have been observed to increase total phosphorus in infiltrated water (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>; Hunt and Lord, 2006<ref>Hunt, W.F. and W.G. Lord. 2006. Bioretention Performance, Design, Construction, and Maintenance. North Carolina Cooperative Extension Service Bulletin. Urban Waterways Series. AG-588-5. North Carolina State University. Raleigh, NC</ref> ; TRCA, 2008<ref>. Toronto and Region Conservation Authority. 2008. Performance Evaluation of Permeable Pavement and a Bioretention Swale, Seneca College, King City, Ontario. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario. https://sustainabletechnologies.ca/app/uploads/2013/03/PP_FactsheetSept2011-compressed.pdf</ref>). These findings have been attributed to leaching from filter media soil mixtures which contained high phosphorus content. To avoid phosphorus export, the plant-available (extractable) phosphorus content of the filter media soil mixture should be examined prior to installation and kept between 12 to 40 ppm (see [[Bioretention: Filter media | Filter media]]; Hunt and Lord, 2006). A design option to increase phosphorus removal performance of bioretention is to incorporate [[Additives | additives]] into the filter media bed, either blended into the media or as a layer in the aerobic portion of the filter bed, such as iron filings (i.e., zero valent iron)<ref>Erickson, A.J., Gulliver, J.S., Weiss, P.T. 2012. Capturing phosphates with iron enhanced sand filtration. Water Research. 46(9). 3032-3042. https://www.sciencedirect.com/science/article/abs/pii/S0043135412001728 </ref>, fly ash<ref>Zhang, W., Brown, G.O., Storm, D.E., Zhang, H. 2008. Fly-ash amended sand as filter media in bioretention cells to improve phosphorus removal. Water Environment Research. 80(6). 507-516. https://onlinelibrary.wiley.com/doi/abs/10.2175/106143008X266823 </ref> <ref>Kandel, S., Vogel, J., Penn, C., Brown, G. 2017. Phosphorus Retention by Fly Ash Amended Filter Media in Aged Bioretention Cells. Water. 9, 746. https://www.mdpi.com/2073-4441/9/10/746</ref>, iron (ferric) or aluminum hydroxide-based water treatment residuals (by-product from drinking water treatment)<ref>O'Neill, S.W., Davis, A.P. 2012a. Water treatment residual as a bioretention amendment for phosphorus. I. Evaluation studies. Journal of Environmental Engineering. 138(3). pp 318-327. https://ascelibrary.org/doi/10.1061/%28ASCE%29EE.1943-7870.0000409</ref> <ref>O'Neill, S.W., Davis, A.P. 2012b. Water treatment residual as a bioretention amendment for phosphorus. II. long-term column studies. Journal of Environmental Engineering. 138(3). pp 328-336. https://ascelibrary.org/doi/10.1061/%28ASCE%29EE.1943-7870.0000436</ref>, biochar <ref>Nabiul Afrooz, A.R.M., Boehm, A.B. 2017.  Effects of submerged zone, media aging, and antecedent dry period on the performance of biochar-amended biofilters in removing fecal indicators and nutrients from natural stormwater. Ecological Engineering. 102. 320-330. https://www.sciencedirect.com/science/article/abs/pii/S0925857417301209 </ref> <ref>Mohanty, S.K., Valenca, R., Berger, A.W., Yu, I.K.M., Xiong, X., Saunders, T.M., Tsang, D.C.W. 2018. Plenty of room for carbon on the ground: Potential applications of biochar for stormwater treatment. Science of the Total Environment. 625. 1644-1658. https://www.sciencedirect.com/science/article/abs/pii/S0048969718300378 </ref>, proprietary filter media additives or blends, or by using iron-rich sand in the filter media blend.  Read about a field evaluation comparing the phosphorus retention performance of parking lot bioretention cells featuring iron-rich sand and proprietary reactive media additive (Sorptive P^TM) in the STEP [https://sustainabletechnologies.ca/app/uploads/2019/06/improving-nutrient-retention-in-bioretention-tech-brief.pdf technical brief]<ref>Sustainable Technologies Evaluation Program. 2018. Improving nutrient retention in bioretention. Technical Brief. https://sustainabletechnologies.ca/app/uploads/2019/06/improving-nutrient-retention-in-bioretention-tech-brief.pdf</ref>.  While moderate reductions in total nitrogen and ammonia nitrogen have been observed in laboratory studies (Davis ''et al''., 2001<ref>Davis, A., M. Shokouhian, H. Sharma and C. Minami. 2001. Laboratory . Study of Biological Retention for Urban Stormwater Management. Water Environment Research. 73(5): 5-14.</ref>) and field studies (Dietz and Clausen, 2005<ref>Dietz, M.E. and J.C. Clausen. 2005. A field evaluation of rain garden flow and pollutant treatment. Water Air and Soil Pollution. Vol. 167. No. 2. pp. 201-208.</ref>), nitrate nitrogen removal has consistently been observed to be low. Design innovations to enhance nitrate-nitrogen removal performance of bioretention is an area of active research.  Promising results have been observed from laboratory column and field-scale evaluations of underdrained practices featuring [[Bioretention: Internal water storage |internal water storage reservoirs]] containing mixtures of clear stone aggregate and shredded newspaper or wood chips, which creates low oxygen or anoxic conditions and promotes conversion of nitrate-nitrogen to nitrogen gas via denitrification <ref>Kim, H., Seagren, E.A., Davis, A.P. 2003. Engineered bioretention for removal of nitrate from stormwater runoff. Water Environment Research. 75(4). 335-367. https://onlinelibrary.wiley.com/doi/abs/10.2175/106143003X141169 </ref> <ref> Brown, R.A., Hunt, W.F. 2011. Underdrain configuration to enhance bioretention exfiltration to reduce pollutant loads. Journal of Environmental Engineering. 137(11). 1082-1091. https://ascelibrary.org/doi/abs/10.1061/(ASCE)EE.1943-7870.0000437 </ref> <ref> Wang, C., Wang, F., Qin, H., Zeng, X., Li, X. Yu, S. 2018. Effect of Saturated Zone on Nitrogen Removal Processes in Stormwater Bioretention Systems. Water. 10, 162. https://www.mdpi.com/2073-4441/10/2/162 </ref>.  

 

Roseen et al. (2013) conducted both field and laboratory testing on the performance of bioretention cells featuring filter media amended with drinking water treatment residuals (WTR) with low solids content (5-10% solids) as an [[Additives| additive]]. Water treatment residuals were included at 10-15% of the total filter media mix by volume. Amended bioretention cells had median orthophosphate removal efficiencies of 90-99%. A second study found a bioretention design featuring WTR amended filter media and an [[Bioretention: Internal water storage|internal water storage zone]] optimized to remove phosphorus and nitrogen had an orthophosphate removal efficiency of 20% and effluent concentrations below 0.02 mg/L.<ref>Roseen, R.M., Stone, R.M. 2013. Evaluation and Optimization of Bioretention Design for Nitrogen and Phosphorus Removal. U.S. Environmental Protection Agency. https://www3.epa.gov/region1/npdes/stormwater/research/epa-final-report-filter-study.pdf</ref>  More recently, LeFevre et al. (2015) present a state-of-the-art review of dissolved stormwater pollutant sources (focusing on nutrients, toxic metals and organic compounds), typical concentrations, and removal mechanisms and fate in bioretention, along with design options to enhance their retention <ref>LeFevre, G.H., Paus, K.H., Natarajan, P., Gulliver, J.S., Novak, P.J., Hozalski, R.M. 2015. Review of Dissolved Pollutants in Urban Storm Water and Their Removal and Fate in Bioretention Cells. Journal of Environmental Engineering. 141(1). https://ascelibrary.org/doi/abs/10.1061/(ASCE)EE.1943-7870.0000876 </ref>.<br>

The mechanisms involved in, and ability of bioretention to reduce bacteria and other microbial pathogen concentrations is also an area of active research. Preliminary laboratory and field study results report good but variable removal rates for fecal coliform bacteria from biofilters and bioretention cells (Rusciano and Obropta, 2005<ref> Rusciano, G.M., Obropta, C.C. 2007. Bioretention Column Study: Fecal Coliform and Total Suspended Solids Reductions. Transactions of the ASABE. 50(4): 1261-1269. https://elibrary.asabe.org/abstract.asp??JID=3&AID=23636&CID=t2007&v=50&i=4&T=1 </ref>; Hunt ''et al''., 2006<ref>Hunt, W.F., A.R. Jarrett, J.T. Smith, and L.J. Sharkey. 2006. Evaluating Bioretention Hydrology and Nutrient Removal at Three Field Sites in North Carolina. ASCE Journal of Irrigation and Drainage Engineering. 132(6): 600-608.</ref>; TRCA, 2008<ref>. Performance Evaluation of Permeable Pavement and a Bioretention Swale, Seneca College, King City, Ontario. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario.</ref>). In a recent review, Clary et al. report bioretention E.coli removal efficiency of 42.5% and fecal coliform removal efficiency of 99.4% based on median inlet and outlet concentrations from 12 and 8 studies, respectively <ref> Clary, J. Jones, Leisenring, M., Hobson, P., Strecker, E. 2020. International Stormwater BMP Database 2020 Statistical Summary. https://www.waterrf.org/system/files/resource/2020-11/DRPT-4968_0.pdf</ref>. In a recent article, Peng et al. (2016) review factors influencing microbial removal and effects of design choices on treatment performance.  They found that approaches for improving the removal of microorganisms by biofilters could involve altering the grain size range and surface properties of the filter media. This could involve the use of filter media with smaller average grain sizes, the inclusion of [[Additives |additives]] (e.g., activated carbon, zeolite, or biochar) to improve filtration rates, or chemical modifications of filter media grain surfaces (e.g., with biocides) to promote microbial die-off. Including an [[Bioretention: Internal water storage |internal water storage reservoir]] was also found to improve microbial removal rates <ref> Peng, J., Cao, Y., Rippy, M.A., Nabuil Afrooz, A.R.M., Grant, S.B. 2016. Indicator and Pathogen Removal by Low Impact Development Best Management Practices. Water. 8. 600. https://www.mdpi.com/2073-4441/8/12/600 </ref>.

 

The two box plot figures to the right show combined stormwater effluent quality results from STEP monitoring projects conducted over a 16-year time period (between 2005 and 2021) at sites within Greater Toronto Area (GTA) municipalities.  Total Suspended Solid (TSS) effluent concentration results for bioretention practices represent the combined results from 9 sites in the GTA.  Median TSS concentration was found to be 9.5 mg/L and exceeded the Canadian Water Quality Guideline of 30 mg/L (CCME, 2002<ref>Canadian Council of Ministers of the Environment (CCME). 2002. Canadian water quality guidelines for the protection of aquatic life: Total particulate matter. In: Canadian Environmental Quality Guidelines, Canadian Council of Ministers of the Environment, Winnipeg</ref>) during only 15% of the 301 monitored storm events, similar to STEP [[Permeable pavements#Water_Quality| Permeable Pavements performance]] results.  In comparison, median TSS effluent concentration for bioretention in the International Stormwater BMP Database was found to be 10.0 mg/L, based on 685 monitored storm events (Clary et al. 2020)<ref>Clary, J., Jones, J., Leisenring, M., Hobson, P., Strecker, E. 2020. International Stormwater BMP Database: 2020 Summary Statistics. The Water Research Foundation. [https://www.waterrf.org/system/files/resource/2020-11/DRPT-4968_0.pdf</ref>, so quite similar to results from STEP studies.  Median TP concentration was found to be 0.09 mg/L and exceeded the Ontario Provincial Water Quality Objective (PWQO) of 0.03 mg/L (OMOEE, 1994<ref>Ontario Ministry of Environment and Energy (OMOEE), 1994. Policies, Guidelines and Provincial Water Quality Objectives of the Ministry of Environment and Energy. Queen’s Printer for Ontario. Toronto, ON.</ref>) during 86% of the 355 monitored storm events.  In comparison, median TP effluent concentration for bioretention in the International Stormwater BMP Database was found to be 0.240 mg/L, based on 667 monitored storm events (Clary et al. 2020)<ref>Clary, J., Jones, J., Leisenring, M., Hobson, P., Strecker, E. 2020. International Stormwater BMP Database: 2020 Summary Statistics. The Water Research Foundation. [https://www.waterrf.org/system/files/resource/2020-11/DRPT-4968_0.pdf</ref>, which is well above the Ontario PWQO of 0.03 mg/L. These results indicate that the design of bioretention draining to phosphorus-limited receiving waterbodies should include variations to improve [[Phosphorus]] retention.  An example of such a design variation is including sorption [[Additives| additives]] in [[Bioretention: Filter media]].  Please refer to the [[Phosphorus]] and [[Additives]] pages for further guidance.  Another example of a design variation to enhance retention of phosphorus is including a sorption media filter manufactured treatment device as part of the treatment train design.

The mechanisms involved in, and ability of bioretention to reduce bacteria and other microbial pathogen concentrations is also an area of active research. Preliminary laboratory and field study results report good but variable removal rates for fecal coliform bacteria from biofilters and bioretention cells (Rusciano and Obropta, 2005<ref> Rusciano, G.M., Obropta, C.C. 2007. Bioretention Column Study: Fecal Coliform and Total Suspended Solids Reductions. Transactions of the ASABE. 50(4): 1261-1269. https://elibrary.asabe.org/abstract.asp??JID=3&AID=23636&CID=t2007&v=50&i=4&T=1 </ref>; Hunt ''et al''., 2006<ref>Hunt, W.F., A.R. Jarrett, J.T. Smith, and L.J. Sharkey. 2006. Evaluating Bioretention Hydrology and Nutrient Removal at Three Field Sites in North Carolina. ASCE Journal of Irrigation and Drainage Engineering. 132(6): 600-608.</ref>; TRCA, 2008<ref>. Performance Evaluation of Permeable Pavement and a Bioretention Swale, Seneca College, King City, Ontario. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario.</ref>). In a recent review, Clary et al. (2020) report bioretention E.coli removal efficiency of 42.5% and fecal coliform removal efficiency of 99.4% based on median inlet and outlet concentrations from 12 and 8 studies, respectively <ref> Clary, J. Jones, Leisenring, M., Hobson, P., Strecker, E. 2020. International Stormwater BMP Database 2020 Statistical Summary. https://www.waterrf.org/system/files/resource/2020-11/DRPT-4968_0.pdf</ref>. In a recent article, Peng et al. (2016) review factors influencing microbial removal and effects of design choices on treatment performance.  They found that approaches for improving the removal of microorganisms by biofilters could involve altering the grain size range and surface properties of the filter media. This could involve the use of filter media with smaller average grain sizes, the inclusion of [[Additives |additives]] (e.g., activated carbon, zeolite, or biochar) to improve filtration rates, or chemical modifications of filter media grain surfaces (e.g., with biocides) to promote microbial die-off. Including an [[Bioretention: Internal water storage |internal water storage reservoir]] was also found to improve microbial removal rates <ref> Peng, J., Cao, Y., Rippy, M.A., Nabuil Afrooz, A.R.M., Grant, S.B. 2016. Indicator and Pathogen Removal by Low Impact Development Best Management Practices. Water. 8. 600. https://www.mdpi.com/2073-4441/8/12/600 </ref>.<br>

Recent research into the role of plants in bioretention confirms they play an important roles in hydraulic and nitrogen removal performance. In a recent review of scientific literature, Dagenais ''et al.'' (2018) found that planted facilities are more effective than unplanted ones, as the presence of plants increases filter bed permeability and nitrogen removal. Plant species selection can considerably affect hydraulic and nitrogen removal performance, with root traits (e.g., thickness and depth) identified as playing important roles. They identified further research needed to test the hypothesis that native or diversely-planted facilities perform better than ones planted with exotic or fewer species.<ref>Dagenais, D., Brisson, J. and Fletcher, T.D. 2018. The role of plants in bioretention systems; does the science underpin current guidance?. Ecological Engineering, 120, pp.532-545. http://www.phytotechno.com/wp-content/uploads/2018/10/Dagenais-2018-Bioretention.pdf</ref>

Recent research into the role of plants in bioretention confirms they play an important roles in hydraulic and nitrogen removal performance. In a recent review of scientific literature, Dagenais ''et al.'' (2018) found that planted facilities are more effective than unplanted ones, as the presence of plants increases filter bed permeability and nitrogen removal. Plant species selection can considerably affect hydraulic and nitrogen removal performance, with root traits (e.g., thickness and depth) identified as playing important roles. They identified further research needed to test the hypothesis that native or diversely-planted facilities perform better than ones planted with exotic or fewer species.<ref>Dagenais, D., Brisson, J. and Fletcher, T.D. 2018. The role of plants in bioretention systems; does the science underpin current guidance?. Ecological Engineering, 120, pp.532-545. http://www.phytotechno.com/wp-content/uploads/2018/10/Dagenais-2018-Bioretention.pdf</ref>

*''Reduced thermal aquatic impacts'': Bioretention and other filtration and infiltration practices benefit aquatic life by reducing thermal impacts on receiving waters from urban runoff (Jones and Hunt, 2009<ref>Jones, M.P. and Hunt, W.F. 2009. Bioretention Impact on Runoff Temperature in Trout Sensitive Waters. Journal of Environmental Engineering. Vol. 135. No. 8. Pp. 577-585.</ref>). Unlike detention ponds, bioretention does not raise water temperature and can help maintain baseflows through infiltration.

*''Reduced thermal aquatic impacts'': Bioretention and other filtration and infiltration practices benefit aquatic life by reducing thermal impacts on receiving waters from urban runoff (Jones and Hunt, 2009<ref>Jones, M.P. and Hunt, W.F. 2009. Bioretention Impact on Runoff Temperature in Trout Sensitive Waters. Journal of Environmental Engineering. Vol. 135. No. 8. Pp. 577-585.</ref>). Unlike detention ponds, bioretention does not raise water temperature and can help maintain baseflows through infiltration.

*''Snow storage'': Bioretention areas can be used for snow storage and snow melt treatment from the contributing drainage area during winter, especially those located adjacent to parking lots and roadways. To function as snow storage, bioretention must include an overflow for snow melt in excess of the designed ponding depth. Additionally, the plant material must be salt-tolerant, perennial and tolerant of periodic inundation.

*''Snow Storage'': Bioretention areas can be used for snow storage and snow melt treatment from the contributing drainage area during winter, especially those located adjacent to parking lots and roadways. To function as snow storage, bioretention must include an overflow for snow melt in excess of the designed ponding depth. Additionally, the plant material must be salt-tolerant, perennial and tolerant of periodic inundation.

*''Reduced urban heat island'': Bioretention is able to reduce the local urban heat island by introducing soils and vegetation into urban areas, such as parking lots. Vegetation absorbs less solar radiation than hard urban surfaces. Also, the water vapor emitted by plant material also cools ambient temperatures.

*''Reduced Urban Heat Island'': Bioretention is able to reduce the local urban heat island by introducing soils and vegetation into urban areas, such as parking lots. Vegetation absorbs less solar radiation than hard urban surfaces. Also, the water vapor emitted by plant material also cools ambient temperatures.

==See also==

==See also==