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'''Operation and Maintenance'''
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#REDIRECT [[Operation and maintenance of stormwater infiltration practices]]
  
'''Overview'''
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[[file:MN Manual updated.png|100px|thumb|alt=image showing Manual logo|Information on this page has recently been added or updated. [[Acknowledgements for bioretention|Acknowledgements]].]]
  
The most frequently cited maintenance concern for bioretention is surface and under-drain clogging caused by organic matter, fine silts, hydrocarbons, and algal matter. Common operational problems include:
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[[File:Chesapeake Stormwater Network logo.jpg|150px|thumb|alt=Chesapeake stormwater Network logo|<font size=3>The Chesapeake Stormwater Network has developed [http://chesapeakestormwater.net/training-library/design-adaptations/stormwater-bmp-maintenance/ two videos] that illustrate inspection and maintenance of BMP practices. '''NOTE: These videos provide useful tips but should not be used for compliance with Minnesota permits.'''</font size>]]
* Standing water
 
* Clogged filter surface
 
* Inlet, outlet or under-drains clogged
 
Recommendations described in this chapter are aimed at preventing these common problems.
 
  
'''Design Phase Maintenance Considerations'''
+
{{alert|The following changes have been made to this page:
Implicit in the design guidance in the previous sections is the fact that many design elements of bioretention systems can minimize the maintenance burden and maintain pollutant removal efficiency. Key examples include: limiting drainage area, providing easy site access (REQUIRED), providing pre-treatment (REQUIRED), and utilizing native plantings.
+
*added information on sustainable service life of bioretention BMPs based on pollutant of concern;
 +
*added information on maintenance of vegetation;
 +
*minor modifications to the bioretention-construction inspection checklist.
 +
|alert-info}}
  
'''Construction Phase Maintenance'''
+
The most frequently cited maintenance concern for bioretention is surface and underdrain clogging caused by organic matter, fine silts, hydrocarbons, and algal matter. Common operational problems include
Proper construction methods and sequencing play a significant role in reducing problems with operation and maintenance (O&M). In particular, with construction of bioretention practices the most important action for preventing operation and maintenance difficulties is to ensure that the contributing drainage area has been fully stabilized prior to bringing the practice on line (this is a REQUIRED practice).
+
:*standing water;
 +
:*clogged filter surface; and
 +
:*inlet, outlet or under-drains clogged.
  
Inspections during construction are needed to ensure that the bioretention practice is built in accordance with the approved design and standards and specifications. Detailed inspection checklists should be used that include sign-offs by qualified individuals at critical stages of construction, to ensure that the contractor’s interpretation of the plan is acceptable to the professional designer. An example construction phase inspection checklist is provided in Appendix D.
+
Recommendations described below are aimed at preventing these common problems.
  
'''Post-construction Operation and Maintenance'''
+
==Design phase maintenance considerations==
 +
Implicit in the [[Design criteria for bioretention|design guidance for bioretention]] is the fact that many design elements of [[Glossary#B|bioretention]] systems can minimize the maintenance burden and maintain pollutant removal efficiency. Key examples include
 +
*limiting [[Design criteria for bioretention#Physical feasibility initial check|drainage area]];
 +
*providing easy site access (''REQUIRED'');
 +
*providing [[Glossary#P|pre-treatment]] (''REQUIRED''); and
 +
*utilizing native plantings (see [http://www.pca.state.mn.us/publications/manuals/stormwaterplants.html Plants for Stormwater Design]).
  
A maintenance plan clarifying maintenance responsibility is REQUIRED. Effective long-term operation of bioretention practices necessitates a dedicated and routine maintenance schedule with clear guidelines and schedules. Proper maintenance will not only increase the expected life span of the facility, but will also improve aesthetics and property value. Some important post-construction considerations are provided below along with RECOMMENDED maintenance standards. A more detailed checklist of maintenance activities and associated schedules is provided in Appendix D.
+
==Construction phase maintenance==
* A site specific O&M plan that includes the following considerations should be prepared by the designer prior to putting the stormwater filtration practice into operation:
+
Proper construction methods and sequencing play a significant role in reducing problems with operation and maintenance (O&M). In particular, with construction of bioretention practices, the most important action for preventing operation and maintenance difficulties is to ensure that the contributing drainage area has been fully stabilized prior to bringing the practice on line.
** Operating instructions for outlet component
 
** Vegetation maintenance schedule
 
** Inspection checklists
 
** Routine maintenance checklists
 
* A legally binding and enforceable maintenance agreement should be executed between the practice owner and the local review authority.
 
* Adequate access must be provided for all bioretention facilities for inspection, maintenance, and landscaping upkeep, including appropriate equipment and vehicles.
 
* The surface of the ponding area may become clogged with fine sediment over time. Core aeration or cultivating of non-vegetated areas may be required to ensure adequate filtration.
 
* Bioretention areas should not be used as dedicated snow storage areas:
 
** Areas designed for infiltration should be protected from excessive snow storage where sand and salt is applied
 
** Specific soil storage areas should be assigned that will provide some filtration before the stormwater reaches the infiltration areas.
 
** When used for snow storage, or if used to treat parking lot runoff, the bioretention area should be planted with salt tolerant, and non-woody plant species
 
* Bioretention areas should always be inspected for sand build-up on the surface following the spring melt event.
 
* General maintenance activities and schedule are provided in Table 12.BIO.4.
 
  
 +
{{alert|It is required that the contributing drainage area has been fully stabilized prior to bringing the practice on line|alert-danger}}
  
'''Table 12.BIO.8 Design Infiltration Rates'''
+
Inspections during construction are needed to ensure that the bioretention practice is built in accordance with the approved design and standards and specifications. Detailed inspection checklists should be used that include sign-offs by qualified individuals at critical stages of construction, to ensure that the contractor’s interpretation of the plan is acceptable to the professional designer. An example construction phase inspection checklist is provided here.
  
# Hydrologic Soil Group A* This rate is consistent with the infiltration rate provided for the lower end of the Hydrologic Soil Group A soils in the Wisconsin Department of Natural Resources Conservation Practice Standard: Site Evaluation for Stormwater Infiltration
+
{{:BIORETENTION - Construction inspection checklist}}
## <nowiki>Infiltration Rate [inches/hour] </nowiki> - 1.6”
 
### Soil Textures  - Gravel, sandy gravel and silty gravels
 
### Corresponding Unified Soil Classification
 
#### GW - Well-graded gravels, sandy gravels
 
#### GP – Gap-graded or uniform gravels, sandy gravels
 
#### GM - Silty gravels, silty sandy gravels
 
## <nowiki>Infiltration Rate [inches/hour]  - 0.8”</nowiki>
 
### Soil Textures  - Sand, loamy sand or sandy loam
 
### Corresponding Unified Soil Classification
 
#### SP - Gap-graded or uniform sands, gravelly sands
 
# Hydrologic Soil Group B
 
## <nowiki>Infiltration Rate [inches/hour] </nowiki> - 0.6”
 
### Soil Textures  - Silt Loam
 
### Corresponding Unified Soil Classification
 
#### SM - Silty sands, silty gravelly
 
## Infilt<nowiki>ration Rate [inches/hour]  - 0.3</nowiki>”
 
### Soil Textures  - Loam
 
### Corresponding Unified Soil Classification
 
#### MH – Micaceous silts, diatomaceous silts, volcanic ash
 
# Hydrologic Soil Group C
 
## <nowiki>Infiltration Rate [inches/hour] </nowiki> - 0.2”
 
### Soil Textures  - Sandy clay loam
 
### Corresponding Unified Soil Classification
 
#### ML - Silts, very fine sands, silty or clayey fine sands
 
# Hydrologic Soil Group D
 
## Infilt<nowiki>ration Rate [inches/hour]  - &lt;0.2”</nowiki>”
 
### Soil Textures  - Clay loam, silty clay loam, sandy clay, silty clay or clay
 
### Corresponding Unified Soil Classification
 
#### '''GC '''– Clayey gravels, clayey sandy gravels
 
#### '''''''''SC '''– Clayey sands, clayey gravelly sands
 
#### '''CL '''– Low plasticity clays, sandy or silty clays
 
#### '''OL '''– Organic silts and clays of low plasticity
 
#### '''CH '''– Highly plastic clays and sandy clays
 
#### '''OH '''– Organic silts and clays of high plasticity
 
  
Source: Thirty guidance manuals and many other stormwater references were reviewed to compile recommended infiltration rates''. ''All of these sources use the following studies as the basis for their recommended infiltration rates: (1) Rawls, Brakensiek and Saxton (1982); (2) Rawls, Gimenez and Grossman (1998); (3) Bouwer and Rice (1984); and (4) Urban Hydrology for Small Watersheds (NRCS). The rates presented in this infiltration table use the information compiled from these sources as well as eight years of infiltration rates collected in various infiltration practices located in the metro area.
+
==Post-construction operation and maintenance==
 +
{{alert|A maintenance plan clarifying maintenance responsibility is ''REQUIRED''. Effective long-term operation of bioretention practices necessitates a dedicated and routine maintenance schedule with clear guidelines and schedules. Proper maintenance will not only increase the expected lifespan of the facility but will improve aesthetics and property value.|alert-danger}}
 +
{{alert|A maintenance plan clarifying maintenance responsibility is ''REQUIRED''.|alert-danger}}
 +
 
 +
Effective long-term operation of [[Glossary#B|bioretention]] practices necessitates a dedicated and routine maintenance schedule with clear guidelines and schedules. Proper maintenance will not only increase the expected life span of the facility, but will also improve aesthetics and property value. Some important post-construction considerations are provided below along with ''RECOMMENDED'' maintenance standards.
 +
:* A site specific O&M plan that includes the following considerations should be prepared by the designer prior to putting the stormwater filtration practice into operation:
 +
:** Operating instructions for outlet component
 +
:** Vegetation maintenance schedule
 +
:** Inspection checklists
 +
:** Routine maintenance checklists
 +
:* A legally binding and enforceable maintenance agreement should be executed between the practice owner and the local review authority.  It is recommended that the practice be bonded.
 +
:* Adequate access must be provided for all bioretention facilities for inspection, maintenance and landscaping upkeep, including appropriate equipment and vehicles.
 +
:* The surface of the ponding area may become clogged with fine sediment over time. Core aeration or cultivating of non-vegetated areas may be required to ensure adequate filtration.
 +
:* Bioretention areas should not be used as dedicated snow storage areas:
 +
:** Areas designed for infiltration should be protected from excessive snow storage where sand and salt is applied.
 +
:** Specific soil storage areas should be assigned that will provide some filtration before the stormwater reaches the infiltration areas.
 +
:** When used for snow storage, or if used to treat parking lot runoff, the bioretention area should be planted with [[Minnesota plant lists#Salt tolerance|salt tolerant]], and non-woody plant species.
 +
:* Bioretention areas should always be inspected for sand build-up on the surface following the spring melt event.
 +
:* General maintenance activities and schedule are provided below.
 +
 
 +
===Recommended maintenance activities for bioretention areas===
 +
*'''First year after planting'''
 +
**Adequate water is crucial to plant survival and temporary irrigation will be needed unless rainfall is adequate until plants mature
 +
* '''As needed'''
 +
** Prune and weed to maintain appearance
 +
** Stabilize or replace mulch when erosion is evident
 +
** Remove trash and debris
 +
** Mow filter strip
 +
** Renew mulch to replace that which has broken down into organic matter
 +
** Replace vegetation whenever percent cover of acceptable vegetation falls below 90 percent or project specific performance requirements are not met. If vegetation suffers for no apparent reason, consult with horticulturist and/or test soil as needed.
 +
* '''Semi-annually'''
 +
** Inspect inflow points for clogging (off-line systems) and remove any sediment
 +
** Inspect filter strip/grass channel for erosion or gullying and sod as necessary
 +
** Herbaceous vegetation, trees and shrubs should be inspected to evaluate their health and replanted as appropriate to meet project goals
 +
** Remove any dead or severely diseased vegetation
 +
* '''Annually in fall'''
 +
** Inspect and remove any sediment and debris build-up in pre-treatment areas.
 +
** Inspect inflow points and bioretention surface for build up of road sand associated with spring melt period, remove as necessary and replant areas that have been impacted by sand/salt build up.
 +
*'''Annually in spring'''
 +
** Cut back and remove previous years plant material and remove accumulated leaves  if needed (or controlled burn where appropriate).
 +
 
 +
For proper nutrient control, bioretention cells must not be fertilized unless a soil test from a certified lab indicates nutrient deficiency.  The one exception is a one-time fertilizer application during planting of the cell, which will help with plant establishment. Irrigation is also typically needed during establishment. 
 +
 
 +
Pre-treatment devices need to be maintained for long-term functionality.  Accumulated sediment in the forebay will need to be cleaned out at a minimum when it is half-full, which should be approximately every 10 to 20 years.  In an especially dirty watershed, the frequency may be increased to every 2 to 3 years.  Sediment should also be cleaned out of rip rap and sumps. A vacuum truck is typically used for sediment removal. If a [[Vegetated filter strips|grassed filter strip]] or [[Filtration|swale]] is used as [[Pre-treatment|pre-treatment]], they should be mowed as frequently as a typical lawn.  Depending on the contributing watershed, grassed BMPs may also need to be swept before mowing. All grassed BMP’s should also be swept annually with a stiff bristle broom or equal to remove thatch and winter sand. The University of Minnesota’s [http://www.sustland.umn.edu/maint/maint.htm Sustainable Urban Landscape Series website] provides guidance for turf maintenance, including mowing heights.
 +
 +
Maintenance of vegetation after establishment is similar to adjacent gardens (except for application of fertilizer).  Weeding is especially important during the plant establishment period, when vegetation cover is not 100 percent yet, but some weeding will likely always be needed. It is also important to budget for some plant replacement (at least 5 to 10 percent of the original plantings) during the first few years after planting, in case some of the plants that were originally planted die. Rubbish and trash removal will likely be needed more frequently than in the adjacent landscape, since the hydraulic loading ratio is high.  Trash removal is important for prevention of mosquitoes.  Mulch renewal will be needed two or three times after establishment (first five years).  After that, the plants are typically dense enough to make it difficult to mulch, and the breakdown of plant material will provide enough organic matter to the infiltration/filtration device.  It is recommended that bioretention performance evaluations follow the four level assessment system in ''Stormwater Treatment: Assessment and Maintenance'' (Gulliver et al., 2010; also see [http://stormwater.safl.umn.edu/sites/stormwater.safl.umn.edu/files/021611gulliver.pdf]).  More detailed information about maintenance procedures, a maintenance schedule, and estimated maintenance costs are also available in Gulliver et al. 2010.
 +
 
 +
The following are minimum requirements for plant coverage.
 +
*at least 50 percent of specified vegetation cover at end of the first growing season
 +
*at least 90 percent of specified vegetation cover at end of the third growing season
 +
*supplement plantings to meet project specifications if cover requirements are not met
 +
*tailoring percent coverage requirements to project goals and vegetation. For example, percent cover required for turf after 1 growing season would likely be 100 percent, whereas it would likely be lower for other vegetation types.
 +
 
 +
Owner’s Representatives may wish to consider deducts and liquidated damages for bad construction practices. Regulating authorities may wish to consider fines for bad construction practices.
 +
 
 +
==Sustainable service life for infiltration and bioretention BMPs==
 +
 
 +
The service life of bioretention practices depends upon the pollutant of concern. 
 +
===Nitrogen reduction===
 +
An important mechanism of nitrogen removal in bioretention systems is plant uptake since nitrogen is essential for plant growth. Soluble nitrogen is also removed through denitrification in internal water storage zones, a microbially-mediated process that only occurs under anoxic conditions.  Denitrification requires organic matter as a carbon source, which is supplied by decaying root matter and mulch.  Particulate bound nitrogen in stormwater runoff will typically be removed through sedimentation.  All of these processes are self-sustaining, and the service life of a bioretention system designed for nitrogen reduction should be very long. In bioretention systems where denitrification is not an important process, leaching of nitrate is likely, particularly if the bioretention soil has a high organic matter content ([[Operation and maintenance of bioretention#References|Liging and Davis]], 2014).
 +
 
 +
===Phosphorus reduction===
 +
With design optimized for phosphorus reduction, phosphorus reduction service life can be more than three decades ([[Operation and maintenance of bioretention#References|Lucas and Greenway]], 2011c). Sediment bound phosphorus is removed through sedimentation, while removal of soluble phosphorus in bioretention depends on the type of media used.  If the media is already saturated with P (i.e. its P binding sites are full), it will not be able to retain additional dissolved P and the P in stormwater will tend to leach from the media as it passes through the biofilter (Hunt et al. 2006).  It is highly recommended that the P-index of the media at installation be below 30, which equates to less than 36 milligrams per kilogram P, to ensure P removal capacity.  Laboratory research has suggested an oxalate extractable P concentration of 20 to 40 milligrams per liter will provide consistent removal of P ([[Operation and maintenance of bioretention#References|O’Neill and Davis]], 2012).  After an effective loading of the equivalent of more than three decades of P into bioretention mecocosms optimized for P reduction, researchers in Australia showed that excellent P retention was still occurring. Keys to maximize P reduction in these systems included P sorptive soils or soil amendments (e.g. aluminum water treatment residuals [WTR] or Krasnozem soils [K40], a highly aggregated clay), use of coir peat (a source of organic matter low in phosphorus), and healthy vegetation. The systems with aluminum water treatment residuals still retained up to 99 percent of applied PO4-P in storm water after the equivalent of 32 years of treatment. After 110 weeks of effluent loading at typical stormwater concentrations, the equivalent to 48 years of bioretention loads, PO4-P retention from storm water by the K40 soils treatment was 85 percent. “Comparison with the K40 treatments over the loading and dosing regimes suggest that the WTR treatments will perform at least as well as the K40 treatment under similar exposure of 48 years” ([[Operation and maintenance of bioretention#References|Lucas and Greenway]], 2011).
 +
 
 +
===Heavy metals retention===
 +
Metals are typically retained in bioretention systems through sedimentation and adsorption processes.  Since there are a finite amount of sorption sites for metals on a particular soil, there will be a finite service life for the removal of dissolved metals.  [[Operation and maintenance of bioretention#References|Morgan et al.]] (2011) investigated cadmium, copper, and zinc removal and retention with batch and column experiments. Using synthetic stormwater at typical stormwater concentrations, they found that 6 inches of filter media composed of 30 percent compost and 70 percent sand will last 95 years until breakthrough (i.e. when the effluent concentration is 10 percent of the influent concentration). They also found that increasing compost from 0 percent to 10 percent more than doubles the expected lifespan for 10 percent breakthrough in 6 inches of filter media for retainage of cadmium and zinc. Using accelerated dosing laboratory experiments, [[Operation and maintenance of bioretention#References|Hatt et al.]] (2011) found that breakthrough of Zn was observed after 2000 pore volumes, but did not observe breakthrough for Cd, Cu, and Pb after 15 years of synthetic stormwater passed through the media.  However, concentrations of Cd, Cu, and Pb on soil media particles exceeded human and/or ecological health levels, which could have an impact on disposal if the media needed replacement.  Since the majority of metals retainage occurs in the upper 2 to 4 inches of the soil media ([[Operation and maintenance of bioretention#References|Li and Davis]], 2008), long-term metals capture may only require rejuvenation of the upper portion of the media.
 +
 
 +
===Polycyclic Aromatic Hydrocarbons (PAHs) reduction===
 +
Accumulation of polycyclic aromatic hydrocarbons (PAHs) in sediments has been found to be so high in some stormwater retention ponds that disposal costs for the dredging spoils were prohibitively high. Research has shown that rain gardens, on the other hand, are “a viable solution for sustainable petroleum hydrocarbon removal from stormwater, and that vegetation can enhance overall performance and stimulate biodegradation.” ([[Operation and maintenance of bioretention#References|Lefevre]], 2012b).
 +
 
 +
===Infiltration rate service life before clogging===
 +
Infiltration rate appears to drop immediately after installation and then level off at a sustainable level ([[Operation and maintenance of bioretention#References|Jenkins et al.]] 2010; [[Operation and maintenance of bioretention#References|Barrett et al.]] 2013).  Planted bioretention columns even showed a slight increase in infiltration rate after the initial drop ([[Operation and maintenance of bioretention#References|Barrett et al.]] 2013).  Plant roots are essential in macropore formation, which help to maintain the infiltration rate.  If proper pre-treatment is present, service life for infiltration should be unlimited. However, if construction site runoff is not kept from entering the bioretention cell, clogging will occur, limiting or eliminating the infiltration function of the system and restorative maintenance or repair will be needed ([[Operation and maintenance of bioretention#References|Brown and Hunt]], 2012).
 +
 
 +
==Links to additional information==
 +
*[[file:Bioretention Basin Maintenance Guide public use.pdf|Bioretention Basin Maintenance Guide]]. Source:[http://www.rwmwd.org/ Ramsey-Washington Watershed District]
 +
*[[file:Rain Garden Maintenance Guide public use.pdf|Rain Garden Maintenance Guide]]. Source:[http://www.rwmwd.org/ Ramsey-Washington Watershed District]
 +
 
 +
==References==
 +
*Aprill, W. and Sims, Ronald C. 1990. ''Evaluation of the Use of Prairie Grasses for Stimulating Polycyclic Aromatic Hydrocarbon Treatment in Soil''. Biological Engineering Faculty Publications. Paper 41.
 +
*Brown, R.A. and Hunt, W.F. 2010. ''Impacts of construction activity on bioretention performance''. Journal of Hydrologic Engineering. 15(6), 386-394.
 +
*Gulliver, J.S., A.J. Erickson, and P.T. Weiss (editors). 2010. Stormwater Treatment: Assessment and Maintenance. University of Minnesota, St. Anthony Falls Laboratory. Minneapolis, MN.
 +
*Hatt, B.E., Steinel, A., Deletic, A., and Fletcher, T.D. 2011. ''Retention of heavy metals by stormwater filtration systems: Breakthrough analysis''. Water, Science, and Technology. 64(9), 1913-1919.
 +
*Henderson, C.F.K. 2009. ''The Chemical and Biological Mechanisms of Nutrient Removal from Stormwater in Bioretention Systems''. Thesis. Griffith School of Engineering, Griffith University.
 +
*Hunt, W.F., Jarrett, A.R., Smith, J.T., and Sharkey, L.J. 2006. ''Evaluating bioretention hydrology and nutrient removal at three field sites in North Carolina''. Journal of Irrigation and Drainage Engineering. 132(6), 600-608.
 +
*Jenkins, G,  J.K., Wadzuk, B.M., and Welker, A.L. 2010. ''Fines accumulation and distribution in a storm-water rain garden nine year postconstruction''. Journal of Irrigation and Drainage Engineering. 136(12), 862-869.
 +
*LeFevre, G.H., M. Raymond, P. Hozalski, J. Novak. 2012a. ''The role of biodegradation in limiting the accumulation of petroleum hydrocarbons in raingarden soils''. Water Research 46: 6753-6762.
 +
*Lefevre, G.H., P.J. Novak, R.M. Hozalski. 2012b. ''Fate of naphthalene in laboratory-scale bioretention cells: implications for sustainable stormwater management''. Environmental Science and Technology 46(2):995-1002.
 +
*Li, H. and Davis, A.P. 2008. ''Heavy metal capture and accumulation in bioretention media''. Environmental Science & Technology. 42, 5247-5253.
 +
*Liging, Li, and A.P. Davis. 2014. ''Urban stormwater runoff nitrogen composition and fate in bioretention systems''. Accepted for publication in ES&T.
 +
*Lucas, W.C. 2005. [http://www.dnrec.state.de.us/dnrec2000/Divisions/Soil/Stormwater/New/DURMM_TechnicalManual_01-04.pdf Green Technology: The Delaware Urban Runoff Management Approach]. Prepared For Delaware Department of Natural Resources And Environmental Control Division of Soil And Water Conservation.
 +
*Lucas, , W. C. and M. Greenway. 2007a. [http://documents.irevues.inist.fr/bitstream/handle/2042/25537/1089_318lucas.pdf?sequence=1 A Comparative Study of Nutrient Retention Performance In Vegetated and Non-Vegetated Bioretention Mecocosms]. Novatech 2007 Session 5.2.
 +
*Lucas, W. C. and M. Greenway. 2007b. ''Phosphorus Retention Performance in Vegetated and Non-Vegetated Bioretention Mecocosms Using Recycled Effluent''. Conference Proceedings: Rainwater and Urban Design Conference 2007.
 +
*Lucas, W. C. and M. Greenway. 2008. ''Nutrient Retention in Vegetated and Non-vegetated Bioretention Mesocosms.'' Journal of Irrigation and Drainage Engineering. 134 (5): 613-623.
 +
*Lucas, W. C. and M. Greenway. 2011a. ''Hydraulic Response and Nitrogen Retention in Bioretention Mesocosms with Regulated Outlets: Part I—Hydraulic Response''. Water Environment Research 83(8): 692-702.
 +
*Lucas, W. C. and M. Greenway. 2011b. ''Hydraulic response and nitrogen retention in bioretention mesocosms with regulated outlets: part II--nitrogen retention''. Water Environment Research 83(8): 703-13.
 +
*Lucas, W. C. and M. Greenway. 2011c. ''Phosphorus Retention by Bioretention Mesocosms Using Media Formulated for Phosphorus Sorption: Response to Accelerated Loads''. Journal of Irrigation and Drainage Engineering. 137(3): 144–153.
 +
*Morgan, J.G., K.A. Paus, R.M. Hozalski and J.S. Gulliver. (2011). [http://purl.umn.edu/116560 Sorption and Release of Dissolved Pollutants Via Bioretention Media]. SAFL Project Report No. 559, September 2011.
 +
*O’Neill, S.W. and Davis, A.P. (2012). ''Water treatment residual as a bioretention amendment for phosphorus. I: Evaluation studies''. Journal of Environmental Engineering. 138(3), 318-327.
 +
 
 +
<noinclude>
 +
==Related pages==
 +
*[[Bioretention terminology]] (including types of bioretention)
 +
*[[Overview for bioretention]]
 +
*[[Design criteria for bioretention]]
 +
*[[Construction specifications for bioretention]]
 +
*[[Operation and maintenance of bioretention]]
 +
*[[Assessing the performance of bioretention]]
 +
*[[Cost-benefit considerations for bioretention]]
 +
*[[Calculating credits for bioretention]]
 +
*[[Soil amendments to enhance phosphorus sorption]]
 +
*[[Summary of permit requirements for bioretention]]
 +
*[[Supporting material for bioretention]]
 +
*[[External resources for bioretention]]
 +
*[[References for bioretention]]
 +
*[[Requirements, recommendations and information for using bioretention with no underdrain BMPs in the MIDS calculator]]
 +
*[[Requirements, recommendations and information for using bioretention with an underdrain BMPs in the MIDS calculator]]
 +
</noinclude>
 +
 
 +
 +
[[Category:Operation and maintenance]]

Latest revision as of 19:12, 21 September 2016

image showing Manual logo
Information on this page has recently been added or updated. Acknowledgements.
Chesapeake stormwater Network logo
The Chesapeake Stormwater Network has developed two videos that illustrate inspection and maintenance of BMP practices. NOTE: These videos provide useful tips but should not be used for compliance with Minnesota permits.
Information: The following changes have been made to this page:
  • added information on sustainable service life of bioretention BMPs based on pollutant of concern;
  • added information on maintenance of vegetation;
  • minor modifications to the bioretention-construction inspection checklist.

The most frequently cited maintenance concern for bioretention is surface and underdrain clogging caused by organic matter, fine silts, hydrocarbons, and algal matter. Common operational problems include

  • standing water;
  • clogged filter surface; and
  • inlet, outlet or under-drains clogged.

Recommendations described below are aimed at preventing these common problems.

Design phase maintenance considerations

Implicit in the design guidance for bioretention is the fact that many design elements of bioretention systems can minimize the maintenance burden and maintain pollutant removal efficiency. Key examples include

Construction phase maintenance

Proper construction methods and sequencing play a significant role in reducing problems with operation and maintenance (O&M). In particular, with construction of bioretention practices, the most important action for preventing operation and maintenance difficulties is to ensure that the contributing drainage area has been fully stabilized prior to bringing the practice on line.

Warning: It is required that the contributing drainage area has been fully stabilized prior to bringing the practice on line

Inspections during construction are needed to ensure that the bioretention practice is built in accordance with the approved design and standards and specifications. Detailed inspection checklists should be used that include sign-offs by qualified individuals at critical stages of construction, to ensure that the contractor’s interpretation of the plan is acceptable to the professional designer. An example construction phase inspection checklist is provided here.

Infiltration practices construction inspection checklist.
Link to this table
To access an Excel version of form (for field use), click here.

Project:
Location:
Site Status:
Date:
Time:
Inspector:
Construction Sequence Satisfactory / Unsatisfactory Comments
1. Pre-Construction
Pre-construction meeting
Runoff diverted (Note type of bypass)
Facility area cleared
Soil tested for permeability
Soil tested for phosphorus content (include test method)
Verify site was not overdug
Project benchmark near site
Facility location staked out
Temporary erosion and sediment protection properly installed
2. Excavation
Lateral slopes completely level
Soils not compacted during excavation
Longitudinal slopes within design range
Stockpile location not adjacent to excavation area and stabilized with vegetation and/ or silt fence
Verify stockpile is not causing compaction and that it is not eroding
Was underlying soil ripped or loosened
3. Structural Components
Stone diaphragm installed per plans
Outlets installed pre plans
Underdrain installed to grade
Pretreatment devices installed per plans
Soil bed composition and texture conforms to specifications
4. Vegetation
Complies with planting specs
Topsoil complies with specs in composition and placement
Soil properly stabilized for permanent erosion control
5. Final Inspection
Dimensions per plans
Pre-treatment operational
Inlet/outlet operational
Soil/ filter bed permeability verified
Effective stand of vegetation stabilized
Construction generated sediments removed
Contributing watershed stabilized before flow is diverted to the practice
Comments:
Actions to be taken:


Post-construction operation and maintenance

Warning: A maintenance plan clarifying maintenance responsibility is REQUIRED. Effective long-term operation of bioretention practices necessitates a dedicated and routine maintenance schedule with clear guidelines and schedules. Proper maintenance will not only increase the expected lifespan of the facility but will improve aesthetics and property value.
Warning: A maintenance plan clarifying maintenance responsibility is REQUIRED.

Effective long-term operation of bioretention practices necessitates a dedicated and routine maintenance schedule with clear guidelines and schedules. Proper maintenance will not only increase the expected life span of the facility, but will also improve aesthetics and property value. Some important post-construction considerations are provided below along with RECOMMENDED maintenance standards.

  • A site specific O&M plan that includes the following considerations should be prepared by the designer prior to putting the stormwater filtration practice into operation:
    • Operating instructions for outlet component
    • Vegetation maintenance schedule
    • Inspection checklists
    • Routine maintenance checklists
  • A legally binding and enforceable maintenance agreement should be executed between the practice owner and the local review authority. It is recommended that the practice be bonded.
  • Adequate access must be provided for all bioretention facilities for inspection, maintenance and landscaping upkeep, including appropriate equipment and vehicles.
  • The surface of the ponding area may become clogged with fine sediment over time. Core aeration or cultivating of non-vegetated areas may be required to ensure adequate filtration.
  • Bioretention areas should not be used as dedicated snow storage areas:
    • Areas designed for infiltration should be protected from excessive snow storage where sand and salt is applied.
    • Specific soil storage areas should be assigned that will provide some filtration before the stormwater reaches the infiltration areas.
    • When used for snow storage, or if used to treat parking lot runoff, the bioretention area should be planted with salt tolerant, and non-woody plant species.
  • Bioretention areas should always be inspected for sand build-up on the surface following the spring melt event.
  • General maintenance activities and schedule are provided below.

Recommended maintenance activities for bioretention areas

  • First year after planting
    • Adequate water is crucial to plant survival and temporary irrigation will be needed unless rainfall is adequate until plants mature
  • As needed
    • Prune and weed to maintain appearance
    • Stabilize or replace mulch when erosion is evident
    • Remove trash and debris
    • Mow filter strip
    • Renew mulch to replace that which has broken down into organic matter
    • Replace vegetation whenever percent cover of acceptable vegetation falls below 90 percent or project specific performance requirements are not met. If vegetation suffers for no apparent reason, consult with horticulturist and/or test soil as needed.
  • Semi-annually
    • Inspect inflow points for clogging (off-line systems) and remove any sediment
    • Inspect filter strip/grass channel for erosion or gullying and sod as necessary
    • Herbaceous vegetation, trees and shrubs should be inspected to evaluate their health and replanted as appropriate to meet project goals
    • Remove any dead or severely diseased vegetation
  • Annually in fall
    • Inspect and remove any sediment and debris build-up in pre-treatment areas.
    • Inspect inflow points and bioretention surface for build up of road sand associated with spring melt period, remove as necessary and replant areas that have been impacted by sand/salt build up.
  • Annually in spring
    • Cut back and remove previous years plant material and remove accumulated leaves if needed (or controlled burn where appropriate).

For proper nutrient control, bioretention cells must not be fertilized unless a soil test from a certified lab indicates nutrient deficiency. The one exception is a one-time fertilizer application during planting of the cell, which will help with plant establishment. Irrigation is also typically needed during establishment.

Pre-treatment devices need to be maintained for long-term functionality. Accumulated sediment in the forebay will need to be cleaned out at a minimum when it is half-full, which should be approximately every 10 to 20 years. In an especially dirty watershed, the frequency may be increased to every 2 to 3 years. Sediment should also be cleaned out of rip rap and sumps. A vacuum truck is typically used for sediment removal. If a grassed filter strip or swale is used as pre-treatment, they should be mowed as frequently as a typical lawn. Depending on the contributing watershed, grassed BMPs may also need to be swept before mowing. All grassed BMP’s should also be swept annually with a stiff bristle broom or equal to remove thatch and winter sand. The University of Minnesota’s Sustainable Urban Landscape Series website provides guidance for turf maintenance, including mowing heights.

Maintenance of vegetation after establishment is similar to adjacent gardens (except for application of fertilizer). Weeding is especially important during the plant establishment period, when vegetation cover is not 100 percent yet, but some weeding will likely always be needed. It is also important to budget for some plant replacement (at least 5 to 10 percent of the original plantings) during the first few years after planting, in case some of the plants that were originally planted die. Rubbish and trash removal will likely be needed more frequently than in the adjacent landscape, since the hydraulic loading ratio is high. Trash removal is important for prevention of mosquitoes. Mulch renewal will be needed two or three times after establishment (first five years). After that, the plants are typically dense enough to make it difficult to mulch, and the breakdown of plant material will provide enough organic matter to the infiltration/filtration device. It is recommended that bioretention performance evaluations follow the four level assessment system in Stormwater Treatment: Assessment and Maintenance (Gulliver et al., 2010; also see [1]). More detailed information about maintenance procedures, a maintenance schedule, and estimated maintenance costs are also available in Gulliver et al. 2010.

The following are minimum requirements for plant coverage.

  • at least 50 percent of specified vegetation cover at end of the first growing season
  • at least 90 percent of specified vegetation cover at end of the third growing season
  • supplement plantings to meet project specifications if cover requirements are not met
  • tailoring percent coverage requirements to project goals and vegetation. For example, percent cover required for turf after 1 growing season would likely be 100 percent, whereas it would likely be lower for other vegetation types.

Owner’s Representatives may wish to consider deducts and liquidated damages for bad construction practices. Regulating authorities may wish to consider fines for bad construction practices.

Sustainable service life for infiltration and bioretention BMPs

The service life of bioretention practices depends upon the pollutant of concern.

Nitrogen reduction

An important mechanism of nitrogen removal in bioretention systems is plant uptake since nitrogen is essential for plant growth. Soluble nitrogen is also removed through denitrification in internal water storage zones, a microbially-mediated process that only occurs under anoxic conditions. Denitrification requires organic matter as a carbon source, which is supplied by decaying root matter and mulch. Particulate bound nitrogen in stormwater runoff will typically be removed through sedimentation. All of these processes are self-sustaining, and the service life of a bioretention system designed for nitrogen reduction should be very long. In bioretention systems where denitrification is not an important process, leaching of nitrate is likely, particularly if the bioretention soil has a high organic matter content (Liging and Davis, 2014).

Phosphorus reduction

With design optimized for phosphorus reduction, phosphorus reduction service life can be more than three decades (Lucas and Greenway, 2011c). Sediment bound phosphorus is removed through sedimentation, while removal of soluble phosphorus in bioretention depends on the type of media used. If the media is already saturated with P (i.e. its P binding sites are full), it will not be able to retain additional dissolved P and the P in stormwater will tend to leach from the media as it passes through the biofilter (Hunt et al. 2006). It is highly recommended that the P-index of the media at installation be below 30, which equates to less than 36 milligrams per kilogram P, to ensure P removal capacity. Laboratory research has suggested an oxalate extractable P concentration of 20 to 40 milligrams per liter will provide consistent removal of P (O’Neill and Davis, 2012). After an effective loading of the equivalent of more than three decades of P into bioretention mecocosms optimized for P reduction, researchers in Australia showed that excellent P retention was still occurring. Keys to maximize P reduction in these systems included P sorptive soils or soil amendments (e.g. aluminum water treatment residuals [WTR] or Krasnozem soils [K40], a highly aggregated clay), use of coir peat (a source of organic matter low in phosphorus), and healthy vegetation. The systems with aluminum water treatment residuals still retained up to 99 percent of applied PO4-P in storm water after the equivalent of 32 years of treatment. After 110 weeks of effluent loading at typical stormwater concentrations, the equivalent to 48 years of bioretention loads, PO4-P retention from storm water by the K40 soils treatment was 85 percent. “Comparison with the K40 treatments over the loading and dosing regimes suggest that the WTR treatments will perform at least as well as the K40 treatment under similar exposure of 48 years” (Lucas and Greenway, 2011).

Heavy metals retention

Metals are typically retained in bioretention systems through sedimentation and adsorption processes. Since there are a finite amount of sorption sites for metals on a particular soil, there will be a finite service life for the removal of dissolved metals. Morgan et al. (2011) investigated cadmium, copper, and zinc removal and retention with batch and column experiments. Using synthetic stormwater at typical stormwater concentrations, they found that 6 inches of filter media composed of 30 percent compost and 70 percent sand will last 95 years until breakthrough (i.e. when the effluent concentration is 10 percent of the influent concentration). They also found that increasing compost from 0 percent to 10 percent more than doubles the expected lifespan for 10 percent breakthrough in 6 inches of filter media for retainage of cadmium and zinc. Using accelerated dosing laboratory experiments, Hatt et al. (2011) found that breakthrough of Zn was observed after 2000 pore volumes, but did not observe breakthrough for Cd, Cu, and Pb after 15 years of synthetic stormwater passed through the media. However, concentrations of Cd, Cu, and Pb on soil media particles exceeded human and/or ecological health levels, which could have an impact on disposal if the media needed replacement. Since the majority of metals retainage occurs in the upper 2 to 4 inches of the soil media (Li and Davis, 2008), long-term metals capture may only require rejuvenation of the upper portion of the media.

Polycyclic Aromatic Hydrocarbons (PAHs) reduction

Accumulation of polycyclic aromatic hydrocarbons (PAHs) in sediments has been found to be so high in some stormwater retention ponds that disposal costs for the dredging spoils were prohibitively high. Research has shown that rain gardens, on the other hand, are “a viable solution for sustainable petroleum hydrocarbon removal from stormwater, and that vegetation can enhance overall performance and stimulate biodegradation.” (Lefevre, 2012b).

Infiltration rate service life before clogging

Infiltration rate appears to drop immediately after installation and then level off at a sustainable level (Jenkins et al. 2010; Barrett et al. 2013). Planted bioretention columns even showed a slight increase in infiltration rate after the initial drop (Barrett et al. 2013). Plant roots are essential in macropore formation, which help to maintain the infiltration rate. If proper pre-treatment is present, service life for infiltration should be unlimited. However, if construction site runoff is not kept from entering the bioretention cell, clogging will occur, limiting or eliminating the infiltration function of the system and restorative maintenance or repair will be needed (Brown and Hunt, 2012).

Links to additional information

References

  • Aprill, W. and Sims, Ronald C. 1990. Evaluation of the Use of Prairie Grasses for Stimulating Polycyclic Aromatic Hydrocarbon Treatment in Soil. Biological Engineering Faculty Publications. Paper 41.
  • Brown, R.A. and Hunt, W.F. 2010. Impacts of construction activity on bioretention performance. Journal of Hydrologic Engineering. 15(6), 386-394.
  • Gulliver, J.S., A.J. Erickson, and P.T. Weiss (editors). 2010. Stormwater Treatment: Assessment and Maintenance. University of Minnesota, St. Anthony Falls Laboratory. Minneapolis, MN.
  • Hatt, B.E., Steinel, A., Deletic, A., and Fletcher, T.D. 2011. Retention of heavy metals by stormwater filtration systems: Breakthrough analysis. Water, Science, and Technology. 64(9), 1913-1919.
  • Henderson, C.F.K. 2009. The Chemical and Biological Mechanisms of Nutrient Removal from Stormwater in Bioretention Systems. Thesis. Griffith School of Engineering, Griffith University.
  • Hunt, W.F., Jarrett, A.R., Smith, J.T., and Sharkey, L.J. 2006. Evaluating bioretention hydrology and nutrient removal at three field sites in North Carolina. Journal of Irrigation and Drainage Engineering. 132(6), 600-608.
  • Jenkins, G, J.K., Wadzuk, B.M., and Welker, A.L. 2010. Fines accumulation and distribution in a storm-water rain garden nine year postconstruction. Journal of Irrigation and Drainage Engineering. 136(12), 862-869.
  • LeFevre, G.H., M. Raymond, P. Hozalski, J. Novak. 2012a. The role of biodegradation in limiting the accumulation of petroleum hydrocarbons in raingarden soils. Water Research 46: 6753-6762.
  • Lefevre, G.H., P.J. Novak, R.M. Hozalski. 2012b. Fate of naphthalene in laboratory-scale bioretention cells: implications for sustainable stormwater management. Environmental Science and Technology 46(2):995-1002.
  • Li, H. and Davis, A.P. 2008. Heavy metal capture and accumulation in bioretention media. Environmental Science & Technology. 42, 5247-5253.
  • Liging, Li, and A.P. Davis. 2014. Urban stormwater runoff nitrogen composition and fate in bioretention systems. Accepted for publication in ES&T.
  • Lucas, W.C. 2005. Green Technology: The Delaware Urban Runoff Management Approach. Prepared For Delaware Department of Natural Resources And Environmental Control Division of Soil And Water Conservation.
  • Lucas, , W. C. and M. Greenway. 2007a. A Comparative Study of Nutrient Retention Performance In Vegetated and Non-Vegetated Bioretention Mecocosms. Novatech 2007 Session 5.2.
  • Lucas, W. C. and M. Greenway. 2007b. Phosphorus Retention Performance in Vegetated and Non-Vegetated Bioretention Mecocosms Using Recycled Effluent. Conference Proceedings: Rainwater and Urban Design Conference 2007.
  • Lucas, W. C. and M. Greenway. 2008. Nutrient Retention in Vegetated and Non-vegetated Bioretention Mesocosms. Journal of Irrigation and Drainage Engineering. 134 (5): 613-623.
  • Lucas, W. C. and M. Greenway. 2011a. Hydraulic Response and Nitrogen Retention in Bioretention Mesocosms with Regulated Outlets: Part I—Hydraulic Response. Water Environment Research 83(8): 692-702.
  • Lucas, W. C. and M. Greenway. 2011b. Hydraulic response and nitrogen retention in bioretention mesocosms with regulated outlets: part II--nitrogen retention. Water Environment Research 83(8): 703-13.
  • Lucas, W. C. and M. Greenway. 2011c. Phosphorus Retention by Bioretention Mesocosms Using Media Formulated for Phosphorus Sorption: Response to Accelerated Loads. Journal of Irrigation and Drainage Engineering. 137(3): 144–153.
  • Morgan, J.G., K.A. Paus, R.M. Hozalski and J.S. Gulliver. (2011). Sorption and Release of Dissolved Pollutants Via Bioretention Media. SAFL Project Report No. 559, September 2011.
  • O’Neill, S.W. and Davis, A.P. (2012). Water treatment residual as a bioretention amendment for phosphorus. I: Evaluation studies. Journal of Environmental Engineering. 138(3), 318-327.


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This page was last edited on 21 September 2016, at 19:12.

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