Low Impact Development Training

Module 11: Maintenance Practices

Dennis Chestnut

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Sponsors

District Department of Transportation

U.S. Department of Transportation Federal Highway Administration

The Low Impact Development Center, Inc.

University of the District of Columbia

Funding for this project was provided through a grant from the Federal Highway Administration, U.S. Department of Transportation

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Contributors

The Low Impact Development Center, Inc.

John Shorb Landscaping, Inc.Logo

Groundwork Anacostia River, D.C.

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Copyright

Unless otherwise noted, Low Impact Development Training, funded by DDOT & DDOE, is licensed under a Creative Commons Attribution-NonCommerical-ShareAlike 3.0 Unported License.

Content provided by cited entities remains the property of those entities and may not be used without their explicit permission.

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Outline

• Routine maintenance of bioretention cells• Minor repairs to bioretention cells• Maintenance of rain barrels and cisterns• Maintenance of small permeable paver

installations

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Expected Outcomes

• Know how to perform routine maintenance of bioretention cells, as well as minor repairs

• Be able to perform basic maintenance of rain barrels and permeable pavers

• Primary maintenance requirement - regular inspection and repair / replacement of damaged components

• Can be incorporated into regular landscaping maintenance contract, as there issignificant overlap in the tools and skills required to maintain bioretentioncells and other landscaped areas.

Maintenance – BioretentionBioretention maintenance

Graphic Courtesy of the Low Impact Development Center, Inc.

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Training

• Maintenance techniques are similar to other landscaped areas, but with additional procedures to maintain stormwater function

• Proper training is important for maintenance of bioretention cells

• Learn to spot, prevent, and correct maintenance issues that can compromise bioretention performance

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Facility Assessments

• Module 7 of this course presented a detailed methodology for assessing bioretention performance and maintenance needs

• The Guidebook contains a maintenance inspection checklist

• Bioretention in the right-of-way must follow DDOT’s bioretention maintenance schedule, presented in Module 9 of this course

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Preventive maintenance

• Procedures carried out according to a maintenance schedule, in order to avoid loss of bioretention function– Examples:

• Irrigation• Pruning• Mulch replacement

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Corrective maintenance

• Actions taken in response to a problem that develops within the bioretention cell

• Examples:– Replacing stone that has washed away– Removing accumulated sediment– Repairing erosion– Replacing dead plants

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Upon Establishment

• After storms– Inspect the bioretention cell and its drainage

area after storm events with more than ½ inch of rainfall. Inspect at least twice in the first six months of operation. Conduct any needed repairs or stabilization.

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Upon establishment

• In the drainage area:– Watch for bare or eroding areas, and stabilize

immediately

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Drainage System Maintenance

• Clear debris, sediment, and blockages from inflow and outflow points

• Check inflow points for stone placement. If stone has moved or been washed away, it should be replaced

• If bioretention cell has standing water for more than 2 days after a storm, underdrains may need to be flushed

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Removing Sediment

Photo Courtesy of the Low Impact Development Center, Inc.

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Removing sediment

• Sediment should be removed manually, using a shovel, or vacuumed from large rocks in velocity dissipators

• Place sediment in buckets or wheelbarrows

• Rake the mulch surface to break up remaining sediment

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Sediment Disposal

• Sediment should be removed from the site and disposed of appropriately

• Dispose of sediment along with other solid waste

• Sediment should not be disposed of as yard waste

• Sediment captured in bioretention cells is highly polluted - do not dump sediment into natural areas!

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Replacing stone

• Large storm events may wash stone from velocity dissipators and weirs, leaving these areas vulnerable to erosion

• Stone should be replaced when depleted• Follow as-built stone specification for size

and placement

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Calculating stone replacement volume

• Ideally, the volume of stone required to rebuild the structure will be shown on the as-built plans

• Where this volume is not given, it can be determined by measuring the dimensions of the structure in the field

• Use the methods covered in Module 1 to calculate the volume of the stone structure

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Example – replacing velocity dissipator stone at inlet

Plans Courtesy of the Low Impact Development Center, Inc.

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Calculate stone volume

• For each apron, you will need:• Class 0 riprap

– Length = 6 feet– Width = 6 feet– Depth = 1 foot– Volume = Length x width x depth– Volume = 6 ft x 6 ft x 1 ft = 36 cubic feet

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Convert cubic feet to cubic yards

convert 36 cubic feet to cubic yards

Cross-multiply

Solve for x

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Calculate river rock volume

• 2” river rock to fill in surface• Surface dimensions:

– Width = 6 feet– Length = 6 feet

• Depth: assume a layer 2 rocks deep to ensure there is enough – Depth = 2 x 2 inches = 4 inches = 0.3 feet– Volume = W x L x D = 6 x 6 x 0.3 = 10.8 cu ft

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Convert to cubic yards

• Convert to cubic yards:• 1 cu yd = 27 cu ft

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Clearing cleanout pipes and underdrains

• If underdrains become clogged with sediment, it may be necessary to flush them

• Two options:– High pressure water hose– Drain snake

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Plant maintenance

Photo Courtesy of the Low Impact Development Center, Inc.

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Plant Identification and Assessments

• Modules 5.2 and 11 of this course concern learning to identify common bioretention landscaping plants, weeds, and invasive species

• For installations owned by the District, DDOT has certified arborists on staff, who can assist with identifying trees and other plants, and who can recommend maintenance and/or control methods

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Irrigation best practices

• Immediately after installation, water plant material for 14 consecutive days (unless sufficient natural rainfall).

• During extended drought, look for physical signs of stress (unrevived wilting; yellow, spotted or brown leaves; loss of leaves, etc.). Water in the early morning if needed

• Water deeply and infrequently

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Dealing with diseases and pests

• Inspect regularly to catch infestations early• Use the least toxic method available

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Control of Invasives

• In general, it’s best to avoid using herbicides in bioretention cells whenever possible

• Hand-pulling or cutting is preferable• May need to be repeated multiple times

before seed banks and roots are exhausted

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Use of Herbicides

• When dealing with large infestations of particularly pernicious invasives, herbicide use may be warranted

• Spot treatment of specific plants is preferable to spraying

• Must use only herbicides certified by the EPA as safe for use around water

• Herbicide applicators must be trained and licensed

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Pruning

• Recommendations vary from species to species

• Prune vegetation so that it remains clear of inlets and does not pose a safety hazard or block visibility

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Replacing dead plants

• Individual dead plants should be replaced with the same cultivar, as indicated by the as-built planting plan

• Stake, protect, and irrigate new plants during establishment

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What to do if an entire group of plants has died

• If an entire group of plants has died, the species or cultivar may not be suitable for the location where they were placed

• In these situations, it may be appropriate to try an alternate species or cultivar

• Consult DDOE and DDOT bioretention plant lists for candidate species, along with their sunlight and moisture preferences

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Soil and mulch maintenance

• Repairing erosion and bare areas• Replacing mulch

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Repairing erosion

• Mild erosion at inlet or on the soil bed may be the result of a particularly large storm event, and can be repaired by replacing the soil and mulch that have washed away

• More severe erosion may indicate the need for inlet stabilization using rock or riprap, or the installation of velocity dissipating structures

Replacing mulch

• Uniformly applied approximately 2 inches deep. Do not pile the mulch around trees or other plantings

• Fresh bark mulch (either standard landscape fine shredded hardwood mulch or hardwood chips). Make sure it is free from weed seeds, soil, roots or any other substance not consisting of bole, branch wood, or bark.

• Once a year, add a fresh mulch layer. Once every 3 years, remove the old mulch layer before applying the new one.

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Standing water

• Bioretention cell should not have standing water more than 2 days after a storm event

• Prolonged standing water is a health hazard, and indicates a malfunction somewhere in the system

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Potential causes

• Clogged underdrain• Accumulated sediment at bioretention

surface• Excessive fines in bioretention media

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Checking underdrains

• Check observation wells– Standing water in underdrain

• Underdrain is clogged and must be cleaned out

– No standing water in underdrain• Clog is somewhere in the bioretention soil

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Soil Clogging

• To determine where bioretention media is clogged, dig a test pit

• Look for:– Sediment layer at surface– Accumulation of fines in gravel surrounding

underdrain, or above geotextile filter fabric, if present

– Excessive fines in soil media

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Sediment at Surface

• Thin layers of sediment can be broken up by raking the mulch surface

• For excessive sedimentation, remove sediment and mulch, and till sand into upper 6-12 inches of soil media

• Eliminate sources of sediment (e.g. erosion within drainage area)

Photo Courtesy of Emily Ayers

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Fines in soil media

• Usually caused by unapproved material substitutions during construction

Sticks together = Too much clay

Photo Courtesy of Emily Ayers

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Fines in soil media

• Sometimes can be corrected by installing sand wicks to the underdrain layer (vertical columns filled with sand)

• In severe cases, the media must be replaced

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Minor repairs to structures

• Replace missing/broken inlet grates, observation well caps

• Repair cracked or chipped concrete inlets

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Major corrective actions

• Major corrective actions will usually require the involvement of civil and geotechnical engineers, and will be handled by DDOT.

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Maintaining Tree Spaces

• Contact DDOT arborists for tree identification and maintenance recommendations

Maintenance – Street Tree-Box Filter

• The maintenance requirements for street tree-box filters are similar to those of other bioretention devices, although less complicated

Courtesy of Low Impact Development Center, Inc.

Maintenance – Street Tree-Box Filter

Inspections• Bimonthly• If possible, conduct during or immediately after a

rain event• Debris removal:

– Inspect system and clear drainage path of accumulated leaves, debris, and trash

– Remove accumulated materials on the top layer of the soil media, test, and dispose

– Inspect discharge pipe for clogging and clean if necessary

Maintenance – Street Tree-Box Filter

Planting Maintenance• Same maintenance as

bioretention cells

Soils Maintenance• Same maintenance as bioretention cells• Runoff bypassing the tree-box = clogged inflow area, or

reduced infiltration properties of soil mixture• Soils analysis, disposal requirements, and corrective

measures are the same as bioretention cells • For remediation assistance, contact Americast at

(800) 999-2278 or (804) 798-6068

Graphic Courtesy of Virginia Department of Conservation and Recreation

Maintenance – Street Tree-Box Filter

• First two years of maintenance typically included with the purchase of single and multiple-unit tree box filters – These would include removal of trash, debris and sediment,

replenishment of the mulch, and care or replacement of plants

• Annual maintenance = $500 per unit (performed by the manufacturer) or $100 per unit (performed by the owner) (sample cost estimate based on the Filterra™ Stormwater Bioretention Filtration System.)

Photo Courtesy of Filterra

Maintenance – Street Tree-Box Filter

Corrective Actions• Plants may have to be replaced because:

– they have overgrown the filter– environmental stress– they are mistaken as weeds growing through the

grate, and are removed

Photo Courtesy of Filterra

Maintenance Schedule – Street Tree-Box Filter

Description Frequency

1) Overall system

a) Inspect and clear drainage paths Every other month

2) Plants

a) Water plant material for fourteen consecutive days after planting has been completed unless there is sufficient natural rainfall

Immediately after completion ofproject

b) Inspect for disease/pest problems Spring/summer/fall

c) Treatment of diseases As needed, refer to manufacturer

d) Removal and replacement of all dead and diseased vegetation considered beyond treatment

Spring and fall

e) During times of extended drought, look for signs of stress. Water as needed.

Summer

f) Weed and prune excess growth Spring/summer

3) General

a) During major rainstorms, inspect site and make sure that infiltration is occurring as expected.

Every other month.

b) Clear the top layer of soil of accumulated material As needed

c) Clean the drainage pipes As needed

d) Seek remediation if infiltration function is not adequate after cleaning efforts

As needed

• Virtually maintenance free• Periodic inspections of system components• Most important - ensure spigot is set to slowly

release the barrel’s water

Maintaining rain barrels and cisterns

Photo Courtesy of Robb Lukes

Inspections

• Bimonthly inspection:– rain barrel is free of debris– filtration screen and downspout not clogged– overflow system properly directing the water away

from siding and foundations and not causing erosion problems

– mosquito screen properly installed

• Once a year, wash the barrel with mild (preferably biodegradable) soap and water

Graphic Courtesy of the Maryland DNR Green Building Program

Corrective Action• There are few mechanical parts on cisterns or rain barrels • Spigot, valve, and screen replacements can be ordered

from the manufacturer • Cracked rain barrel = replace rain barrel

• Large cisterns constructed out of materials such as metal or concrete may need repairs to walls by parging (for concrete) or welding (for metal)

Corrective Actions

Graphic Courtesy of the Texas Water Development Board

Maintenance Schedule – Rain Barrels & Cisterns

Description Frequency

Make use of the stored water! Regularly

Check for clogging of the entrance/outlet points Every other month

Check for proper diversion of the overflow system Every other month

Check for proper installation of the mosquito screen

Every few weeksin the summer

Wash the barrel with mild soap and waterAnnually,preferably in thespring

Prepare the system for winter conditions Pre-freezing

• Primary maintenance requirement - clean the surface drainage voids

• Can be incorporated into regular street sweeping program

• Annual inspections 

Maintaining small permeable pavement installations

Photo Courtesy of the Low Impact Development Center

Maintenance schedule

• Inspections • Routine maintenance is key:

– Conventional street sweepers equipped with vacuum sweepers and high-pressure water can used to restore permeability

– Street sweeping frequency varies depending on drainage area inputs (leaf debris, erosion, etc.). An active street sweeping program in the site’s drainage area will also help to prolong the functional life of the pavement

– If necessary, add additional gravel chips to fill pore spaces after vacuum sweeping

• In case of localized settling, individual paver blocks can be removed, new gravel added, and the blocks replaced

Preventive maintenance

• Restrict use by heavy vehicles

• Limit use of de-icing chemicals and sand

• Implement stringent sediment control plan

• Failure of systems:– poor design– inadequate construction

techniques– low permeability soils– heavy vehicular traffic– resurfacing with nonporous

materials Photo Courtesy of the Low Impact Development Center

Maintenance Schedule Permeable Pavers

Description Frequency

Initial Inspections Monthly for first several months following construction

Vacuum sweeping and highpressure hosing

4 times/year

Encourage active street cleaningin the site’s area

Regularly

Annual inspections Yearly, after large storms

Fill potholes and cracks As needed

Address spot-clogging problemsby drilling holes

As needed

Maintenance – Permeable Pavement

Routine Maintenance• Similar to permeable pavers • Recommended: Vacuum

sweep twice per year

Photo Courtesy of the New York City Department of Transportation

Photo Courtesy of JJ Harrison

Maintenance – Permeable Pavement

Corrective Action• Fill potholes and

cracks with permeable patching mixes

• Fix spot clogging by drilling ~0.5-inch holes through the porous pavement layer every few feet

Graphic Courtesy of Cahill Associates

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Review

• Regular preventive maintenance of bioretention cells is important to sustain optimal performance

• When problems arise, corrective maintenance is needed

• Minor corrective maintenance can be performed by trained landscaping contractors

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Resources

• DDOT Bioretention Maintenance Schedule• 2013 District of Columbia Stormwater Management

Guidebook (http://ddoe.dc.gov/swregs) • Low Impact Development (LID) Construction and

Maintenance Guidance Manual, Version 1.0. DDOE. 2009. (http://ddoe.dc.gov/riversmarthomes)

• Field Guide to Maintaining Rain Gardens, Swales, and Stormwater Planters. Oregon State University. (http://extension.oregonstate.edu/stormwater/sites/default/files/fieldguide.pdf)