Difference between revisions of "Inspection and Maintenance: Underground Infiltration Systems"

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|'''[[Pretreatment]]'''
|'''[[Pretreatment]]'''
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Devices or features that retain trash, debris and sediment, oil and grease; help to prevent obstructions and [[clogging]] of the infiltration area. Examples are eavestrough screens, [[Pretreatment|catch basin]] inserts (screens, baffles, fitlers) and sumps, [[oil and grit separators]], [[inlets|geotextile-lined inlets]], filters, isolator rows, and water quality [[forebay]] units.  
Devices or features that retain trash, debris and sediment, oil and grease; help to prevent obstructions and [[clogging]] of the infiltration area. Examples are eavestrough screens, [[Pretreatment|catch basin]] inserts (screens, baffles, filters) and sumps, [[oil and grit separators]], [[inlets|geotextile-lined inlets]], filters, isolator rows, and water quality [[forebay]] units.  
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*Remove trash, debris and sediment annually to biannually or when the device sump is half full;
*Remove trash, debris and sediment annually to biannually or when the device sump is half full;
*Measure sediment depth or volume during each cleaning, or annually to estimate accumulation rate and optimize frequency of maintenance.
*Measure sediment depth or volume during each cleaning, or annually to estimate accumulation rate and optimize frequency of maintenance.
|[[File:Pretreat Pass p.p.JPG|280px|thumb|center|Although permeable pavers are generally considered [[pretreatment]] for other BMPs in a [[Low impact development treatment train tool|treatment train]] system, using eavestrough screens can act as pretreatment as they don't add to sediment build up and accumulation on the paver surface. (Photo Source: Guertin, 2010)<ref>Guertin, M. 2010. Simple Screen Gutter Guards Better Than Pro-Installed Systems (and way cheaper). Fine Homebuilding - The Daily Fix. Accessed July 17 2022. https://www.finehomebuilding.com/2010/08/17/simple-screen-gutter-guards-better-than-pro-installed-systems-and-way-cheaper</ref>]]  
|[[File:Pretreatment inlet pass underground.PNG|280px|thumb|center|[[Geotextile]]-lined stone inlet is free of sediment, trash and debris. Stones to slow down and spread out inflowing water remain in place.]]
|[[File:Pretreat Fail p.p.JPG|300px|thumb|center|Build up of leads, sediment and leaf detritus in an eavestrough downspout disconnection leading to a permeable pavement surface. If not cleaned regularly this can lead to clogged pores between the pavers reducing the infiltration rate where the downspout deposits water onto the feature. (Photo Source: My Gutter Pro, 2021)<ref>My Gutter Pro. 2021. Clogged Downspout : Causes and Solutions. 10 April 2021. Accessed July 19 2022. https://mygutterpro.com/downspout-clog/</ref>]]  
|[[File:Pretreatment inlet Fail underground.PNG|300px|thumb|center|Accumulated sediment, trash and debris in the hydrodynamic (i.e., oil and grit) separator is occupying greater than 50% of its storage capacity. (Photo Source: SWC Canada, 2020)<ref>Storm Water Compliance (SWC) Canada Inc. 2020. OIL GRIT SEPARATORS/WATER QUALITY STRUCTURES. Accessed 02 August 2022. https://www.swccanada.com/system-types/oil-grit-separators</ref>]]  
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|'''[[Inlets]]'''
|'''[[Inlets]]'''
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*Remove trash, sediment and debris biannually (spring and late fall) to quarterly (spring, summer, early fall, late fall/early winter);
*Remove trash, sediment and debris biannually (spring and late fall) to quarterly (spring, summer, early fall, late fall/early winter);
*Make note of sediment depth or volume during each cleaning or annually to estimate accumulation rate and optimize frequency of maintenance.
*Make note of sediment depth or volume during each cleaning or annually to estimate accumulation rate and optimize frequency of maintenance.
|[[File:Inlet Pass p.p.JPG|285px|thumb|center|Impermeable pavement edges along the edge of the pervious concrete and impermeable asphalt graded so excess sheet flow is infiltrated down through the pores of the infiltration BMP. (Photo Source: Fairfax County, 2014)<ref>Fairfax County. 2014. Protecting our Environment, one Stormwater Practice at a Time - Permeable Pavements. April 2014. Accessed: July 20 2022. https://www.fairfaxcounty.gov/publicworks/sites/publicworks/files/assets/documents/pdf/factsheets/permeable-pavement.pdf</ref>]]  
|[[File:Inlets pass underground.PNG|285px|thumb|center|There are no obstructions at the inlet and stormwater can freely flow into the BMP.]]  
|[[File:Curb inlet grade.jpg|300px|thumb|center|Accumulated sediment, poor grading and vegetation is preventing stormwater from entering the [[swale]]. Sediment on the curb cut surface behind of the inlet indicates ponding is also occurring and is depositing water towards the permeable paver surface.]]  
|[[File:Inlets fail underground.PNG|300px|thumb|center|Sediment has accumulated in the inlet pipe to the infiltration trench and is fully obstructing flow of stormwater into the BMP.]]  
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|'''[[Overflow|Overflow Outlet]]'''
|'''[[Overflow|Overflow Outlet]]'''
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*Keep free of obstructions;
*Keep free of obstructions;
*Remove trash, sediment, debris, oil and grease biannually (spring and late fall) to quarterly (spring, summer, early fall, late fall/early winter).
*Remove trash, sediment, debris, oil and grease biannually (spring and late fall) to quarterly (spring, summer, early fall, late fall/early winter).
|[[File:Overflow Pass p.p.JPG|320px|thumb|center|The overflow outlet is free of damage and obstruction and functions as designed to safely convey excess water from the BMP.]]  
|[[File:Outlet & overflow pass underground.PNG|320px|thumb|center|The overflow outlet weir wall and storm sewer pipe in the control manhole of this infiltration chamber system is free of damage and obstruction and functions as designed to safely convey excess water from the BMP.]]  
|[[File:Overflow Fail p.p.JPG|280px|thumb|center|The overflow outlet is obstructed with sediment which impairs its function to convey excess water from the BMP.]]  
|[[File:Overflow Fail p.p.JPG|280px|thumb|center|Sediment and debris has accumulated in the overflow outlet pipe which impairs its function to convey excess water from the BMP.]]  
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|'''[[Underdrain|Sub-drain]]'''
|'''[[Underdrain|Sub-drain]]'''
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*Keep perforated pipes and flow restrictors free of obstructions;
*Keep perforated pipes and flow restrictors free of obstructions;
*Inspect flow restrictor and flush with a garden hose or pressure washer regularly (biannually to quarterly);
*Inspect flow restrictor and flush with a garden hose or pressure washer regularly (biannually to quarterly).
|[[File:Underdrain Pass p.p.JPG|310px|thumb|center|The solid section of the sub-drain pipe is not obstructed by sediment, debris or roots and shows no signs of damage.]]  
|[[File:Underdrain pass underground.PNG|310px|thumb|center|The sub-drain outlet pipe from the infiltration chamber system is not obstructed by sediment, debris or roots and shows no signs of damage.]]  
|[[File:Underdrain Fail p.p.JPG|300px|thumb|center|A section of the sub-drain pipe has been crushed which substantially reduces its conveyance capacity]]  
|[[File:Underdrain fail underground.PNG|300px|thumb|center|A perforated pipe in an exfiltration storm sewer system is clogged by sediment and debris which inhibits its drainage function.]]  
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|'''[[Monitoring well]]'''
|'''[[Monitoring well]]'''
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*[[Wells|Standpipes]] should be securely capped on both ends and protected from damage by vehicular traffic or foot traffic by a lockable casing.
*[[Wells|Standpipes]] should be securely capped on both ends and protected from damage by vehicular traffic or foot traffic by a lockable casing.
|[[File:Monitor Pass p.p.JPG|340px|thumb|center|The well is undamaged and accessible and the cap is in place and secured to prevent unauthorized access]]  
|[[File:Monitoring well pass underground.PNG|340px|thumb|center|The well is undamaged and accessible and the cap is in place and secured to prevent unauthorized access]]  
|[[File:Monitor Fail p.p.JPG|300px|thumb|center|The well cap is missing and the casing is clogged by sediment, preventing access for monitoring and allowing sediment to flow into the sub-drain system.]]  
|[[File:Monitoring well fail underground.PNG|300px|thumb|center|The well was buried during landscaping and found covered only by filter cloth (i.e. cap missing).]]  
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Revision as of 19:23, 2 August 2022

Inspection & Maintenance Guidance of underground infiltration systems' best management practices that refers to LIDs that capture and temporarily store rainwater and snowmelt from hard surfaces (e.g., roofs and pavements) below ground in geotextile filter fabric lined excavations filled with washed gravel or other void space forming structures (TRCA, 2018)[1]

Overview[edit]

Underground infiltration systems is a general term that refers to best management practices (BMPs) that capture and temporarily store stormwater from hard surfaces. These systems treat stormwater by detaining it to allow suspended sediments to settle out and soaking it into the ground where it is filtered and cleansed by interaction with soil. Runoff water is delivered to the practice through pipes connected to catchbasins, hydrodynamic (i.e., oil and grit) separators, filters, manholes, sub-drains of other features or roof downspouts. They are installed below the local maximum frost penetration depth to ensure they continue to drain year-round. Water that is in excess of the storage capacity overflows to an adjacent drainage system (e.g., municipal storm sewer or other BMP), typically via pipe or manhole containing a control structure (e.g., weir wall), to safely convey flows during flood events. Depending on the permeability of the underlying soil, such practices may be designed without a sub-drain for full infiltration or with a sub-drain for partial infiltration. The sub-drain pipe may feature a flow restrictor (e.g., orifice cap, valve) for gradually releasing detained water and optimizing the amount drained by infiltration.

General plan and profile (cross-section) views showcasing key components and sections of a typical infiltration trench.

Key components of Underground Infiltration Systems to pay close attention to are the:

Trash, debris and sediment builds up at these locations and can prevent water from flowing into or out of the practice.

Associated Practices[edit]

  • Soakaways: Typically service individual lots and receive only roof and walkway runoff but can also be designed to receive overflows from other BMPs (e.g., rain barrels or cisterns, rain gardens, green roofs. Also known as infiltration galleries, French drains, dry wells or soakaway pits.
  • Infiltration trenches: Linear oriented soakaways designed to fit into narrow strips of land between structures or properties, or along road rights-of-way; can also receive road runoff with adequate pretreatment devices upstream of inlets.
  • Infiltration chambers: Include a range of proprietary modular structures installed underground that create large void spaces for temporary storage of stormwater while providing sufficient load bearing capacity to allow construction of structures on top of them. Applications are similar to infiltration trenches. Also known as infiltration tanks or vaults.
  • Perforated pipe storm sewer systems or Exfiltration trenches: Linear-oriented infiltration trenches installed parallel with conventional storm sewer pipes and catchbasins that receive stormwater from them. May include manholes with perforated risers. Also known as exfiltration storm sewer, percolation drainage, or clean water collector systems.

Inspection and Testing Framework[edit]

An inlet to an infiltration trench during the fall in need of maintenance (TRCA, 2018).[1]
Visual Indicators Framework - Underground Infiltration Systems

Component

Indicators

Construction Inspection

Assumption Inspection

Routine Operation Inspection

Verification Inspection
Contributing Drainage Area
CDA condition x x x x
Inlet
Inlet/Flow Spreader Structural Integrity x x x
Inlet/Flow Spreader Structural Integrity x x x x
Perimeter
BMP dimensions x x x
Filter Bed
Filter bed sediment accumulation x x x
Underdrain & Monitoring Well
Monitoring well condition x x x x
Sub-drain/Perforated pipe obstruction x x
Outlets
Overflow outlet obstruction x x x x
Control Structure
Control structure condition x x x x
Control structure sediment accumulation x x x x



An example of a soakaway under construction with a newly installed monitoring well. To ensure performance assessment and infiltration testing can be conducted efficiently over the life cycle of this LID feature, the well condition must stay in good condition and be repaired immediately upon notice of significant damage (TRCA, 2018)[1].
Testing Indicators Framework - Underground Infiltration Systems

Component

Indicators

Construction Inspection

Assumption Inspection

Routine Operation Inspection

Verification Inspection
Testing Indicators
Sediment accumulation testing x x x x
Natural or simulated storm event testing x (x)
Continuous monitoring x (x)
Note: (x) denotes indicators to be used for Performance Verification inspections only (i.e., not for Maintenance Verification inspections)

Construction Inspection Tasks[edit]

Construction inspections take place during several points in the construction sequence, specific to the type of LID BMP, but at a minimum should be done weekly and include the following:

  1. During site preparation, prior to BMP excavation and grading to ensure the CDA is stabilized and/or flow diversion devices are in place and confirm that construction materials meet design specifications
  2. At completion of excavation and grading, prior to backfilling and installation of pipes to ensure depths, slopes and elevations are acceptable
  3. At completion of installation of geotextile/pipes, prior to completion of backfilling to ensure slopes and elevations are acceptable
  4. After final grading, prior to surface course installation to ensure depths, slopes and elevations are acceptable
  5. Prior to hand-off points in the construction sequence when the contractor responsible for the work changes (i.e., hand-offs between the storm sewer servicing, paving, building and landscaping contractors)
  6. After every large storm event (e.g., 15 mm rainfall depth or greater) to ensure ESCs and pretreatment or flow diversion devices are functioning and adequately maintained. View the table below, which describes critical points during the construction sequence when inspections should be performed prior to proceeding further. You can also download and print the table here


A pretreatment device (catchbasin insert) upstream of an underground infiltration system inlet in need of cleaning out. These devices are designed to limit the amount of trash, debris, sediment, oil and grease entering the infiltration system, which helps to prevent clogging and maintain its drainage performance (Source: TRCA, 2018[1]).
Underground Infiltration Systems: Construction Inspections

Construction Sequence Step & Timing

Inspection Item

Observations*
Site Preparation - after site clearing and grading, prior to BMP excavation and grading, prior to BMP excavation and grading Natural heritage system and tree protection areas remain fenced off
ESCs protecting BMP layout area are installed properly
CDA is stabilized or runoff is diverted around BMP layout area
BMP layout area has been cleared and is staked/delineated
Benchmark elevation(s) are established nearby
Construction materials have been confirmed to meet design specifications
BMP Excavation and Grading - prior to backfilling and installation of geotextile/pipes Excavated soil is stockpiled outside the CDA
Excavation location, footprint, depth and slope are acceptable
Compaction of subsoil where load-bearing portions of the system will be installed is acceptable
Excavation bottom and sides roughened to reduce smearing and compaction
BMP Installation – after installation of geotextile/ pipes/structures, prior to completion of backfilling Installation of structural components (e.g., control manhole, maintenance hatches) is acceptable
Sub-drain trench dams installed correctly (location, elevation)
Installations of sub-drain pipes (e.g., locations, elevations, slopes) & maintenance access hatches are acceptable

Routine Maintenance - Key Components and I&M Tasks[edit]

Regular inspections (twice annually, at a minimum) done as part of routine maintenance tasks over the operating phase of the BMP life cycle to determine if maintenance task frequencies are adequate and determine when rehabilitation or further investigations into BMP function are warranted.

Table below describes routine maintenance tasks for underground infiltration systems (infiltration chambers, infiltration trenches, bioswales, etc.) organized by BMP component, along with recommended minimum frequencies. It also suggests higher frequencies for certain tasks that may be warranted for BMPs located in highly visible locations or those receiving flow from high traffic (vehicle or pedestrian) areas. Tasks involving removal of trash, debris and sediment and weeding/trimming of vegetation for BMPs in such contexts may need to be done more frequently (i.e., higher standards may be warranted).

Underground Infiltration Systems: Key Components, Descriptions and Routine I&M Requirements
Component Description Inspection & Maintenance Tasks (Pass) Photo Example (Fail) Photo Example
Contributing Drainage Area (CDA)

Area(s) from which runoff directed to the BMP originates; includes both impervious (i.e., roofs and pavements) and pervious (i.e., landscaped) areas.

  • Remove trash, debris and sediment from pavements (biannually to quarterly) and eavestroughs (annually);
  • Replant or seed bare soil areas as needed.
CDA has not changed in size or land cover. Sediment, trash or debris is not accumulating and point sources of contaminants are not visible.
Point sources of contamination are present (i.e. accumulated sediment and debris from melted snow piles)
Pretreatment

Devices or features that retain trash, debris and sediment, oil and grease; help to prevent obstructions and clogging of the infiltration area. Examples are eavestrough screens, catch basin inserts (screens, baffles, filters) and sumps, oil and grit separators, geotextile-lined inlets, filters, isolator rows, and water quality forebay units.

  • Remove trash, debris and sediment annually to biannually or when the device sump is half full;
  • Measure sediment depth or volume during each cleaning, or annually to estimate accumulation rate and optimize frequency of maintenance.
Geotextile-lined stone inlet is free of sediment, trash and debris. Stones to slow down and spread out inflowing water remain in place.
Accumulated sediment, trash and debris in the hydrodynamic (i.e., oil and grit) separator is occupying greater than 50% of its storage capacity. (Photo Source: SWC Canada, 2020)[2]
Inlets

Structures that deliver water to the BMP such as curb-cuts and geotextile-lined inlets or pipes connected to catchbasins, hydrodynamic (oil and grit) separators (HDS), filters, manholes, sub-drains of other features or roof downspouts.

  • Keep free of obstructions;
  • Remove trash, sediment and debris biannually (spring and late fall) to quarterly (spring, summer, early fall, late fall/early winter);
  • Make note of sediment depth or volume during each cleaning or annually to estimate accumulation rate and optimize frequency of maintenance.
There are no obstructions at the inlet and stormwater can freely flow into the BMP.
Sediment has accumulated in the inlet pipe to the infiltration trench and is fully obstructing flow of stormwater into the BMP.
Overflow Outlet

Structures (e.g., sub-drain/underdrain pipe connected to a manhole, conventional storm sewer pipe, or control manhole with weir wall) that convey flow exceeding the storage capacity to another drainage system or BMP.

  • Keep free of obstructions;
  • Remove trash, sediment, debris, oil and grease biannually (spring and late fall) to quarterly (spring, summer, early fall, late fall/early winter).
The overflow outlet weir wall and storm sewer pipe in the control manhole of this infiltration chamber system is free of damage and obstruction and functions as designed to safely convey excess water from the BMP.
Sediment and debris has accumulated in the overflow outlet pipe which impairs its function to convey excess water from the BMP.
Sub-drain

Comprised of perforated pipe(s) surrounded by gravel and may be wrapped in geotextile filter fabric; installed in the gravel water storage layer or chamber unit openings to collect and convey treated water to an adjacent drainage system or other BMP; may also include a flow restrictor.

  • Keep perforated pipes and flow restrictors free of obstructions;
  • Inspect flow restrictor and flush with a garden hose or pressure washer regularly (biannually to quarterly).
The sub-drain outlet pipe from the infiltration chamber system is not obstructed by sediment, debris or roots and shows no signs of damage.
A perforated pipe in an exfiltration storm sewer system is clogged by sediment and debris which inhibits its drainage function.
Monitoring well

Perforated standpipe that extends from the bottom of the excavation to just below the pavement surface and contains perforations or slots to allow measurement of subsurface water level; used to track drainage performance over the operating life cycle of the BMP.

  • Standpipes should be securely capped on both ends and protected from damage by vehicular traffic or foot traffic by a lockable casing.
The well is undamaged and accessible and the cap is in place and secured to prevent unauthorized access
The well was buried during landscaping and found covered only by filter cloth (i.e. cap missing).
  1. 1.0 1.1 1.2 1.3 TRCA. 2018. Fact Sheet - Inspection and Maintenance of Stormwater Best Management Practices: Underground Infiltration Systems. https://sustainabletechnologies.ca/app/uploads/2018/02/Underground-Infiltration-Systems-Fact-Sheet.pdf
  2. Storm Water Compliance (SWC) Canada Inc. 2020. OIL GRIT SEPARATORS/WATER QUALITY STRUCTURES. Accessed 02 August 2022. https://www.swccanada.com/system-types/oil-grit-separators