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Line 1: {{float right|{{#widget:YouTube|id=8Hl4S-_G9-E}}}} The following presents a summary of considerations when planning the construction of a low impact development project. More details can be found in the following reference:<ref>[https://cvc.ca/wp-content/uploads/2013/03/CVC-LID-Construction-Guide-Book.pdf Construction Guide for Low Impact Development, CVC (2013)</ref>
*The site of the infiltration facility must remain outside the limit of disturbance and blocked from site traffic until construction of the facility begins, to prevent soil compaction by heavy equipment. *This area must not be used as the site of sediment basins during construction, as the concentration of fines will reduce post-construction infiltration. *This area must not be use as a staging area, for storing materials.*To prevent sediment from clogging the surface, stormwater must be diverted away from the facility until the drainage area is fully stabilized.*As many infiltration facilities are installed in the road right-of-way or tight urban spaces, considerations of traffic control and utility conflicts must be part of the plans and inspections.
==Sequencing==The following is a typical construction sequence to properly install an infiltration practice:#The area should be fully protected by silt fence or construction fencing to prevent compaction by construction traffic and equipment.#Installation may only begin after entire contributing drainage area has been either stabilized or flows have been safely routed around the area. The designer should check the boundaries of the contributing drainage area to ensure it conforms to original design.#The pretreatment part of the design should be excavated first and sealed until full construction is completed.#Excavators or backhoes '''working adjacent to the proposed infiltration area''' should excavate to the appropriate design depth.#The soil in the bottom of the excavation should be ripped to promote greater infiltration.#Any accidental sediment accumulation from construction should be removed at this time.
# Excavate subsurface water storage reservoir to base elevation,#Check base elevation and slope, #Fracture/rip bottom and roughen side of the excavation to remove smeared surfaces, #Install optional [[geotextiles]] (or [[liner]] for [[biofilters|biofilter]]); overlapping according to design drawings,#Install coarse [[reservoir gravel]], and any void forming structures (e.g. [[underdrains]], [[infiltration chambers]], or [[wells]]), #Check elevation and slope at top of reservoir, #Install [[choking layer]] and optional geotextile (typically only over the perforated [[pipe]]),#Check elevation and slope at top of choking layer, #Install [[filter media]] with additional 30 cm over finish grade of the filter bed, #Thoroughly saturate and allow to settle for at least one week. After this time, tamp manually to check settling is complete. Alternatively, installations made in the fall can be left to settle over the whole [[winter]] season at this point, #Install temporary erosion and sediment control practices,#:'''Conduct all other site construction activities (buildings/servicing etc.)'''#Check condition of bioretention after settling period, remediate any deficiencies, #Install curbs and pavements and concrete [[pretreatment]] devices,#Check elevations of [[curb cuts]] and other [[inlets]]#Install erosion control to all inlets!!#Remove excess filter media along with any accumulated construction sediment, #Install any surface applied [[additives]],#Conduct fine grading to surface of filter bed, checking elevations/slopes/compaction,#Apply [[stone]] or [[mulch]] cover for decorative systems, or [[turf reinforcement]] for grassed systems,#Install [[erosion control blankets]] or matting#[[Plants|Plant]] or lay [[turf|sod]],#Saturated system thoroughly to settle filer media particles around the roots of new plants,#Irrigated the system as required to establish healthy vegetation cover, #Inspect and remediate deficiencies after any significant rainfall within the next 3 months or remainder of the first growing season.
===Infiltration construction==={{:Infiltration: Construction}}<h4>Bioretention specific construction</h4> The options at this step depending on the design:<br><strong>Full infiltration:</strong>Pack 50 mm diameter clear stone to storage design depth, top with 100 mm of pea gravel and the geotextile drainage fabric.<br><strong>Partial infiltration:</strong>Place design depth of 50 mm diameter clear stone for the infiltration volume on bed and then lay the perforated underdrain pipe over it. Pack more clear stone to 75 mm above the top of the underdrain, top with 100 mm of pea gravel and the geotextile drainage fabric.<br><strong>No infiltration:</strong> Place an impermeable liner on the bed with 150 mm overlap on sides. Lay the perforated underdrain pipe, Pack 50 mm diameter clear stone to 75 mm above top of underdrain, top with 100 mm of pea gravel and the geotextile drainage fabric.<br><strong>Rain garden:</strong> No storage or drainage is required, biomedia is laid onto native soils. <br>*Biomedia is installed over the geotextile fabric in 0.3 m lifts until desired top elevation is achieved. Each lift must be thoroughly wetted and drained before adding the next. Wait three weeks to check for settling, and add additional media and regrade as needed.<br>*Prepare planting holes for any trees and shrubs, install vegetation, and water accordingly. *Install any temporary irrigation.*Plant landscaping materials as shown in the landscaping plan, and water them weekly in the first two months.*Lay down surface cover in accordance with the design (mulch, riverstone, or turf). *Conduct final construction inspection, checking inlet, pretreatment, bioretention cell and outlet elevations.*Remove erosion and sediment controls, only when the entire drainage area is stabilized
*[[Bioretention: Construction checklist|Bioretention construction inspection checklist]]
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→Overview
[[File:Construction page lead photo.JPG|500px|thumb|right|CVC staff conducting a construction inspection at Kenollie Public School, Mississauga, Ontario. (Photo source: CVC, 2015)]]
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==Overview==
[[Definition of Low Impact Development|LID techniques and technologies]] are new to many municipalities, consulting engineers, and contractors. STEP's construction guidance aims to give practical advice, specific to LID construction, to enable practitioners to successfully construct LID practices.
Common reasons LID projects fail at the construction stage are:
*lack of detail in designs and construction documents
**Contractors can struggle to build LID facilities properly without enough detail in the contract drawings and without guidance and inspection throughout the construction process.
*lack of knowledge
**Designers often do not understand the complexities of the construction process, and contractors often don't understand the purpose of LID practices or the technologies they employ.
*lack of effective erosion and sediment control during construction
**LID practices are most vulnerable to sedimentation and [[clogging]] during their own construction or construction of adjacent lands.
*lack of planning and communication
**Poor communication protocols and the pace and extent of construction may preclude proper inspections and certifications.
Published research corroborates STEP’s experiences in the field (e.g., (DelGrosso et al., 2019 <ref> Delgrosso, Z.L., Clayton, C.H., Dymond, R.L. 2019 Identifying Key Factors for Implementation and Maintenance of Green Stormwater Infrastruture. Journal of Sustainable Water in the Built Environment. 5 (3): 05019002. https://ascelibrary.org/doi/10.1061/JSWBAY.0000878</ref>); LSRCA, 2011<ref>Lake Simcoe Region Conservation Authority (LSRCA). 2011. Stormwater Pond Maintenance and Anoxic Conditions Investigation. Final Report. Newmarket, ON. https://sustainabletechnologies.ca/app/uploads/2015/01/LSRCA-Stormwater-Maintenance-and-Anoxic-Conditions-2011.pdf</ref>); ([https://www.chesapeakebay.net/channel_files/19219/cwp_james_river_tech_report_final_draft_062509.pdf.pdf CWP, 2009])<ref>Centre for Watershed Protection. 2009. Technical Report
Stormwater BMPs in Virginia’s James River Basin: An Assessment of Field Conditions & Programs (part of the Extreme BMP Makeover project). Prepared by David Hirschman, Laurel Woodworth, and Sadie Drescher Center for Watershed Protection, Inc. Final Draft. June 2009. https://www.chesapeakebay.net/channel_files/19219/cwp_james_river_tech_report_final_draft_062509.pdf.pdf</ref>.; see the [[inspection and maintenance]] page’s overview for a more detailed discussion). Del Grosso et al., 2019 provide a helpful summary of positive considerations for LID construction: “[LID] requires more considerations during construction compared to traditional stormwater management facilities. … The proper construction of [LID] is centered around thoughtful construction sequencing, ensuring all parties involved know their responsibilities, protecting soils and media from compaction and clogging, property installing filter media and aggregate, and ensuring facilities are kept off-line until the entire drainage area is stabilized. More generally, it is important for contractors to be aware of the sensitivity of GSI and for municipalities to ensure that facilities are being inspected by qualified inspectors at critical points (Del Grosso et al., 2019, pg. 8).
Regular inspections throughout the construction process of LID practices prevent end products that are not built to the design specifications. Specifically, they ensure that:
*the LID practice has the proper layout, location, footprint, and volume;
*materials meet design specifications;
*any material substitutions and field changes to the design are verified and documented;
*the contributing drainage area is stabilized before the LID practice becomes operational;
*environmentally sensitive areas and the LID practices themselves are protected during construction; and
*[[inlet]], outlet, [[pretreatment]], and [[pipes|piped]] elements have the correct elevations and inverts.
Furthermore, keeping records of these inspections helps to certify the works after construction and makes for a smooth assumption process.
==Construction stages and LID types==
[[File:construction process.jpg|400px|thumb|right|The five-step construction process for ground-level LIDs.]]
STEP divides the construction process for LID practices into five over-arching stages:
#[[Pre-construction]]
#[[Excavation and grading]]
#[[Sub-surface components]]
#[[Finishing grades and surface layer installation: vegetated LIDs]] and [[finishing grades and surface layer installation: permeable pavements]], and
#[[Post-construction]]
Most LID practices work at the sub-surface and ground-level by routing stormwater flows from impervious surfaces into excavated or natural depressions or by allowing stormwater to pass through a pervious surface, as is the case with [[permeable pavements]]. These depressions are designed and constructed to the meet goals of the LID practice, which may be quality control, quantity control, or water balance restoration. [[Bioretention]] gardens, [[stormwater planters]], [[bioswales]], [[rain gardens]], [[enhanced swales]], [[exfiltration trenches]], [[permeable pavements]], infiltration systems ([[infiltration chambers|chambers]], [[infiltration trenches|trenches]], and [[soakaways]]), and [[Stormwater Tree Trenches| stormwater tree trenches]] fall into this category.
For this reason, Stages 1-2 and 5 of the LID construction process are fundamentally similar for all sub-surface and ground-level LID types. To illustrate, STEP's recommended processes for excavation do not differ between LID practice types. Excavation procedures are the same, whether for a bioretention garden or a permeable pavement parking lot. On the other hand, stage 4 sub-tasks will vary depending on whether the LID practice's surface is vegetated or permeable pavement. Some sub-tasks in stage 3 will also vary depending on the LID type. For example, permeable pavements often require compaction of sub-surface storage layers. The following sections give a brief description of each over-arching stage, a list of sub-tasks for each stage, and links to the page dedicated to each main LID construction stage.
STEP has developed practice-specific construction inspection checklists for [[Inspection and Maintenance: Bioretention & Dry Swales|bioretention and dry swales]], [[Inspection and Maintenance: Permeable Pavement|permeable pavement]], [[Inspection and Maintenance: Enhanced Swales|enhanced swales]], [[Inspection and Maintenance: Vegetated Filter Strips|vegetated filter strips]], [[Inspection and Maintenance: Underground Infiltration Systems|underground infiltration systems (exfiltration systems, trenches, chambers, soakaways)]], [[Inspection and Maintenance: Green Roofs|green roofs]], and [[Inspection and Maintenance: Rainwater Harvesting|rainwater harvesting]].
[[Green roof|Green roofs]] and [[rainwater harvesting]] systems have specific construction sequences and requirements that differ from the main sequence described above. STEP has developed guidance for [[green roof construction]]; '''guidance on installing rainwater harvesting practices is forthcoming'''. When installing these BMP types, always consult the product manufacturer's guidance.
==Pre-construction==
Pre-construction activities set the stage for the successful construction of an LID practice. The [[Pre-construction|pre-construction]] page gives guidance on:
*design verification and site walk-through
*LID construction notes
*tendering and contract
*communication, inspection plan, and utilities coordination
*erosion and sediment control measures
*mobilization, access, staging, and perimeter controls
==Excavation and grading==
[[File:Excavation belfountain swale.JPG|400px|thumb|right|Excavation of a rain garden at Belfountain Public School, Caledon, Ontario. (Photo source: CVC, 2021)]]
Excavation and grading are necessary for installing LID practices with sub-surface components, re-grading land to hold more water, and re-routing overland flow routes into an LID practice. The [[Excavation and grading|excavation and grading]] page gives guidance on:
*clearing and grubbing
*excavation and rough grade
*sub-grade
*final excavated grade and verification
==Sub-surface components==
Most LID practices use a combination of sub-surface features such as gravel storage reservoirs, liners, underdrains, monitoring wells, and other components to meet their design objectives. The construction process for sub-surface components works from the ground up. While some LID practices include all the sub-surface components listed below, most designs will not include one or more of these layers or components. [[Permeable pavements]] can have different construction requirements at this stage, mostly regarding compaction of sub-surface layers. Installing [[infiltration chambers]] also requires guidance specific to that LID type. [[Stormwater Tree Trenches]], which consist of subsurface trenches filled with modular structures and growing medium, or structurally engineered soil medium to supporting an overlying pavements, also require advice specific to them.
The [[sub-surface components]] page gives guidance on:
*[[geotextile]]
*[[underdrain]]
*[[liner|impermeable liner]]
*[[overflow]]
*[[wells|monitoring wells]]
*storage reservoir
**sub-base reservoir (permeable pavements)
**base course (permeable pavements)
**[[infiltration chambers]]
*[[choker layer]]
*curbing and [[curb cuts]]
*[[pretreatment]] and [[inlets]]
==Finishing grades and surface layer installation==
[[File:Planting CVC Janet I McDougald.JPG|400px|thumb|right|CVC and Toronto Zoo staff planting the surface layer of a rain garden at Janet I McDougald Public School in Mississauga, Ontario. (Photo source: CVC, 2021)]]
This construction stage differs between LID practice type. The [[finishing grades and surface layer installation: vegetated LIDs]] page has guidance for vegetated LIDs, and the [[finishing grades and surface layer installation: permeable pavements]] page has guidance for and non-vegetated LIDs. In many cases the surface of infiltration systems will be traditional asphalt, concrete, or pavers; STEP does not provide guidance on installing non-permeable surfaces.
{| class="wikitable"
|+ Stage 4 guidance for vegetated LIDs and permeable pavements
|-
!LID practices with vegetated surfaces
!Permeable pavements
|-
|soil media installation and soil amendments
|bedding layer
|-
|finish grading
|placement and finishing
|-
|large stone and riprap
|paver installation
|-
|plant verification and installation
|tamping
|-
|mulch placement
|joint cutting
|-
|stabilizing contributing drainage area and planting adjacent vegetation
|joint aggregate
|-
| --
|curbing
|-
| --
|stabilizing contributing drainage area
|}
==Checklists==
==Post-construction==
Post-construction tasks ensure that the LID practice was built to specs and that any outstanding issues with it are resolved before assumption. The [[post-construction]] page give guidance on:
*Addressing deficiencies
*Final certification
==References==