Construction considerations

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:[https://cvc.ca/wp-content/uploads/2013/03/CVC-LID-Construction-Guide-Book.pdf Construction Guide for Low Impact Development, CVC (2013)
*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 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
#Plant or lay 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.
==Facilities containing media==
===Bioretention=== 
Sequencing depends on the design:
*Full infiltration:Pack 50 mm diameter clear stone to storage design depth, top with 100 mm of the choker course,
*Partial infiltration: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 choker layer.
===Stormwater planters===
*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 choker layer;
===Rain gardens===
No storage or drainage is required, filter media or amended topsoil is laid onto native soils
===Media installation===
Media installed over the choker course 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.
*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.
==Checklists==
*Bioretention construction checklist
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