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==Overview==

==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.  

[[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 projects fail at the construction stage are:

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 detail in designs and construction documents  

*'''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.

**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 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 knowledge  

*'''Lack of planning and communication.''' Poor communication protocols and the pace and extent of construction may preclude proper inspections and certifications.

**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.

 

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:

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 contributing drainage area is stabilized before the LID practice becomes operational;

*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

*environmentally sensitive areas and the LID practices themselves are protected during construction; and

*[[inlet]], outlet, [[pretreatment]], and piped elements have the correct elevations and inverts.   

*[[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.

Furthermore, keeping records of these inspections helps to certify the works after construction and makes for a smooth assumption process.

#[[Post-construction]]

#[[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, [[bioswales]], [[rain gardens]], [[enhanced swales]], [[exfiltration trenches]], [[permeable pavements]], underground infiltration systems ([[infiltration chambers|chambers]], [[infiltration trenches|trenches]], and [[soakaways]]), and [[Stormwater Tree Trenches| stormwater tree trenches]] all fall into this category.   

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.

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.

'''[[Green roof construction]], blue roofs, stormwater planters, and rainwater harvesting systems have specific construction sequences that differ from the main sequence described above. These pages are in development'''

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==

==Excavation and grading==

==Excavation and grading==

[[File:Excavation belfountain swale.JPG|200px|thumb|right|Excavation of a rain garden at Belfountain Public School, Caledon, Ontario. (Photo source: CVC)]]

[[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:  

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:  

The [[sub-surface components]] page gives guidance on:  

The [[sub-surface components]] page gives guidance on:  

*geotextile

*[[geotextile]]

*underdrain

*[[underdrain]]

*impermeable liners

*[[liner|impermeable liner]]

*overflow

*[[overflow]]

*monitoring wells

*[[wells|monitoring wells]]

*storage reservoir

*storage reservoir

**sub-base reservoir (permeable pavements)

**sub-base reservoir (permeable pavements)

**base course (permeable pavements)

**base course (permeable pavements)

**infiltration chamber installation

**[[infiltration chambers]]

*stone choker layer

*[[choker layer]]

*curbing

*curbing and [[curb cuts]]

*pre-treatment and inlet

*[[pretreatment]] and [[inlets]]

==Finishing grades and surface layer installation==

==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)]]

[[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.   

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.   

*Addressing deficiencies

*Addressing deficiencies

*Final certification

*Final certification