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| LID designs typically have very specific grading requirements. Verifying depths and slopes is critical for optimal performance of the facility. For example, if the design calls for a channel with a 1% slope, the channel may not function as designed if it has a 2% slope instead. Similarly, if the designs call for 1 metre of excavation from grade and only 90 cm are excavated, it will not have enough storage space to meet the design criteria. <br/> | | LID designs typically have specific grading requirements. Verifying depths and slopes is critical for the optimal performance of the facility. For example, if the design calls for a channel with a 1% slope, the channel may not function as designed if it has a 2% slope instead. |
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| | [[File:trimble unit.JPG|400px|thumb|right|Always confirm elevations throughout construction. (Photo source: CVC)]] |
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| | <u>Excavation to the sub-grade</u> will differ depending on whether the design is for a [[Bioretention: Variations|full infiltration, partial infiltration, or no infiltration LID system]]. If it’s a full infiltration or partial infiltration practice, the sub-grade should be as level as possible to promote even infiltration across the facility’s footprint. For no infiltration designs, excavate sub-grade slopes to the design grade in the direction of the underdrain, typically 1 to 2%. |
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| | As with all infiltrating LID practices, avoid compaction of sub-grade soils whenever possible. However, depending on the design and the local municipality, compaction of the sub-grade may be required for permeable pavement LIDs. |
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| '''Construction steps''' | | '''Construction steps''' |
| #Excavate from the rough grade to the finish grade using appropriate equipment. This is often done with hand tools. | | #Excavate the final 100 mm, to the final design grade, using appropriate equipment. This is often done with hand tools. |
| #Confirm excavation depths and slopes using appropriate equipment (transit levels, global navigation satellite systems, etc.) | | #Confirm excavation depths and slopes using appropriate equipment (transit levels, global navigation satellite systems, etc.) |
| '''Key inspection points''' | | '''Key inspection points''' |
| *Confirm final excavated depths and slopes. | | *Confirm final excavated depths and slopes. |
| '''Mistakes to avoid''' | | '''Mistakes to avoid''' |
| *“Eye-balling” depths and slopes | | *“eye-balling” depths and slopes |