Contents
Design Variants
Infiltration Basin
An infiltration basin is a natural or constructed impoundment that captures, temporarily stores and infiltrates the design volume of water over several days. In the case of a constructed basin, the impoundment is created by excavation or embankment. Infiltration basins are commonly used for drainage areas of 5 to 50 acres with land slopes that are less than 20 percent. Typical depths range from 2 to 12 feet, including bounce in the basin. An infiltrates basin construction detail is located in the Computer-aided design and drafting (CAD/CADD) drawings section.
Infiltration Trench and infiltration basin - Construction inspection checklists.
Link to this table
To access an Excel version of form (for field use), click here.
| Project: | ||
| Location: | ||
| Site Status: | ||
| Date: | ||
| Time: | ||
| Inspector: | ||
| Construction Sequence | Satisfactory / Unsatisfactory | Comments |
|---|---|---|
| 1. Pre-Construction | ||
| Pre-construction meeting | ||
| Runoff diverted | ||
| Soil permeability verified | ||
| Groundwater / bedrock verified | ||
| Project benchmark established | ||
| Facility location staked out | ||
| Temporary erosion and sediment control established | ||
| 2. Excavation | ||
| Size and location per plans | ||
| Side slopes stable | ||
| Depth adjusted to soil layer with specified soil type and permeability | ||
| Sub-soil not adjacent to excavation area and stabilized with vegetation and/ or silt fence | ||
| Stockpile location not adjacent to excavation area and stabilized with vegetation and/ or silt fence | ||
| 3. Filter Fabric Placement | ||
| Fabric per specifications | ||
| Fabric per specifications | ||
| Placed per plan location | ||
| 4. Aggregate Material | ||
| Size as specified | ||
| Clean / washed material | ||
| Placed properly | ||
| 5. Observation Well | ||
| Pipe size per plans | ||
| Under-drain installed per plans | ||
| Inlet installed per plans | ||
| Pre-treatment devices installed per plans | ||
| 6. Vegetation | ||
| Complies with planting specifications | ||
| Topsoil complies with composition and placement in specifications | ||
| Permanent erosion control measures in place | ||
| 7. Final Inspection | ||
| Dimensions per plans | ||
| Check dams operational | ||
| Inlet / outlet operational | ||
| Effective stand of vegetation and stabilization | ||
| Contributing watershed stabilized before flow is routed to the facility | ||
| Comments: | ||
| Actions to be taken: | ||
Infiltration Trench (a.k.a. infiltration gallery)
An infiltration trench is a shallow excavated trench, typically 3 to 12 feet deep, that is backfilled with a coarse stone aggregate allowing for the temporary storage of runoff in the void space of the material. Discharge of this stored runoff occurs through infiltration into the surrounding naturally permeable soil. Trenches are commonly used for drainage areas less than 5 acres in size.
Dry Wells (a.k.a. infiltration tubes, french drains, soak-away pits or soak holes)
A dry well or soak away pit is a smaller variation of an infiltration trench. It is a subsurface storage facility (a structural chamber or an excavated pit backfilled with a coarse stone aggregate) that receives and temporarily stores stormwater runoff. Discharge of this stored runoff occurs through infiltration into the surrounding naturally permeable soil. Due to their size, dry wells are typically designed to handle stormwater runoff from smaller drainage areas, less than one acre in size (e.g. roof tops).
Underground Infiltration Systems
Several underground infiltration systems, including pre-manufactured pipes, vaults, and modular structures, have been developed as alternatives to infiltration basins and trenches for space-limited sites and stormwater retrofit applications. These systems are similar to infiltration basins and trenches in that they are designed to capture, temporarily store and infiltrate the design volume of stormwater over several days. Underground infiltration systems are generally applicable to small development sites (typically less than 10 acres) and should be installed in areas that are easily accessible to routine and non-routine maintenance. These systems should not be located in areas or below structures that cannot be excavated in the event that the system needs to be replaced.