5.4.15
5.4.15.1 BMP Description
Infiltration basins (BMP T7.10 in Volume 5, Chapter 5 of the Ecology Manual) are earthen impoundments used for the collection, temporary storage and infiltration of influent stormwater runoff.
5.4.15.2 Performance Mechanism
Pollutant removal and flow control occur through infiltration of stormwater into the underlying soils. Secondary pollutant removal mechanisms include filtration, adsorption, and biological uptake.
5.4.15.3 Application and Limitations
Infiltration basins can be designed to meet on-site stormwater management, runoff treatment (basic and enhanced), and flow control requirements (see Infiltration Basins Applicability.a).
| BMP | MR #7: Flow Control | ||||||
|---|---|---|---|---|---|---|---|
|
List |
LID Performance Standard |
Basic |
Enhanced |
Oil Control |
Phosphorus |
||
|
Infiltration Basin |
X |
X |
X |
|
X | ||
|
Notes:
|
|||||||
5.4.15.4 Site Considerations
See Vol II–5.3.2 Determine Infiltration Feasibility and Volume V, Section 5.6 of the Ecology Manual for site suitability criteria related to infiltration basins.
5.4.15.5 Design Information
If this BMP is proposed to be used for Runoff Treatment, the design shall show that the criteria for Runoff Treatment in Volume V, Section 5.6 (Site Suitability Criteria) in the Ecology Manual are met. See BMP T7.10 in Volume V, Chapter 5 of the Ecology Manual for detailed design guidance and criteria on infiltration basins.
5.4.15.6 Minimum Construction Requirements
Conduct initial basin excavation to within 1 foot of the final elevation of the basin floor. Excavate infiltration trenches and basins to final grade only after all disturbed areas in the upgradient project drainage area have been permanently stabilized. The final phase of excavation shall remove all accumulation of silt in the infiltration BMP before putting it in service. After construction completion, prevent sediment from entering the infiltration BMP by first conveying the runoff water through an appropriate pretreatment system such as a pre-settling basin, wetpond, or sand filter.
Generally, do not use infiltration BMPs as temporary sediment traps during construction. If an infiltration BMP has been pre-approved by DCD for use as a sediment trap, do not excavate to final grade until after the stabilizing the upgradient drainage area. Remove any accumulation of silt in the basin before putting it in service. Approval for use of an infiltration BMP as a temporary sediment trap may be considered by DCD on a case-by-case basis.
Relatively light-tracked equipment is recommended to avoid compaction of the basin floor. Consider the use of draglines and trackhoes for constructing infiltration basins. Flag or mark the infiltration area to keep heavy equipment away.
5.4.15.7 Operations and Maintenance
See BMP T7.10 in Volume V, Chapter 5 of the Ecology Manual for maintenance practices for infiltration basins.