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Last Updated: Thursday, January 5, 2012 1:08 PM

Extended Detention Basins

An extended detention basin is an empoundment lined with either vegetated soil or concrete. Stormwater runoff is conveyed from freeways to these basins through the storm drain system. Stormwater collects in the basins and the outlet allows water to drain slowly, while sediment and other particulate forms of pollutants settle out. Automated sampling equipment collects stormwater samples for lab analysis, both before and after the storm event. At full capacity, the basins are designed to drain in at most 24 hours and at least 72 hours to prevent mosquito production and allow for capture of subsequent storms. These basins are designed to remain dry except during a runoff event and the detention period afterward. When maintenance thresholds are reached, accumulated sediment is removed, characterized, and disposed of appropriately.

Site Location: I-5/SR 56

Directions: I-5 to Carmel Valley Road, near SR 56 eastbound and I-5 southbound connector

Site Location: I-15/SR 78

Directions: Eastbound SR 78, 400 feet prior to I-15 overpass off shoulder

Site location: I-5 Manchester (east)

Directions: I-5 to Manchester Avenue inside northeast cloverleaf

Site Location: I-5/I-605

Directions: I-5 southbound, just past the I-605 northbound connector

Site Location: I-605/SR 91 intersection

Directions: Westbound SR 91 to southbound Studebaker Road, right on Artesia Blvd, on right after I-605 overpass


Division of Environmental Analysis, Stormwater Unit
California Department of Transportation
P.O. Box 942874, MS-27
Sacramento, CA 94274-0001
Email: Division of Environmental Analysis, Stormwater Unit