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Last Updated: Wednesday, February 7, 2018 10:25 AM

Caltrans Stormwater Program

Preventing pollution from storm water runoff is a growing concern for many communities across the nation. As the agency responsible for managing California's highway system, Caltrans is addressing this concern with its Storm Water Program. State-of-the-art methods and equipment are being used to study stormwater runoff. Information from these studies will be used to refine the Caltrans Stormwater Program.

Stormwater runoff from Caltrans highways and facilities can contain oil and grease, litter, particles from vehicle exhaust, and brake and tire materials, to name a few.These potential pollutants get washed by rain water through the storm drain system into our rivers,lakes, and ocean.

Technical Information

For a technical review of the Pilot Studies, click HERE.

How much will it cost to reduce stormwater pollution? How much cleaner will our water be?

To answer these questions...

Caltrans is retrofitting highways, park and ride lots, and maintenance stations in urban areas of San Diego and Los Angeles counties to control or treat stormwater runoff.

Caltrans is testing a wide variety of the most promising types of structural BMPs for facilities and highway runoff.

The goal of the BMP Retrofit Pilot Studies is to determine the cost-effectiveness and water quality benefits of structural Best Management Practices (BMPs) when retrofitted to existing facilities.Caltrans may then evaluate the wide-scale use of BMPs for improving stormwater quality.

What's being done...

Extended detention basinsExtended Detention Basins
These basins hold stormwater runoff for 48-72 hours to remove particulates and other potential pollutants through sedimentation.
Drain Inlet Insertsstorm drain inlet inserts
Devices are inserted into storm drain inlets to filter or absorb sediment, pollutants, and oil and grease.
Continuous Deflection Separators (CDS)continuous deflection separators
CDS units treat runoff by screening sediment and debris and depositing the debris in a sump.Pre-cast CDS units create a vortex of water that allows water to escape through the screen, while contaminants are deflected into the storage sumsp.
media filtersMedia Filters
Fine sediments and pollutants are filteredthrough sand orpearlite/zeolite media. Pollutants include nutrients, heavy metals, oil and grease, and bacteria/viruses.
Biofiltration Swales and Stripsbiofiltration swales and strips
Grassy pathways, also known as biofilters, filter and deposit pollutants from stormwater when water flows through the grass.
infiltration trenchesInfiltration Trenches
These trenches are typically long and narrow, lined with filter fabric and filled with gravel.Stormwater runoff captured in the trenches then infiltrates into the soil.
Multi - Chambered Treatment Train (MCTT)multi-chambered treatment train
Three-chambered vaults capture sediment and debris, remove oil and grease with absorbent pillows, and filter constituents through layers of sand and filter fabric.
Infiltration Basinsinfiltration basins
As excavated depressions, these basins capture stormwater and allow the runoff to percolate into permeable soils.
oil and water separatorsOil/Water Separators
These plate separators treat runoff from Caltrans facilities that generate oil and grease.Vertical plates separate oil from water, while a vault traps and collects sediments.
wet basinsWet Basins
A wet basin removes sediment, nutrients, and particulate metals from stormwater runoff.An in-line permanent pool or basin allows settling.

Caltrans appreciates the cooperation given by the following in conducting the BMP Retrofit Pilot Studies

  • Environmental Protection Agency
  • Department of Health Services
  • University of California at Davis, Center for Environmental and Water Resources Engineering
  • University of California at Riverside, Department of Entomology
  • Local Vector Control Districts and County Health Departments
  • Natural Resources Defense Council
  • San Diego BayKeeper
  • Santa Monica BayKeeper
  • BMP manufacturers and designers

Highlights of pilot studies

  • 33 locations are being retrofitted with39 structural BMPs of different types -an unprecedented scale for studyingstormwater treatment technologies
  • Automated monitoring stations are being installed for each BMP site
  • Pollutants being monitored in stormwater include:suspended solids (sediment), metals, nutrients, andorganics (gasoline)
  • A comprehensive operations and maintenance program maintains the structural BMPs at peak performance
  • A comprehensive operations and maintenance program maintains the structural BMPs at peak performance
  • Monitoring results will show how mucheach pollutant has been reduced
  • Results of the studies are due in the Fall of 2001

Technical Information

For a technical review of the Pilot Studies, click HERE.

BMPS or Best Management Practices…

are defined as the most promising methods to reduce stormwater pollution

refers to structural changes being made to existing facilities, such as adding inserts to existing storm drain inlets


To view reports on this subject CLICK HERE


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