California Department of Transportation

Division of Environmental Analysis (DEA) LINKS

square icon

Adobe Acrobat Reader is required to view and print PDF files. Adobe Acrobat is required to edit online forms and save them to your computer.

Get Acrobat Reader Image


Last Updated: Friday, March 9, 2018 10:01 AM

BMP RETROFIT PILOT STUDIES (Technical Information)

This review of the Pilot Studies is presented in three sections:

  • Background
  • Study Components
    • A discussion of the design, scope, and methodology of the Studies.
  • BMPs
    • Descriptions of the kinds of BMPs being used in the studies. Also, site location maps and site characteristics table.


A five-year $30 million research effort to retrofit selected Caltrans facilities in the Los Angeles and San Diego areas. Caltrans began an extensive program in 1997 to retrofit selected facilities with structural Best Management Practices (BMPs) in District 7 (Los Angeles) and District 11 (San Diego). Cost effectiveness and water quality benefits will be determined for retrofitting structural BMPs to freeways, interchanges, park and rides, and maintenance stations. Thirty-nine BMPs are being constructed; 26 BMPs in District 7 (at 21 sites) and 13 BMPs in District 11 (at 12 sites). Thirty-seven of the sites are currently in operation.

The goal of these studies is to determine the cost-effectiveness and water quality benefits of structural BMPs

  • Constituents to be monitored in the BMPs.
  • Total suspended solids
  • Zinc (total and dissolved)
  • Copper (total and dissolved)
  • Nitrate
  • Total Kjeldahl nitrogen
  • Total phosphorus
  • Fecal coliform
  • Total recoverable petroleum
  • Hydrocarbons
  • Gasoline
  • Oil
  • Diesel
  • pH
  • Hardness
  • Specific conductance

Study Components

Site Selection

Prior to construction, Caltrans conducted scoping and siting studies to determine the design criteria and appropriate sites for the BMPs. Numerous site locations in both the Los Angeles and San Diego Districts were assessed to determine their compatibility with the selected BMPs. Research objectives and methods were developed in the project's scoping study, which provided guidance for site selection, BMP design maintenance, water quality monitoring, schedules, and costs. The siting study evaluated potential sites by using a weighted decision matrix to compare physical site characteristics and potential constituents in runoff with the monitoring requirements and performance characteristics of the selected BMPs. Specific sites were carefully selected to ensure that the data collected in the studies would be accurate and transferable.

Design and Construction

Design of the BMPs was based on the latest published design criteria. Construction began in September 1998 and was substantially complete in March 1999. Total construction costs are estimated to be about $5 million for District 7, and about $4 million for District 11.

Operation, Maintenance and Monitoring

These pilot studies are intended to produce data for each BMPs retrofit requirements, construction costs, efficiency of constituent removal, and operation and maintenance requirements. To accomplish these objectives, Operation, Maintenance, and Monitoring (OMM) Plans have been developed to ensure that project data will be collected uniformly using established protocols. The OMM Plans provide detailed guidelines for monitoring and recording each BMP site including

  • Stormwater sample characteristics,
  • Flow into and out of the BMP,
  • Analyses of the BMP influent and effluent as collected by flow-weighted samples with automated monitoring equipment,
  • Analyses of grab samples for the BMP influent and effluent,
  • Empirical observations on the performance of the BMP during storm and post-storm periods and
  • Man-hour and equipment-hour requirements for maintaining the BMP, and the resulting costs.

A Maintenance Indicator Document provides a long-term protocol for maintaining the pilot BMPs. This will encourage consistency and control efficiency of maintenance and operation of the BMPs.

Vector and Biological Assessments

Coordination with vector control agencies has been incorporated into the studies. The Department of Health Services will review the design and operations data to help determine the tendency of BMPs to produce vectors (e.g.,mosquitos and rodents).

A Biological Assessment is being prepared to determine the extent that protected and sensitive species are attracted to the BMPs and how these species affect operations. Both the Vector and Biological assessments will be used to refine guidelines for BMP maintenance protocols.

Documentation and Reporting

A standardized documentation and reporting format is being used for these studies. Detailed records will be maintained for each of the 39 BMP sites to document the complete process: siting, design, construction, and operation and maintenance (O&M) for each BMP.

A final report will be prepared with detailed documentation for each BMP site. In addition, deviations from standard designs that were necessary to accommodate site constraints will be documented. The performance of these BMPs will be compared to other BMPs in similar projects.

Types of BMPs

Nine types of BMPs are being used in these studies representing a broad base of state-of-the-art BMP technology...

  1. Extended Detention Basin
    • These basins capture stormwater runoff and allow for an extended drain time to remove particulates and other associated pollutants through sedimentation. DETAILS
  2. Drain Inlet Inserts
    • Devices are inserted into storm drain inlets to filter or absorb sediment, oil and grease, and other pollutants. DETAILS
  3. Summary of Site CharacteristicsInfiltration Basins and Trenches
    • Trenches are lined with filter fabric and filled with rock. Stormwater runoff captured in the trenches then infiltrates into the soil. Basins are excavated depressions that infiltrate captured stormwater. DETAILS
  4. Oil/Water Separator
    • 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. DETAILS
  5. Media Filters
    • Fine sediments and pollutants are filtered through chambers containing sand or perlite/zeolite media. DETAILS
  6. Multi-Chambered Treatment Trains (MCTT)
    • Three vaults capture sediment and debris, remove oil and grease with absorbent pillows, and filter pollutants through fabric and a mixture of peat and sand. DETAILS
  7. Biofiltration Swales and Strips
    • Grassy pathways, also known as biofilters, filter and deposit pollutants from stormwater when water flows through the vegetation. DETAILS
  8. Continuous Deflection Separators (CDS)
    • 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 pollutants are deflected into the storage sump. DETAILS
  9. Wet Basin
    • A wet basin removes sediment, nutrients, and particulate metals from stormwater runoff. An in-line permanent pool or basin enhances settling. DETAILS


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