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Last Updated: Wednesday, February 7, 2018 10:08 AM



In the mid-1990s, the Transportation Corridor Agency (TCA) designed and constructed the San Joaquin Hills Transportation Corridor, State Route 73. Originally, SR-73 was constructed with 39 Compost Stormwater Filter™ (CSF) systems as stormwater Best Management Practices (BMPs). These CSF systems are located within the Santa Ana and San Diego Regional Water Quality Control Board jurisdictions.

A CSF system typically consists of a flow equalization basin and a CSF unit. The CSF unit consists of an open concrete box that is divided into cells containing compost filter media.

Following construction, ownership of 38 of the 39 CSF systems was transferred to Caltrans. Because Caltrans was not satisfied with the performance of the CSFs, and because the CSFs used an outdated and proprietary compost filter media, Caltrans began a comprehensive and aggressive program to replace all of the CSFs with other types of treatment technology BMP pilots, including:

  • Optimized detention basins
  • Gross solids removal devices (GSRDs) with sediment traps
  • Austin-type sand filters

Currently, 17 of the 18 detention basins, and two of the four GSRDs have been constructed. Construction of the remaining BMPs is expected to be complete by 2005. The remaining 12 CSF are being replaced with Caltrans Stormwater Management Plan (SWMP)-approved detention basins.

Construction of pilot detention
Influent monitoring structure
Detention basin



The objective of these pilot studies is to evaluate the performance of the various treatment technology BMP pilots. To accomplish this, the study will determine the:

  • Quantity of runoff treated by the BMP
  • Reduction or change in analyte concentrations between the influent and the effluent from the BMP
  • Mass and volume of gross solids removed by the GSRDs
  • Level of effort required to operate and maintain the BMP
  • Level of effort required to control vectors of human disease and nuisance insects, and rodents.

To effectively estimate the reduction or change in pollutant concentrations, the quantity and quality of runoff entering the BMP will be compared to the quantity and quality of water discharged from the BMP. These data will allow direct estimations of the total reduction in the amounts of a variety of contaminants.

The effectiveness of a BMP is also determined by implementing proper maintenance procedures and by documenting observations about each site. Erosion, bank stability, vegetation height, trash and sediment build-up, and infiltration capabilities may directly affect the performance of the BMPs as stormwater treatment facilities.


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