Ahead of its Time

Feb. 7, 2007

About the author: Karl Dreher, California Department of Transportation Headquarters, Environmental Analysis Division, can be reached at 916/653-3352 or by e-mail at [email protected]. Scott Taylor, RBF Consulting, Storm Water Management, can be reached at 949/427-3505 or by e-mail at [email protected].


Treatment of storm water pollution from highways has been a growing concern, especially in highly urbanized areas like southern California. For state and local departments of transportation, the pressure to clean up storm water pollution on roadways has been fierce. In steps, the largest and most complex freeway system in the continental U.S.—the California Department of Transportation (Caltrans)—assessed and developed possible solutions and technologies to the problem.

Caltrans invested $30 million in an extensive five-year research and development study to see how successful various types of best management practices (BMPs) would be in treating storm water runoff from highways and its own facilities. It conducted full-scale testing of treatment controls throughout Los Angeles and San Diego counties.

Retrofitting existing facilities

Using state-of-the-art technologies, Caltrans retrofitted freeways, interchanges, park-and-ride lots and maintenance stations with various types of structural BMPs. Twelve types of technologies at 32 sites were installed and monitored for pollutant-removal efficiencies, operation and maintenance. Treatment BMPs tested included wet basins, infiltration basins and trenches, vegetated strips and swales, extended detention basins, media filters, multi-chambered treatment trains, drain inlet inserts, oil-water separators and hydrodynamic separators.

Construction began in September 1998 and substantially finished in March 1999. Construction on the project lasted about six months. Once completed, documentation of operation, maintenance and monitoring began, continuing through 2003. The final report was completed in January 2004. The data collected on pollutant types and effects was nothing less than staggering, so much so that the science-based research on BMP performance has been used by other municipal agencies, including other state departments of transportation, as well as national and international professional organizations. Over 50,000 data points were collected on over 20 constituents, including total suspended solids (TSS), nutrients (phosphorus, nitrogen), total and dissolved metals (copper, lead, zinc) and hydrocarbons.

Data produced for each BMP retrofit included pollutant removal efficiencies, construction costs, constituent removal efficiencies, and operation and maintenance requirements. Published information was developed, such as a report on findings, operation and maintenance monitoring (O&MM) and a maintenance indicator document to provide a long-term BMP maintenance protocol. The data collected were contributed to the American Society of Civil Engineers’ (ASCE) International BMP Database to provide the public and storm water dischargers and professionals with enhanced knowledge on BMP performance.

As part of the BMP pilot program, Caltrans proactively coordinated with federal and state regulatory agencies to assess whether any new BMP installation would present an environmental and public health hazard. By working with agencies such as the California Department of Health Services, the potential for BMPs to harbor vectors was minimized to eliminate the possible risk to public health and safety. Caltrans prepared a biological assessment to determine protected and sensitive species attraction to the BMPs and how it could affect operations.

A significant component of the overall constituent load reduction in several BMPs was infiltration of runoff into the soil, such as occurs with infiltration basins and trenches, where infiltration is the primary mechanism for mitigation of storm water impacts, and in unlined extended detention basins (EDBs) and biofiltration swales and strips.

The BMP Retrofit Pilot Program succeeded in demonstrating the effectiveness of several BMP types in reducing pollutant concentrations and mass loadings. The program further yielded substantial information on the technical feasibility of the BMPs as retrofits in highway and support facility settings. The determination of the technical feasibility at any particular location requires site-specific evaluation. The safety, maintenance and operation of each BMP were observed and tracked for over six years. A Maintenance Indicator Document (MID) was created to provide a long-term protocol for maintaining the pilot BMPs and to encourage consistency and control efficiency of their maintenance and operation. The MID was modified and updated as the study progressed; it described specific maintenance protocols and identified the conditions under which maintenance of each BMP would be required, including an estimate of resource needs.

The BMPs evaluated are of various types consisting of concrete devices, earthen basins, vegetation and underground structures. Treatment BMPs function by collecting storm water and treating various pollutants, including gross pollutants (trash and debris). Treatment of storm water runoff improves the quality and visual appeal of receiving water. Routine inspection and maintenance of the BMPs were conducted to maintain functionality as well as aesthetics. Aesthetic maintenance includes graffiti, trash and debris removal, grass trimming, weed control, tree pruning and painting. Devices are designated to be low profile and at or below grade, which improves the visual appeal.

A lasting contribution

The Caltrans BMP Retrofit Pilot Program research study is available on the Caltrans storm water program website (www.dot.ca.gov/hq/env/stormwater), and is accessible to storm water professionals and storm water program managers throughout the state, as well as out-of-state agencies. Findings of the study have been shared with other interested state departments of transportation, and local and state agencies. Information from the study has provided knowledge to state agencies, municipalities, other storm water dischargers and regulators, and its studies and research results have been the focus of numerous research papers and presentations.

Although research on the BMP Retrofit Pilot Program culminated in 2003, it continues to serve as a valuable resource to help Caltrans improve its storm water management program. The storm water community is faced with meeting more stringent regulatory requirements to ensure that adequate treatment controls can achieve surface water quality effluent limits. For this reason, the department continues to research and develop new storm water treatment control technologies and methods to achieve greater surface water quality protection that is effective, efficient, environmentally safe and economical.

Full or partial treatment prevents overburden of downstream treatment devices and, in some cases, municipal treatment devices. Caltrans BMPs remove or reduce the need for municipal treatment devices. The implementation of advanced storm water controls and measures evaluated in this research project can benefit the storm water community by improving water quality conditions. Doing so could reduce the need and high cost for municipal treatment devices, as well as avoid the need to direct storm water to wastewater treatment plants to meet stringent water quality standards.