Vegetated Treatment Systems

The primary objective of the RVTS study was to determine if standard Caltrans roadway design requirements result in vegetated side slopes with stormwater treatment capabilities equivalent to biofiltration strips specifically engineered for water quality performance. Runoff through existing, vegetated slopes along Caltrans roadways was assessed at locations throughout California. At each location, concrete channels were constructed to capture highway runoff after it passed through existing, vegetated slopes of varying widths. The quantity and quality of runoff discharged from each vegetated slope was compared to that observed at the edge-of-pavement. The performance of each vegetated slope was evaluated in terms of changes in concentration for contaminants commonly found in highway runoff, and load reductions caused by stormwater infiltration into these areas. The RVTS data were also compared to the results of similar studies that assessed engineered biostrips.

OWP Tasks:

• Assisted in Study Planning
• Reviewed Designs of Monitoring Systems
• Provided Review of Monitoring System Installation Activities
• Provided Monitoring Assistance
• Reviewed Data Assessment and Reporting

Report/Study Link: Caltrans Roadside Vegetated Treatment Sites (RVTS) Study

OWP Contacts: Maureen Kerner

The primary objective of the ORVTS study was to evaluate the ability of ornamental/groundcover vegetative species to provide treatment of runoff from Caltrans highways. Runoff from the highway drained into roadside slopes planted with ornamentals and was collected in slotted PVC pipes. Flow from the pipes was measured throughout the storm, along with site rainfall. Flow-weighted samples were collected and composited to assess the water quality from each event at each monitoring station. This water quality was compared to that from edge-of-pavement stations to assess concentration and load reductions.

OWP Tasks:

• Assisted in Study Planning
• Reviewed Designs of Monitoring Systems
• Provided Monitoring Assistance
• Reviewed Data Assessment and Reporting

OWP Contacts: Maureen Kerner

The goals of the Tahoe RTS study were (1) to determine whether, and how large, a difference in water quality exists between highway edge-of-pavement runoff and runoff leaving the highway right-of-way in sheet flow drainage situations; and (2) to determine the relative effects of different site characteristics on water quality and treatment. Runoff samples were collected from several locations throughout the Lake Tahoe Basin. The locations represented various conditions of highways and right-of-ways in terms of degree and length of slope, amount of obstacles impeding sheet flow (rocks, logs, shrubs, trees, etc.), amount of duff cover, and relative elevation. Slotted PVC pipes were installed within the right-of-way to collect runoff. Edge-of-pavement runoff was collected from double-barreled sand traps. Water quality, including the distribution of small particles (~0.8 to 20 m), was compared among the various stations.

OWP Tasks:

• Assisted in Study Planning
• Reviewed Designs of Monitoring Systems
• Provided Monitoring Assistance
• Conducted Small Particle Distribution Testing and Data Analysis
• Reviewed Data Assessment and Reporting

OWP Contacts: Maureen Kerner