The Effectiveness of Compost Amended Vegetated Filter Strips Using a Compost Blanket Application Method for Pollutant Removal from Highways

Focus Area

Water Quality/Wetlands


Natural Resources






2-3 years

Research Idea Scope

Research Idea Scope Background: Current municipal and transportation-related stormwater permits in western Washington require the use of low impact development (LID) as the preferred and commonly used approach to managing stormwater in development and redevelopment projects. The compost amended vegetated filter strip (CAVFS) is an LID best management practice (BMP) that received general use level designation (GULD) and approval by the Washington State Department of Ecology (Ecology). The CAVFS BMP promotes filtering of stormwater through compost amended soils, and infiltration stormwater into the native underlying soils. The typical cross section of a CAVFS is a 3-inch layer of compost tilled into eight to nine inches of existing soil to achieve approximately a foot depth of CAVFS soils. The resulting CAVFS embankment is not compacted in an effort to promote infiltration of stormwater into the underlying soils. Vehicle safety concerns make it undesirable to have a foot of uncompacted CAVFS material next to the highway. Research Objective: This research proposal seeks to change the method of designing the CAVFS in an effort to make the CAVFS BMP perform the same, if not better, and make the CAVFS safer as a roadway embankment. The proposal would seek to change the CAVFS by requiring only a 3-inch medium compost blanket over an existing roadway embankment that meets the vegetated filter strip (VFS) BMP guidelines in the Washington State Department of Transportation’s (WSDOT) Highway Runoff Manual (WSDOT 2014). No tilling of the compost into the underlying soils would be necessary. Monitoring would evaluate the stormwater treatment effectiveness of the modified 3-inch compost blanket VFS design, and compare performance of the BMP to the current 12 inch deep CAVFS soils design. The modified 3-inch compost blanket VFS design would provide a safer and more durable roadway embankment for vehicles making an emergency stop. Specific Tasks: Task 1: Conduct a literature review. The literature review will include a survey of state practices and experience as well as a compilation of existing data. Task 2: Find a Test Location. Find a highway site that can accommodate the current CAVFS design as well as the proposed modified 3-inch compost blanket VFS design. Make sure there is room for monitoring setup and equipment. Task 3: Write a Quality Assurance Project Plan. Develop a Quality Assurance Project Plan (QAPP) that describes monitoring goals and objectives, methods, quality assurance, and study site designs following guidance and procedures in Ecology’s Technical Guidance Manual for Evaluating Emerging Stormwater Treatment Technologies: Technology Assessment Protocol – Ecology (TAPE) (Ecology 2011). Ecology will have to approve the QAPP before monitoring can begin. Task 4: Build the test site and monitor the site The research proposal would need a control CAVFS design built in accordance with the WSDOT Highway Runoff Manual as well as a modified 3-inch compost blanket VFS design to compare both stormwater quality and flows. Task 5: Evaluate the monitoring results. Make recommendations based on results. If monitoring shows the proposed 3-inch compost blanket VFS proves to be just as effective for runoff treatment as the current CAVFS design, this task will require the development of a Technical Evaluation Report (TER). The TER will be submitted to Ecology to justify the change in the CAVFS criteria.

Urgency and Payoff

If the research project proves that the modified 3-inch compost blanket VFS design works just as well as the current WSDOT Highway Runoff Manual CAVFS design, then all state and local agencies that build roadways will have immediate benefit. The 3-inch compost blanket VFS could be used in stormwater retrofit situations where the simple application of a 3-inch compost blanket over an existing roadway embankment would improve storm water quality discharges from highways. Also, the roadway embankment would still be compacted as any other roadway embankment so that emergency parking and roadway recovery would not be an issue.

Suggested By

Alex Nguyen Washington State Department of Transportation 206.440.4537

[email protected]