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

Low Impact Development (LID) techniques that are economical and appropriate for the highway environment are important tools for departments of transportation (DOTs) faced with meeting increasingly demanding water quality and hydrologic management requirements. Vegetated filter strips along highways, an accepted LID Best Management Practice (BMP), are a valuable and cost-effective alternative to hydraulically engineered BMPs. However, their use is limited by site constraints such as vegetation density, limited right-of-way, and steep side slopes. Furthermore, their effectiveness may vary greatly depending on climate, soils, and other factors. Compost amended vegetated filter strips (CAVFS) can overcome some of these limitations by promoting stormwater filtration through compost amended soils and infiltration of stormwater into the native underlying soils. CAVFS have received general use designation and approval by the Washington State Department of Ecology TAPE protocol for dissolved metals removal, including zinc and copper. CAVFS are relatively low cost and low maintenance, which makes them attractive to DOTs. Unfortunately, they can be a driving hazard since their design, consisting of an uncompacted layer of mixed compost and soil 12 inches deep, can trap the wheels of vehicles leaving the highway. This hazard limits where CAVFS can be used along highways. A proposed modified CAVFS, consisting of a 2- to 4-inch thick blanket of coarse to medium textured yard waste compost placed on the untilled highway embankment, has the potential to match the pollutant removal and hydrologic benefits of the standard CAVFS. The thin layer of compost eliminates the risk of tire trapping associated with the deep amended soil in the standard CAVFS. Before a compost blanket CAVFS can become a standard LID BMP, it is necessary to confirm its performance and develop design guidance. This involves determining pollutant removal capability and capacity; the ability to detain and retain runoff; and the effect of climate, soils, compost composition, compost blanket thickness, and other parameters on its water quality and hydrologic effectiveness. DOTs are facing increasing costs due to stricter stormwater management requirements intended to protect water quality and avoid adverse hydromodification of receiving waters. The large increase in the number of stormwater BMPs installed is placing an increasing burden on projects and DOTs’ maintenance divisions. For example, between 2012 and 2014 the Oregon Department of Transportation more than doubled the number of its stormwater quality facilities (377 to 786). This burden magnifies the need for BMPs with demonstrated effectiveness and low construction and maintenance costs. Developing design guidance for compost blanket CAVFS will provide DOTs with an effective and economical BMP of wide applicability, without the safety issues associated with the standard CAFVS. Results produced by testing the water quality effectiveness of compost blanket CAVFS would support the appropriate use of these BMPs to meet regulatory treatment requirements. In situations where a stormwater retrofit is needed, a compost blanket CAVFS could be very cost-effective option and its construction is very straight forward. If compost blanket CAVFS are shown to have substantial hydrologic benefits, their use could lead to a reduced size of detention basins for flow control and significantly lessen the financial strain on DOTs for stormwater management. A literature review suggests that the research involving vegetated filter strips (VFS) looked at the standard VFS design and did not include any compost blankets on the VFS. The research generally concluded that the effectiveness of the VFS was based on the vegetation cover. In contrast to standard VFS design, compost blanket CAVFS would allow a substantial portion of highway runoff to filter into and through the compost layer. The rate of runoff is reduced, more of the runoff comes in contact with organic material that can remove dissolved metals, and the longer contact with the underlying soil promotes infiltration. The compost blanket studies looked at the benefits of applying compost to roadway embankments for erosion purposes. The studies didn’t look at using compost blankets as a modification to an existing stormwater BMP (i.e., VFS) and monitoring its effectiveness over the standard VFS design. The focus of this research is to test the compost blanket CAVFS, a design variation of the standard CAVFS BMP, to determine if it provides the same, or better, level of stormwater treatment while also providing a safer roadway embankment. The research has two main objectives: Objective 1: Test and establish the water quality and hydrologic management capabilities of compost blanket CAVFS, and determine the effect of various design and site factors on performance over a range of conditions typical of the highway environment. Some of these site factors include compost blanket depths, existing embankment soil types, and roadway embankment slopes. Maintenance-related factors should also be addressed. Objective 2: Develop guidance on the use, limitations, design, and implementation of compost blanket CAVFS for use along highways, based on the results of field and laboratory testing and literature review. The guidance is intended to be a practical manual for those who select and design stormwater management facilities. It will be broadly applicable and not limited to a narrow range of conditions or geography. The guidance will also be useful in evaluating the impact of highway runoff on the natural environment. Achieving the project’s objectives involves the following tasks: Task 1: Survey and synthesis of existing literature related to the water quality and hydrologic characteristics of compost blankets, and the use and stability of compost blankets on highway or other embankments. The survey should focus on the following areas: compost blanket ability to remove various types of pollutants associated with highway runoff; leaching of pollutants from the compost used for the blanket; hydrologic capabilities of compost blankets, including detention capacity; effective lifespan of compost blankets along roadsides; stability on slopes receiving runoff; effects of climate and various underlying soil types in roadway embankments on the above characteristics; and the effect of compost blanket composition and quality on the above characteristics. The synthesis report should cover the above elements and include a gap analysis of information required to complete the project. Task 2: Design and implement testing of compost blanket CAVFS. Field testing should occur at two highway test locations. One test location could have a low gradient roadway embankment slope while the other location could be steeper. At each location, ensure it can accommodate three compost blanket CAVFS. One of the objectives is to test how deep the compost blanket should be. The compost blanket CAVFS should be 2 inches, 3 inches, and 4 inches in depth. There should be enough room for monitoring setup and equipment. Build and monitor the test sites. The compost blanket CAVFS sites would be sized per the VFS BMP design criteria with compost blankets that vary in thickness. This will help the study compare both stormwater quality and flow control benefits. Field and possibly laboratory testing will be conducted to address the information gaps in Task 1 and establish, and as appropriate confirm, the capabilities of compost blankets to manage highway runoff in varying roadside situations. Analyze data collected in Tasks 1 and 2. Task 3: Develop guidance on the use and design of compost blanket CAVFS in the highway environment. Include information on when and where compost blanket CAVFS are an appropriate stormwater BMP and the factors that support these conclusions. Develop design criteria for compost blanket CAVFS, taking into account varying roadside, climate, and traffic variables. Criteria should address compost characteristics, layer thickness, range of slopes, seeding etc. Discuss techniques and information required to estimate the water quality and hydrologic performance of CAVFS for project specific situations. Discuss what type and how often maintenance is needed for a compost blanket CAVFS.


  • English


  • Status: Proposed
  • Contract Numbers:

    Project 14-39

  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Sundstrom, Lori

  • Start Date: 20160512
  • Expected Completion Date: 0
  • Actual Completion Date: 0
  • Source Data: RiP Project 40842

Subject/Index Terms

Filing Info

  • Accession Number: 01598991
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 14-39
  • Files: TRB, RiP
  • Created Date: May 12 2016 1:01AM