Construction specifications for pretreatment vegetated filter strips

Pretreatment vegetated filter strips, also sometimes called buffer strips or buffers, are sloped surfaces that rely on shallow (i.e., water level less than the height of the vegetation), distributed flow through dense vegetation to reduce flow velocity, allow particles to settle, and allow particle interception by the vegetation as their primary mechanism of pollutant removal. Properly designed, constructed, and maintained pretreatment vegetated filter strips reduce the sediment burden on full treatment practices (e.g. bioretention, constructed pond, etc.), thus improving the effectiveness and lifespan of full treatment practices. This page provides information on design, construction, and maintenance of pretreatment vegetated filter strips.

Construction specifications
References for vegetated filter strips
Related pages

Construction specifications

Pre-construction

After designing a pretreatment vegetated filter strip, considerations need to be taken before, during, and after the construction process. Before breaking ground, methods to achieve site easement and site protection must be planned.

Access agreements

Before starting construction, a site easement will need to be established in cases where the party that is installing the pretreatment vegetated filter strip needs access to land owned by another party. An easement is defined as “a non-possessory right to use and/or enter onto the real property of another without possessing it.” The easement can be temporary or permanent. Temporary easements are necessary when land that is needed for construction extends into another party’s land. Permanent easements are needed to establish authority to access the site for maintenance if crossing another party’s land is required to reach the pretreatment vegetated filter strip with maintenance equipment. An example of an access agreement can be located online here.

Site protection

Sediment- and erosion-control measures such as silt fences, are necessary to protect the downstream BMP from the construction site erosion, as well as protecting the construction site from receiving runoff. Sites that result in land disturbance of 1 acre or more that will result in a common plan of development or sale that disturbs more than 1 acre need to meet the National Pollutant Discharge Elimination System (NPDES) and State Disposal System (SDS) Construction Stormwater General Permit. The permit describes the necessary sediment and erosion control practices at the site.

Construction

During construction, the ground must be stabilized, accurately graded, protected, and made suitable for healthy vegetation establishment.

Site erosion and sediment control

During construction, exposed soil will require soil stabilization and sediment-control measures. Erosion control is particularly important if the pretreatment vegetated filter strip is being installed upstream of an existing full-treatment BMP. If sediment is not contained within the construction boundaries, excess soil will clog the downstream BMP and require additional cleanup and maintenance. Measures that can be considered for soil stabilization include mulching and erosion-control blankets. When mulching is used, either straw or woodchips should be used while achieving at least 90 percent soil coverage. Erosion-control blankets and mulch are also used to provide structural stability to the soil during seed application to aid in vegetation establishment. For detailed construction site stabilization requirements, see the MPCA construction stormwater program page online.

Sediment-control measures will be used along with soil stabilization and includes BMPs such as silt fences, rock checks, bio rolls, drainage swales, and sediment traps. In addition to soil stabilization and sediment-control measures, managing soil stockpiles and sweeping tracked sediment on pavement near the construction site is required. If construction occurs in late summer to fall and is expected to carry into the winter, ensure that all of the exposed areas are covered before the first freeze. For more information on general erosion-control practices, see the Erosion Prevention Practices website.

Areas that will receive flows from impervious surfaces need to receive additional erosion-control protection to ensure that flows do not cause erosion while vegetation is being established. An aggregate of #57 stone with a depth of 3 to 4 inches North Carolina State Cooperative Extension Service, 2006 may be used at the leading edge or entrance to the filter strip as a buffer to slow flow velocity but should not be included in the vegetated filter strip length.

Grading

For pretreatment vegetated filter strips to be effective, the ground must be uniformly sloped perpendicular to the flow (i.e. zero lateral slope) to prevent channelization of runoff. This slope includes the slope upstream of the pretreatment vegetated filter strip (or installing a level spreader), as well as the pretreatment vegetated filter strip itself. During the grading process, efforts should be taken to minimize and reduce soil compaction to the best degree, as well as stabilizing any exposed soil. See the section on Site erosion and sediment control.

Compaction prevention and alleviation

To prevent soil compaction, ensure that no construction traffic occurs on the site of the pretreatment vegetated filter strip and that foot traffic is minimized as much as possible. Marking the boundaries of the pretreatment vegetated filter strip with paint and/or stakes can help keep away traffic. If compaction occurs or soil at the site is already compacted, measures can be used to alleviate the soil compaction. Methods indicated by the MPCA include soil ripping, scarifying, or mixing organic matter with the soil. These methods are often combined. For additional information, see the MPCA’s website.

Vegetation establishment

Establishing full and healthy vegetation is vital to ensuring that the pretreatment vegetated filter strip will perform as designed. For the best results, weeds should be removed from the bare soil before planting. To ensure that vegetation will become established and survive the winter freeze, a minimum of 60 days before the first expected frost should be allowed for the vegetation to grow. Soil stabilization practices such as erosion-control blankets should be used during vegetation establishment. To avoid damaging the emerging vegetation and causing site compaction, vehicle and foot traffic should not be allowed during the vegetation establishment phase. Achieving a minimum of 80 percent cover on the pretreatment vegetated filter strip, per the design guidelines, will ensure that the site is stabilized after construction. Following rain events, additional inspections and possible maintenance on the full-treatment BMP downstream of the pretreatment vegetated filter strip is recommended during the vegetation establishment phase.

Post-construction

After construction is completed, the boundary that marks the extents of the pretreatment vegetated filter strip must be maintained during vegetation establishment to keep away vehicle and foot traffic. Maintaining this boundary during vegetation establishment will prevent soil compaction and damage to the vegetation. Once the vegetation is fully established, the boundary can be removed, but foot traffic should still be minimized.

References for vegetated filter strips

Abu-Zreig, M., R. P. Rudra, M. N. Lalonde, H. R. Whiteley, and N. K. Kaushik, 2004. Experimental Investigation of Runoff Reduction and Sediment Removal by Vegetated Filter Strips. Hydrological Processes, Vol. 18, No. 11, pp. 2029–2037.
Barrett, M. E.; P. M. Walsh; J. F. Malina, Jr.; R. J. Charbeneau, 1998. Performance of Vegetative Controls for Treating Highway Runoff. Journal of Environmental Engineering, Vol. 124, No. 11, pp. 1121–1128.
Barret, M. E., A. Lantin, and S. Austrheim-Smith, 2004. Storm Water Pollutant Removal in Roadside Vegetated Buffer Strips. Transportation Research Record: Journal of the Transportation Research Board 1890, No. 1, pp. 129-140.
Blanco-Canqui, H., C. J. Gantzer, S. H. Anderson, and E. E. Alberts. 2004. Grass Barriers for Reduced Concentrated Flow Induced Soil and Nutrient Loss. Soil Science Society of America Journal, Vol. 68, No. 6, pp. 1963-1972.
California Environmental Protection Agency, 2014. Draft Amendments to Statewide Water Quality Control Plans to Control Trash. Prepared by the California Environmental Protection Agency, Division of Water Quality, State Water Resources Control Board, Sacramento, CA.
Clar, M. L., B. J. Barfield, and T. P. O’Connor, 2004. Stormwater Best Management Practice Design Guide Vegetative Biofilters. EPA/600/R-04/121A, prepared by the US Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, Cincinnati, OH.
Comprehensive Environmental Inc. and New Hampshire Department of Environmental Services, 2008. New Hampshire Stormwater Manual, Volume 2. Post-Construction Best Management Practices Selection & Design, prepared by Comprehensive Environmental Inc., Merrimack, NH, and the New Hampshire Department of Environmental Services, Concord, NH.
District Department of the Environment, 2013a. Stormwater Management Guidebook. Prepared by the District Department of the Environment, Washington, DC.
District Department of Environment, 2013b. Anacostia River Watershed Trash TMDL Implementation Strategy. Prepared by the District Department of Environment, Stormwater Management Division, Washington, DC.
Goel, P. K., R. P. Rudra, B. Gharabaghi, S. Das, and N. Gupta, 2004. Pollutants Removal by Vegetated Filter Strips Planted with Different Grasses. Proceedings, 2004 American Society of Association Executives/Canadian Society for Engineering in Agricultural, Food, and Biological Systems, Paper Number 042177, Fairmont Chateau Laurier, The Westin, Government Centre, Ottawa, ON, Canada, August 1–4.
Gharabaghi, B., R. P. Rudra, H. R. Whiteley, and W. T. Dickinson, 2000. Sediment-Removal Efficiency of Vegetative Filter Strips. 2000 Annual Research Report, prepared by the Guelph Turfgrass Institute, Guelph, ON, Canada.
Kayhanian, M., Suverkropp, C., Ruby, A., and Tsay, K. 2007. Characterization and Prediction of Highway Runoff Constituent Event Mean Concentration. Journal of Environmental Management, Vol. 85, No. 2, pp. 279–295.
Lantin, A. and Barrett, M. 2005. Design and Pollutant Reduction of Vegetated Strips and Swales. Impacts of Global Climate Change, pp. 1-11.
Maestre, A., and Pitt, R. 2005. The National Stormwater Quality Database, Version 1.1: A Compilation and Analysis of NPDES Stormwater Monitoring Information. Prepared for the US Environmental Protection Agency, Office of Water, Washington, DC.
Massachusetts Department of Environmental Protection, 2008. Massachusetts Stormwater Handbook, Volume 2. Prepared by the Massachusetts Department of Environmental Protection, Boston, MA.
Maniquiz-Redillas, M. C., F. K. Geronimo, and L. H. Kim, 2014. Investigation on the Effectiveness of Pretreatment in Stormwater Management Technologies. Journal of Environmental Sciences, Vol. 26, No. 9, pp. 1824–1830.
North Carolina State Cooperative Extension Service, 2006. Level Spreaders: Overview, Design, and Maintenance. Prepared by Jon M. Hathaway and William F. Hunt, North Carolina State University.
New Jersey Department of Environmental Protection, 2014. NJ Stormwater Best Management Practices Manual. Chapter 9.10 Standard for Vegetative Filters, prepared by the New Jersey Department of Environmental Protection, Division of Watershed Management, Trenton, NJ.
Battiata, J., S. Claggett, S. Crafton, D. Follansbee, D. Gasper, R. Greer, C. Hardman, T. Jordan, S. Stewart, A. Todd, R. Winston, and J. Zielinski, 2014. Recommendations of the Expert Panel to Define Removal Rates for Urban Filter Strips and Stream Buffer Upgrade Practices. Prepared by the Center for Watershed Protection, Elliott City, MD, for the Chesapeake Bay Program, Annapolis, MD.
Virginia Department of Ecology, 1999. Virginia Stormwater Management Handbook. First Edition, Volumes 1 and 2. Prepared by the Virginia Department of Conservation and Recreation, Division of Soil and Water Conservation, Richmond, VA.