Low Impact Development (LID) techniques that are economical and appropriate for the highway environment are important tools for state departments of transportation (DOTs) faced with increasingly demanding water quality and hydrologic management requirements. Vegetated filter strips along highways, an accepted LID Best Management Practice (BMP), are a cost-effective alternative to hydraulically engineered BMPs. Their use is limited however, by site constraints such as limited right-of-way and steep side slopes, and their effectiveness may vary greatly depending on climate, soils, and other factors. Vegetated compost blankets (VCBs) can overcome some of these limitations by promoting stormwater filtration, retention of runoff, and infiltration of stormwater into the underlying soils—potentially removing pollutants and reducing flow volumes. VCBs have the potential to be relatively low cost and low maintenance, which makes them attractive to state DOTs. VCBs also can be a relatively simple retrofit on a roadside embankment. Research is needed to evaluate hydrologic and water quality benefits of VCBs. 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 performance. Design guidance will be needed in order to provide state DOTs with an effective and economical BMP that can be used in a wide variety of roadway settings.
The objectives of this research are to:
1. Develop performance curves for surface-applied, VCBs on slopes of 3:1 or flatter that (a) remove pollutants of concern, (b) control erosion, (c) reduce volume, and (d) support vegetation when placed on an existing roadway embankment. 2. Provide construction specifications, standard details, and a decision matrix that provides guidance on the use, limitations, design, and implementation of vegetated compost blankets on existing roadway embankments. The guidance is intended to be a practical manual for practitioners who select, design, and implement stormwater management facilities and should be broadly applicable to a wide range of conditions and geography. Accomplishment of the project objectives will require at least three phases and the following tasks.
(1) Conduct a critical review of the 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, focusing at a minimum on the following areas:The ability of compost blankets to remove various types of pollutants associated with highway runoff
- Types of compost material, including gradation and sources of feedstock
- Pollutant leachate from the compost used in the blanket
- Hydrologic capabilities of compost blankets, including retention capacity
- Effective lifespan of compost blankets along roadsides
- Ongoing maintenance requirements
- Stability on slopes receiving runoff
- Effects of climate
- Underlying soil types
- Rutting caused by vehicles during and after installation
- The U.S. Composting Council’s Seal of Testing Assurance
The budget for Task 1 should not exceed $25,000. Results should be documented in a technical memorandum.
(2) Based on literature values, design an experiment to test the performance of VCBs. Laboratory testing may be used to supplement field testing. At a minimum, the experimental design should consider:
- VCB depths
- VCB dimension
- Drainage area
- Site selection criteria
- Site preparation requirements
- Existing embankment soil types
- Roadway embankment slopes
- Roadway longitudinal slopes
- Quantification of pollutant removal rates
- Quantification of volume reductions
- Commencement of monitoring not later than Fall of 2018
- Monitoring should occur throughout a continuous 24 month period
- Locations that provide geographic/climate variations
- Contingency plans in case monitoring is not possible
- Sampling methods
- Analytical methods (using an Environmental Laboratory Accreditation Program certified laboratory)
- Draft Quality Assurance Project Plan
- Reporting format including photographic documentation
(3). Prepare Interim Report 1 that includes the findings and conclusions from Tasks 1 and 2. Interim Report 1 shall also contain a detailed work plan for Phase II.
An in-person meeting of the project panel to discuss Interim Report 1 with the contractor will be required. The research plan shall provide a 2-month period for review and approval of the interim report. NCHRP approval of the interim report is required before work can begin on the remaining tasks.
(4). Finalize the Quality Assurance Project Plan and submit for NCHRP approval. (5). Implement the experimental design as approved by NCHRP in Task 4. ( Analyze the data collected. (Prepare Interim Report 2 that includes the findings and conclusions from Tasks 5 and 6. An in-person meeting of the project panel to discuss Interim Report 2 with the contractor will be required. The research plan shall provide a 2-month period for review and approval of the interim report. NCHRP approval of the interim report is required before work can begin on the remaining tasks.
(8).Based on the results of field and laboratory testing and literature review, develop guidance on the use, limitations, design, and implementation of VCBs for use along highways. At a minimum, the guidance will include the following: 1. Performance curves for surface-applied VCBs on slopes of 3:1 or flatter that (a) remove pollutants of concern, (b) control erosion, (c) reduce volume, and (d) support vegetation when placed on an existing roadway embankment. 2. Construction specifications and standard details, and a decision matrix that provides guidance on the use, limitations, design, and installation and maintenance of vegetated compost blankets on existing roadway embankments. (Prepare final deliverables including (1) a report that documents the conducts of the research and provides guidance on designing and install VCBs, (2) recommendations on needs and priorities for additional research, and (3) a PowerPoint presentation that presents an overview of the research. ( Upload all project monitoring data to the International BMP database at www.bmpdatabase.org.
STATUS: Research is underway.