Effectiveness of Compost and Recycled Highway Soil Amendment Products for Reduction of Dissolved Copper Concentrations in Highway Stormwater Runoff

Focus Area

Water Quality/Wetlands


Natural Resources




Under $99k


1-2 years

Research Idea Scope

Environmental agencies in the Pacific Northwest are concerned about dissolved copper in stormwater.  Extremely low concentrations of dissolved copper (1 to 5 parts per billion) have been shown to have detrimental effects on fish species listed as threatened or endangered pursuant to the federal Endangered Species Act. Highway stormwater can exceed these concentrations of dissolved copper. Regulatory requirements regarding dissolved copper can delay projects and have increased project costs. For these reasons many state Departments of Transportation (DOTs) in the Pacific Northwest are concerned about copper in highway stormwater and are interested in developing practical and affordable methods to control this pollutant.
Dissolved metal pollutants are difficult to remove from stormwater. Research projects have shown that compost can capture dissolved metals. Compost and sand filters have had some success in reducing dissolved metal concentrations; however, filter facilities are expensive to design and construct and can be difficult to maintain. More cost-effective methods to control levels of dissolved copper in highway stormwater are needed. Surface application of compost in a landscape setting would reduce costs; however, the effectiveness in reducing pollutant loads is not known.     
DOTs are also concerned about efficient, sustainable, and environmentally sound ways of managing street sweeping materials and other road waste. DOTs operating in the Portland, Oregon area estimate that the disposal of highway materials generated from local roads and highways could be reduced by over 50,000 tons per year if appropriate recycling practices can be developed for street sweeping materials alone. This reduction would translate into substantial monetary savings for DOTs and environmental benefits for the local community. One proposal is to mix road waste with compost for use in landscaping. However, information is lacking on how the addition of other highway materials may affect the ability of compost to improve stormwater quality.
A study with positive results would provide support for the use of an effective and relatively inexpensive technique of highway runoff water quality treatment, with the potential to reduce maintenance costs. Regulatory issues would also be addressed by having more data to support choices in treatment and evaluation of project effects.
Research Objectives
1.             Determine if the use of compost and related soil amendment products as top dressing or landscaping medium on highway projects can reduce levels of dissolved copper and other highway stormwater pollutants.
2.             Determine the effectiveness of various compost/road waste blends for stormwater pollutant removal. Road waste to be investigated include street sweepings, winter road sand, and possibly other materials.
3.             Support the development of guidance for the use of compost and compost blends for stormwater treatment.
4              Support the development of guidance for the recycling of compostable road waste.
5.             Provide information for use by biologists in the preparation of Biological Assessments and Biological Opinions pursuant to the federal Endangered Species Act for projects using landscape compost as a water quality treatment technique.
Specific Tasks
1.             Conduct a literature review on:
·         The effectiveness and efficiency of compost for removal of dissolved copper and other pollutants from highway stormwater runoff; and
·         The bio-availability and effects of dissolved copper in its various forms on several fish species, with the intent of identifying which form of dissolved copper should be the target of analysis.
2.             Develop monitoring and testing protocols, including bench and field testing, as well as specifying target pollutants.
3.             Test a variety of recycled highway soil/compost blends for their effect on dissolved copper concentrations and other associated highway stormwater pollutants. The project would test pure leaf compost and several soil blends and compost mixes made from other highway recycled materials. 

Suggested By

Jennifer Sellers (Oregon Department of Transportation), Jeff Moore (Oregon Department of Transportation), William Fletcher (Oregon Department of Transportation), Tom Melville (Oregon Department of Environmental Quality)