Spring 2021

Talking Trash: Developing a Compost Site Evaluation Toolkit

By Amy Dale, Ph.D.

Working with a composting operator, Gradient developed a toolkit to evaluate potential environmental impacts from its operations.

Composting is a valuable waste management tool. In addition to reducing the volume of waste that might otherwise be sent to landfills or incinerators, composting generates a high-quality product that can be used to improve soil quality, reduce erosion, and control stormwater runoff. In recent decades, the amount of waste composted each year has grown greatly. However, large amounts of compostable material continue to be sent to landfills and incinerators. Over 30% of the municipal solid waste generated annually in the US has the potential to be composted, but less than 9% is composted currently (US EPA, 2021).

One of the major challenges that composters face in starting and expanding their businesses is a complex regulatory environment. Environmental regulations and permitting requirements vary widely by state and are often confusing. Another challenge that composters face is that little guidance is currently available to composters interested in evaluating the potential environmental impacts of their sites. Compostable materials may contain trace quantities of several contaminants of potential health concern, including pathogens, metals, and pesticides. These contaminants can impact both compost and compost pile leachate. Contaminants in leachate may either travel overland via stormwater or infiltrate into groundwater, with the potential to impact surface water and groundwater. There is therefore a need for guidance to help composters evaluate site-specific, contaminant-related impacts and comply with state and federal regulations.

Over 30% of the municipal solid waste generated annually in the US has the potential to be composted, but less than 9% is composted currently (US EPA, 2021).”

On behalf of a composting company in the northeastern US, Gradient evaluated the regulations applicable to composters in 10 states, including requirements for siting, operation and management, compost quality assurance, stormwater control, and monitoring and reporting. Based on this review, Gradient developed a user-friendly toolkit to help the company evaluate current and prospective composting sites with respect to potential for both environmental impacts and regulatory noncompliance. Two major tools were developed as part of this work: a Site Evaluation Checklist and a Sampling and Analysis Plan.

The Site Evaluation Checklist included 19 benchmarks that compost site operators should achieve, if possible, to meet regulatory requirements and minimize environmental risks. Items on this checklist included recommended buffer distances between the site and water supply wells, surface water features such as streams and wetlands, and nearby structures such as public roads, residences, businesses, and solid waste landfills. Evaluation criteria were also provided for soil percolation rates, depth to groundwater, and whether or not the site was located within the 100-year floodplain.

To aid in completion of the Site Evaluation Checklist, Gradient also compiled a list of publicly available, web-based resources for site evaluation. Resources on this list included several state and federal databases and web-based Geographic Information System (GIS) tools for the evaluation of site topography, soil, and groundwater properties, as well as the identification of nearby features such as water supply wells, streams and wetlands, protected natural resource areas, restricted land use areas, residences, industrial operations, contaminated sites, and other waste management sites. The resources list also included several online databases of historical maps, local newspapers, town records, and other historical documents. In addition to helping composters identify potential site-specific contaminant risks due to composting operations, these resources can help composters identify potential risks at their sites due to industrial operations at neighboring properties and/or industrial operations undertaken at their own property prior to its use as a compost site.

Tons of Material Composted Annually in the US, 1980-2018

Flowchart of Medical Device Safety Assessment Steps

Figure adapted from US EPA (2021). Click to Enlarge Figure.

In addition to the Site Evaluation Checklist and the associated list of resources, Gradient developed a Sampling and Analysis Plan (SAP). The SAP included recommended sampling frequencies and analytical test methods for several contaminants found in finished compost and stormwater runoff, including physical contaminants (e.g., film plastic, sharps), metals, nutrients, PCBs, pathogens, and pesticides. To aid in the evaluation of sample results, Gradient compiled look-up tables of the recommended maximum allowable concentrations of these contaminants in finished compost and stormwater runoff.

As the composting industry grows, there is a need for guidance to help composters evaluate site-specific, contaminant-related impacts and comply with state and federal regulations for the protection of environmental quality. Toolkits such as the ones discussed here can empower composters to develop more environmentally conscious and cost-effective strategies for compost site monitoring and management.

Contact Info

The author can be reached at adale@gradientcorp.com.


US EPA. 2021. “National Overview: Facts and Figures about Materials, Waste and Recycling.” Accessed at https://www.epa.gov/facts-andfigures-about-materials-waste-and-recycling/national-overviewfacts-and-figures-materials.