Commercial Compost Testing
Compost and mulch are both useful products sold to a variety of markets, contributing to a strong circular economy. Such markets include agricultural and horticultural, landscape and nursery, vegetable and flower gardens, sod production and roadside projects, as well as sports fields and golf courses.
Before a compost manufacturer can sell or distribute their product to the public, it must meet certain time and temperature requirements to ensure product safety. Testing and finished product analytical requirements depend on the facility type and division managing their permit. Additionally, a facility may choose to participate in voluntary tests and/or certifications to verify quality and assist in marketing their products.
This guidance is not a substitute for the applicant reviewing and understanding the applicable North Carolina Statutes and Administrative Code.
See the NC Compost Rules 15A NCAC 13B .1407 Classification, Testing, and Distribution of Solid Waste Compost Products to learn more about testing requirements for Solid Waste Facilities.
Testing Requirements for Permitted Facilities
Compost or mulch that is produced at a Type 1 Solid Waste Compost Facility must meet the following conditions to be classified as Grade A and have unrestricted application and distribution:
- Free from offensive odor;
- Contains no sharp particles; and
- Compost process maintained at or above 55 degrees Celsius (131 degrees F) for three days and aerated to maintain elevated temperatures.
Compost analytical testing is not required for Type 1 compost if the above temperature requirement has been met and documented.
Type 2, 3, and 4 Solid Waste Compost Facilities have stricter testing requirements because of the pathogen risk for the type of feedstocks processed. Compost produced from these facilities must be sampled and analyzed as described below:
Conduct metal and pathogen testing at intervals of every 20,000 tons of compost produced or every six months (whichever comes first).
Meet the metal and pathogen concentrations set forth by federal regulations.
A fecal coliform or salmonella test is accepted for pathogen testing and must not exceed concentration limits listed in 40 CFR 503.32(a)(3).
Analytical testing methods must be in accordance with procedures from the EPA’s SW-846 Compendium or U.S. Department of Agriculture/U.S. Composting Council's publication "Test Methods for the Examination of Composting and Compost" (TMECC) unless an equivalent method has been approved by NCDEQ.
| Metal Testing Required for Compost Products | Facility Required |
|---|---|
| Arsenic | Type 3 & 4 |
| Cadmium | Type 2, 3, & 4 |
| Copper | Type 2, 3, & 4 |
| Lead | Type 2, 3, & 4 |
| Mercury | Type 4 |
| Molybdenum | Type 2, 3, & 4 |
| Nickel | Type 2, 3, & 4 |
| Selenium | Type 3 & 4 |
| Zinc | Type 2, 3, & 4 |
Optional Testing for Compost Facilities
Compost manufacturers may choose to test their products for persistent herbicides, though it is currently not a state requirement.
Compost manufacturers may find it helpful to test their compost for carbon dioxide (CO2) and ammonia (NH3) emissions. These readings indicate compost maturity, or whether or not compost is finished and ready to be used. Tools like the Solvita Compost Maturity Test are available for independent purchase and use or can be added to some testing lab orders.
The Compost Testing Laboratories Serving NC list (linked above) was produced by the Division of Environmental Assistance and Customer Service (DEACS). DEACS is a non-regulatory division of the N.C. Department of Environmental Quality (DEQ). The information contained in this list is based on data supplied by listed organizations; some information may have changed since it was collected. This list may not be all-inclusive or comprehensive. DEACS does not recommend or endorse the services or products of any particular company listed herein.
NC Department of Agriculture and Consumer Services (NCDA&CS) provide waste and compost testing to both in-state and out-of-state farmers, producers, and homeowners. The lab offers a standard analysis with the option to add additional tests to the standard panel.
Standard analysis: total nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, zinc, manganese, copper, boron, sodium, and aluminum
- Samples qualify for in-State if they were collected in North Carolina.
Optional tests: Inorganic nitrogen (NO3-N & NH4-N), heavy metals (As, Cd, Cr, Ni, Pb, and Se), calcium carbonate equivalent (CCE), Molybdenum (Mo)
- Customers must have also requested a standard analysis.
Note: NCDA&CS soil laboratory does not offer pathogen testing, therefore only using this lab does not meet the full testing requirements for the NC Compost Rules (15A NCAC 13B .1407)
Voluntary Certifications
Compost manufacturers can apply for voluntary certifications to better market their material. These certifications ensure the safety and quality of their compost. Two of the most common certifications are Seal of Testing Assurance (STA) Certified Compost and the Organics Materials Review Institute (OMRI) certifications. Certified compost meets strict quality, safety, and environmental standards, while ensuring compost is made from organic materials and processed to eliminate pathogens and contaminants.
Seal of Testing Assurance (STA) is a program administered by the US Composting Council (USCC) that certifies compost is high-quality and meets rigorous testing from a STA-certified lab.
The Organic Materials Review Institute (OMRI) is a nonprofit that reviews and lists the input products, such as fertilizers, pest controls, and livestock care products, that are compliant with organic standards. OMRI does not certify food or fiber products as organic.
A compost manufacturer may decide to pursue an OMRI listing to market their product to organic producers.
Home Composters
While commercial composting operations are required to test finished material before distribution, residents composting material at home are not required to have any testing done. See subsection15A NCAC 13B .1402 (f) of the NC Compost Rules for details.
Need help composting at home? Check out the Guide to Backyard Composting.