The EPA began developing the RCRA regulations and the definitions of hazardous waste in the late 1970’s. During that time their primary focus was on establishing the listings and characteristics necessary to properly identify which wastes deserved to be regulated as hazardous. As with most things, however, people had questions and concerns.

One such question asked, “Once a waste is identified as hazardous, what happens if that waste changes in some way? If the hazardous waste is changed, either by mixing it with other wastes or by treating it to modify its chemical composition, should it still be regulated as hazardous?” Due to the pressure to make decisions on these types of difficult questions quickly the EPA decided on a fairly simple and strict answer. They developed the mixture and derived-from rules.

One of the most important things to know about these rules is that they operate differently for listed waste and characteristic wastes. For listed wastes, the mixture rule says that a mixture made up of any amount of a nonhazardous solid waste and any amount of listed waste is considered a listed hazardous waste. So basically, if you have 10 pounds of nonhazardous waste and you mix it with 8 ounces of listed hazardous waste, your entire 10 pounds 8 ounces becomes a listed hazardous waste and bears the same waste code and regulatory status of the original listed component of the mixture. This principle applies regardless of the actual health threat posed by the waste mixture or by the mixture’s chemical composition.

The derived-from rule deals with the regulatory status of materials that are created by treating or changing a hazardous waste in some way. For example, if you have a hazardous waste and you send it to an incinerator, the resulting ash is considered derived-from the initial waste. For listed wastes, this rule means that any material that comes from the changing of a listed waste is a listed waste which bears the same waste code and regulatory status as the initial listed waste.

Basically this all means that if a waste matches a listing description it will never not be considered a hazardous waste, no matter what is done to it. Additionally, any material that comes into contact with a waste that matches a listing description is considered a listed waste, regardless of actual chemical composition.

The reason these rules are so strict it because if the EPA relied on the narrative listings alone to decide when a waste stopped being hazardous, industry might be able to easily go around regulations. For example, a generator or handler could mix two different wastes and say that they no longer perfectly matched the waste description and as such were no longer in need of regulation. This would be dangerous because the chemicals would still pose the same risks to human health and the environment. These rules also help encourage generators and handlers to keep listed wastes well segregated from other nonhazardous or less dangerous wastestreams since the more listed waste you have the more storage, treatment, and disposal you’ll have to pay for.

We mentioned above that the mixture and derived-from rules are different for characteristic wastes. This is because characteristic wastes can change once they no longer exhibit their hazardous characteristic. So, if a flammable waste is mixed with something that makes it cease to be flammable, it is no longer considered hazardous. Similarly, treatment residue or materials derived from characteristic wastes are only hazardous if they continue to exhibit the hazardous characteristic.

All information for this blog post was gathered from the EPA document, “Introduction to Hazardous Waste Identification.” As always, this blog post is not intended to be comprehensive and it is always best to check with the EPA and local government for full, up-to-date, rules and regulations.