Prior to discarding a material, a waste determination process must be undertaken to decide how to dispose of it appropriately and legally.

You can meet waste determination requirements using two methods, sampling and analysis or generator knowledge. Often the preferred method is sampling and analysis of the waste because this method is more accurate and defensible than applying generator knowledge.

If you use generator knowledge alone or in with sampling and analysis, you must maintain detailed documentation that clearly demonstrates the information is sufficient to identify the waste. Documenting both the generator knowledge chemicalsand any analytical data is essential. Documentation used to support generator knowledge may include, but is not limited to:

  • Material safety data sheets or similar documents,
  • A thorough process description, including data on all raw materials used in the process, and/or
  • Other forms of detailed documentation.

In Wisconsin, hazardous waste determination is governed by Chapter NR 661 Hazardous Waste Determination and Listing. Campus environmental managers should be familiar with NR 661 and refer to it often.

Accurate hazardous waste determination:

Step 1 – The first thing you need to determine is that this is solid waste – something you want to discard. It may be a spent item or it may be something you no longer use or you may have an overstock of the item. Don’t be misled by the term “solid waste.” The item can be a gas, liquid or solid – physical state does not matter. NR 661.04(1) contains a list of exclusions, that is, material that is not solid waste for the purposes of hazardous waste determination. NR 661.04(2) contains a material that is solid waste, but is excluded from the definition of hazardous waste for the purposes of hazardous waste determination. If a material is not excluded from the definition of solid or hazardous waste under NR661.04, proceed to Step 2.

Step 2 – To find out if your solid waste is a hazardous waste, check the NR 661 lists. If it appears on one of these lists it is a hazardous waste.

  • The “K” list is waste that comes from a specific process. Most campuses do not generate this type of waste.
  • The “F” lists includes many spent solvents. Campuses may generate waste on this list.
  • The “P” list substances are unused chemicals considered acutely hazardous. P-listed waste has a significant impact on the campus generator status.
  • The “U” list substances are unused chemicals considered hazardous but not as dangerous as the acutely hazardous substances on the P-list.

Step 3 – If a substance does not appear on one of the above lists it may still be a hazardous waste if it exhibits one or more of the “characteristic” hazards defined in NR 661. These include:

Ignitability – flash points < 140 degrees F, is a flammable solid or gas or is an oxidizer. See NR 661.21 Ignitability characteristic.
Corrosivity – pH ≤ 2 or pH ≥ 12.5 or corrodes steel > 0.25 inches per year. NR 661.22 Corrosivity characteristic.
Reactivity – includes air- and water- reactives, pyrophorics See NR 661.23 Reactivity characteristic.
Toxicity – relates to the waste’s ability to contaminate groundwater. Wastes are considered toxic if they release or leach any of 39 specific heavy metals, pesticides or organic chemicals above their regulatory level concentrations. WIDNR logo

   If your solid waste is either a listed substance or demonstrates one of more characteristics defined in NR 661 it is considered a hazardous waste. Hazardous waste must be managed by the
state- approved hazardous waste contract.

    If your waste is not a hazardous waste, it may still be forbidden from landfill or incineration in Wisconsin (see WIDNR Recycling law)


It may also be regulated as a different waste-type under a different chapter. See for example:

Reference material, files, and websites

Wisconsin Department of Natural Resources

Chapter NR 661 Hazardous Waste Determination and Listing

Stony Brook University waste determination presentation
(Rules in other states may vary)

Healthcare Environmental Resource Center (HERC)


This publication was prepared for environmental, health and safety staff at University of Wisconsin System campuses, to assist in finding resources and information for regulatory compliance. It is not intended to render legal advice.

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