TCLP and WET Test Methods

Toxic List swf

Toxic Characteristic Leaching Procedure (TCLP) and Waste Extraction Test (WET) are test methods used in California to determine whether a waste is a toxic hazardous waste. They are similar in that they:

  • simulate what happens to a waste in a landfill setting with simulated landfill leachates and are both reported in milligrams of chemical per liter of extractant, and
  • have a list of chemicals with concentration thresholds (regulatory thresholds), and are used to determine toxicity.

However, the similarity ends there: TCLP is not interchangeable with the WET and total analysis is not interchangeable with TCLP or WET.           

The main differences between TCLP and WET are found both in laboratory analysis methods and the regulated chemicals that are tested:


TCLP WET
Involves 20-fold dilution of the solid portion of the waste to extractant fluid Involves a 10-fold dilution of the solid portion of the waste to extractant fluid
Acetic acid extractant Citric acid extractant
18 hours extraction 48 hours extraction
7 inorganic (less aggressive than WET) 19 inorganic (in general, more aggressive than TCLP)
23 organic (volatiles use a zero headspace extractor) 18 organic (zero headspace extractor not used)

When a chemical in a solid waste is 100% soluble in the waste, then the theoretical maximum extractable concentration is:

    • TCLP: 1/20 the total concentration
    • WET: 1/10 the total concentration

For example, let’s say a solid waste has a 530 mg/kg total lead concentration. Without conducting a TCLP or WET, the theoretical the maximum soluble results are:

TCLP Wet swf