Toxicity characteristic leaching procedure

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Toxicity characteristic leaching procedure (TCLP) is a soil sample extraction method for chemical analysis.

An analytical method to simulate leaching through a landfill. The leachate is analysed for appropriate substances.

The Resource Conservation and Recovery Act (RCRA) established US federal laws for the disposal of wastes. Industrial waste streams and other wastes must be characterized following protocols laid out in SW-846. TCLP is one of these tests.

The gatekeeper (environmental compliance supervisor) at a typical municiple (Title D) landfill uses TCLP data to determine whether a waste may be accepted into the facility. If TCLP analytical results are below the TCLP D-list MCL's (maximum contamination levels)the waste can be accepted. If they are above these levels, the waste must be taken to a hazardous waste disposal facility. The cost of disposal goes up from about $20/ton to as much as $500/ton.

TCLP comprises four fundamental procedures:

Sample preparation for leaching
Sample leaching
Preparation of leachate for analysis
Leachate analysis

The TCLP procedure is generally useful for classifying waste material for disposal options. Extremely contaminated material is expensive to dispose. Grading is required to ensure safe disposal and to avoid paying for disposal of 'clean fill'. The main problem is that the TCLP test is based on the assumption that the waste material will be buried in landfill along with organic material. Organic matter is not really buried with other waste anymore (composting usually applies) and other leachate techniques may be more appropriate.

The pH of the sample material is first established, and then leached with an acetic acid / sodium hydroxide solution at a 1:20 mix of sample to solvent. The leachate solution is sealed in extraction vessel for general analytes, or possibly pressure sealed as in zero-headspace extractions (ZHE) for volatile organic compounds and tumbled for 18 hours to simulate an extended leaching time in the ground.