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Toxicity characteristic leaching procedure (TCLP) is a soil sample extraction method for chemical analysis employed as an analytical method to simulate leaching through a landfill. The testing methodology is used to determine if a waste is characteristically hazardous (D-List). The extract is analyzed for substances appropriate to the protocol.
In the United States, the Resource Conservation and Recovery Act (RCRA) of 1976 led to establishment of federal standards for the disposal of solid waste and hazardous waste. RCRA requires that industrial wastes and other wastes must be characterized following testing protocols published by the Environmental Protection Agency (EPA). TCLP is one of these tests.
The Environmental Compliance Supervisor (the "gatekeeper") at a typical municipal landfill (as defined by RCRA Subtitle D) uses TCLP data to determine whether a waste may be accepted into the facility. If TCLP analytical results are below the TCLP D-list maximum contamination levels (MCLs) the waste can be accepted. If they are above these levels the waste must be taken to a hazardous waste disposal facility and the cost of disposal may increase from about $20/ton to as much as $500/ton.
TCLP comprises four fundamental procedures:
As extremely contaminated material is expensive to dispose, grading is necessary to ensure safe disposal and to avoid paying for disposal of "clean fill." The TCLP procedure is generally useful for classifying waste material for disposal options.
A concern has arisen in recent years regarding TCLP analysis in that the test is based on the assumption that the waste material will be buried in landfill along with organic material, however organic matter is rarely buried with other waste anymore (composting usually applies).[dubious ] In light of this issue, other leachate techniques may be more appropriate.
Spent abrasive or soil from a construction site usually need to have a TCLP for lead done to determine where the waste goes next.
In the TCLP procedure 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. For example, a TCLP jug may contain 100g of sample and 2000 mL of solution. The leachate mixture 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. It is then filtered so that only the solution (not the sample) remains and this is then analyzed.