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Exposure: Chemical Leaching
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Toxicity Characteristic Leaching Procedure (TCLP)

By Jason Zheng

In 1976, the United States formed the Resource Conservation and Recovery Act (RCRA) to establish federal guidelines of the disposal of solid and hazardous waste. The RCRA requires industrial wastes and other wastes to be characterized by the following protocols established by the Environmental Protection Agency (EPA). The toxicity characteristic leaching procedure (TCLP) is also one of these test.

An ideal landfill is defined by the RCRA Subtitle D, the Environmental Compliance Supervisor uses the TCLP data to determine whether a waste may be accepted by the facility. If the TCLP results are below the TCLP D-list maximum contamination levels (MCLs), then the waste can be accepted. The scope behind the TCLP D-list is a testing methodology of classifying hazardous waste. A detailed TCLP D-list can be found here.

The TCLP is composed up of four fundamental procedures: (1) sample preparation for leaching; (2) sample leaching; (3) preparation of leachate for analysis; and (4) leachate analysis.  If the tested waste is above the levels listed in the TCLP D-list then the waste must be taken to a hazardous waste disposal facility. The cost of disposal may be between from about $20 per ton to as much as $500 per ton. Extremely contaminated material is generally expensive to dispose because there are addition protocols to adhere to ensure safe disposal.

One of the main concerns regarding to TCLP analysis is that the test is based on the assumption that the waste material will be buried in landfill along with organic materials. However, organic matters are rarely buried to accompany waste. It is necessary to develop more efficient leachate techniques. Another problem is that abrasive or soil from a construction site needs to be examined according by the protocols of TCLP in order to determine the destination of the waste.

When TCLP testing, the pH of the sample is first determined, and then leached with an acetic acid or sodium hydroxide solution of 1:20 mix of sample to the solution. Then the leachate mixture is sealed in an extraction vessel or pressure sealed as in “zero-headspace extraction” (ZHE) for volatile organic compounds and tumbled 18 hours to simulate the leaching time in the ground. The waste is then filtered so that the solution (not the original sample) remains and then analyzed.


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