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In the ever expanding world of regulatory acronyms TTLC, STLC, and TCLP seem to cause more than their share of confusion and questions. Here are some of the most often asked questions that we receive about these analyses and some basic information to help answer them.

• What does TTLC, STLC and TCLP stand for? • When do I need STLC or TCLP analysis? • Why is 10X the STLC limit referred to when looking at TTLC results? • What is the difference between STLC and TCLP?

TTLC and STLC are used when determining the hazardous waste characterization under California State regulations as outlined in Title 26 of the California Code of Regulations (CCR). TCLP is the characterization based on Federal guidelines. These apply to organic as well as inorganic analytes. The intent of the leachate procedures are to simulate the conditions that may be present in a landfill where water may pass through the landfilled waste and travel on into the groundwater carrying the soluble materials with it.

TCLP, STLC, TTLC - Hazardous Waste Characterization

TTLC - Total Threshold Limit Concentration

This analysis determines the total concentration of each target analyte in a sample. Samples are analyzed using published EPA methods. When any target analyte exceeds the TTLC limits the waste is classified as hazardous and its waste code is determined by the compound(s) that failed TTLC. The results of this analysis can be used to determine if analysis for STLC level is necessary by comparing 10 times the STLC limit to the TTLC results. A factor of ten is necessary to compensate for a 1:10 dilution factor that is present in one analysis but not the other. If the TTLC results do not exceed 10 times the STLC limit then normally no further analysis is required.

STLC - Soluble Threshold Limit Concentration

This analysis determines the amount of each analyte that is soluble in the "Waste Extraction Test", (W.E.T.) leachate. This W.E.T. leachate procedure is used for solid samples or for samples containing > 0.5% solids. The sample is tumbled in 10 times its weight of a 0.2M sodium citrate buffer for 48 hours. This leachate is then analyzed to determine the soluble concentrations.

Environtmental Testing - TTLC, STLC, TCLP

TCLP - Toxicity Characteristic Leaching Procedure

This analysis, like the W.E.T., determines the soluble portion of the analytes. This is a Federal guideline and differs from the State in several ways. The alkalinity of the sample must first be determined in order to know which of two different extraction fluids should be used. Samples with a low alkalinity use extraction fluid #1 which is a sodium acetate solution with a pH of 4.93. Samples with a high alkalinity use extraction fluid #2 which is a dilute acetic acid solution with a pH of 2.8. The sample is then tumbled in the appropriate extraction fluid for 18 hours. However the choice of extraction fluids does not apply to volatiles. When analyzing for volatiles, fluid #1 is always used and a Zero Headspace Extraction (ZHE) apparatus is required.

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