TCLP or WET Method? Determining Hazardous Waste Toxicity

Posted on 2/3/2017 by Roger Marks

This blog is intended to help EHS professionals in California achieve compliance with the unique, additional DTSC rules for managing hazardous waste in the Golden State. 
When hazardous waste is disposed of in a landfill, a small amount of the toxic constituents in the waste may “leach out” into the soil and groundwater. To mitigate the risks posed by chemicals seeping out of buried waste, US EPA requires generators to prove that the volume of hazardous substances that will “leach out” into the environmental is below thresholds set by US EPA. 
Two major test methods for determining “leachability” and identifying hazardous wastes are the Toxic Characteristic Leaching Procedure (TCLP) and the Waste Extraction Test (WET). While these two tests share a common goal, critical differences between the two methods make selecting the right test crucial to compliance. 

The TCLP and WET Tests for Toxic Hazardous Wastes 

hazardous waste managementThe TCLP and WET tests are designed to measure the hazardous waste characteristic of “toxicity” for the purpose of identifying hazardous wastes. 
The TCLP is the only method approved for use under the Federal RCRA hazardous waste regulations. That said, hazardous waste requirements often vary by state. California, for example, may require the use of the WET test in addition to the TCLP to determine toxicity. 

What’s Similar About the WET and TCLP Methods?

While the TCLP and WET methods share some similarities, they are not interchangeable. That said, the three most striking similarities are: 
  • Both the TCLP and WET methods use leachate solutions to simulate a landfill environment and determine how much of a hazardous constituent will “leach out” of the waste. 
  • Both measure their results in milligrams (of hazardous chemical) per liter (of leachate). 
  • Both reference lists of chemicals and acceptable thresholds for toxicity.

How Are the WET and TCLP Methods Different?

There are a number of differences between the two tests. Of the two, the WET method is the more stringent measurement of leachability. 
Major differences between the TCLP and WET include: 
  • The TCLP uses acetic acid as an extractant, while the WET uses citric acid. 
  • The TCLP calls for a 20-to-1 dilution of solid waste to extractant fluid. The WET calls for a 10-to-1 dilution. 
  • The TCLP measures results over 18 hours, while the WET lasts 48 hours. 
  • The list of hazardous constituents under the TCLP procedure covers 30 materials (23 organic, 7 inorganic). The WET list covers 38 (18 organic, 19 inorganic). 

When Should I Run the WET Test?

If you are managing waste under Federal RCRA rules, the TCLP is the only accepted method for determining leachability. 
In California, however, there may be cause to run both tests. If the waste tests positive for the toxicity characteristic under TCLP, no further testing is necessary. Wastes identified as hazardous under the EPA’s RCRA rules are always hazardous wastes in California. 
If you test your waste using the TCLP and the result is “too close to call,” you may then run the Waste Extraction Test to verify your results. In California, if the results of the WET indicate the waste is hazardous, it must be managed as hazardous under DTSC’s Title 22 regulations and the California Health and Safety Code. 
Lastly, as mentioned above, the WET is the more stringent test and California’s list of toxic constituents is more expansive than the Federal RCRA list. So, even if your waste is not a RCRA hazardous waste based on the TCLP, the WET may still be required to ensure your waste is not regulated as a non-RCRA hazardous waste in the state of California.  

Knowing which test or tests to run is crucial to make sure all potentially hazardous waste at your site is properly identified and managed. DTSC fines for hazardous waste management mistakes are as high as $25,000 per day, per violation, and EPA’s RCRA civil penalties just rose for the second time in 6 months. 

Next Month: Title 22 Hazardous Waste Training for California Generators

If you manage hazardous waste in California, you must know the unique, stringent Title 22 requirements that apply to your site. Knowing the Federal rules is not enough—California’s hazardous waste regulations are more complex and stricter than the US EPA RCRA standards.  At the Hazardous Waste in California Workshop, learn the latest rules, discover exceptions and reliefs you can use, and be confident you know what it takes to keep your site safe and in compliance.

San Diego – March 27—28 

Ontario – March 30—31 

San Jose – April 3—4

Sacramento – April 6—7 

Can’t make the workshop this year? The same expert training is now available in an interactive online course format. Packed with exercises to keep you engaged, this online course is an effective, convenient way to meet DTSC’s annual training requirement for hazardous waste personnel.  

Tags: California, CUPA, hazardous waste, RCRA, Waste ID

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