This is the second in a series of columns on endangered test methods. Last time we discussed the fate of the test for Total Petroleum Hydrocarbons (TPH). Now we turn our attention to a controversial proposal to eliminate the use of the Waste Extraction Test (WET) for hazardous waste identification in California.

The WET was originally developed as part of guidance called the California Assessment Manual (CAM) - some labs still refer to the regulated elements as the "CAM Metals." The test was originally a series of four sequential extractions over a period of 30 days, in order to simulate what might leach from a waste if disposed in a municipal landfill. In response to objections over the sequential extractions, the test was shortened to a single 48-hour extraction, using a 0.2 M citrate buffer at pH 5.0. At the time the WET was adopted into regulations, the U.S. EPA had already adopted the Extraction Procedure (EP), the predecessor to the Toxicity Characteristic Leaching Procedure (TCLP), which is currently used in RCRA federal hazardous waste criteria.

The principal difference between the WET and the TCLP is the use of citrate in the WET vs. acetate in the TCLP. Citrate is known to chelate several of the regulated elements; acetate generally forms weaker complexes with regulated elements. As a result, the WET is generally more aggressive than the TCLP in extracting elements from wastes.

The California Department of Toxic Substances Control (DTSC) is currently conducting a Regulatory Structure Update (RSU) of hazardous waste regulations. As part of the RSU, DTSC is proposing changes to the definition of a hazardous waste. The Department had proposed elimination of the WET, but the proposal received challenges from some members of the RSU External Advisory Group, which represents a variety of interested parties. DTSC's Hazardous Materials Lab then conducted a study of the extraction of elements, comparing the extraction using the WET, the TCLP, and extraction with actual leachate from municipal solid waste (MSW) landfills in California. One notable result of the study was that the MSW leachates generally had low total organic carbon (TOC); most leachates had TOC less than 1,000 mg/L. The pH of the leachates ranged from 6.2 to 9.0, higher than the pH 5 used in the WET and TCLP. The relatively low TOC and high pH appears to explain why the leachates generally extracted less than either the WET or TCLP. The major conclusion of this study was that the TCLP generally better simulated extraction with MSW leachate than did the WET. One interesting finding was that a few MSW leachates extracted more arsenic than the TCLP, likely because arsenic is generally more soluble in the higher pH of the MSW leachates.

Based on the review of literature and the results of the RSU study, DTSC has begun a Phase 2 study to gather data on elements which were not included in Phase 1, and to do a longer term extraction, up to ten days, to simulate the extraction over a longer time period. Meanwhile, DTSC has proposed to use the TCLP in lieu of the WET and to use the results of the RSU Extraction Project to adjust the regulatory limits, if necessary, to compensate for any deficiencies found in the TCLP.

The elimination of the WET could result in the reclassification of a large volume of waste which is now regulated as non-RCRA hazardous waste. How this waste would be regulated will depend on the overall changes from the RSU process. The current schedule for completion of the draft regulations is June 1997. Until regulations are revised, the WET is very much alive, but its life expectancy may be short.