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Environmental Leachate vs. WET Extracts Waste Extraction Test (WET) extract concentrations (laboratory extractions) are not intended to mimic those in landfill or environmental leachates. As stated in the 1984 Final Statement of Reasons (SOR) for the adoption of the CCR, Title 22 hazardous waste identification regulations, including the WET: "... it was assumed that under environmental leaching conditions the maximum concentration of extractable contaminant in the initial leachate in mg/l would reach, if not exceed, its concentration in mg/kg in the waste. This assumption is valid for the following reasons: "a. In a typical environmental leaching or extraction situation, the ratio of waste to aqueous extractant will be high. EPA has likened the situation to a drop of the leachate percolating through the mass of a landfill (EPA 1980g). "b. Under a range of conditions the mass of contaminant extracted from a waste in terms of mg/kg is largely independent of the waste-to-extract ratio. However, the concentration of the contaminant in the extractant in milligrams per liter varies directly with the ratio (Ham et al. 1980)." In the Designated Level Methodology, as in the SOR for the hazardous waste identification regulations, the initial environmental leachate concentration is assumed to be numerically equal to the concentration in the waste prior to leaching. And further: "The concentration of substances in a laboratory-derived leachate (i.e., extract) is an irrelevant factor,because these concentrations depend on the quantity of extractant, as well as other factors. Under nonequilibrium conditions, the concentration of an extracted substance in the extract will be proximately proportional to the waste-to- liquid ratio maintained during the test (i.e., the more extract solution used, the more dilute will be the extracted substance in the extract). When conducting an extraction in the laboratory, low waste-to-liquid ratios of 1:10 to 1:20 are required for ease in conducting the test (i.e., stirring, filtering, etc.). These low ratios of waste-to- extraction solution artificially lower the resulting concentrations of metals in the extract. "In an actual landfill environment, the waste-to-liquid ratios will be very high as leachate percolates slowly through a deposit of waste. The situation cannot be duplicated in a laboratory batch extraction test. The concentrations seen in laboratory-derived extracts, using low waste-to-liquid ratios, will have no bearing on concentrations existing at any instance within the landfills. "... Within the waste-to-liquid ratios normally used in laboratory extraction tests, researchers have demonstrated that the ratio has little effect on the Quantim of metal extracted."