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account of a waste. A ratio of NP to AGP of less than 3:1 indicates that an acidic leachate may be formed, while a ratio of NP to AGP of 3:1 or greater indicates that an acidic leachate will probably not be formed by the waste The selection of the 3:1 ratio,in which NP Wemainly eds AGP, accounts for the greater leachability of many of the minerals responsible for carbonates) as compared with those responsible for AGP(mainly sulfides), and accounts for the uneven distribution of these rxunerals within a waste which may cause localized pockets of acid generation. The results of the acid-base account would indicate which extraction solution should be used in the WET. The citrate buffer is appropriate for any waste which has a NP to AGP ratio of less than 3:1. Deionized water could be substituted for the citrate buffer for wastes having a NP to AGP ratio of 3:1 or greater. (In some cases,it may be appropriate to adjust the deionized water to the pH of local rainwater to be able to assess the resulting leachability of waste constituents from this increasingly important environmental factor.) The appropriateness of choosing deionized water may cross checked by performing other analytical procedures such as the use of the humidity cell method, which attempts to demonstrate acid generation in accelerated bench scale oxidation test.' Analysis for Volatile Constituents The current WET procedure cannot be used to accurately determine extractable concentrations of purgeable (volatile) constituents of a solid waste. Examples of these constituents include trichloroethylene,vinyl chloride and other volatile organic contaminants (VOCs) and organic lead compounds. Due to their high vapor pressures and Watively low solubilities in water, significant fractions of the concentrations of these nstituents would be lost to the air space(head space)in the extraction vessel during the extraction procedure. Losses to the atmosphere would also occur during other portions of the waste and extract handling phases of the WET. For these reasons, soluble or extractable concentrations may not be used as an accurate measure of the potential threat to water quality posed by most volatile components of wastes. Total concentrations must be used. however,recognizing the need for an extraction procedure for volatiles, the U.S. EPA has proposed a new test called the "Toxicity Characteristic Leaching Procedure" or TCLP.7 k This procedure includes a "Zero Headspace Extraction Vessel" in which extractions for volatile constituents could be performed without appreciable loss to the atmosphere. If these or other similar vessels become available for general use,they could be substituted for the standard vessel in the WET,making extraction for volatiles possible. 3.2 Water Quality Goals The basis of the Designated Level Methodology is the assessment of concentrations of - waste constituents which, if equalled or exceeded,could be mobilized and transported to ground and/or surface waters in amounts which would cause degradation of the quality of those waters. The assessment must, therefore,begin with the identification of the bodies of water which could be affected by a particular waste disposal and of numerical parameters ,lWdicative of existing water quality at the proposed site of waste disposal. These parameters will be called "water quality goals" in this report. Page 24 Designated Level Methodology `I J