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disposed with 'nonhazardous solid waste' in a Class III landfill,if the waste is to be discharged to some other potentially acidic environment,or if the waste itself is capable of generating acidic leachate (see "Acid-Base Account" below), the standard citrate buffer should be used in the WET. If the waste 1s not to be discharged to a Class III landfill with .� 'nonhazardous solid waste' or to some other potentially acidic environment and if the waste is not capable of generating acidic leachate, deionized water could be substituted for r the citrate buffer extract solution in the WET to more accurately assess the leachability of waste constituents. Another reason for choosing to perform a deionized water extraction on a solid waste is to determine the extractable concentrations of constituents or parameters for which the citrate buffer would interfere in the analysis. Common examples are hexavalent chromium (Cr VD, total dissolved solids (TDS), specific conductivity (EC), and pH. As mentioned in Subsection (e) of the WET procedure(see Appendix I), a deionized water extraction must be performed to determine extractable Cr VI concentrations in wastes. In the presence of the acidic citrate buffer,Cr Vi is reduced to trivalent chromium (Cr III), thereby making analysis for Cr VI invalid. The citrate buffer contains dissolved solids and has a fixed pH of 5.0 that can prevent the assessment of TDS, EC,or pH contributed by the waste itself. Deionized water extraction should not replace citrate buffer extraction if the waste is to be discharged to a Class III landfill or some other acidic environment or if the waste itself is capable of generating acidic leachate. Deionized water extraction should be performed in addition to the citrate buffer extraction in these cases where information on extractable Cr ' VI,TDS,EC,or pH is desired. Acid-Base Account Even if the waste is not to be discharged td a Class III landfill with 'nonhazardous solid waste' or to some other potentially acidiCenvironment,acidic leachate could be generated by the waste itself:Thus is particularly true of some mining wastes which contain pyritic minerals.''These-sulfur-containing-minerals become oxidized when the waste materials are--- exposed to air for the first time. The oxidation process produces sulfurous acid-(H1S03), a - -- - mayor component of acid mine drainage. The acidic leachate so formed can readily mobilize toxic heavy metals in the mining waste. However, minerals such as calcium r _ carbonate (CaCO) may also be present in the mining waste which have sufficient capacity to neutralize acid formed from pyrite oxidation. EMining wastes will be discussed further in Chapter 5 below.) In order for the waste to be able to produce acid, the ability of the waste to generate acid must exceed its ability to neutralize acid over the life of the waste management unit in which the waste is to be placed. The potential of a waste to produce acid is termed the "acid generation potential" (AGP), f while the ability of a waste to neutralize acid is called the neutralization potential" (NP). AGP may be expressed in pounds of CaCO3 required to neutralize the acid formed by 1,000 pounds of waste; while NP may be expressed in pounds of CaCO3 equivalents per 1,000 Lpounds of waste. When expressed in these terms, the ratio of NP to AGP is a measure of the overall ability of the waste to produce acid. Analytical procedures exist for determining AGP and NP, and thereby determining the overall acid-base account,of a •� waste.-5,6 Appendix II of this report contains procedures for determining the acid-base Designated Level Methodology rage 23