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9/30/93 <br />Responses to Comments <br />San Luis Reclamation Evaluation Report <br />Page 7 <br />The geochemical program utilized for the Reclamation Evaluation <br />Report has been used to characterize mine waste throughout the <br />world and is recognized by geochemical experts as not only <br />appropriate, but also as having reliability when com ared to <br />actual field results. The Canadian government com~leted a <br />study in 1989 which evaluated all methods for characterization <br />of the acid generating potential for mine waste material (and <br />the subsequent ability to mobilize metals). This study is <br />entitled "Investigation of Prediction Techniques for Acid Mine <br />~ <br />~ <br />Drainage" and was performed by Coastech Research Inc. for the 11,,,.w, <br />" <br />~f <br />Canada Centre for Mineral and Energy Technology, Energy, Mines ~`~~ {.:~ ~Y- , r <br />and Resources Canada. The study showed that the humidity cell /,, t <br />~~FO,,r. <br />~ <br />test method was the most accurate test method for det@rmining ~ <br />~r~ r <br />actual acid generating potential of mine waste. A copy of this ~Q' <br />paper is included with these responses. <br />The geochemical test program focused on those species which <br />could be mobilized from the tailings. Only if the chemical <br />species from the tailings can be mobilized will they Mave the <br />potential to be transported. It is worth noting, however, that <br />as previously discussed the tailings themselves have similar <br />permeability characteristics to an earthen soil liner and it is <br />highly unlikely that water movement through the tailings will <br />occur, therefore potential leachability will be further limited <br />by the physical characteristics of the material itself. <br />As in the approved permit amendment, the reclamation evaluation <br />test program had three main components: 1) acid geherating ~ <br />potential/acid neutralizing potential (AGP/ANPI), 2) 2 <br />leachability using the U.S. Environmental Protection llgency's ., <br />(EPA's) Method 1312 leachability testing, and 3) humidity cell <br />testing. Each of these test methods is described in detail in <br />the Reclamation Evaluation Report and will not be rep@ated in <br />this preamble. However, there are several aspects of the test <br />program which raised questions among the reviewers and will be <br />discussed further. <br />4.1 Acid Generating Potential/Acid Neutralizing Potential <br />(AGP/ANP1 <br />The AGP/ANP tests were extremely conservative since they based <br />the AGP determination on total sulfur. The evaluation 0f total <br />sulfur is conservative, since the AGP number assumes tthat all <br />sulfur is present as sulfides and that all sulfides are <br />chemically reactive and will generate acid. This assumption is <br />not true, particularly in the case of tailings such as those at <br />the San Luis facility which have been treated using some form <br />