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• ~i <br />EXECUTIVE SUMMARY <br />The data presented in the reviewed document is well presented and focuses on the issues <br />of likely acid generation and metals mobilization from the Cresson overburden materials. <br />In analyzing both the composition of the Cresson materials and their behavior in various <br />dynamic tests, the authors present credible arguments for the relationship of these <br />materials to the general complex of materials in the Cresson depositional environment and <br />to the likely reactions which have gone on and continue during the post-depositional <br />weathering of that deposit. <br />Both bulk analytical data and data on the dynamic behavior of a variety of materials at the <br />project site are presented. The results of the bulk testing have identified compositional <br />levels of both major, minor, and trace elements in the various materials and the dynamic <br />tests have modeled behavior of these materials under laboratory conditions which simulate <br />exposure in the natural environment. <br />The materials reported on were shown to contain varying levels of pyrite as the primary <br />potential acid forming mineral and varying levels of basic minerals which might react with <br />acid formed when pyrite is oxidized by atmospheric oxygen in the presence of water. <br />In most samples, the materials which were highest in total sulfur content were also highest <br />in sulfide sulfur and the majority of that sulfide sulfur was present in the form of pyrite. <br />Thus, the potential for acid generation in these materials is generally directly related to the <br />amount of total sulfur in the sample. <br />While all of the samples tested contained low levels (typically less than 200 parts per <br />million or less than 0.02%) of any environmentally significant trace elements, the potential <br />for mobilization or solubilization of these elements was highest for the samples which <br />showed highest levels of acid release. <br />Based upon the results of the testing, the authors of the report have proposed a <br />management approach for the Cresson overburden materials which centers around <br />segregating materials based on total sulfur content and then handling the resultant two <br />groups of materials in different ways. Sulfur determinations to classify materials would be <br />performed with the Leco sulfur analyzer. <br />The TYPE A material with lower total sulfur content (proposed as <0.8%) is postulated <br />to present a minimal risk of developing acid drainage and thus of mobilizing trace metals. <br />This material would be deposited in Arequa Gulch, near the site of the ore leaching pads. <br />In earlier mine plans, this area was to be a repository for overburden materials but the <br />plans were to segregate the higher sulfide materials in the center of the disposal area and <br />surround them with the more acid neutralizing and lower sulfur waste materials. <br />OMLR951DEH <br />