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'~ <br />The TYPE B material with higher sulfur content (>0.8%) represents the material with the <br />higher risk of acid generation and metals mobilization. This overburden would be <br />disposed of as fill in the Ironclad, Globe Hi11, and Cresson pits. The Ironclad and Globe <br />Hill pits aze currently available to receive waste overburden while the Cresson pit would <br />not be a suitable disposal site until later in the mines life. <br />Data presented in the report on the existing quality of waters in the Arequa Gulch <br />drainage were compared with the effluent from laboratory test cells (humidity cells) <br />containing Cresson overburden materials. In some cases, waters which had contacted the <br />Cresson materials were of compazable quality with respect to acidity and trace metals to <br />the naturally occurring waters from Arequa Gulch. In other cases, particularly the waters <br />contacting the higher sulfide materials, the etlluents were more acidic (had lower pH <br />levels) and/or contained higher levels of trace metals (most typically zinc) than the Arequa <br />Gulch water. <br />Data presented on the laboratory simulated release of acid and metals from a selected suite <br />of waste rock taken from sites in the vicinity of the Cresson project suggest that they <br />behave much like some of the (higher sulfur content) Cresson materials. Earlier reports on <br />the Cresson project have suggested that there is no significant evidence of highly acid <br />discharges from existing waste materials in proximity to the project (such as these waste <br />rocks) even though these materials have been exposed to ambient oxidation and leaching <br />for relatively long times. <br />While there is a recognition in the report that the overburden materials have a varying risk <br />for acid release and metals mobilization, and while a plan is put forth to segregate these <br />materials on the basis of sulfur content and thus on the probable basis of acid development <br />risk, there is little discussion of the need or plans for monitoring waters from the disposal <br />areas where highest sulfur materials aze stored. <br />If the highest sulfur materials are deposited in the Ironclad, Globe Hill, and Cresson pits as <br />proposed, then monitoring of the quality of any waters accumulating in those pits and <br />techniques for detecting seepage from the pits should be considered. In the cases of the <br />Ironclad and Globe Hill pits, drainage or seepage would appeaz to enter Squaw Gulch and <br />the report makes no mention of monitoring of waters in that location. <br />If acid development and/or metals mobilization in the in the Cresson overburden <br />repository prove to be a problem, then it will be necessary to address ways to minimize the <br />amount of this eflluent, to deal with any discharge from the contairunent area if necessary, <br />and to assure control over future risk of polluted water discharge. Options might <br />including capping of the area, provision for pumping and treating contaminated waters, or <br />possibly for modifying the overburden depositional process to include some grinding of <br />waste rock with excess neutralization capacity and incorporating it or another basic <br />material in with the higher sulfur waste rock. My approach will require careful analysis <br />from both a technical and cost standpoint since large amounts of material and capital are <br />likely to be involved in any of these or other choices. <br />OMLR951DEH <br />