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_~ <br /> <br />other waste dump areas. These dump areas not only increase the <br />areal extent but provide considerably more surface area <br />exposure of sulfides to infiltrating waters. <br />3) The neutralizing capability of the mining area in contact <br />with the ARD is less than assumed. The diatreme is not <br />uniform down to the level of the Carlton Tunnel; the <br />unmineralized part of the diatreme considered to have acid - <br />neutralizing capability is only a layer of the diatreme and <br />comprises a greater percentage of rock at the surface than it <br />does at depth. <br />4) The HCI models do not predict the Zn (or other metals) <br />content of the discharge due to insufficent data. <br />As a result of the above, the Division considers that HCI has, thru <br />their calculations and modeling, failed to adequately support their <br />conclusion that there is no potential for a significant impact of <br />the mine on the Carlton Tunnel discharge. <br />The Division understands that CC&V intends, at this time, neither <br />to cover the Ironclad dump nor to introduce neutralizing agents <br />into the material to reduce the acid-generating potential. As <br />stated to you during the meeting on April 4, 1997, however, the <br />Division believes that the change made in the value used by the <br />mine to separate "high" sulfide rock from low for disposal <br />purposes, ie. from 1.8 % to 0.8% sulfide, did not eliminate the <br />requirement for the use of neutralizing agents in the high sulfide <br />disposal site. Apparently that was not the mine's understanding <br />since neutralizing materials have not been employed during the <br />disposal. This may become a serious compliance issue since it <br />appears to the Division that there are few alternatives remaining <br />to relieve the Division's clear concern regarding the potential <br />impacts of ARD from the mine. If, however, an agreement could be <br />reached with CC&V to appropriately cover the Ironclad dump and to <br />bond for that cover and interim water treatment until the cover was <br />installed, the Division would be satisfied that some acceptable <br />effort had been made by CC&V to address this troublesome issue. <br />Although the HCI reports did not consider the impacts of ARD from <br />the Cresson Pit and overburden dumps on other than the Carlton <br />Tunnel discharge, the quality of that discharge is not the only <br />ground water concern in the area of the mine. As a result of <br />recent study of the limited data available, the Division is aware <br />that the shallow groundwater in the diatreme in the immediate <br />vicinity of the pit and overburden dumps may not be suitable for <br />beneficial use. However, ground water outside of the diatreme has <br />demonstrably better quality, ie. potentially qualifying for <br />domestic or agricultural use. Because the Arequa Gulch dump appears <br />to extend beyond the margins of the diatreme and either now or in <br />the future may contain overburden with acid generating potential, <br />some effort to protect this down-gradient groundwater is considered <br />necessary. The Division understands that the Arequa Gulch dump <br />will be covered and will therefore have its acid-generating <br />