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Potentially Unstable and Active Landslide Areas <br />The Division has expressed concern about several potentially unstable mapped landslide areas which <br />have been delineated on Exhibit 6-1, Site Specific Geology. These areas will be field verified during <br />the 1993 field season. Since the majority of these potentially unstable areas will not be affected until <br />1999 or later, Seneca will continue to monitor those areas which have been field verified. <br />Additional field verification of the initial geologic and geotechnical mapping of the areas, where Haul <br />Roads C, D, and B extension are proposed, has been completed. A geotechnical analysis of these <br />proposed facilities, will be completed, based on the results of the mapping and subsequent report <br />which will be an addendum to the existing Attachment 13-6. <br />Recommendations for any measures required to ensure the stability of these facilities will be <br />implemented during construction. <br />The mining plan may be revised to minimize the disturbances in these areas based on the outcome of <br />the field surveys and the mining operations which will occur near these areas. In accordance with <br />Rule 4.12121, should any landslides occur, the Division will be notified immediately and a monitoring <br />and remediation plan submitted for approval and implementation. <br />• SCC's experience at the Yoast Mine and at the Seneca II-W operation has shown few problems with <br />"surficial" landslide areas, none of which were significant or life threatening. The only slide of any <br />"consequence" occurred in the II-W area and resulted in a portion of a topsoil stockpile sliding into the <br />pit. An in-depth geological and geotechnical study, associated with pond embankments and haul road <br />construction, was conducted in the Seneca II-W area in 1992. This study served to reinforce the <br />applicability of the methods and measures that Seneca typically uses to design and construct facilities. <br />The strata generally dip steeply toward the west, while the area of concern occurs on an east-facing <br />slope indicating a potential for shallow surficial sloughing rather than deep-seated failure. As <br />mentioned in the Amuedo and Ivey report 11992) for the general area of II-W, the potentially unstable <br />areas do not exhibit the characteristics of catastrophic failure. The mapped landslide area exhibits <br />localized sloughing and hummocky ground, however, more significant rotational slides have not been <br />observed in the area. The nature of the instability is characteristic of creep or slow-moving types of <br />shallow surficial failure (i.e., surficial landslidesl. <br />surficial is geologically defined as: "Characteristic of, pertaining to, formed on, situated at, or <br />occurring on the earth's surface; especially, consisting of unconsolidated residual, alluvial, or glacial <br />deposits lying on bedrock." <br />• <br />PR-02 <br />10 <br />Revised 03/05 <br />