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Longfellow Koehler Project <br /> Page 2 <br /> Description - Cont <br /> Surface diversion of waters is planned to prevent contact with waste material that may lower <br /> the pH of intermittent streams as well as provide a source for heavy metals. <br /> The collapsed portal of the Koehler adit will be opened and studied for the placement of a <br /> hydraulic seal. In order for a hydraulic seal to be placed, SGC feels that a site meeting the following <br /> conditions needs to be found. <br /> 1) Location far enough underground to avoid the near surface fractures and joints caused <br /> by weathering. <br /> 2) Adequate rock compressive strength for structural stability. <br /> 3) A length of the tunnel with minimal faulting and other geologic features that may be a <br /> leakage pathway. <br /> 4) Adequate ground cover over the potential site to resist the hydrostatic forces from the <br /> potential maximum head. <br /> If an acceptable location can be found, SGC will design and install a hydraulic seal. After <br /> sealing is complete,the seal will be contact grouted and the diversion pipe grouted. The near surface <br /> fracture flows typically found will be diverted to avoid contact with waste material and the portal <br /> closed. Surface disturbances will be pH adjusted with the use of limestone addition and planted. <br /> A section 404 permit from the Army Corps of Engineers may be needed for the work in the stream. <br /> See attached paper on hydraulic seals. <br /> Analysis <br /> The headwaters of North Mineral Creek currently have a low pH and are laden with heavy <br /> metals. Removal and consolidation of the mine dumps (including pH stabilization)will isolate this <br /> material from direct contact with rain waters, snow melt and flows from intermittent streams and <br /> neutralize the acid generation process already in progress. These Best Management Practices may <br /> improve the conditions of the headwaters of Mineral Creek. <br /> The hydraulic seal proposed for the Koehler Adit will reduce the unsaturated zone by <br /> removing the drain. This will result in minimizing the oxygen available for reaction with the sulfide <br /> minerals in the area. The hydrological conditions will be restored to an approximation of premining <br /> conditions and should improve the water quality in the area. <br />