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~ III IIIIIIIIIIIII III <br />5 IATE O~ COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of N.vural Resources <br />131 1 Sherman SL, Roam 215 <br />Dc•nvor, Gdurarlu AO2U7 <br />Phone' 1 4071 Ahh~35hi <br />FAY' (.A) f1 fl 1281 Oh <br />DATE: March 30, 1998 <br />TO: Steve Shuey <br />FROM: Allen Sorenson <br />n l <br />~I~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Ruy Romer <br />Governor <br />lames 5. Lnchheul <br />E~ecufive Oinrmr <br />m¢hael B Long <br />RE: 9360 Adit Plug, Homestake Mining Company, Bulldog Mine, Division Director <br />Technical Revision TR-007, Permit No. M-77-215 <br />I offer the following comments on the response package submitted by Homestake Mining Company dated <br />March 16, 1998 related to technical revision TR-007 to the Bulldog Mine reclamation permit. <br />1. The cement type and aggregate gradation proposed by Homestake for the concrete bulkhead are <br />appropriate to this type of installation. <br />2. The specifications provided by Homestake for the bypass pipe aze appropriate. Homestake must <br />further commit to the installation of stainless steel fittings and valve on the bypass pipe. <br />3. The monitoring plan provided by Homestake is not adequate to secure the approval of technical <br />revision TR-007. With the limited and widely fluctuating water quality baseline data in Windy Gulch, it <br />would be difficult to determine if changes in water quality are do to the installation of the 9360 adit <br />bulkhead or some other cause; however, the plan to monitor water quality in Windy Gulch should be a <br />component of the monitoring plan, and Homestake should submit details to incorporate the specific <br />protocols involved. The purpose of the overall monitoring plan must be to detect any significant near-term <br />discharge of water impounded by the bulkhead to the surface water system. Discharges of this type would <br />be point sources subject to regulation through an NPDES permit. It is irrelevant from a regulatory <br />standpoint whether water from the adit entering Windy Gulch is derived from a pool impounded behind the <br />bulkhead, and percolates through the formation to the gulch, or if the water enters the gulch via subsurface <br />flow paths originating at the infiltration trench. It is the Division's position that the most direct mechanism <br />for determining if water from the 9360 adit is emerging in Windy Gulch is through the use of a ground <br />water tracer, and that Homestake should provide a tracer plan for Division review. <br />4. Homestake has adequately addressed the Division's concern with the potential for surface <br />subsidence related to caving in the 9360 adit. Particularly, Homestake has committed to monitoring the <br />surface for any signs of subsidence, and implementing mitigation if surface effects are detected. The <br />subsidence monitoring areas should be periodically inspected by the Division during routine site <br />inspections. <br />c:\.. \bulldog4.wpd <br />