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i STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Deparlmenl of Natural Resources 1313 Sherman $1., Koum 215 Denver, Colorado PU'_Ol Phone. (7031 BGL-1567 FA%: 13031 P32 PI06 DEPARTMENT OF NATURAL RESOURCE DATE: June 24, 1994 ~ ~e °,o ei TO: Tony Waldron James S lochheail Evecmive one~~n~ Michael B Long FROM: Susan Burgmaier olvlslnn Dhean~ RE: Eagle Mines (C-81-044) Technical Revision 24 I have reviewed the submittal from Cyprus Empire Corporation (CEC) in support of the above mentioned revision application. Following are my concerns with the submittal, worded for forwarding to the operator. 1. CEC submitted an assessmem of the predicted subsidence effects and recommended mitigation as determined by Peng and L.uo. Part of their recommendation is that various sections of the pipeline be uncovered to relieve strain resulting from movement of soil surrounding the pipe. For the areas to be undermined over the next year, Peng and Luo recommend that portions of the "B-C" and "C-D" segments (as depicted on Fig. 1 of the report) be uncovered. CEC has indicated that only the "C-D" portion will be uncovered. Please explain the discrepancy between the recommendations made and the proposed plan. 2. The upland diversion for the uncovered pipe section crosses an existing drainage at an angle of approximately 90'. What measures will be taken to ensure that flow in the temporary channel will continue across the existing drainage rather than flowing through the drainage and into the livestock pond? 3. CEC is greatly expanding the watershed of the existing drainage to which the upgradient diversion will be directed. Is the existing drainage adequately sized and protected to safely convey the additional flow? 4. What measures, such as pond/ditch lining, will be employed to protect groundwater resources in the event of an oil spill? 5. Rule 4.05.3(2) states that temporary diversions shall be constructed to pass safely the peak runoff from a precipitation event with a 2 year recurrence interval, or a larger event as specified by the Division for good cause shown. Given the amount of oil that could be spilled, the close proximity to and resulting potential for contamination of the .Williams Fork River, the Division will require that the diversions be sized fora 10-year, 24-hour event. 6. Please submit detailed drawings of the livestock pond, as required by Rule 2.05.3(4). Please provide additional information regarding the determination of the appropriate curve number used for the watershed contributing to the ditches and pond. Specifically, we need the crop type and relative cover data used.