2005-06-24_REVISION - M2000016 (13)

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~1FARG E NORTH AMERIt:A AGGREGATES, CONCRETE Ik ASPHALT 3. Memo Item 4.• The applicant also states, "Lafarge will not discharge more water than a ditch, ste~:m, or river can accommodate; all dewatering discharges will be assessed, monitored, and modified as necessary during operations. "What will the bases be for determining tivhat each type of waterway can "accommodate" and how will the discharges be assessed and monitored? What will be the bases for modifying the discharges? Lafarge will not dischazge into the Lupton Bottom ditch or Big Dry Creek, please see response to Item 1. 4. Memo Item 5: Since the slope stability analyses conducted to determine mining and stream offsets -minimum distances to be maintained between mining excavations and neighboring structures and streams - used a %:1 slope angle, the applicant modified the Mining Plan to reflect the same slope angle, instead of indicating that mining may occur up to vertical. Mining at t his prescribed angle will be problematic due to equipment limitations and the mechanics of earthmoving. Another concern is that the requirements to mine at prescribed slope angles may not'be communicated from the permit requirement, through company management to pit supervision to the equipment operators. Although the division in the past has approved and will approve a mine plan using a prescribed pit slope angle protective of structures, the applicant must be aware that if this is the compliance mechanism employed, it will be considered a violation of the permit if it is determined that mining has occurred at angle steeper than those prescribed. The applicant should reconsider the selection of a compliance method that requires mining the pit slope at a prescribed angle. If the applicant chooses to stay with this compliance method, they must describe in detail and in terms of the mechanics of earthmoving how these pit slope angles will be maintained in the field. Otherwise, revised setback distances should be provided based on stability under a ver[icat higllwall condition. Laf:~u~ge acknowledges the Division's comment pertaining to the difficulty of maintaining a '/::1 mining face to maintain the validity of the slope stability analysis and potential for violation if a %:1 ~ slope is not maintained. Lafazge will ensure operations do not violate the prescribed slope angles by staking the required offset plus the distance to the toe of the slope. 5. Menlo Item 5.• The applicant noted that instead of modeling surcharge loads from topsoil/overburden piles, all such piles would be located outside the offset limits. There are a number ofoversights on the Exhibit CMining Plan maps resulting in topsoil and overburden pilev outside the mapped affected areas and some still within the offsets. The applicant must correct these discrepancies. All maps have been modified to show all topsoil/overburden piles outside the prescribed offset limii:s. 6. Menlo Item 6: It would expedite the Division's geotechnical review to receive drill hole records in electronicform, if they are already contained in a spreadsheet. If available, and the applicant is amendable to this request, please e-mail theftle to Kathleen.Sullivan(a~state.co.us. LAFARGE NORTH AMERICA INC. -Lafarge Construction Materials 10170 Church Fanch Way, Suite 200, Westminster, Colorado 80021 Telephone: (303) 657-4000 Facsimile: (303) 657-4037