2005-07-12_REVISION - M2000016 (3)

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~FARGE NORTH AMERICA AGGREGATES, CONCRETE & ASPHALT Please see enclosed response prepared by Weiland, Inc. regarding ground water levels utilized for the geotechnical slope stability analyses. I reanalyzed the slope stability for this east wall (Phase 5, Cell 5) using the materials depths from the representative drill hole. This analysis reveals that the 94 feet from the toe of the slope and 69 feet from the top of the slope setbacks are inadequate to protect the significant man-made structures along this slope (e.g., gas well, gas and power lines). Depending upon the location of the phreatic surface, the setbacks need to be increased between S and 30 feet for the east slope of this cell. Because of this finding, where using averages instead of either representative or maximum depths resulted in the calculation of insuff dent setbacks, please review each cell to determine if any other setbacks require reanalysis and report your findings to the Division. The offset along the east wall of Phase 5, Ce115 has been modified to 110.5 feet; please see supporting documentation in the enclosed Weiland, Inc. response. Weiland has also reviewed the offset calculations for each of the other cells within the permit boundary, see enclosed response supporting the original calculations. Upon the Division's acceptance of the offset, Exhibit C will be modified to reflect the new offset. Additional Responses to Kathleen Sullivan Memo, Second Adeguacy Review, April 22, 2005 The groundwater maps have been enlarged to a 24 by 36 inch format, showing the maximum drawdown for each of the three zones. One map has been submitted for the post-reclamation groundwater elevations. Because the post-reclamation groundwater elevations indicate insignificant mounding as a result of the lined reservoirs, no impact to nearby structures is anticipated. The Division requested nearby houses with potentially impacted basements be shown on the groundwater map; however, no houses with potential for impact were identified. Rule 6.4.7 EXHIBIT G -Water Information (AMEC, pp.ll-12) Regarding Well Permit No. 2216, the report concludes, "The estimated drop in groundwater level at this well should have a minimal impact to the historic use of the well. " Table S shows that the modeled water level change at this well during mining is -3.0 feet. What is the basis for this conclusion? The Well Permit for this well was enclosed in the Second Adequacy Review Response submitted June 25, 2005; however, the letter did not include a comment providing additional clarification. Please see Don Frick's comment below: As the map shows, and as described in the AMEC report, the maximum drawdown for Well No. 2216 is 3 feet. The well completion report, included with the well permit, LAFARGE NORTH AMERICA INC. -Lafarge Construction Materials 10170 Church Ranch Way, Suite 200, Westminster, Colorado 80021 Telephone: (303) 6574000 Facsimile: (303) 657-4037