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Re~~s~ o rv <br />INTEROFFICE MEMORANDUM <br />COLORADO DIVISION OF MINERALS AND GEOLOGY <br />]373 Sherman St., Rm. 215 <br />Denver, CO 80203 <br />TO: Gregg R. Squire _ ` <br />FROM: Kathleen L. Sullivan, P.E. <a1^^xn'/`)'~--r-~ <br />SUBJECT: M-2000-016, Lafarge West, Inc.: Riverbend Operation, AM-01 <br />Adequacy Review No. 6 <br />DATE: September 1, 2005 <br />CC: Carl Mount, DMG (via e-mail); Kate Pickford, DMG (via a-mail) <br />For the purposes of documentation, this memo recaps the status of the adequacy review process <br />and addresses the adequacy responses submitted on August 12, 2005. I have directed my <br />comments to the applicant. The applicant may contact me with any questions at (303) 866-4060. <br />During our August 12, 2005 meeting, Lafarge and Applegate Group provided responses to many <br />items identified in Adequacy Review No. 4 (AR#4). Lafarge's August 12, 2005 "Fourth Adequacy <br />Review Response" letter requests that the Division "Please see response and amended maps <br />prepared by TetraTech RMC for comments 1-8." However, as of the writing of this memo, the <br />referenced response and revised Mining Plan and Reclamation Plan maps have not been submitted <br />to the Division. Likewise, no written response has been received regarding the geotechnical issues <br />noted in Adequacy Review No. 5. <br />Although questions remain regarding the hydrologic model, it clearly predicts sizable offsite impacts, <br />including drops in the water table likely to kill offsite cottonwood tree groves and to deem at least two <br />wells unusable during pit dewatering. Consequently, the Division has decided to direct its attention <br />towards ensuring adequate ground water monitoring; minimization of disturbances to the hydrologic <br />balance, especially protecting offsite cottonwoods; and sufficient mitigation of impacts to offsite wells <br />and vegetation. <br />Please submit a revised Ground Water Monitoring Plan (Plan) that incorporates all changes made <br />during the adequacy review process and also addresses the following. <br />1. The supplied hydrologic model and data does not sufficiently assure the Division that impacts will <br />not be seen across the South Platte River from mine operations. Monitoring wells must be <br />identified to monitor the impacts of pit dewatering on area wells and vegetation. If available and <br />appropriate, these may be existing wells near other wells across the river. <br />The Division recommends monitoring wells be selected or installed at a minimum, at or near the <br />following locations, to monitor impacts that may affect registered and unregistered wells and <br />vegetation on both sides of the river. The additional monitoring wells must be included in the <br />Plan. However, it is the operator's responsibility to propose and ensure adequate monitoring is <br />in place to protect offsite wells and vegetation. <br />• The southwest comer of Phase 1, south of the river. <br />