2005-06-24_REVISION - M2000016 (13)

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~-FARG E NORTH AMERICA AGGREGATES, CONCRETE Ei ASPHALT 22. Memo Item 14: Lafarge needs to commit to specific mitigation measures to remedy expected permanent impacts to ground water jlorov in the area. This includes addressing permanent impacts to vegetation. Using a triggerpoint of a 2 feet change from historic ground water levels is acceptable, once adequate monitorinl; well sites are identified However, this trigger point cannot be coupled with `physical injury to a structure. "Please remove all references to regxiring physical injury to a structure. The trigger point of 2 feet should result in the Initiation of a' study to determine potential impacts to vegetation and surface and ground water users, followed by permanent mitigation measures, if necessary. In the case of vegetation effects, especially the cottonwoods in the wildlife corridor, immediate interim mitigation measures must be specified to protect this vegetation. Since the applicant indicated that significant changes are expected from the silt ponds, mitigation measures should also address these impacts (e.g., French drains around silt ponds as well,): We do not anticipate any long-term or permanent impacts to the groundwater flow in the area, including long-term impacts that would affect vegetation. The only reference to mitigation measures triggered by "physical injury to a structure" was in the last Adequacy Review response, we aclmowledge the removal of that lan);uage. Lafarge and its consultants did not indicate expectations of significant changes resulting from the silt ponds. See comment 9 response to the comzary. However, to meet the concerna of the Division, Lafarge will commit to 6 quarters of post.-reclamation monitoring to verify that changes to the ground water flow in the area will not cause permanent impacts. Groundwater Monitoring Plan: 23. On the Monitoring Wetl Locations map, [he cells shown do not entirety match those on the Reclamation Plan maps of Exhibit R Please modify the Monitoring Well Locations map to correct all discrepancies. The enclosed Monitoring Well Location:; map has been revised to reflect the most recent mining cell configurations. This map reflects the maximum extent of mining, with a note referencing Exhibit C. 24. Men:o Item 16: The applicant must provide the list or table requested in the previous adequacy review showing well permit numbers ana' constructed depths for all the monitoring wells. Please see the attached well permits for the Riverbend monitor wells. The Rittenhouse monitor well applications are pending submittal to the SEO office and will be provided once complete. 25. Mema Item 16: In addition to providing a baseline monitoring well for Well Permit No. 7208 (see item 17 on p. 4 of this memo), as requested by the previous Memo Item 16, additional monrtoring wells wi1L need to be selected and/or installed to monitor impacts not only to `potentially impacted wells, "but the overall hydrologic balance, including silt storage and lined pond impacts. There needs to be a minimum of one monitoring well up gradient and one monrtoring well down gradient of each ca>Il. There must be monitoring wells both up- and down gradient of all of the silt storage ponds aixd lined ponds, as well as to monitor unlined pits during dewktering activities. In addition to the general guidelines just provided, there needs to be two monitoring wells on each side of Phase 3, Cell l (48-acre silt storage pond). Ground water LAFARGE NORTH AMERICA INC. 'Lafarge Construction Materials 10170 Church Ranch Way, Suite 200, Westminster, Colorado 80021 Telephone: (303) 657-4000 Facsimile: (303) 657-0037