2005-01-24_REVISION - M1999120 - Laserfiche WebLink

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RE: L. G. Everist, Inc., Fort Lupton Sand and Gravel Mine, DMG #M-1999-120; Second Adequacy Response Letter recharge from the river or the ditch. Due to the proximity of the grove to the river, it is probable that the actual decline in groundwater will be less than predicted. Further, the drainage ditch is deep enough that it will intercept shallow groundwater from the south side of CR18. The subject cottonwood grove is not located on land owned by LGE. LGE proposes to install at least one additional monitoring well in the grove, possibly two. On the north side of the drainage ditch, LGE has worked with the landowner and already has monitoring wells on his land, so hopefully the landowner is amenable to LGE placing another monitoring well in the cottonwood grove. LGE will also work with the landowner to the south of the drainage ditch, and if an agreement can be reached, LGE will install a monitoring well in the grove to the south of the drainage ditch. These well(s) will be monitored monthly as part of the monitoring plan. In addition to the monthly well monitoring, LGE will conduct monitoring of the cottonwoods, and if responsible for impacts, will implement appropriate mitigation measures, as both (monitoring and mitigation) are described in the last paragraph of #12. 14. Cottonwoods in Golden property The cottonwood grove along the South Platte River on the east side of the proposed expansion has been observed by LGE, WWE, CDOW and others. The grove consists of old, mature trees, with little to no growth of new cottonwood trees. The understory of the area has a relatively sparse cover of upland species, including some upland weeds. The only wetland plants occur in an old side channel, and on the lower banks of the river. Groundwater has been monitored by LGE in well 13 located in the grove since May 2004. The data show groundwater to average 6.385 feet below the surface at well 13. The variation in groundwater depth has been relatively small (1.01 feet), likely because of the proximity of the well to the river. Groundwater depth has varied by almost 3 feet to over 4 feet at wells further from the river (see MW9 on attached table). In addition to the monthly well monitoring, LGE will conduct monitoring of the cottonwoods, and if responsible for impacts, will implement appropriate mitigation measures, as both (monitoring and mitigation) are described in the last paragraph of #12. 15. Division...otherrneasures ...minimize impacts....installation of a French Drain LGE is fully committed to implementing necessary measures to mitigate for any negative effects to the hydrologic balance caused by the proposed expansion, including construction of a permanent mitigation measure such as a pipe/drain to equalize groundwater levels, which would remain after mining and reclamation is complete. LGE has modified the original proposal to include construction of slurry walls around all pits prior to mining. DMG acknowledges that this will "drastically reduce the impacts to the hydrologic balance...", and is proposed at considerable cost to LGE. LGE will monitor groundwater, wetland areas and cottonwood groves in the vicinity of the proposed expansion and will implement mitigation measures if a specified groundwater trigger is reached and vegetation desiccation is evident, or if any complaint is received and confirmed by an independent expert. We believe that this is a prudent approach given the uncertainty of the extent of any impacts from the expansion and the costs of the mitigation. LM/FL-Resp2ndAdegRev-dmgKP-012105.doc 7