2011-09-19_PERMIT FILE - M2011049 (7)

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transmissivity and low gradient. Groundwater flow is regularly in the same direction as, and slightly towards, the river (see Exhibit G -1, Water Resource Map). The alluvial groundwater elevation and flow direction in these systems are typically influenced by fluctuations in river flow, direct precipitation and infiltration, agricultural irrigation, and withdrawals from water wells. Mounding and shadowing refer to a slightly higher or lower normal groundwater elevation, respectively, and can be caused by obstructions to the natural alluvial groundwater flow regime. Once the slurry wall is complete, and based on the assumed groundwater flow regime, mounding is anticipated west and southwest, or upgradient, of the slurry wall and shadowing is expected east and northeast, or downgradient of the reservoir. These groundwater elevation effects are most pronounced immediately adjacent to the slurry wall, with groundwater returning to normal elevations over relatively short distances away from the slurry wall. Upgradient (west and south) of Treiber Lakes, properties are primarily owned by the applicant and contain additional mining operations. South and west of these mining operations, an underdrain system has already been installed to mitigate mounding affects of future reservoir development (see Exhibit G -1, Water Resource Map). Additional property upgradient (west) of Treiber Lakes includes City of Fort Collins open space. Due to the existing undrain system immediately to the south, and the Cache la Poudre River north of the property, mounding on the open space property is expected to be minimal. Additionally, no structures are known to exist within the open space that could be affected by potential groundwater mounding. Shadowing impacts downgradient of Treiber Lakes are not likely since the Cache la Poudre River is immediately north of the site and mining operations on property owned by the applicant are to the east. Groundwater mounding and shadowing effects are not expected to occur beyond, nor impact, these adjacent properties and features. Therefore, impacts and damages to adjacent properties from installation of the slurry wall are not anticipated. Potential Groundwater Impact Mitigation Plan Although impacts and damages are not anticipated, it is the intent of the City of Greeley to operate responsibly and to mitigate damage to wells or structures that is directly attributable to the reclamation of this site. If installation of the slurry wall creates injury to surrounding wells, the applicant will take all necessary actions to remedy the injury. If water levels are dropping in adjacent wells, due to shadowing from installation of the slurry wall at the Treiber Lakes site, such that well owners historic water production may be injured, the applicant will begin to implement one or more of the following measures. However, if the well has not been put to beneficial use prior to mining, the applicant should have no responsibility to provide mitigation. Mitigation measures may include, but are not limited to: 1. Modify existing wells to operate under lower groundwater conditions. This would include re- drilling existing wells to deeper depths or lowering the pumps. All work would be done at the applicant's expense with the exception of replacing equipment that was non - functional prior to mining. 2. If existing wells cannot be repaired, the applicant will drill a new well for the owner to replace the damaged well. The new well will produce water of the same quantity and quality to support the historic use. Treiber Lakes DRMS 112 Permit Application Page 15