2004-02-24_REVISION - M1977153 (6)

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Water There are no fundamental changes to this section. The original application contained a detailed water analysis. The water table map and water wells within 200 feet were also document in previous applications and there has been no known change in these features. Hydrologic Balance G-2 Installation of the slurry wall could upset the hydrologic balance if certain measures are not implemented. Permit filing documents for Hazeltine and other mining permits in the immediate azea have established the general flow of ground water in this region is from southeast to northwest towazds the South Platte River The slurry wall installation will create a subsurface barrier the may cause the ground water to rise above historical levels on the east side of the slurry wall. This could have adverse effects on the adjacent property owners. Higher than normal ground water could "back up" septic systems and basement drains. To prevent the ground water from raising above historic norms a perforated drain needs to be installed. Prior to start of the slurry wall construction, elevations of the septic systems and basements for adjacent properties were determined by survey. The invert elevation of the mounding drain was set approximately nine feet below the existing ground surface and approximately 2 feet below septic tank elevations. This mounding drain will maintain and preserve the hydrologic balance of the ground water on the east side of the future storage reservoir. The South Platte River is located on the west and north sides of the permitted mining azeas. The Platte River water elevations will control the ground water elevations adjacent to the amended mining area. Because of the South Platte River there is no adverse affect to the ground water caused by the slurry wall and no need to install a mounding drain. Plans for this mounding drain are included in the slurry wall construction drawings. Also included are extensive subsurface soils information, pre slurry wall construction ground water conditions, stability analysis and other supplemental information. A generalized cross section of these completed reservoir is also provide for additional understanding of the effects the slurry wall, mounding drain and river will have on the ground water hydrology. At this time the outfall for the mounding drain is by gravity to the Hazeltine Pit. Denver Water, if necessary, will prepare an augmentation temporary substitute water supply plan for this water. Long term, it is anticipated that from the mounding drain will be measured and accounted for as a reservoir inflow and an equivalent flow will be returned to the South Platte River via a reservoir outlet structure.