2022-11-18_PERMIT FILE - M2022048 (5)

Home Browse Search

Exhibit G Water Information (cont) areas are in place well before installation of the slurry walls will begin. The permit area has two area where the depth below ground level area vastly different . The dividing line between these land features is a natural bank where the river valley transitions from the flood plane on the east side to the upland area along the west side . In the eastern area, Phases 1 and 3 , the natural groundwater depths vary from 2 . 9 to 4 .4 feet, average 3 . 5 ft . below the surface. On the western areas, Phases 2 and 4, the natural groundwater depths vary from 16 . 7 to 23 . 9 feet, average 19 . 5 ft . , below the surface between June 2019 and October 2022 . These ground water depths and averages may change prior to mining commencing. L.G. Everist, Inc' s . experience on other mines in the South Platte River valley indicates that groundwater levels can fluctuate as much as 7 . 0+ feet depending on the season. The data collected confirms that the West Farm Reservoirs site is within a few inches of that number. In a normal mitigation trigger plan, the trigger limits would be set at as a three (3) foot plus or minus change over a 3-month running average. Realistically, in this case the trigger number should be based on a 3-foot change determined by a line that approximates an up or downward trend of the water table and considers outside impacts such as, drought, storm events or decreased irrigation activities . We do not expect this to be a problem where the slurry walls are in close proximity to a flowing water body like the irrigation return flow ditch that bisects the mine site north to south and the South Platte River along the east and north sides . The mining operation will have minimal effect on the South Platte River in the form of minor groundwater depletions due to evaporation and water uses associated with mining. The depletions to the South Platte will be mitigated thru a temporary Substitute Water Supply Plan (as required and approved by the Division of Water Resources) to prevent injury to the vested senior water rights . The reclamation plan proposes the creation of 4 slurry wall, lined reservoirs that will not be hydraulically connected to the South Platte River or any alluvial aquifer. The reservoir areas will be sealed prior to mining, thereby eliminating the groundwater draw down which is typically associated with mine site dewatering. This will also eliminate or minimize the possibility of any adverse impacts to the single nearby alluvial well . If during the course of mining or reclamation complaints from the well owner are received by the permittee, the permittee will commence an evaluation and investigation, including providing replacement water to the well owner if necessary, within 48 hours . L.G. EVERIST, INC. -WEST FARM RESERVOIRS 30 November 2022