2021-03-06_PERMIT FILE - C1981008A

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Recharge to the alluvial aquifers is by discharge from the bedrock aquifers and infiltration of surface waters (return irrigation water and precipitation). Hydrologic Boundaries Aquifer testing of the low yield strata at New Horizon 1 and 2 did not yield the presence of any major hydrologic boundaries. Bedrock aquifer testing of any duration would not yield the presence of hydrologic boundaries because the cones of depression in these aquifers, with low transmissivities, would be very small in areal extent. There are no faults, angular unconformities, or nonconformities within the permit area which would act as impermeable boundaries. Some minor lithologic boundaries are present in the bedrock aquifers as a result of their environment of deposition. There is a no -flow boundary in the unsaturated units in the eastern portion of the New Horizon 1 permit area (NW'/4, Section 31, RI 5W, T4 IN and NE'/4 Section 36, R16W, T41N). Constant and semi -constant discharge boundaries occur where the aquifers crop in the bottom of the draws. Infiltration and Permeability of the Unsaturated Zone Using the soil hydrologic properties defined by the Soil Conservation Service of the U.S. Department of Agriculture, it is possible to estimate the infiltration rates of soils occurring within the vicinity of the New Horizon 1 and 2 mining areas. The New Horizon I and 2 soils have been mapped at a scale of 1 inch equals 400 feet. The soils maps are included in Section 2.04.9 of this permit application. The unsaturated zone can be divided into two categories. The first is the undisturbed areas. At the New Horizon 2 mining area, the majority of the soils have a moderate (0.6 - 2.0 in/hr) permeability and infiltration rate. A minor amount of the soils have a moderately rapid (2.0 - 6.0 in/hr) permeability and infiltration rate. The subsurface strata in these areas consist predominately of tightly cemented sandstones and shales which act as barriers inhibiting vertical percolation. However, field observation of exposed outcrops and aquifer analysis data indicate that secondary porosity (weathered and fractured bedrock strata) play a significant role in allowing vertically infiltrating ground water to infiltrate through the unsaturated to the saturated zone. Quantification of the transmissivity and permeability associated with secondary porosity is difficult because of the lack of reliable aquifer analysis techniques to determine secondary porosity in low yielding aquifers. The entire study area is impacted by irrigation which is a primary source of infiltrating water. Infiltration as a result of precipitation is a component of recharge in the Nucla area, but the majority of infiltration comes from irrigation. The large majority of the soils in the mining area have a slow to medium runoff potential. The second area of concern is the reclaimed areas. The strata at the New Horizon I and 2 mining areas are quite similar. The lithologic logs indicate that the spoils material will generally be composed of more than 50 percent fragments of blasted sandstone with lesser amounts of shale, bentonite and gypsum. Sections 2.05.3 and 2.05.4 describe the details of the mining and reclamation methods. Using the described mining and reclamation techniques the approximate recharge capacity and permeability of the spoils material will be increased due to greater porosity and hydrologic conductivities due to increased void volumes. The resaturation rate of the spoils will be quite rapid because of the irrigation occurring in the area. Infiltration resulting from precipitation is only a very minor (2" per year) component, but does comprise a measurable percentage of the infiltration. Discharge Ground water is discharged through streams, evapotranspiration, wells, springs and seeps, and by subsurface Page 2.04.7-8 March 2017 (TR -77)