2018-12-12_GENERAL DOCUMENTS - C2010088

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22 CAM prepared SEDCAD hydrology demonstrations that show that the silt fence protecting the stream buffer zones can treat runoff to NPDES standards for settleable solids. The SEDCAD demonstrations can be found in Exhibit 9 of the permit application. K. Probable Hydrologic Consequences The operator's discussion of the Probable Hydrologic Consequences (PHC) is presented in Section 2.05.6(3)(b)(iii) of the permit application. Concerning surface water, CAM presents their assessment that the waters of the Colorado River, Reed Wash and the Loma Drain will not be adversely affected by operations at the Loadout. Since the three sediment ponds are total containment ponds and the pond water will be removed from the ponds and disposed of at an approved disposal facility, CAM concluded that Loadout’s operations will not adversely affect the surface water regime and may even improve the water quality in Reed Wash. CAM concluded that sediment ponds will improve the quality of the surface water flowing through and out of the proposed permit area and adjacent area because sediment and water removed from the ponds will be disposed of at an approved disposal facility. This will reduce the amount of suspended solids and reduce the possibility of flood hazards by retaining runoff during storm events. With regard to groundwater, CAM provided a PHC analysis for the alluvial groundwater only. Bedrock groundwater will not be affected by the Loadout’s operations. Alluvial groundwater in the permit area occurs in river alluvium that lies over Mancos shale. It is unlikely that the groundwater within the permit area is directly related to the Colorado River. It is possible that groundwater beneath the property may in part be the result of irrigation in the upland areas, using water from up river diversions. The water quality of the alluvial groundwater is relatively poor. The alluvial groundwater is predominantly a calcium-sodium-sulfate water, with elevated iron and manganese. Total dissolved solids range from 5,800 to 8,800 mg/L, and there are no domestic or irrigation wells located immediately downgradient of the permit and adjacent areas. Soils at the surface are described as silty-clay with low permeability. CAM analyzed infiltration from surface water runoff to shallow alluvial groundwater. CAM concluded that in clayey soils, percolation is slow and most water is held at shallow depths, where it can be lost to evapotranspiration. Intense precipitation produces rapid surface runoff and low percolation. Combining this with the semi-arid climate of the Grand Valley that possesses very high evapotranspiration rates should allow runoff from the loadout to occur without impacting alluvial groundwater, as most runoff water will be lost to evapotranspiration before it can infiltrate the alluvial groundwater.