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Rifle Gravel Pit#1 June 2023 <br /> 4.3 Topography and Aquifer <br /> The existing surface topography is extremely flat and composed of several feet of fine- <br /> textured alluvial sediment overlying a highly permeable alluvial aquifer of coarse gravel. The <br /> coarse gravel material lies on bedrock, adjacent to the Colorado River (based upon <br /> available boring data). The subsurface conditions are typical of gravel pits and aggregate <br /> mines in the Colorado River floodplain with the surface layers consisting of approximately 6 <br /> inches of topsoil, underlain by one (1) to seven (7) feet of alluvially deposited fine sediments <br /> (primarily silts and clays). This overburden covers between seventeen (17) and twenty-two <br /> (22) feet of alluvial gravels that are the target of the extraction operation. Shallow <br /> groundwater, connected to the water table of the Colorado River, saturates the gravels, and <br /> is generally present throughout the project site at a depth of between one and one-half(1.5) <br /> and five (5) feet. The boring logs are included in Attachment C and provide details <br /> regarding the property and subsurface soil and groundwater levels. <br /> The only topography of note is the artificially excavated tailwater return channel of the Last <br /> Chance Ditch, with runs east to west across the property and generally bisects the property <br /> into northern and southern sections. Figure 4, Exhibit C2 depicts this feature. <br /> Figure 4, Exhibit C2 depicts information required by: <br /> • 6.4.3(c)—the existing topography of the area with contour lines of sufficient detail to <br /> portray the direction and rate of slope of the affected land [112(4)(g)] <br /> • 6.4.3(d)—the total area to be involved in the operation, including the area to be <br /> mined and the area of affected lands [112(4)(f)] <br /> 12 <br />