2021-04-20_REVISION - M1983033 (20)

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Walstrum Spur Amendment, Exhibit G— Water Information April 2021 accounting. The results of the analyses indicate that the rocks are non-acid forming and do not represent a risk to the environment. The results of the analyses and interpretation of the data are provided in Appendix G-2. A relatively thin layer of unconsolidated sandy, rocky dry colluvium overlain by very thin (<0.5 feet) rocky topsoil is present on top of the bedrock. The overburden varies in thickness from absent at rock outcrops, to approximately one foot on ground slopes greater than 10 percent to approximately 20 feet near CH-002 where slopes are on the order of less than 10 percent. 4.2 Geologic Structure The structural geology of the site is presented in a series of three geologic cross-sections (Figure G-3), located as shown in Figure G-2. Section A-A' runs from Clear Creek on the southwestern edge of the Spur Amendment, in a northeasterly direction, ending at North Clear Creek. It intersects Corehole CH-005 on the south flank of the topographic high, and CH-001 on top of the hill and shows the stratigraphic relationships beneath the surface at each location. This section intersects the two faults indicated on the USGS maps, and Section B-B' runs from northwest of the Spur Amendment in a southeasterly direction until it reaches Clear Creek. Coreholes CH-001 and CH-002 are located along this section. Section C-C' is oriented approximately south to north, intersecting Coreholes CH-001 and CH-003, and running from Clear Creek to North Clear Creek. The overall sequence of gneiss is locally disrupted by faults and a network of fractures. The mapping by the USGS indicates that the general geologic block within which the Spur Amendment is located, is bounded by major faults located outside the Spur Amendment on the south and east. On the east, the block is bounded by the Black Hawk fault, a left-lateral strike-slip fault that runs along the trace of North Clear Creek. On the south, the Floyd Hill fault, a northwest-trending left-lateral strike-slip fault that follows the trace of Clear Creek adjacent to the mine entrance. Within the Spur Amendment itself, smaller faults have been mapped: one oriented NNW-SSE with left-lateral strike-slip motion, bisecting the topographic high in the Spur Amendment; a second fault to the east, with a similar orientation, but right-lateral offset and bisects a topographic saddle. The USGS mapping indicates a shear zone at the southern end of this fault. Neither of the mapped faults or the shear zone are obvious in the field and they do not extend into Clear Creek. 5.0 WATER SUPPLY Water for the Existing Quarry is supplied by withdrawals from Clear Creek. Water is withdrawn under water court decree 98CW473. Current usage averages 80 acre-feet per year. The primary use for the water is for dust suppression on the roads and on plant crushers, screens, and conveyor transfer points. 6.0 PRECIPITATION AND TEMPERATURE The closest meteorological station with a long period of record is the Georgetown Station. The weather station at Georgetown receives approximately 16 inches of precipitation per year. Table G-1 provides a summary of precipitation and temperature that is representative of the Spur Amendment. The data indicates that, during the summer, evaporation is much higher than precipitation suggesting that any precipitation that remains near the surface will evaporate. For context, annual pan evaporation at Estes Park (located at similar elevation to the north) is estimated to be approximately 41 inches, or nearly three times that of annual precipitation, and concentrated during the summer months when air temperature is higher. DTETRA TECH P a g e 3 � 7