2024-06-07_PERMIT FILE - M2024026 (29)

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Geotechnical Stability Report — Kersey Mine May 24, 2024 Kersey, Colorado Page 3 Table 2: Summary of Laboratory Testing Type of Test Applicable Test Standard Number of Test Conducted Moisture Content AASHTO T265 /ASTM D2216 9 Mechanical Grain-Size Analysis AASHTO T88 /ASTM D422 9 Atterberg Limits AASHTO T89, T90 / ASTM 4318 9 Direct Shear ASTM D3080 3 SITE CONDITIONS Geology According to the Colorado Geologic map, the site is underlain by Eolian deposits and Laramie formation.The Laramie formation is composed of sandstone, shale, claystone, and coal. It known for being the primary coal bearing unit in the Rocky Mountain region. Furthermore, Eolian deposits consists of clay, silt, and fine sands. These types of soils arise an issue of being collapsable soils. Subsurface Conditions This section presents the generalized subsurface conditions observed during the field exploration. During the field activities, TRC's on-site inspector also made observations of existing topsoil (gravel or other surface material) thicknesses, groundwater conditions, surface features, and other site observations deemed important to the proposed project, as applicable. Detailed descriptions of the subsurface conditions encountered within each boring are presented on each individual boring log included in Attachment B. It should be noted that lithological boundaries on the boring logs represent the approximate location of changes of soil types. In situ, the transitions may be gradual. The subsoils encountered in the test borings generally consisted of clayey sands and sandy clays over sandstone and claystone bedrock. Correlated N-values indicate the relative density of the clayey sands and sandy clays range from "loose" to "medium dense". Laboratory testing performed on representative samples indicates in-place moisture contents ranging from approximately 2.1% to 15.7% Atterberg Limits testing on the fine-grained portion of these soils indicates liquid limits ranging from non-plastic to 28% and plasticity indices ranging from non- plastic to 14%. Primarily sandstone bedrock was encountered between approximately 8 and 24 ft bgs and extended to the maximum depths explored. The sandstone was described as brown, rust, white, slightly moist, hard to very hard. Claystone was encountered below the sandstone layer in boring TH-1 and extends to the termination depth of the boring. Claystone can be described as grey, rust, slightly moist, medium hard to hard. Ground Water Observations for groundwater were made during drilling and shortly after completion in each test boring. Groundwater was not encountered at all test boring locations except for boring TH-5where it was encountered at a depth of approximately 24 feet bgs. It should be noted the presence, depth, and quantity of hydrostatic groundwater levels and upper (perched) saturation zones should be expected to fluctuate seasonally based on variations in rainfall, climatic conditions, site surface runoff characteristics, evapotranspiration, permeability of on-site soils, continuity of i TRc