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4 Environmental Analysis 4.7 Geology, Soils, and Paleontological Resources 4.7.1.4 Soils The Natural Resources Conservation Service (NRCS) describes the Project site "bedrock" (i.e. the soil parent material) as alluvium derived from sedimentary rock, sandstone, shale, and siltstone (NRCS 2022), with the key word being "alluvium." Given this, these soils were presumably developed on unconsolidated Quaternary sediment. Figure 4.7-3 shows the mapped soil units in and around the Project site and gen-tie corridor. Three of these soils are found within the Project site boundaries; their descriptions and approximate aerial extent are provided below. 114 Calla-Carbona Complex, 8 to 30 percent slopes (29.9 percent of the site). This is a roughly equal combination of Calla clay loam and Carbona clay loam. Both soils are considered very deep and well drained. Permeability is noted as slow to moderately slow in both soils, with rapid runoff and a severe water-erosion hazard. Only the Carbona side of the soils in this complex (not the Calla soils) are noted as having a high shrink-swell potential. 115 Calla-Carbona Complex, 30 to 50 percent slopes (33.5 percent of the site). This is the same soil complex as described above, only they are situated on steeper slopes. Therefore, both soils in the complex are deep and well drained. However, because of the steeper slopes, the complex would have more rapid runoff and more severe water- erosion hazard than on shallower slopes. Shrink-swell potential is, again, only noted as high in the Carbona soil (not the Calla soil). 123 Carbona clay loam, 2 to 8 percent slopes (36.6 percent of the site). This soil is a well- drained and very shallow-sloped clay loam. Primarily due to its shallow slopes, this soil has a slow runoff rate and only a slight hazard for water erosion. Finally,the shrink- swell potential of this soil, as for all Carbona soils, is considered to be high. In addition, three soils identified separately in the Soil Survey for Alameda County are found within the gen-tie corridor boundaries; their descriptions are provided below. CdB Clear Lake clay (3 to 7 percent slopes) is a moderately well-drained clay with a typical two-horizon profile that extends to a depth of 65 inches. This soil is characterized as having high shrink-swell potential. LaC Linne clay loam (3 to 15 percent slopes) is a well-drained clay loam with a typical two- horizon profile that extends to a depth of 40 inches. This soil is characterized as having low shrink-swell potential. RdA Rincon clay loam (0 to 3 percent slopes) is a well-drained clay loam with a soil profile that typically has three horizons and can extend to a depth of 60 inches. This soil is characterized as having high shrink-swell potential. Griffith Energy Storage Project 4.7-8 Tetra Tech/SCH 2022120675 Draft Environmental Impact Report August 2023