2018-10-12_REVISION - C1982056 (2)

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Observations from the test pit excavations included the following: • A thin layer of organic rich topsoil was noted at each test pit location, typically to depths of 6 inches to one foot. • Subsurface materials graded from residual clay soils through an intermediate material to a weathered shale over several vertical feet in each excavation, with the bottom of the excavation typically in the weathered shale unit. Material descriptions were made using the Unified Soil Classification System (USCS) and International Society of Rock Mechanics (ISRM) accepted descriptors for soil and rock materials, respectively. • Residual medium (lean) to high (fat) plasticity clay was observed to depths of 4 to 8 feet in all test pits except TP16-3. • Lean clay was observed to a depth of 3 feet in TP16-3, which was excavated on the South slope of the valley. • The intermediate material, between clay and shale was observed in each excavation and ranged from less than 1 to 4 feet thick. • The material was a highly to completely weathered rock, with the geological fabric of the underlying shale that could be broken apart to a mixed medium of clay and gravel sized shale fragments. • A layer with a notably lighter color (likely alkali precipitate) was observed in TP16-3 from a depth of 3 to 4 feet. This layer had the texture of the intermediate material, but was underlain by a stiff lean clay. • The shale that was excavated was moderately to highly weathered and extremely to very weak rock, which could be easily crumbled to gravel sized shale fragments without additional tools. • Bulk samples were collected from the residual soil layer of each excavation. Grab samples were collected of the three material types observed in each excavation and where any notably different soil conditions were observed (e.g. the alkali layer in TP16-3). Note, no testing was performed on grab samples. • Water seepage was observed in 4 of the 6 excavations. The water table typically occurred at the top of or up to a foot above the top of the shale layer. Table 3-1: Geotechnical Laboratory Soil Testing Results Atterberg Test Sample Date Moisture LimitsPercent AASHTO Soil Type LL PI Pit Ip Type Retrieved % pH Passing #200 Class. (USCS) TP16-1 Bulk 04/14/16 21.4 48 26 TP16-2 Bulk 04/14/16 24.0 53 TP16-3 Bulk 04/14/16 25.9 49 84.9 A-7-6 (23) Lean Clay (CL) 32 8.06 94.1 A-7-6(33) F (CHI) y 30 97.3 A-76(32) Lean Clay (CL) TP16-5 Bulk 04/14/16 24.2 45 27 7.87 95.8 A.7-6 (27) Lean Clay (CL) TP16-6 Bulk 04/14/16 22-1 46 28 97.8 A-7-6 (291 Lean Clay (CL) TP16-7 Bulk 04/14/16 26-1 53 33 99.5 A-7-6 (37) Fat Clay (CH) PEABODY FINAL OESIGN TM 20181010 3-2 COPYRIGHT 2012 BY CH2M HILL INC • COMPANY CONFIDENTIAL