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Geosptecc' <br /> consultants Page 2 of 12 <br /> Client: Arcosa LWB Project: Permit Amendment Project No.: DE0374 Task: Exhibit S—Structures Evaluation <br /> written by: Jonathan Gillen Date: 7/8/2019 Reviewed by: Youngmin Cho Date: 7/9/2019 <br /> Approved by: Poppy Staub Date: 7/15/2019 <br /> Pierre Shale — underlays the Slocum Alluvium, beginning at 9 feet below ground surface (bgs) <br /> and extends to a depth of approximately 8,200 feet bgS2. The Pierre Shale is a thick, laterally <br /> extensive formation dominated by black, thinly bedded, fissile marine shales and silty shales with <br /> numerous, thin, siltstone and sandstone interbeds. Clay minerals in this formation are present and <br /> include montmorillonite and lesser amounts of chlorite. <br /> Groundwater— Groundwater conditions at the site were characterized in the Engineering Design <br /> and Operations Report,dated March 1992 by Sergent et al. According to this report, groundwater <br /> in the surficial alluvial materials ranges between 5 and 20 feet below ground surface (bgs). <br /> However, these materials are not perennially saturated, thus they are often dry. This information <br /> is corroborated by visual observations of the excavation face of the quarry by Site personnel. Site <br /> personnel report that they observe groundwater seeps into the quarry from the alluvium layer after <br /> periods of rain, otherwise the alluvium material appears dry. <br /> Water levels within the Pierre Shale formation were reported by Sergent, et al from observations <br /> made at groundwater monitoring wells MWBR-1, MWBR-2 and MWBR-3. These locations are <br /> provided in Attachment A. Water was observed at these locations between 180 and 270 feet bgs. <br /> Water at these depths is approximately 60 (or more) feet below the bottom of the existing quarry. <br /> Given the reported hydraulic conductivity values for the Pierre Shale formation,groundwater flow <br /> within the Pierre Shale was not considered for this analysis. <br /> STRUCTURES <br /> Division of Reclamation, Mining and Safety (DRMS) requires an evaluation of the stability of <br /> structures on Site and within 200 feet of the Site's permit boundary in lieu of structures agreements <br /> with stakeholders. Structures on Site and within 200 feet of the permit boundary are depicted on <br /> Figures S-1, S-2 and S-3. <br /> Table 1 lists the known structures on Site and within 200 feet of the permit boundary. Structures <br /> are listed in order of proximal distance from the quarry. Structure IDS listed in the table correspond <br /> to the numbers shown on Figures S-1, S-2 and S-3. <br /> METHODOLOGY <br /> Global stability of the structure closest to the quarry was analyzed. Stability of other strictures at <br /> greater distances from the quarry would be evaluated if the stability of the closest structure falls <br /> below the target minimum factor of safety (FS), as described below. Conversely, if the FS of the <br /> closest structure (i.e., Stricture # 1- Highway 93 Right of Way) is adequate, then the FS for all <br /> other structures farther from the quarry operations are assumed to be adequate. <br /> Z Engineering Design and Operations Report. Certificate of Designation Shale Mine Ash Backfill Project,prepared <br /> by Sergent,Hauskins&Beckwith in March 1992,for Western Aggregates,Inc. <br /> Structures Evaluation <br /> Arcosa LWB Plan-Permit Amendment 2019-07-16 <br />