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Denmar US 19113.000.001 American Soda Ash Terminal at Port of Stockton December 3, 2021 PRELIMINARY DEWATERING ANALYSIS Page 2 MODELING METHODOLOGY To evaluate dewatering flow rates and approximate impacts, we performed modeling in the three-dimensional finite difference groundwater modeling software MODFLOW. We reviewed the logs of four CPTs (1-CPT-7, 2-CPT-29, 2-CPT-30, and 2-DPT-43) and one boring (2-139)that were performed in the area of the Railcar Unloading Building (See Reference 2). Based on these explorations, we created the following idealized stratigraphy. TABLE 1: Idealized Subsurface Profile MODELGEOLOGIC ELEVATION LAYER (feet) 1 Lean Silty Clay 0 to -12 2 Sand and Silty Sand -12 to -28 3 Fat Sandy Clay -28 to -35 4 Sand and Silty Sand -35 to -41 5 Lean Silty Clay -41 to -60 Based on information on the logs, our experience with soil in the project area, and the Department of Water Resources' Guidance Document for Geotechnical Analyses (Reference 4), we assigned the following parameters for modeling. TABLE 2: MODFLOW Groundwater Modeling Parameters MODELHORIZONTAL HYDRAULIC • - • - LAYER CONDUCTIVITY, 1 0.0028 4 2 2.8 4 3 0.028 4 4 2.8 4 5 0.0028 4 In our analyses,we assumed that groundwater is at Elevation -5 feet(or 5 feet below existing grade). We performed a steady-state analysis to estimate the long-term pumping rates assuming a soldier pile and wood lagging system and a sheet pile system. We performed analyses varying the permeability of various layers to evaluate the impact of varying conditions on flow rates. When we evaluated the sheet piles,we assumed they are essentially impervious; our experience indicates that sheet piles often leak at the seams and either care should be used to align and seal the seams during construction or the contractor should expect to need to capture additional flow at leaking seams that will need to be captured and discharged in addition to the values estimated. With the sheet piles, we performed two analyses, the first assuming that the sheets are embedded approximately 5 feet into Layer 5 (referred to as the "deep sheet pile" analysis) and the second assuming that most of the sheets are terminated in Layer 3 and only sheets near the deeper part of the excavation are terminated in Layer 5 (referred to as the "hybrid sheet pile" analysis); in order for this hybrid sheet pile analysis to be successful, the presence, depth, and continuity of Layer 3 will need to be verified prior to construction.