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Denmar US 19113.000.001 American Soda Ash Terminal at Port of Stockton December 3, 2021 PRELIMINARY DEWATERING ANALYSIS Page 3 We estimated dewatering to approximately 6 feet below finished floor level at each below-grade level to allow for preparation of subgrade and placement of the floor slab. This resulted in groundwater drawdown to Elevation -16 feet at the first below-grade level excavation and Elevation -30 feet at the second below-grade level excavation. MODELING RESULTS AND RECOMMENDATIONS Our modeling indicated a range of steady-state flow rates (total of all wells) between 10 and 20 gallons per minute (gpm) for the soldier pile analyses. For the deep sheet pile analysis, we estimate steady-state flow rates on the order of 1 gpm. For the hybrid sheet pile analysis,we estimate steady-state flow rates on the order of 5 gpm. Regardless of the shoring system used, the flow rates will be much higher for the first 2 to 3 days until the wells reach steady-state conditions. Figures 1, 2, and 3 show the dewatering model results and estimated radii of influence for each shoring scenario. In the upper silty sand (Model Layer 2), we anticipate on the order of 40 to 80 wells may be needed to effectively dewater the excavation, spaced every 5 to 20 horizontal feet around the perimeter. Where dewatering is needed to Elevation -30 feet in the vicinity of the tunnel, we anticipate an additional 5 to 10 wells may be needed in the lower silty sand (Model Layer 4) to relieve pressure buildup below the fat sandy clay aquitard (Model Layer 3). Prior to construction, we recommend the dewatering contractor perform additional analyses, as needed, to design the dewatering system. Because of the uncertainty inherent with construction dewatering, actual pumping rates may vary from our model results. For example, concentrated regions of lower hydraulic conductivity where the soil is more consolidated or cemented may reduce overall pumping rates. On the other hand, pumping rates may drastically increase if clean sand lenses are encountered. The spacing and depth of actual wells used during dewatering could impact the flow rates and drawdown influence. If desired, we can evaluate other scenarios to see how different dewatering system designs from those assumed in this letter would impact flow rates. If you have any questions or comments regarding this letter, please call and we will be glad to discuss them with you. Sincerely, QROF ESS/0/q ENGEO Incorporated �� A. w No. 2631 r'1 7U Chas emming, PE Fippin, GE ��yT OF N, FF CA��F ch/jf/dt Attachments: Figure 1 — Soldier Pile Dewatering Model Figure 2 — Deep Sheet Pile Dewatering Model Figure 3 — Hybrid Sheet Pile Dewatering Model