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Denmar US American Soda Ash Terminal at the Port of Stockton 19113.000.001 Work Plan for Groundwater Characterization WORK PLAN FOR GROUNDWATER CHARACTERIZATION This document presents a work plan for the planned groundwater sampling for the proposed American Soda Ash Terminal project at the Port of Stockton. The purpose of the work plan is to provide an overview of the proposed groundwater characterization program developed to meet the Notice of Intent (NOI) requirements for Central Valley Regional Water Quality Control Board (RWQCB) Order No. R5-2022-0006, Waste Discharge Requirements for Limited Threat Discharges to Surface Waters (General Order). The following sections provide descriptions of the planned field visits, explorations, and associated equipment to be used. A copy of this work plan will be available on-site for field staff to reference. PROJECT SITE AND BACKGROUND The American Soda Ash Terminal project is located on Rough and Ready Island within the Port of Stockton. Temporary dewatering and discharge of pumped groundwater will be required during construction of the below-grade dumper pit and underground utilities. The proposed dewatering area is located west of Humphreys Street and east of Burns Cutoff, as shown in Figure 1, labeled as "Limits of Excavation". The discharge point will be determined later, upon completion of analytical testing and coordination with RWQCB staff. We modeled the potential effects of the temporary dewatering in our December 3, 2021 "Preliminary Dewatering Analysis," attached. We evaluated two dewatering scenarios based on different shoring permeability options. One option is a relatively impermeable shoring, such as sheet piles or soil mix, and the other is a high-permeability shoring, such as soldier piles and lagging. Because the relatively impermeable shoring option would be dewatered from inside the excavation, the zone of influence for this option is very small (with drawdown outside the shoring only extending for a few feet). The high-permeability option would require significantly more wells and the wells would need to be outside the shoring. As such, the zone of influence for the high-permeability option is significantly greater(on the order of 700 feet from the excavation). This work plan includes groundwater characterization for either dewatering option to inform the project of any significant difference in groundwater quality based on the zone of influence created during dewatering. We will collect groundwater samples from seven locations, as shown in Figure 1. We will conduct two supplemental borings within the planned excavation footprint; these are shown at 1-S1 and 1-S2. One sample will be collected from each supplemental boring to characterize groundwater quality within the smaller zone of influence. In addition, five samples will be collected from existing wells surrounding the planned dewatering location to characterize groundwater quality within the larger zone of influence.All groundwater samples will be transported to a State-certified laboratory under documented chain-of-custody. Laboratory analysis will be performed for the applicable constituents identified in Attachment I of the General Order. Additional information about the proposed field exploration and laboratory analysis is provided below. ENGEOApril 6, 2023 Expect Excellence—