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site and is located approximately 100 feet to the southeast of the Site. The Advanced GeoEnvironmental, Inc. (AGE) Site Conceptual Model Pacific Pride—South El Dorado Street, dated May 10, 2007 (SCM), describes"a preliminary subsurface model of the hydrostratigraphy consisting of a vadose zone and seven informal hydrogeologic units...". The SCM identifies four hydrogeologic units considered by AGE to be high-flow aquifers (Hydrogeologic Units 1 through 4) separated by less permeable soils identified as low- flow units or aquitards. AGE illustrates their subsurface model on Figure 3 - Site Plan, Figure 4 — Geologic Cross Section D-D', Figure 5 — Geologic Cross Section E-E' and Figure 6 — Geologic Cross Section F-F', included here for reference as Appendix A. These figures define an unsaturated fine to medium sand with trace gravel interval between approximately 10 and 25 feet bgs designated as the vadose zone in the SCM. In 2007 the groundwater surface elevation at both the Site and Pacific Pride occurred approximately 8- to 15-feet lower than its current depth. For example, the average recorded depth to water in 2017 on Pacific Pride wells MW-l0A and MW-12 is 28.82 and 28.38 feet bgs, respectively. (These wells are located near four of the six IES groundwater monitoring wells proposed in this report and the Work Plan). The average depth to water for the same wells recorded over the last four documented annual gauging events (between 2017 and 2021)was 19.09 for well MW-10A and 18.92 for well MW-12A. Therefore, the interval described in 2007 as vadose zone by AGE between approximately 10 and 25 feet bgs is now saturated to a depth of 19 feet bgs. This interval coincides with the Site's A zone while AGE's Hydrogeologic Unit 1, defined as"located between 35 and 55 feet bgs" corresponds to the Site's B zone. Proposed groundwater monitoring wells MW-15B,MW-17B and MW-19B proposed in the Work Plan are designed to investigate the B zone. Hydrogeologic Unit 2, defined by AGE in the SCM as "located between 60 and 80 feet bgs" corresponds to the Site's C zone. Proposed groundwater monitoring wells MW-16C, MW-18C and MW-20C are designed to investigate the C zone. The Site's A zone appears to be adequately delineated at this point of the environmental investigation. Existing Site groundwater monitoring well MW-1213, installed in 2019, southeast and down-gradient of the former northern USTs, has reported increasing dissolved petroleum hydrocarbon concentrations since its installation. There are no Site network wells to the southeast and east of MW-12B, therefore IES intends to target the B and C zones in this direction for additional assessment in order to adequately determine the nature and extent of the release. Based on the results of previous site characterization activities at both Site and Pacific Pride, and in accordance with the CVRWQCB Letter, IES proposes the following: 1. Update the existing Health and Safety Plan(HASP) for all phases of field activities; 2. Prepare and submit an encroachment permit application to the City of Stockton to allow for the installation of six groundwater monitoring wells (MW-15B, MW-16C, MW-1713, MW-18C, MW-19B and MW-20C)within the public right-of-way easement of South El Dorado Street; 3. Prepare a well permit application for the installation of six off-site monitoring wells and submit the permit package to the San Joaquin County Environmental Health Department (SJCEHD) for approval; California Tank Lines Innovative Environmental Solutions Addendum to Work Plan -2- Encinitas,California