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Quarterly Monitoring Report— First Quarter 2026 conducted every 5 years. The next 5-year analyses will be conducted in third quarter 2028 (MRP Table 10 [RWQCB 2024]). The MRP also states that each lysimeter will be screened for methane or VOCs by a gas analyzing device or photo ionization detector, and a USEPA Method TO-15 VOC sample may be obtained (MRP Section B.2.b and Table 7 [RWQCB 2024]). This process began in second quarter 2025. The prescreening of methane was conducted using a gas analyzing device for methane detection. A USEPA Method TO-15 VOC sample should only be collected if the methane concentration exceeds 1% by volume. The screening results are included in Table 5a. During the prescreening activities, three suction lysimeters (93-A, FU-04E-A, and FU-05-A) had concentrations of 43.0%, 17.0%, and 25% methane respectively. Suction lysimeters 93-A, FU-04E-A, and FU-05- A were then sampled for VOCs by USEPA Method TO-15 and the results are presented in Table 5b. 2.2.2 Quarterly Results Field inspection results are provided in Appendix B. All but two of the lysimeters were dry or contained insufficient soil pore liquids for sampling. Two suction lysimeters (LY-A and LY-Pond-N) at the Site contained sufficient liquid for analysis of VOCs, and LY-A contained sufficient volume to additionally analyze for 1,2,3-trichloropropane. Tables 5a and 5c present analytical results for suction and pan lysimeter locations, respectively. As shown in Table 5a, VOCs were detected at concentrations exceeding the applicable MDLs or PQLs at the Site during first quarter 2026. Cumulative data for all monitoring points for the unsaturated zone for the past year(first quarter 2025 through first quarter 2026) are included in Appendix D. 2.3 Surface Water Monitoring This section describes surface water monitoring conducted during first quarter 2026 and the associated results. Surface water monitoring is conducted in accordance with MRP Section B.3 (RWQCB 2024). 2.3.1 Monitoring Program Two creeks are present near the Site (Figure 1). The north fork of Littlejohn's Creek borders the north and west sides of the Site. The south fork of Littlejohn's Creek borders the south side of the landfill area on the east and west sides of the Site. Both creeks are dammed upstream by Farmington Dam and usually are dry. Surface runoff from the landfill areas is channeled to sedimentation basins, which are located near the southwest corner of the Site, adjacent to the creeks, as shown on Figure 5. The water in the sedimentation basins typically is evaporated. Four surface water monitoring points have been established for the Site (MRP Table 11 [RWQCB 2024]). The surface water monitoring locations are described in Table 2-1 below and shown on Figure 5. Table 2-1 Surface Water Detection Monitoring Network Program or Function Monitoring Point Location FSW-2 Background (upstream) South fork of Littlejohn's Creek, operational FSW-1 Downstream South fork of Littlejohn's Creek, operational www.arcadis.com Forward Landfill 1Q26 QMR 5