COMPLIANCE INFO_REV.4TH QTR-ANNUAL REPORT 6/26/2025

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Revised Quarterly Monitoring Report – Fourth Quarter/Annual 2024 www.arcadis.com Revised - Forward Landfill 4Q24 Quarterly Mon Report 06262025 4 (RWQCB 2024a); equipment, field, and trip blanks were analyzed for VOCs by United States Environmental Protection Agency (USEPA) Method 8260. Toluene was measured in two of the trip blanks at quantifiable concentrations of 0.12 J and 0.56 micrograms per liter (µg/L). PCE was measured in one field blank at a quantifiable concentration of 0.75 µg/L. PCE was also measured in one equipment blank at a quantifiable concentration of 0.69 µg/L. No VOCs were measured in the laboratory method blanks analyzed with the groundwater samples. Inorganic constituents (chloride, dissolved antimony, dissolved copper, dissolved sodium, total dissolved solids (TDS), hexavalent chromium, sulfate, and total iron) were measured at estimated trace concentrations in one or more of the laboratory method blanks analyzed with the groundwater samples. Several samples contained similar reported concentrations of these compounds, which are considered suspected laboratory contaminants. Results from the duplicate groundwater samples collected from monitoring wells MW-10 and AMW-36S are presented in Tables 3a through 3c along with the primary results for the wells. Comparison of the primary and duplicate results for both wells and their duplicates indicate a relative percent difference of 20% or less for the routine monitoring parameters (i.e., turbidity, temperature, specific conductance, and pH). All results had a relative percent difference of 20% or less. Based on evaluation of the laboratory QA/QC data, the laboratory results generated for fourth quarter 2024 were deemed acceptable, and the water quality samples collected are representative of water quality at the Site. 2.2 Unsaturated Zone Monitoring This section describes monitoring conducted within the vadose zone of the Site during fourth quarter 2024 and the associated monitoring results. The unsaturated zone monitoring is conducted in accordance with MRP Section B.2 (RWQCB 2024a). 2.2.1 Monitoring Program The unsaturated zone monitoring network in the MRP includes 23 suction lysimeters and eight pan lysimeters (MRP Table 6 [RWQCB 2024a]). The current unsaturated zone monitoring network includes 18 suction lysimeters and 12 pan lysimeters, which includes four additional pan lysimeters than the MRP (TS-1 [FU-23], TS-2 [FU-23], TS-3 [FU-24], and TS-4 [FU-24]). The lysimeter locations are shown on Figures 2 and 3 and listed in Table 1. Five suction lysimeters (LY-E1A, LY-E1B, LY-E2A, LY-E2B, and D93B) are included in MRP Table 6 (RWQCB 2024a) and shown on Figure 2; however, these suction lysimeters were assumed destroyed and are proposed to be removed from the MRP in the next revision. The lysimeters samples were analyzed in accordance with MRP Tables 8 and 9 (RWQCB 2024a). Tables 5a and 5b detail results of soil pore liquids if they are present during the monitoring event. Supplemental analyses are conducted every 5 years. The next 5-year analyses will be conducted in third quarter 2028 (MRP Table 10 [RWQCB 2024a]). The MRP also states that if a lysimeter location is dry, the location will be screened for methane and VOCs, and a methane sample and USEPA Method TO-15 VOC sample may be obtained (MRP Section B.2.b and Table 7 [RWQCB 2024a]). This process will begin in second quarter 2025. The prescreening of methane and total VOCs will be conducted using a gas analyzing device for methane detection and a photo ionization detector for total