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Quarterly Monitoring Report – Third Quarter 2025 <br />www.arcadis.com <br />Forward Landfill 3Q25 Quarterly Mon Report 4 <br />2.1.4 Quality Assurance/Quality Control Results <br />The quality assurance (QA)/quality control (QC) samples collected at the Site during third quarter 2025 and the <br />associated analytical results are described in this section. <br />QA/QC samples at the Site included 15 trip blanks, four field blanks, 11 equipment blanks, laboratory method <br />blanks, and two duplicate samples. The method blanks were analyzed for all the analytes included in the MRP <br />(RWQCB 2024); equipment, field, and trip blanks were analyzed for VOCs by United States Environmental <br />Protection Agency (USEPA) Method 8260. <br />Toluene was measured in one of the trip blanks at a concentration of 2.3 micrograms per liter (μg/L) and acetone <br />was measured in one of the trip blanks at an estimated concentration of 5.4 J μg/L. PCE was detected in two of <br />the field blanks at estimated concentrations of 0.33 J μg/L and 0.28 J μg/L. No VOCs were measured in any <br />equipment blank. No VOCs were measured in the laboratory method blanks analyzed with the groundwater <br />samples. Inorganic constituents (chloride, dissolved sodium, and sulfate) were measured at estimated trace <br />concentrations in one or more of the laboratory method blanks analyzed with the groundwater samples. Several <br />samples contained similar reported concentrations of these constituents, which are considered suspected <br />laboratory contaminants. <br />Results from the duplicate groundwater samples collected from monitoring wells AMW-4 and AMW-28 are <br />presented in Table 3a along with the primary results for the wells. Comparison of the primary and duplicate results <br />for both wells indicates a relative percent difference of 20% or less for the routine monitoring parameters (i.e., <br />turbidity, temperature, specific conductance, and pH). All analytical results had a relative percent difference of <br />20% or less. Based on evaluation of the laboratory QA/QC data, the laboratory results generated for third quarter <br />2025 were deemed acceptable and the water quality samples collected are representative of water quality at the <br />Site. <br />2.2 Unsaturated Zone Monitoring <br />This section describes monitoring conducted within the vadose zone of the Site during third quarter 2025 and the <br />associated monitoring results. The unsaturated zone monitoring is conducted in accordance with MRP Section <br />B.2 (RWQCB 2024). <br />2.2.1 Monitoring Program <br />The unsaturated zone monitoring network in the MRP includes 23 suction lysimeters and eight pan lysimeters <br />(MRP Table 6 [RWQCB 2024]). The current unsaturated zone monitoring network includes 18 suction lysimeters <br />and 12 pan lysimeters, which includes four additional pan lysimeters than the MRP (TS-1 [FU-23], TS-2 [FU-23], <br />TS-3 [FU-24], and TS-4 [FU-24]). The lysimeter locations are shown on Figures 2 and 3 and listed in Table 1. <br />Lysimeter analytical results are provided in Tables 5a through 5c. <br />Five suction lysimeters (LY-E1A, LY-E1B, LY-E2A, LY-E2B, and D93B) are included in MRP Table 6 <br />(RWQCB 2024) and shown on Figure 2; however, these suction lysimeters were assumed destroyed as shown in <br />the Revised Quarterly Monitoring Report – Fourth Quarter/Annual 2024 (Arcadis 2025c) and were proposed to be <br />removed from the MRP in the next revision.