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Water Quality Monitoring Report <br />First Quarter 2024 <br />www.arcadis.com <br />Forward Landfill 1Q24 Water Quality Mon Report_05012024 15 <br />2.10 Corrective Action Monitoring <br />This section describes the corrective action monitoring conducted during first quarter 2024 associated with the <br />Site and provides the associated monitoring results. <br />2.10.1 Monitoring Groups <br />For evaluation purposes, the groundwater monitoring wells at the Site were divided into the three groups (shallow, <br />intermediate, and deep) based on the depth of the screened interval, as described below: <br /> Shallow wells are screened predominantly at elevations greater than -50 feet relative to mean sea level <br />(MSL). The isoconcentration contours for PCE, TCE, cis-1,2-DCE, carbon tetrachloride, and chloroform in <br />shallow wells during first quarter 2024 are shown on Figures 3, 4A, 4B, 5, 6, and 7, respectively. The four <br />monitoring wells located at 7833 Newcastle Road are also shown on the figures. <br /> Intermediate wells are screened predominantly at elevations of -50 to -125 feet relative to MSL. The <br />isoconcentration contours for PCE, TCE, and cis-1,2-DCE in intermediate wells during first quarter 2024 are <br />shown on Figures 8, 9, and 10, respectively. <br /> Deep wells are screened predominantly at elevations less than -125 feet relative to MSL. The <br />isoconcentration contours for PCE and TCE in deep wells during first quarter 2024 are shown on Figures 11 <br />and 12, respectively. <br />In addition, isoconcentration maps for total VOCs, regardless of depth, are compiled for the annual corrective <br />action reports. A total VOC isoconcentration map for first quarter 2024 is shown on Figure 13. <br />2.10.2 Quarterly Results <br />Analytical data for the Forward and Austin Road Unit monitoring wells are presented in Tables 4 and 8, <br />respectively. The data for two domestic wells included in the Austin Road Unit monitoring program are presented <br />in Table 14. <br />The monitoring results suggest that the PCE and TCE plumes in the shallow zone (Figures 3 and 4A) and <br />intermediate zone (Figures 8 and 9) have become separated. This change follows upgrades to the groundwater <br />extraction and treatment system, including the addition of extraction well EW-5, at the end of 2019 (Section <br />2.10.3). <br />The recent installation of monitoring wells AMW-58S, AMW-58M, AMW-59S, and AMW-59M in August 2023 has <br />further defined the distribution of carbon tetrachloride (Figure 6) and chloroform (Figure 7) near existing <br />monitoring well AMW-22S. Based on the fourth quarter 2023 and first quarter 2024 monitoring results, the <br />elevated carbon tetrachloride and chloroform concentrations historically observed in the shallow zone at <br />monitoring well AMW-22S appear to be limited in extent. <br />2.10.3 Groundwater Treatment System <br />The groundwater treatment system (GWTS) at the Austin Road Unit has been operated since 1994 to mitigate <br />VOC impacts in groundwater. Five groundwater extraction wells (EW-1, EW-2, EW-3R, EW-4, and EW-5) are