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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 4 <br />2.1.3 Groundwater Elevations and Contours <br />DTW measurements were collected at each well before purging and sampling using a weighted electronic <br />sounder with an accuracy of 0.01 foot and recorded on a field data sheet (Appendix B). The groundwater <br />elevations at each well were calculated by subtracting the DTW measurement from the top of casing elevation. <br />The current groundwater elevation data for the Forward and Austin Road Units are presented in Tables 2 and 3, <br />respectively. <br />The groundwater elevation contour map (Figure 2) was generated using groundwater elevation data from January <br />17 to February 2, 2024. Groundwater in the site area generally flowed to the northeast, with an average hydraulic <br />gradient of approximately 0.002 foot per foot. Groundwater elevations rose significantly between fourth quarter <br />2022 and first quarter 2023 due to heavy winter rains and have remained at relatively high levels through first <br />quarter 2024. <br />2.1.4 Detection Monitoring Program, Forward Unit <br />Field and laboratory results for the DMP samples collected at Forward Unit groundwater monitoring wells during <br />first quarter 2024 are presented in Tables 4 and 5, and summarized below: <br />Non-statistical data analysis. The California non-statistical data analysis method (CNSDAM) was performed <br />for VOCs detected in background samples less than 10 percent of the time. Under the CNSDAM, a <br />monitoring well is to be resampled during the following quarter when concentrations of two or more VOCs <br />exceed their respective MDLs, or the concentration of one or more VOCs equals or exceeds its respective <br />PQL. <br />As presented in Table 4, the following VOCs were detected at the Forward Unit during first quarter 2024 at <br />concentrations that exceeded the applicable MDL or PQL: <br />-MW-2A. 1,1-Dichloroethane (greater than MDL), dichlorodifluoromethane (CFC-12; greater than MDL), <br />tetrachloroethene (PCE; greater than MDL), and trichloroethene (TCE; greater than MDL). <br />-MW-3. 1,1-Dichloroethane (greater than MDL), chloroform (greater than MDL), cis-1,2-dichloroethene <br />(cis-1,2-DCE; greater than MDL). <br />-MW-10. 1,1-Dichloroethane (greater than MDL), carbon tetrachloride (greater than PQL), <br />trichlorofluoromethane (CFC-11; greater than MDL), chloroform (greater than PQL), cis-1,2-DCE (greater <br />than MDL), PCE (greater than MDL), and TCE (greater than MDL). <br />-MW-19R. 1,1-dichloroethane (above MDL), carbon tetrachloride (above MDL), and chloroform (above <br />MDL). <br />Concentration limit thresholds. In accordance with the MRP (RWQCB 2014), the routine inorganic monitoring <br />data from the Forward Unit for the first quarter 2024 monitoring period were compared to concentration limits <br />(CLs) established for each well. CLs were recalculated through fourth quarter 2022 (Arcadis 2023). Details on <br />the statistical analysis for the established CLs are presented in Appendix I to the Forward Landfill Water <br />Quality Monitoring Report – Fourth Quarter/Annual 2023 (Fourth Quarter Report; Arcadis 2024). <br />As presented in Table 5, the following CLs were exceeded at the Forward Unit during first quarter 2024: <br />MW-1. Nitrate as nitrogen (N).