COMPLIANCE INFO_2023 Q4 WATER QUALITY RPT

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Forward Landfill – 2023 Annual Corrective Action Evaluation Report www.arcadis.com Forward Landfill 2023 Annual CA Eval Rpt_08012023 2 Tables 2 through 5 present a quarterly summary of the VOC groundwater monitoring results from the monitoring period, including the TVOC concentration for each well. Estimated (trace) detections of VOCs between the laboratory reporting limit (RL) and method detection limit (MDL) are also presented on Tables 2 through 5, but such trace detections are not included in the calculation of TVOC concentrations. Of note, suspected and/or confirmed field/laboratory contaminants for acetone that were not repeated in subsequent sampling events were not included in the TVOC calculations. In an August 19, 2005 letter, the RWQCB specified that future Annual Corrective Action Evaluation Reports shall include:  A discussion of the landfill cover, including any performance issues from the previous year;  A summary and discussion of the previous year's monitoring data from the facility's landfill gas monitoring system and landfill gas extraction system;  A comparison of the previous year's groundwater monitoring results to computer simulations originally presented in the August 6, 2001 Revised Engineering Feasibility Study; and  A discussion of the overall corrective action progress, including any proposed enhancements to the program. The RWQCB later incorporated these requirements and quarterly groundwater potentiometric maps into Section B.5 of the MRP. These requirements are addressed in Sections 5, 6, 7, and 8 of this report. 2 Total VOC Mass Isoconcentration maps of groundwater TVOC concentrations for the monitoring period are presented in Figures 1 through 4. Consistent with the Evaluation Procedures Report, these maps utilize a contour interval of 25 µg/L and do not include contouring for concentrations less than 1 µg/L. The isoconcentration maps presented include all of the ARU groundwater monitoring wells. For each quarter, the TVOC mass was estimated using the following procedures:  The TVOC mass between each pair of isoconcentration contours was first estimated by multiplying the average TVOC concentration between those contours by the assumed aquifer thickness and porosity. (For example, the average TVOC concentration between the 25 µg/L and 50 µg/L contours would be 37.5 µg/L.) Consistent with the Evaluation Procedures Report, the aquifer thickness was assumed to be 40 feet and the aquifer porosity was assumed to be 0.25.  The TVOC masses corresponding to all contour pairs on a given quarter's isoconcentration map were then summed to estimate the total, plume-wide TVOC mass for that quarter. Tables 6 through 9 summarize the quarterly TVOC mass estimation calculations for the monitoring period; the historical TVOC masses for the facility are summarized on Table 10; and the corresponding quarterly groundwater potentiometric maps are presented in Appendix A. The TVOC mass for each quarter was compared to the TVOC mass TL of 789.5 kg. As shown in Tables 6 through 9, the calculated quarterly TVOC mass between the third quarter of 2022 and the second quarter of 2023 ranged from a minimum of 127.7 kg to 222.7 kg. There were no exceedances of the TL during the monitoring period.