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 4 waste. As demonstrated by the results of the historical TO-15 testing, the NMOC concentrations in LFG vary across the landfill from well to well. The concentrations varying from point to point with no distinct pattern is consistent with the expectations for the heterogeneous environment of an MSW landfill. The gas collection and control system at the Forward Landfill complex currently includes 215 active landfill gas extraction wells, a flare for thermal destruction (Flare A-2), a backup flare (Flare A-1), and a methane gas recovery facility that generates electricity (Ameresco plant). It is estimated that the combined Forward flare and Ameresco plant are operating at 75% of full capacity and in compliance with regulations. The LFG collection and combustion system is upgraded on a routine basis to optimize LFG collection and reduce the potential for LFG impacts in the unsaturated zone through source control measures. In accordance with the Point of Compliance LFG Monitoring Program, Forward installed an additional 12 nested perimeter monitoring probes around the Austin Unit to evaluate the effectiveness of the existing LFG extraction system in the 2017. In response to requirement 2.G of Cleanup and Abatement Order R5-2017-0703, Forward also installed 10 additional LFG extraction wells within the unlined Austin Road Unit to mitigate LFG migration and replaced lateral header piping to increase vacuum. The work was completed in September 2018 and summarized in Cornerstone Environmental’s 2018 Gas Collection and Control System Improvements Construction Completion Report dated October 19, 2018. The Forward Landfill includes 27 perimeter landfill gas monitoring probes spaced 1,000 feet apart, pursuant to Title 27 of the CCR. These probes include multi-level monitoring of shallow and deep intervals. Several of the probes also include monitoring of a medial interval. Combined, the perimeter monitoring system includes 77 individual monitoring points. Thirteen of the 27 permanent probes are located around the perimeter of the ARU: GP-13 through GP-25. These 13 probes comprise 39 of the complex's 77 individual monitoring points. ARU perimeter gas monitoring probes were monitored quarterly for methane, carbon dioxide, oxygen, balance gas, and static pressure. Quarterly landfill gas sample results for ARU, provided by SCS Field Services (SCS), are in Appendix C. Quarterly results are generally consistent at the ARU, and methane was not detected in any ARU perimeter monitoring probe above a concentration of 1% during the monitoring period, with the exception of three LFG monitoring probe during third quarter 2022, three probes during fourth quarter 2022, seven probes during first quarter 2023 and three probes during second quarter 2023. Given the general lack of detectable methane above 1% in the Title 27 perimeter gas probes over the past year, it can be concluded that the gas collection system continues to operate effectively. Forward will continue to enhance the landfill gas extraction system through regular maintenance and adjustments of the LFG well field. 7 Comparison of Current to Modeled Groundwater Quality The August 8, 2001 Revised Engineering Feasibility Study for Austin Road Landfill (EFS) presented projected isoconcentration contour maps for select VOCs in groundwater based on computer modeling simulations. The four VOCs that were modeled were tetrachloroethene (PCE), trichloroethene (TCE), cis-1,2-dichloroethene (cis- 1,2-DCE), and vinyl chloride. These simulations projected how the concentrations of individual VOCs could potentially change following the initiation of recharge within the artificial basin. The EFS presented projected maps corresponding to each year following the initiation of recharge.