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Revised Quarterly Monitoring Report –
<br />Fourth Quarter/Annual 2024
<br />www.arcadis.com
<br />Revised - Forward Landfill 4Q24 Quarterly Mon Report 06262025 21
<br />LRCS Testing
<br />The LCRSs at the Site are tested annually. The LCRSs were successfully tested in fourth quarter 2024, indicating
<br />that a conduit exists across the LCRS units (Appendix B). In addition, an annual inspection of each sump is
<br />performed by Del-Tech, which most recently occurred on November 8 and 9, 2024.
<br />6.6 Landfill Gas Monitoring
<br />SCS Field Services conducts quarterly monitoring of perimeter gas probes and onsite structures in accordance
<br />with Title 27 California Code of Regulations, Article 6 and the MRP Corrective Action Monitoring Program (MRP
<br />Section C.4 [RWQCB 2024a]). Results of the quarterly monitoring are summarized as follows:
<br /> During first quarter 2024, perimeter gas monitoring probes GP-10D, GP-10M, and GP-10S exhibited methane
<br />concentrations in exceedance of the regulatory limit of 1% by volume. In addition, probes GP-1AD, GP-2AD,
<br />GP-4AD, GP-10D, GP-10M, GP-10S, GP-11D, GP-11M, GP-11S, GP-12D, GP-12M, and GP-12S exhibited
<br />VOC concentrations greater than 10 parts per billion (ppb).
<br /> During second quarter 2024, perimeter gas monitoring probes GP-10D, GP-10M, and GP-10S exhibited
<br />methane concentrations in exceedance of the regulatory limit of 1% by volume. In addition, probes GP-1AD,
<br />GP-10D, GP-10M, GP-10S, GP-11D, and GP-12D exhibited VOC concentrations greater than 10 ppb.
<br /> During third quarter 2024, perimeter gas monitoring probes GP-10D, GP-10M, and GP-10S exhibited
<br />methane concentrations in exceedance of the regulatory limit of 1% by volume. In addition, probes GP-1AD,
<br />GP-10D, GP-10M, GP-10S, and GP-11D exhibited VOC concentrations greater than 10 ppb.
<br /> During fourth quarter 2024, perimeter gas monitoring probes GP-10D, GP-10M, and GP-10S exhibited
<br />methane concentrations in exceedance of the regulatory limit of 1% by volume. In addition, probes GP-2AM,
<br />GP-4AD, GP-5AM, GP-10D, GP-10M, GP-10S, and GP-12D exhibited VOC concentrations greater than 10
<br />ppb.
<br />6.7 Seep Monitoring
<br />No seeps were observed at the Site during 2024. Inspection forms for the first through third quarters of 2024 were
<br />previously provided by Arcadis (2024b, 2024g, 2024k). The seep monitoring for fourth quarter 2024 is addressed
<br />in Section 4.2.
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