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<br />North County Recycling Center & Sanitary Landfill Public Works/Solid Waste <br />First Semiannual 2024 Groundwater Monitoring 8 ©2024 COUNTY of San Joaquin. All Rights Reserved. <br /> <br />limit methods, and were most recently updated during the second semiannual period of 2016. <br />Analytical results from this monitoring event were compared to the 2016 concentration limits that <br />were developed from G-1A and the WDR concentration limits. Due to dropping water levels at <br />the site, which caused G-1A to go dry in 2016, well G-10 had been proposed as a background <br />replacement well for G-1A. However, based on groundwater flow direction evaluation provided <br />in the November 2021 DMP Evaluation, the predominant flow direction appears to be towards <br />the east or southeast and a new proposed background well (G-12) was installed in the northwest <br />portion of the facility in the first semiannual 2022 period. This new background well will be used <br />for interwell concentration limit updates after a minimum of 8 data points have been collected. <br />In the interim period until sufficient data points are available for a concentration limit update, the <br />MRP concentration limits will be used. See Appendix D—Statistical Methods to Determine <br />Concentration Limits and Appendix E—Tabular Summary of Historical Monitoring Data. <br />Detection monitoring wells on northern side of the landfill consist of G-7 and G-8. Detection <br />monitoring wells on western side of the landfill consist of G-5B and G-9. Detection monitoring <br />well G-11 is on southern side of the landfill. Detection monitoring well G-10 is on eastern side of <br />the landfill. <br />Landfill Gas Collection System <br />The landfill gas (LFG) collection system was first installed in 2006. Currently there are seventeen <br />(17) vertical extraction wells and seven horizontal collectors. The LFG system is also connected <br />to the Leachate Risers at five locations. The system is operated in accordance with the Permit <br />to Operate issued by the San Joaquin Valley Air Pollution Control District. <br />MONITORING RESULTS <br />Groundwater <br />Field and Monitoring Parameters <br />Monitoring well depth-to-water measurements were taken on January 23, 2024 for the first <br />quarter (Table 3) and on April 2, 2024 for the second quarter (Table 4). Groundwater samples <br />were collected for analysis during first quarter from detection monitoring wells G-7 through G-14 <br />(See Appendix B for the Water Sample Field Data Sheets). The concentration of field and <br />monitoring parameters were below established concentration limits (CLs), except for turbidity in <br />wells G-11 and G-14 and bicarbonate in G-12. See Appendix C Laboratory Certification for <br />analytical results. <br />Due to dropping groundwater levels, samples for chemical analysis are no longer collected from <br />wells G-1A, G-2A, G-3D, G-4, G-5A, and G-6. Insufficient water was present in monitoring well <br />G-5B to be sampled. The dropping groundwater conditions at the landfill are due to over- <br />pumping of regional aquifers for irrigation in the Central Valley. <br />Statistical Analysis <br />The concentration limits from the WDR/MRP were used in this report and will be used until new <br />interwell concentration limits can be calculated from the new background monitoring well <br />installed in the first semiannual 2022 period. Field parameter results did not exceed the CLs