COMPLIANCE INFO_JTD APPENDIX A -L 2024

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North County Recycling Center & Sanitary Landfill Public Works/Solid Waste First Semiannual 2024 Groundwater Monitoring 10 ©2024 COUNTY of San Joaquin. All Rights Reserved. Leachate The WDRs require monthly monitoring of leachate volume, pH, and electrical conductivity (Table 2). In addition, the County is monitoring any liquid level in the secondary sump below Areas 3 and 4. A comparison of the leachate monitoring data to groundwater monitoring data shows that leachate generally contains significantly higher TDS, electrical conductivity, and chloride than groundwater. Leachate is also slightly more acidic than groundwater. Leachate was sampled at collection points L-1, L-3, L-4, and L-5 (Table 7). Thirty different VOCs (some at trace concentrations) were reported in the February 2024 leachate samples. The highest VOC concentrations reported at each sample point were naphthalene in L-1, methyl ethyl ketone in L-3, 2-hexanone in L-4, and methyl ethyl ketone in L-5. Results are consistent with past leachate monitoring events. Presence of VOCs in the leachate does not indicate groundwater contamination, but rather the success of the liners at North County Landfill in preventing groundwater contamination. Secondary Sump Monitoring The liquid level in the secondary sumps of Area 3, 4 and 5 are monitored quarterly. No liquid was measured in the secondary sumps. The lack of liquid indicates that the primary liners are not leaking. Area 1 is not equipped with a secondary sump. GROUNDWATER DIRECTION AND FLOW RATE Groundwater elevations at the site vary seasonally, but overall trends at the site have been decreasing since 2001. During this reporting period, wells G-1A, G-2A, G-4 and G-5A were dry and wells G-3D, G-5B, and G-6 had insufficient water present to sample. Groundwater gradients and flow directions were based on the elevations in the remaining eight wells (Figures 3 and 4). Groundwater elevations at G-14 were anomalously high compared to the rest of the monitoring network during this reporting period (approximately 16.5 feet higher than the average elevation of the rest of the monitoring network). As a result, G-14 was not used in contouring. Local groundwater flow beneath the site is variable and appears to vary depending on agricultural pumping, infiltration due to storm events, and regional changes in the aquifer. First Quarter 2024 During First Quarter 2024, groundwater elevations ranged from -67.92 feet MSL (G-9) to -49.27 feet MSL (G-14). The average groundwater elevation for wells G-7 through G-13 was -66.33 feet MSL. During First Quarter 2024, groundwater flow was to the south-southwest. Groundwater gradients ranged from 0.0005 ft/ft (between wells G-12 and G-5B) to 0.001 ft/ft (between wells G-7 and G-9). Based on the calculated gradients at the site, the groundwater velocity ranged from approximately 17 ft/year to approximately 34 ft/year (Appendix F).