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Foothill Sanitary Landfill 12 Department of Public Works/Solid Waste <br />First Semiannual 2025 Groundwater Monitoring ©2025 County of San Joaquin. All rights reserved. <br /> <br />4.0 UNSATURATED ZONE MONITORING <br />4.1 Soil-Pore Gas <br />Ten soil gas probes, SG-1 through SG-7 and SG-9 through SG-11, are located around Module <br />“I” and Module 1 (Figure 5). Probe SG-8 was removed during the construction of Module 1. <br />These initial single soil gas monitoring devices extended to depths varying from 25 feet to 68 feet <br />below the surface. Soil gas probes SG-10, SG-11, SG-2, SG-3 and SG-6 were re-drilled deeper <br />during the summer of 2016 and completed as tri-level probes SG-10A, SG-11A, SG-2A, SG-3A <br />and SG-6A. <br />Soil gas wells are monitored semiannually for methane and VOCs (USEPA Method TO-15). <br />4.2 Lysimeters <br />During the routine monitoring event in August 2018, fluid was extracted from Lysimeter LZ-4 <br />which was reported to contain ten (10) VOCs. A Work Plan for the Detection of Fluid at Lysimeter <br />LZ-4 was submitted on September 18, 2018 which proposed monthly monitoring for the <br />presence of extractable water which would switch to quarterly monitoring if insufficient water was <br />present for extraction. Based on the Work Plan, the monitoring would then revert to semi-annual <br />after a year if insufficient water was present for sampling. <br />Lysimeter samples, if available, are currently monitored semiannually for the same field and <br />monitoring parameters as for leachate specified above.