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Environmental <br />Consultants & Contractors <br />April 11, 2023 <br />File No. 07218279.01, Task 4 <br />Mr. Joyesh Chandra <br />County of San Joaquin <br />Post Office Box 1810 <br />Stockton, California 95201 <br />Subject: First Quarter 2023, Landfill Gas (LFG) Perimeter Probe and Structure Testing at the <br />Foothill Sanitary Landfill, Lodi, California <br />Dear Mr. Chandra: <br />This letter provides results of LFG perimeter probes and structure testing for the first quarter of 2023 <br />(January through March) performed by SCS Field Services (SCS). All testing, monitoring protocols <br />and reporting were performed in general conformance with Title 27 California Code of Regulations <br />(CCR) Article 6. Briefly, these regulations require that solid waste disposal site owners/operators <br />implement LFG control or monitoring provisions to ensure that methane gas concentrations in soils <br />at the property boundary do not exceed the lower explosive limit (LEL, or 5 percent by volume) and <br />that interiors of on-site structures do not exceed 1.25 percent by volume in air. Below is a summary <br />of our quarterly monitoring activities. <br />SUMMARY, CONCLUSIONS AND RECOMMENDATIONS <br />As of the dates of our testing, no methane gas (the combustible component of LFG) in excess of 5 <br />percent by volume was detected at any subsurface perimeter location tested (i.e., structures and <br />monitoring probes). These results indicate that at the time of our testing the subject site probes and <br />structures were in compliance with requirements of Title 27 CCR Article 6. <br />GAS TESTING INSTRUMENTATION AND METHODS <br />Testing for methane gas, oxygen gas, carbon dioxide gas and pressure was performed using a Landtec <br />GEM -5000 Gas Analyzer calibrated to methane gas. This instrument measures combustible gas <br />concentrations in air directly on either of two scales, the first as percent by volume of the lower <br />explosive limit (LEL) of methane gas in air (0 to 5 percent); the other as percent by volume (0 to 100 <br />percent) in the gas sampled. The detection limit for this instrument is approximately 0.10 percent by <br />volume. <br />Gas monitoring well testing procedures are as follows: <br />• Connect sample tubing, open test valve, observe pressure, and record data. <br />• For probes 20 feet deep or less, turn on sample pump, observe and record methane, <br />oxygen, and carbon dioxide gas concentrations, when readings have stabilized for 30 <br />seconds. <br />A <br />4730 Enterprise Way, Suite A Modesto, CA 95356 1 209-545-8490 :re <br />