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The County is also considering running its flare concurrently with the power plant to maximize LFG destruction (pending Air Board approval). The County expects the adjustments to take effect over the next six (6) months. In short, the County does not believe sufficient time and LFG well field operations have passed in order to see the effects of the four (4) new wells installed in Module I in late 2016. It should be noted that the data for the Annual 2016 and Semi-annual 2017 Monitoring Reports were obtained only a few months after the wells were put into operation in late 2016. Based on historical monitoring of MW -3, the effects of the additional wells may not be evident until 2019 to 2021. However, the County is committed to converting single completion soil gas monitoring probes to tri -level monitoring probes should the new LFG wells and aggressive tuning of Module I prove insufficient in recovering migrated LFG and to reduce the VOC levels at MW -3. Although additional tri -level probes would enable monitoring more accurately the depth LFG constituents are migrating, there currently exists five (5) multi-level soil gas probes within 400 feet of Module I that the County installed in 2016. The effectiveness of aggressive tuning should be detectable within the existing single and multi-level soil gas monitoring probe system installed around Module I. It should be noted that there are twenty-five (25) Title 27 tri -level monitoring probes near the property boundary that do not contain LFG (methane) which makes Foothill Landfill compliant with Title 27 regulations. If the continued aggressive tuning of Module I to overcome the recent spike in LFG generation does not prove helpful in mitigation of LFG constituents (which will be apparent by future monitoring at the existing monitoring probes), the County believes efforts may be better directed toward installing additional LFG extraction wells within Module I versus additional monitoring probes. At this time however, the County seeks to continue aggressive tuning and LFG recovery operations at Module I, combined with continued monitoring of the existing probe network over the next six (6) months in order to assess the effectiveness in controlling LFG migration in the vadose zone. Again, it may take three to five years for the effectiveness to be evident in the groundwater. If LFG constituents continue to be detected at similar concentrations in the existing probe network, the County will further amend the 2016 Work Plan and take corrective actions, which as noted above, may include the installation of additional LFG extraction wells. If you have any questions, please contact me at (209) 953-7316. Sincerely, 1 TAJ M. BAHADORI, PE Senior Engineer TM B: mf N:\1 Foothill\RWQCB\Correspondence\Drafts\2017-08-28 FH Response to WB 071117 NOV.docx Enclosure Jim Stone, Deputy Director/Operations Desi Reno, Integrated Waste Manager Robert McClellon, SJC Environmental Health Department 1810 East Hazelton Avenue I Stockton, California 95205 1 T 209 468 3000 1 F 209 468 2999