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• 1998: ponding corrected. : • March 2000 (five years after the start of ponding): VOCs detected at MW-3 —Conclusion: it took ® about five years for VOC impact from the increased LFG production. • February 2002 (four years after ponding was corrected): VOC impact is no longer seen at MW-3 — Conclusion: it took about four years after the removal of the source of VOC impact at the surface to be observed in groundwater. • 2002 to 2006: MW-3 is free of VOCs without a LFG system in operation. • 2006: Site Improvement Project executed, including a installing a LFG system and a gas-tight HDPE barrier over refuse as required by CVRWQCB staff. County staff expresses concern that adding and gas-impermeable layer over unlined refuse could increase chances for groundwater impacts. July 2007: Landfill gas system operates near-continuously. • September 2010 (five years after installing gas-tight liner over refuse): VOCs (below 2 ppb) detected in MW-3. • July 2012 (approximately five years after continuous operation of the LFG system)VOCs no longer detected at MW-3. Conclusions: 1. Approximately five years is required for VOCs to be detected in groundwater after the condition that could cause groundwater impact is established. 2. Placement of a gas-impermeable barrier over refuse caused groundwater impact. MONITORING PROGRAM Water quality is monitored in accordance with WDR Order No. R5-2003-0020. Groundwater The groundwater well network consists of upgradient well MW-4 and downgradient wells MW-2R,MW-3, and MW-5. MW-1, which had previously been considered the "upgradient" is found to be crossgradient from the landfill, and not downgradient of any portion of the landfill. Groundwater monitoring wells MW-4 and MW-5 were installed during the fall of 2006. Because of decreasing water levels in MW-1, deeper well MW-lA will be installed prior to the next monitoring event. This well will be installed in accordance with a work plan approved by the RWQCB. All monitoring wells are equipped with dedicated purge and sampling pumps. Groundwater samples are analyzed semiannually for the following field and monitoring parameters as specified in the WDRs: • Temperature • Chloride • Electrical Conductivity • Sulfate • pH • Nitrate-Nitrogen • Turbidity • Calcium • Total Dissolved Solids • Magnesium • Potassium • Sodium • Carbonate Alkalinity • Bicarbonate Alkalinity ® Volatile Organic Compounds (VOCs) Foothill Sanitary Landfill 5 Department of Public Works/Solid Waste 1'�Semester 2013 Groundwater Monitoring County of San Joaquin—July 25,2013