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• March 2000 (five years after.the start of ponding): VOCs indicated at MW-3 —Conclusion: it took <br /> about five years for VOC tainted water to migrate through the 270-foot thick vadose zone to reach <br /> ® groundwater <br /> • February 2002 (four years after ponding was corrected): VOC impact is no longer seen at MW-3 — <br /> Conclusion: it took about four years after the removal of the source of VOC impact at the surface to <br /> be observed in groundwater <br /> ® 2002 to 2006: MW-3 is free of VOCs without a LFG system in operation <br /> • 2006: Site Improvement Project executed, including a installing a LFG system and a gas-tight HDPE <br /> "liner"over refuse as required by CVRWQCB staff—Inference: the gas-tight HDPE forces LFG to <br /> enter the vadose zone beneath the refuse <br /> • July 2007: Landfill gas system operates near-continuously <br /> • September 2010 (five years after installing gas-tight liner over refuse): VOCs (below 2 ppb) detected <br /> in MW-3. <br /> • July 2012 (approximately five years after continuous operation of the LFG system)VOCs no longer <br /> detected at MW-3 <br /> Conclusions: <br /> 1. Approximately five years is required for VOCs to be detected in groundwater after the condition that <br /> could cause groundwater impact is established. <br /> 2. Placement of an impermeable plastic layer over refuse caused groundwater impact. <br /> MONITORING PROGRAM <br /> Water quality is monitored in accordance with WDR Order No. R5-2003-0020. <br /> Groundwater <br /> The groundwater well network now consists of upgradient well MW-4 and downgradient wells MW-2R, <br /> MW-3, and MW-5. MW-1,which had previously been considered the "upgradient" is found to be <br /> crossgradient from the landfill, and not downgradient of any portion of the landfill. Therefore,this well is <br /> not needed at this time for the evaluation of potential water quality impact by the landfill. Groundwater <br /> monitoring wells MW-4 and MW-5 were installed during the fall of 2006. <br /> All monitoring wells are equipped with dedicated purge and sampling pumps. <br /> Groundwater samples are analyzed semiannually for the following field and monitoring parameters as <br /> specified in the WDRs: <br /> • Temperature • Chloride <br /> • Electrical Conductivity • Sulfate <br /> • pH • Nitrate-Nitrogen <br /> • Turbidity . Calcium <br /> • Total Dissolved Solids • Magnesium <br /> • Potassium • Sodium <br /> • Carbonate Alkalinity • Bicarbonate Alkalinity <br /> • Volatile Organic Compounds (VOCs) <br /> Foothill Sanitary Landfill 5 Department of Public Works/Solid Waste <br /> 2nd Semester and Annual 2012 Groundwater Monitoring County of San Joaquin—January 15,2013 <br />