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■ Installation landfill gas collection system. ® Placing partial cover on those surfaces of Area"I"that are not covered by the HDPE barrier or final closure. ■ Installation of two groundwater monitoring wells. ® On February 24, 2007, the County transmitted the CQA Certification Report for the Foothill Site Improvement Project to CVRWQCB, noting that this fulfilled the final requirement of the Cleanup and Abatement Order. • In a letter dated March 20, 2007, CVRWQCB accepted the Certification Report for the Site Improvement Project. ® On October 1, 2013,the Countysubmitted the Final Evapotranspiration (ET) Cover Assessment Report. • In a letter dated July 11, 2014, the CVRWQCB accepted the ET Cover. ' • In a letter dated July 29, 2014, CalRecycle accepted the CQA Certification Report. • On August 1, 2014, CVRWQCB issued a Notice of Violation(NOV) for FSL. • In a letter dated August 6, 2014, the County requested that CAO R5-2004-0706 be g tY rescinded, since all of the requirements were completed and subsequently accepted by both the CVRWQCB and CalRecycle. • On August 25, 2014,the County submitted an Engineering Feasibility Study (this document)to address the concerns of the August 1, 2014 NOV. jCORRECTIVE ACTION ANALYSIS AND CONCLUSIONS The first detections of VOCs at Foothill Sanitary Landfill occurred in March of 2000 at well MW-3. The County believes that this impact was the result of ponding which had initially occurred in 1995 and was subsequently repaired in 1998. It should be noted that the time lag between the first ponding and first detection of VOCs was 4.5 years. This time lag between action at the surface and subsequent groundwater impact establishes the hydrogeological temporal dynamics at FSL. This 4 to 5 year time lag was observed again, when ponding was repaired in 1998, MW-3 ceased to be impacted in 2003, a 5-year time lag. MW-3 was not impacted again until the 2nd semiannual period of 2010. To ascertain the cause of this reappearance of VOCs, we note that in 2006 the County installed a landfill gas (LFG) collection system and an impermeable HDPE liner over refuse during the expansion of Area 1. This 4 year time lag is consistent with previous observations, and is a strong indication that the most recent impaction of groundwater at MW-3 was the result of the Site Improvement Project in 2006. The most likely cause is the entrapment of LFG under the impermeable HDPE liner which is migrating downward impacting groundwater. Foothill Sanitary Landfill 3 Department of Public Works/Solid Waste Engineering Feasibility Study County of San Joaquin—August 2014