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E • On October 14, 2014, the County met with the CVRWQCB to discuss proposed revisions to the EFS. • On October 17, 2014, the County received email correspondence from the CVRWQCB indicating what the revised EFS must address in the next submittal. • End of Compliance History Summary. Based on the October 17, 2014 email to the County, the following is being presented to the CVRWQCB. The first detections of VOCs at FSL occurred in March of 2000 at 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 an action at the surface and subsequent groundwater impact establishes the hydrogeological temporal dynamics at FSL. This four (4)- to five (5) -year time lag was observed again, when ponding was repaired in 1998 and MW -3 ceased to show evidence of impacted in 2003. 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 impact to groundwater at MW -3 may be 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. The 4 to 5 year response time between surface actions and groundwater impact is consistent with the relatively thick (200 feet) vadose zone at the site. Therefore, it is our professional opinion that VOCs driven out of the base of Module "I" are present in the vadose zone. This revised EFS was prepared to address the comments contained in an email dated October 17, 2014 from the CVRWQCB staff, which requested the following topics be addressed in this Revised EFS: • Landfill Gas Collection within Module "I" • Landfill Gas Monitoring outside Module "I" • Determination of the Extent of Contamination • Proposed Changes to the Monitoring and Reporting Program Foothill Sanitary Landfill 4 Department of Public Works, Solid Waste Division Revised Engineering Feasibility Study County of San Joaquin — December 19, 2014