CORRESPONDENCE_2007 (1/07 - 6/07)

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It was contemplated that if the refuse extended beneath the drainage ditch,then puddling of water along the ditch alignment prior to the grading in 2003 could cause groundwater impact. In February 2004 the County's consultant performed a geophysical survey in an attempt to define the extent of refuse by non-invasive means(soil conductivity and magnetic resonance). This effort was unsuccessful. In 2005 the groundwater analyses from MW4 indicate an improvement in groundwater quality. It is speculated that this improvement is the result of grading the drainage ditch at the eastern edge of the landfill in 2003, and that preventing puddles along that alignment has minimized infiltration. In March 2006 the County reported the results of an investigation (Phase 1)to determine if refuse was present beneath the drainage ditch, and how much and what type of cover was provided over refuse, if present. This investigation was by back-hoe excavation at both sides of the eastern access road, including the drainage ditch. Refuse was found below the middle and northern portion of the drainage ditch west of the access road, but not apparently east of the access road. The soil cover over the refuse was usually less than one-foot thick: final closure cover did not extend over the refuse in the ditch where refuse was present. The landfill access road itself was not excavated due to the presence of a high-pressure petroleum product pipe in the road. In 2006 the CIWMB and San Joaquin County Environmental Health Department has requested that the County define the edge of the closure cap. A revised plan for that investigation was submitted in January 2007, incorporating comments to an earlier submittal of that Plan. In August 2006 staff of the Regional Water Quality Control Board issued a violation for "inadequate detection monitoring program", due to failure to monitor the shallow aquifer west of the landfill footprint. County staff provided historical information documenting that the shallow aquifer does not exist beneath the western portion of the landfill. In December 2006 the staff of the Regional Water Quality Control Board issued a violation because the objectives of the Waste Discharge Requirement have not been met and because corrective action"has not been effective". In response to that violation, and the continued detection of VOCs in the groundwater at MW-5,the County submits this proposal to increase the effectiveness of corrective action at the Corral Hollow Landfill. Approach The County proposes to increase the effectiveness of corrective action against VOC impacts by increasing LFG collection along the perimeter of the landfill footprint near well MW-5 (Figure 2). The County would install a plastic membrane (HDPE or equivalent) as extension of the closure cap, and a horizontal collection trench beneath that membrane (Figures 3 and 4). This horizontal collector would be connected to the LFG header. This is an ideal condition under which to attempt to collect LFG via a collector trench. Overlaying the trench with a membrane and soil fill should dramatically increase LFG collection in that area by dramatically reducing the potential for air to intrude; minimal "breakthrough"will occur, maximizing collection of LFG from the soil Increase in Corrective Action 3 Corral Hollow Sanitary Landfill January 23,2007 San Joaquin County Public Works/Solid Waste