CORRESPONDENCE_2008 (1/08 TO 6/08)

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In 1996, CHSL was certified closed with the installation of the closure cap, Landfill gas (LFG) migration monitoring wells and groundwater monitoring wells. The cap consists of a 2- to 6 -foot foundation layer under a 1 -foot minimum thick, low -permeability soil layer, with a 1 -foot thick vegetative surface layer. In 2003, slight increasing trend in Nitrate and Nitrogen and a decreasing trend in pH, which effected the water quality parameters in shallow aquifer ground water monitoring well MW -4, was detected (Figure 6). The findings of possible contamination concerned the County. An investigation of offsite contamination was not conclusive. Prior to 2003 ponding was observed during the rainy season in the drainage ditch adjacent to the eastern access road of CHSL. In late 2003, the drainage ditch was improved to reduce ponding and minimize infiltration along the ditch. In September 2005, a subsequent investigation was initiated to determine if refuse was present below the drainage ditch, the access road, and east of the road at the eastern edge of the landfill due to an increasing trend in Nitrate at MW -4 (Figure 6). The County suspected that if the closure cap was insufficient below the drainage ditch, then concentration of water at the drainage ditch, and percolation of that water though any refuse below, could impact the shallow aquifer. The County investigation included excavating at intervals along the drainage ditch, and revealed refuse below significant portions of the ditch without final closure cap. In June 2007, the County delineated the extent of the edge of the closure cap and refuse outside the closure cap. The investigation revealed some areas where refuse extended beyond the closure cap on County property. The County also provided initial investigation of the presence of refuse into adjacent property, now owned by Caltrans, at CalTrans request (Figure 3). This preliminary investigation indicated that refuse was present in the CalTrans property, and this area was not closed in accordance with Title 27. 2.3 SHELL OIL EASEMENT The County has granted a 20 -foot wide easement through the proposed closure cap extension area to Shell pipeline (Figure 2). A high pressure oil pipeline was installed in that easement in 1967, prior to the closure of CHSL. It is assumed that refuse is under the pipeline. The County has notified Shell Oil Pipeline that the Landfills closure cap will be extended over this easement. Closure Plan Addendum San Joaquin County Corral Hollow Sanitary Landfill 2 Department of Public Works April 4, 2008 Solid Waste Division