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Background <br /> Heavy rains on January 2 and 3, 2006,caused significant local erosion at a location on the <br /> southern slope of the Primary Site (Figure 1). The erosion was three to four feet deep, and <br /> between one to four feet wide at the top of the erosion "cut" (Photo 1). <br /> A member of Solid Waste Division staff was on site during these rains, and observed that the <br /> plastic pipe of the downcomer inlet was floating in the ponded water. The pipe was able to float <br /> because it was a double-walled HDPE pipe, with air enclosed in the space between the two walls, <br /> giving the pipe buoyancy (Photo 2). This raised the inlet to the downcomer caused water to pond <br /> against a berm at that location. Apparently, this ponded water was able to flow through a rodent <br /> burrow in the berm, undermining the berm. <br /> The vegetative layer and a portion of the closure barrier layer (bentonite-amended clay) had been <br /> eroded. Neither the foundation layer nor refuse was visible. <br /> Materials <br /> The closure cap was repaired using geocomposite clay liner(GCL) to replace the barrier layer, in <br /> accordance with repair method previously approved and used at this site. <br /> Geocom osite Clay Liner Specifications <br /> GCL Model: Bentofix Thermal Lock NWL <br /> Bentonite content (minimum) 0.84 lb/ft2 at 12% moisture <br /> Grab Strength (minimum) 150 lb average. roll value <br /> Permeability (maximum) 5x10 cm/sec <br /> Procedure <br /> The repair area was smoothed with a Caterpillar 332C tracked excavator(Photo 3), exposing a <br /> portion of the slope approximately six feet wide and three feet deep (Photo 4). All exposed areas <br /> were covered by GCL (Photo 5). A minimum one-foot shingle overlap was provided between the <br /> two GCL sections, and powdered bentonite placed on the overlapped areas,to that ensure water <br /> would not pass upward in the overlap section (Photo 6). The GCL extended over and beyond all <br /> areas of exposed barrier layer(Figure 2). A vegetative layer of approximately two-foot thickness, <br /> but not less than one foot, was placed over the GCL(Photos 7 and 8). These repairs were <br /> complete by June 14, 2006. The area will be hand-seeded before the next rains to minimize <br /> erosion. <br /> Corrective Action <br /> Downcomer inlet was secured on the surface of the landfill to prevent floating (Photo 9). <br /> Harney Lane Sanitary Landfill I-1 Department of Public Works/Solid Waste <br /> 4th Quarter 2005 Groundwater Monitoring Report County of San Joaquin—December 31,2005 <br />